Observed Climate Trend Analysis in the Districts and Physiographic Zones of Nepal
(1971-2014)
June 2017
Government of Nepal
Ministry of Population and Environment Department of Hydrology and Meteorology
2
Published by Government of Nepal Ministry of Population and Environment Department of Hydrology and Meteorology Naxal, Kathmandu NEPAL
Phone: (+977-1) 4436272, 4432409 Fax: (+977-1) 4429919, 4432136 Website: www.dhm.gov.np E-mail: [email protected]
Copyright: ©Government of Nepal, Ministry of Population and Environment, Department of
Hydrology and Meteorology, 2017 Any part of this publication may be used for educational and non-profit purposes without special permission from the copyright holder, provided acknowledgement of the source is accurately made. Use of any part of it for commercial purpose is strictly prohibited.
Citation: DHM, 2017. Observed Climate Trend Analysis in the Districts and Physiographic Regions of Nepal (1971-2014). Department of Hydrology and Meteorology, Kathmandu
ISBN: Printed at:
Steering Committee Dr. Rishi Ram Sharma, Director General Coordinator Mr. Saraju Kumar Baidya, Deputy Director General Member Mr. Durga Prakash Manandhar, Deputy Director General Member Dr. Jagdishwor Karmacharya, Deputy Director General Member
Technical Committee Dr. Archana Shrestha, Senior Divisional Meteorologist Coordinator Ms. Pratibha Manandhar, Senior Divisional Meteorologist Member Mr. Bikash Nepal, Meteorologist Member Mr. Lasakusa Samir Shrestha, Meteorologist Member
http://www.dhm.gov.np/mailto:[email protected]
3
Foreword
4
Acknowledgements
5
Acronyms
APHRODITE Asian Precipitation - Highly-Resolved Observational Data Integration Towards
Evaluation
CDR Central Development Region
CL Confidence Level
DJF December-January (Winter Season)
DHM Department of Hydrology and Meteorology
EDR Eastern Development Region
FMI Finnish Meteorological Institute
FWDR Far-Western Development Region
GrADS Grid Analysis and Display System
ICIMOD International Centre for Integrated Mountain Development
ISBN International Standard Book Number
JJAS June-August(Monsoon Season)
LDC Least Developed Country
LEG Least Developed Country Expert Group
MAM March-May (Pre-monsoon Season)
masl meters above sea level
MoPE Ministry of Population and Environment
MWDR Mid-Western Development Region
NAP National Adaptation Plan
NAPA National Adaptation Programme of Action
ON October-November(Post-Monsoon season)
PAN Practical Action Nepal
ON October-November(Post-Monsoon season)
QC Quality Control
WDR Western Development Region
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Contents
Foreword............................................................................................................................................. 3
Acknowledgements ............................................................................................................................ 4
Acronyms ............................................................................................................................................ 5
List of figures ....................................................................................................................................... 9
List of Tables ..................................................................................................................................... 11
Executive Summary .................................................................................................................................. 12
1 Background ....................................................................................................................................... 14
1.1 Introduction .............................................................................................................................. 14
1.2 Objectives ................................................................................................................................. 15
1.3 The Report ................................................................................................................................ 15
1.4 Study Units ................................................................................................................................ 15
1.5 Seasons ..................................................................................................................................... 17
2 Data and Methodology ..................................................................................................................... 17
2.1 Data ........................................................................................................................................... 17
2.2 Methodology ............................................................................................................................ 19
2.2.1 Data Quality Check............................................................................................................ 19
2.2.2 High Altitude Station Missing Data Filling ......................................................................... 19
2.2.3 Gridding and Interpolation of Temperature Data ............................................................ 20
2.2.4 District level and Physiographic Region Seasonal and Annual Time series Calculation ... 20
2.2.5 Trend Analysis ................................................................................................................... 21
2.2.6 Extreme Indices Analysis ................................................................................................... 22
2.2.7 Report preparation process .............................................................................................. 22
3 Climatic Normal ................................................................................................................................ 23
3.1 Normal Precipitation for Districts and Physiographic Regions ................................................. 23
3.1.1 Winter Precipitation ......................................................................................................... 23
3.1.2 Pre – Monsoon Precipitation ............................................................................................ 24
3.1.3 Monsoon Precipitation ..................................................................................................... 26
3.1.4 Post-Monsoon Precipitation ............................................................................................. 27
3.1.5 Annual Precipitation ......................................................................................................... 28
3.2 Normal Maximum Temperature ............................................................................................... 29
3.2.1 Winter maximum temperature ........................................................................................ 29
3.2.2 Pre – Monsoon maximum temperature ........................................................................... 30
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3.2.3 Monsoon maximum temperature .................................................................................... 32
3.2.4 Monsoon maximum temperature .................................................................................... 34
3.2.5 Annual maximum temperature ........................................................................................ 35
3.3 Nepal averaged Minimum Temperature .................................................................................. 37
3.3.1 Winter minimum temperature ......................................................................................... 37
3.3.2 Pre – Monsoon minimum temperature ............................................................................ 38
3.3.3 Monsoon minimum temperature ..................................................................................... 40
3.3.4 Post-Monsoon minimum temperature............................................................................. 42
3.3.5 Annual minimum temperature ......................................................................................... 43
4 All Nepal Climatic Trends .................................................................................................................. 45
4.1 All Nepal Maximum Temperature Trend .................................................................................. 45
4.2 All Nepal Minimum Temperature Trend .................................................................................. 46
4.3 All Nepal Precipitation Trend .................................................................................................... 46
4.4 Summary of All Nepal Climate Trends ...................................................................................... 47
5 Precipitation Trends for Districts and Physiographic Regions .......................................................... 48
5.1 Winter Precipitation Trend ....................................................................................................... 48
5.2 Pre-Monsoon Precipitation Trend ............................................................................................ 50
5.3 Monsoon Precipitation Trend ................................................................................................... 52
5.4 Post-monsoon Precipitation Trend ........................................................................................... 54
5.5 Annual Precipitation ................................................................................................................. 56
5.6 Summary of Precipitation Trend ............................................................................................... 57
6 Maximum Temperature Trend for Districts and Physiographic Regions .......................................... 58
6.1 Winter Maximum Temperature Trend ..................................................................................... 58
6.2 Pre-monsoon Maximum Temperature Trend .......................................................................... 60
6.3 Monsoon Maximum Temperature Trend ................................................................................. 62
6.4 Post-monsoon Maximum Temperature Trend ......................................................................... 64
6.5 Annual Maximum Temperature Trend ..................................................................................... 66
6.6 Summary of Maximum Temperature Trend ............................................................................. 68
7 Minimum Temperature Trend for Districts and Physiographic Regions .......................................... 69
7.1 Winter Minimum Temperature Trend ...................................................................................... 69
7.2 Pre-monsoon Minimum Temperature Trend ........................................................................... 71
7.2.1 Districts ............................................................................................................................. 71
7.3 Monsoon Minimum Temperature Trend ................................................................................. 73
7.4 Post-monsoon Minimum Temperature Trend ......................................................................... 75
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7.5 Annual Minimum Temperature Trend ...................................................................................... 77
7.6 Summary of Minimum Temperature Trends ............................................................................ 79
8 Extreme Event Trends ....................................................................................................................... 80
8.1 Number of Rainy Days .............................................................................................................. 80
8.2 Very Wet Days .......................................................................................................................... 80
8.3 Extremely Wet Days .................................................................................................................. 81
8.4 Consecutive Dry Days ............................................................................................................... 82
8.5 Consecutive Wet Days .............................................................................................................. 82
8.6 Cool Days .................................................................................................................................. 83
8.7 Cool Nights ................................................................................................................................ 84
8.8 Warm Nights ............................................................................................................................. 85
8.9 Warm Days ................................................................................................................................ 86
8.10 Warm Spell Duration ................................................................................................................ 87
8.11 Cold Spell Duration ................................................................................................................... 88
8.12 Summary: Extreme Climate Trends .......................................................................................... 89
9 Comparison with Previous Studies in Nepal ..................................................................................... 90
10 Conclusions ................................................................................................................................... 91
References: ........................................................................................................................................... 92
Appendix ............................................................................................................................................... 93
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List of figures
Figure 1.1 Districts of Nepal...................................................................................................................... 16
Figure 1.2: Physiographic Regions of Nepal.............................................................................................. 16
Figure 2.1a: Distribution of 93 stations used for this study ..................................................................... 18
Figure 2.1b: Districtwise number of stations used in this study .............................................................. 18
Figure 2.2 Schematic diagram of methodology ........................................................................................ 20
Figure 3.1.1a Winter precipitation normal for districts ............................................................................ 23
Figure 3.1.1b Winter precipitation normal for physiographic regions ..................................................... 24
Figure 3.1.2a Pre-Monsoon precipitation normal for districts ................................................................. 25
Figure 3.1.2b Pre-Monsoon precipitation normal for physiographic regions .......................................... 25
Figure 3.1.3a Monsoon precipitation normal for districts ....................................................................... 26
Figure 3.1.3b Monsoon precipitation normal for physiographic regions. ................................................ 26
Figure 3.1.4a Post-Monsoon precipitation normal for districts ............................................................... 27
Figure 3.1.4b Post-Monsoon precipitation normal for physiographic regions ........................................ 27
Figure 3.1.5a Annual precipitation normal for districts ........................................................................... 28
Figure 3.1.5b Annual precipitation normal for physiographic regions ..................................................... 28
Figure 3.2.1a Winter maximum temperature normal for districts ........................................................... 29
Figure 3.2.1b Winter maximum temperature normal for physiographic regions .................................... 30
Figure 3.2.2a Pre-Monsoon maximum temperature normal for districts ................................................ 31
Figure 3.2.2b Pre-Monsoon maximum temperature normal for physiographic regions ......................... 32
Figure 3.2.3a Monsoon maximum temperature normal for districts ...................................................... 33
Figure 3.2.3b Monsoon maximum temperature normal for districts ...................................................... 33
Figure 3.2.4a Post Monsoon maximum temperature normal for districts .............................................. 34
Figure 3.2.4b Post Monsoon maximum temperature normal for districts .............................................. 35
Figure 3.2.5a Annual maximum temperature normal for districts .......................................................... 36
Figure 3.2.5b Annual maximum temperature normal for physiographic regions .................................... 36
Figure 3.3.1a Winter minimum temperature normal for districts ........................................................... 37
Figure 3.3.1b Winter minimum temperature normal for physiographic regions .................................... 38
Figure 3.3.2a Pre-Monsoon minimum temperature normal for districts ................................................ 39
Figure 3.3.2b Pre-Monsoon minimum temperature normal for physiographic regions .......................... 40
Figure 3.3.3a Monsoon minimum temperature normal for districts ....................................................... 41
Figure 3.3.3b Monsoon minimum temperature normal for districts ....................................................... 41
Figure 3.3.4a Post Monsoon minimum temperature normal for districts ............................................... 42
Figure 3.3.4b Post Monsoon minimum temperature normal for districts ............................................... 43
Figure 3.3.5a Annual minimum temperature normal for districts ........................................................... 44
Figure 3.3.5b Annual minimum temperature normal for districts ........................................................... 44
Figure 4.1a: Seasonal and annual maximum temperature time series of Nepal ..................................... 45
Figure 5.1a: Winter precipitation trend for districts. .............................................................................. 49
Figure 5.1b: Winter precipitation trend for physiographic regions. ........................................................ 50
Figure 5.2a: Pre-Monsoon precipitation trend for districts. .................................................................... 51
Figure 5.2b Pre-Monsoon precipitation trend for physiographic regions. .............................................. 52
Figure 5.3a Monsoon Precipitation trend for districts. ........................................................................... 53
Figure 5.3b Monsoon Precipitation trend for physiographic regions. ..................................................... 54
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Figure 5.4a Post-Monsoon Precipitation trend for districts. ................................................................... 55
Figure 5.4b Post-Monsoon Precipitation trend for physiographic regions. ............................................ 55
Figure 5.5a Annual Precipitation trend for districts. ............................................................................... 56
Figure 5.5b Annual Precipitation trend for physiographic regions. ......................................................... 57
Figure 6.1a Winter Maximum Temperature trend for districts. .............................................................. 59
Figure 6.1b Winter Maximum Temperature trend for physiographic regions. ........................................ 60
Figure 6.2aPre-Monsoon Maximum Temperature trend for districts. .................................................... 61
Figure 6.2bPre-Monsoon Maximum Temperature trend for districts. ................................................... 62
Figure 6.3aMonsoon Maximum Temperature trend for districts. .......................................................... 63
Figure 6.3bMonsoon Maximum Temperature trend for districts. .......................................................... 64
Figure 6.4aPost-Monsoon Maximum Temperature trend for districts. .................................................. 65
Figure 6.4bPost Monsoon Maximum Temperature trend for districts. .................................................. 66
Figure 6.5a Annual Maximum Temperature trend for districts. ............................................................. 67
Figure 6.5b Annual Maximum Temperature trend for districts. ............................................................. 68
Figure 7.1a Winter Minimum Temperature trend for districts. .............................................................. 70
Figure 7.1b Winter Minimum Temperature trend for physiographic regions. ....................................... 71
Figure 7.2a Pre- Monsoon Minimum Temperature trend for districts. .................................................. 72
Figure 7.2b Pre-Monsoon Minimum Temperature trend for physiographic regions. ............................. 73
Figure 7.3a Monsoon Minimum Temperature trend for districts. ........................................................... 74
Figure 7.3b Monsoon Minimum Temperature trend for physiographic regions. ................................... 75
Figure 7.4a Post-Monsoon Minimum Temperature trend for districts. .................................................. 76
Figure 7.4b Post Monsoon Minimum Temperature trend for physiographic regions. ........................... 77
Figure 7.5a Annual Minimum Temperature trend for districts. .............................................................. 78
Figure 7.5b Annual Minimum Temperature trend for physiographic regions. ....................................... 79
Figure 8.1 District level number of rainy days trend. .............................................................................. 80
Figure 8.2 District level Very Wet Days (R95P) trend. ............................................................................. 81
Figure 8.3 District level Extremely Wet Days (R99P) trend. .................................................................... 81
Figure 8.4 District level Consecutive Dry Days (CDD) trend. ................................................................... 82
Figure 8.5 District Level Consecutive Days (R95P) trend. ........................................................................ 83
Figure 8.6 District level Cool Days trend. ................................................................................................. 84
Figure 8.7 District level Cool Nights trend. .............................................................................................. 85
Figure 8.8 District level Warm Nights trend. ........................................................................................... 86
Figure 8.9 District level Warm Days trend. .............................................................................................. 87
Figure 8.10 District level Warm Spell duration trend. ............................................................................. 88
Figure 8.11 District level Cold Spell Duration Trend. ............................................................................... 89
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List of Tables
Table 2: Extreme indices and their descriptions....................................................................................... 22
Table 4: Climatic Trend of Nepal .............................................................................................................. 45
Table 5.1: Summary of number of districts with positive and negative trends in seasonal and annual
precipitation ............................................................................................................................................. 48
Table 5.2: Seasonal and Annual Precipitation Trends in Physiographic Regions of Nepal ....................... 48
Table 6.1: Summary of number of districts with positive and negative trends in seasonal and annual
maximum temperatures ........................................................................................................................... 58
Table 6.2: Seasonal and Annual Maximum Temperature Trends in the Physiographic Regions ............. 58
Table 7.1: Summary of number of districts with positive and negative trends in seasonal and annual
minimum temperatures............................................................................................................................ 69
Table 7.2: Seasonal and Annual Minimum Temperature Trends in the Physiographic Regions .............. 69
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Executive Summary The Paris Agreement has a provision that adaptation action to climate change should be based on and
guided by the best available science, as appropriate. One of the basic tools to understand climate change
is to analyze climate change from atmospheric observations. This report on observed climate trends
analysis, using improved methods and data, for the NAP process identifies the following key findings:
All Nepal Climate Trend:
Significant trends (positive) are observed in annual and seasonal All Nepal maximum temperature.
All Nepal minimum temperature show significant trend (positive; 0.014oC/yr) only in monsoon
season, while no significant trends are observed in precipitation trends.
All Nepal annual maximum temperature trend is significantly positive (0.056oC/yr) while All Nepal
annual minimum temperature trend is positive (0.002oC/yr) but is insignificant.
Precipitation Trends:
At district level, pre-monsoon and monsoon precipitation shows both significant positive and
negative trends in few districts while winter and post-monsoon precipitation trends are insignificant
in most of the districts. The significantly highest positive rainfall trend is observed in Syangja and
Parbat districts in monsoon season.
Though insignificant, the southern districts of FWDR show positive precipitation trends persistent in
three seasons (winter, pre-monsoon and monsoon seasons). Monsoon precipitation is increasing in
all the districts in FWDR and central part of WDR and is decreasing in majority of districts east of
83E.
In physiographic regions, only pre-monsoon precipitation shows significant trend (positive) in the
High-Himalayan region. In other seasons, precipitation trends are insignificant in all the
physiographic regions. Though insignificant, the High Mountain region shows the highest decreasing
rainfall trend and Terai region shows positive trend in all seasons, except in post-monsoon.
Maximum Temperature Trend:
The positive temperature trend is highly significant in majority of districts (more than 90% of the
total districts) and in all physiographic regions in all the seasons, except in Terai districts in winter.
Both at district and physiographic levels, seasonal and annual maximum temperature trends
(majority of which are significant) show a pattern in relation to altitude with negative or small
positive trend in lower altitudes and high positive trend in higher altitudes.
At the district level, the highest significant positive trend (0.12oC/yr) is observed in winter season
(Manang district).
At physiographic level, all five regions show significant positive trend in all seasons, except in Terai
in winter and pre-monsoon, and in Siwaliks in winter. In High Mountains and High Himalayas, the
highest positive trend is found in winter season and in Terai, Siwaliks and Middle Mountains, the
highest positive trend is found in monsoon season.
Minimum temperature Trend
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The negative minimum temperature trend is significant in the northwestern districts in winter and
post-monsoon seasons while positive minimum temperature trend is significant in majority of
southern (in Terai to Mid Mountains) districts in EDR, CDR and WDR in all the seasons.
Both at district and at physiographic levels, seasonal and annual minimum temperature trends,
though majority are insignificant, show positive trends in lower elevation and negative in the higher
elevation. This pattern is opposite to that of maximum temperature trends.
At the district level, significantly highest positive trend (0.046oC/yr) is found in Dolpa district in
monsoon and the significantly highest negative trend (-0.076oC/yr) in Humla district in winter.
At the physiographic level, Terai and Siwaliks show significant increasing trend in most of the
seasons. Though insignificant, High Mountain and High Himalayan regions show decreasing trend in
all seasons, except in monsoon. The negative trend is significant only in winter season in the High
Himalayas.
Extreme Temperature trends:
Cool days are decreasing in majority of the districts while cool nights are increasing in the northwest
and northern parts and decreasing in the southeast districts significantly. Warm days and warm
nights are in significantly increasing trend in majority of the districts. Warm spell duration is
increasing in majority of the districts significantly and cold spell duration is increasing significantly
only in the FWDR.
Extreme Precipitation Trends:
Number of rainy days is increasing significantly mainly in the northwestern districts. Very wet days
and extremely wet days are also decreasing significantly, mainly in the northern districts.
Consecutively dry days are decreasing significantly, mainly in the northwest districts while
consecutive wet days are increasing significantly in the northern districts of MWDR, central part of
WDR and EDR.
It is noteworthy to point out that the magnitude of maximum temperature trend is higher than minimum
temperature trends in all seasons. Signals from maximum temperature trends are more robust than
from minimum temperature and precipitation signals. Finally, the observed climate trends in districts
and physiographic regions along with the information on significance level presented and analyzed in
this report will provide a better guidance for the NAP process and the thematic groups.
14
1 Background
1.1 Introduction
Realising urgency of building adaptive capacity and resilience, Parties to the UNFCCC at Cancun, Mexico in 2010 established a process to enable LDC Parties to formulate and implement national adaptation plans (NAPs), building upon their experience in preparing and implementing National Adaptation Programme of Action (NAPAs), as a means of identifying medium- and long-term adaptation needs and developing and implementing strategies and programmes to address those needs. The COP 17 held at Durban issued the initial guidelines for NAPs formulation. As per its mandate, the LDC Expert Group (LEG) prepared the NAP Technical Guidelines to provide guidance to LDCs on the NAP formulation process. Each COP decision provides ample opportunities to formulate NAP. Article 7 of the Paris Agreement (2015) urges each Party to, inter alia, engage in adaptation planning processes and implementation of actions, including a process to formulate and implement NAP. The Objectives of the NAP process is to reduce vulnerability to the impacts of climate change, by building adaptive capacity and resilience; and facilitate the integration of climate change adaptation, in a coherent manner, into relevant new and existing policies, programmes and activities, in particular development planning processes and strategies, within all relevant sectors and at different levels, as appropriate. The Paris Agreement has a provision that adaptation action should be based on and guided by the best available science, as appropriate. Each Party is obliged to submit and update periodically an adaptation communication. In this pursuit, the Department of Hydrology and Meteorology (DHM), a dedicated and responsible institution for climate data in Nepal of the Ministry of Population and Environment (MoPE), took a lead role and worked in collaboration with International Centre for Integrated Mountain Development (ICIMOD) and Practical Action to study observed climatic trend of Nepal. The purpose of the study is to analyse climate change trend using most updated climatic data and available methods. Previously detailed study on historical climate trend was conducted by Practical Action Nepal (PAN) in 2009 using data from 1976-2005 and DHM (2015) using data from 1971-2012. Prior to these two studies, most studies focused either only on single climate variable (maximum temperature or precipitation or extremes only) or only on All-Nepal average trend or only on station level trends (Shrestha et al. 1999, Baidya et al., 2008). Taking into consideration the results and limitations of previous studies conducted by PAN (2009) and DHM (2015), in particular linear trend analysis and with no significance test of the trends and lack of trend analysis of extreme events, this study has considered adequately non-linear (skewed) and auto-correlation pattern of climatic time series and use of non-parametric test for non-linear time series and significance test of the trends. This study includes extreme event trend analysis at district levels in the spirit of the NAP process and adaptation planning. This climate trend analysis is a part of Nepal's NAP formulation process. The MoPE has launched the NAP process in September 2015 and engaged the NAP team in May 2016. Nepal's NAP follows a process as per Decision 5/CP.17 (initial guidelines for NAP process) and NAP Technical
15
Guidelines and focuses on analysing current and future climate scenarios. This report provides latest updates on climate trend in Nepal.
1.2 Objectives The main objective of this study is to analyse seasonal and annual climate change trend in Nepal at
district and physiographic levels for the NAP process.
1.3 The Report Following considerations were made during the preparation of this report:
This report is prepared on historic climate trend for Nepal using best available data and tools, as also
provisioned in the Paris Agreement to use the best available science.
This study is based on quality controlled meteorological data in order to enhance the quality of the
report and assure the best output/outcome.
The study is also based on 1km x 1 km for temperature and 5km x 5km for precipitation daily gridded
data set.
This report presents Nepal average, individual district average and individual physiographic zone
average of normal annual and seasonal rainfall and maximum and minimum temperatures using
gridded data. This is the first study in Nepal that uses gridded data to calculate district-wise normal
rainfall and temperature.
This study calculates maximum and minimum temperature and precipitation trend for annual and
four seasons for each district with significance test at 95% and 99% confidence level. Based on
record, this is also the first study in Nepal that analyses climate trend at district level over whole
country.
Maps of eleven extreme climatic indices trend are prepared at district level.
The district and physiographic region normal climate and climate trends are presented in the maps
for annual and four seasons.
This report uses data of only two high altitude stations (> 2800 masl). Weighted average was not
used while averaging precipitation and temperature at district and physiographic levels, and district
trends were calculated using district average timeseries.
1.4 Study Units
The climatic normal and climate trends are calculated in two types of study units: Districts and
Physiographic regions. Figure 1.1 shows 75 districts of Nepal and their political boundaries.
Nepal is divided into five physiographic zones based on elevation, increasing from south to
north. The five zones are: Terai (59-200 masl), Siwaliks (200-1500 masl), Middle Mountains
(1000-2500 masl), High Mountains (2200-4000 masl) and High Himalayas (>4000 masl). Figure
1.2 shows 5 physiographic regions of Nepal.
16
Figure 1.1 Districts of Nepal
Figure 1.2: Physiographic Regions of Nepal
17
1.5 Seasons According to rainfall and temperature there are four seasons in Nepal. The climatic normal and trends
are calculated for these four seasons. December, January and February is winter season in Nepal. It is
the coldest season and driest season. March to May is considered pre-monsoon season. Thunderstorms
are common in this season. June to September is monsoon season. It is the rainiest season. October and
November is post-monsoon season.
2 Data and Methodology
2.1 Data Two types of data are used in this report. For temperature analysis, daily temperature data from 93
climate stations are used. Out of 93, 92 stations are established by DHM and one station, Pyramid, was
established by EVK2 Project. Out of 92 DHM climate stations, 63 Stations were used in DHM (2015)
study. The list of stations along with their meta-data is presented in Table A1 in the Appendix. Figure
2.1a shows spatial distribution of stations and Figure 2.1b shows number of stations in each district. The
number of stations used in each district varies from zero (in 13 districts) to three (in 3 districts). Other
districts have 1-2 stations. The number of stations in each district is listed in Table A2 in the Appendix.
For precipitation analysis, 0.05 degree APHRODITE (Yatagai et al., 2009, 2012) daily gridded data was
used. This data base for Nepal is based only on DHM rain gauge data. APHRODITE data followed 1) 14
objective quality checking process for the gauged data for the errors in station metadata and serial data;
2) the interpolation method based distance-weighted method with consideration of orographic effects
on precipitation. Andermann et al (2014) concludes that APHRODITE data is best gridded data available
in the Himalayan front for the temporal scale of daily or higher. The detail methodology is illustrated in
Yatagai et al (2012). Current study uses daily data from 1971 to 2014, both for temperature and rainfall
analysis.
18
Figure 2.1a: Distribution of 93 stations used for this study
Figure 2.1b: Districtwise number of stations used in this study
19
2.2 Methodology
Figure 2.2 shows schematic diagram of methodology followed in the study. The detail explanation of each step is discussed below:
2.2.1 Data Quality Check
The daily temperature data of 92 DHM stations were first quality checked using RClimdex
software. RClimdex software is free software which also tests quality of the meteorological
data. The methods used in RClimdex quality check is discussed in Alexander et al (2006). The
stations that showed outliers and unusual values in data were further processed. The outliers
and unusual values were corrected for individual stations by replacing them by average of the
value from previous day and the next day. Moreover, for the stations that showed data change
point, DHM regional offices were contacted for the confirmation of station location changes.
No change in location was reported for those stations and thus, those stations were considered
in this analysis.
2.2.2 High Altitude Station Missing Data Filling
Out of 93 stations, only two stations used are located in the altitude at about 3000m or above. These
two stations are: Simikot (2993m) in the west in Humla District and Pyramid (5035m) in the east in
Solukhumbu district. Simikot station was established in 1989 and Pyramid was established in 1993. So,
no data were available in these high Himalayan stations prior to 1989 and 1993 respectively. When the
data was interpolated using RClimdex prior to 1989 for Simikot and 1993 for Pyramid, the temperatures
showed warm bias and this might lead to either no trend or negative trend. Therefore, the missing data
from 1971 was first filled in both of these stations using the data from correlated neighbouring station
(at lower altitude) that has data for 1971 to 1993. For Simikot, Doti station in Doti district and for
Pyramid, Jiri station in Dolkha district showed best correlations. Then for each month average rate of
decrease of temperature from Doti to Simikot and from Jiri to Pyramid due to elevation increase was
calculated. This is based on the assumption that surface air temperature decreases from low elevation
to high elevation. This monthly average rates were used as a coefficient to estimate daily temperature
from low elevation station to high elevation station for the missing data period. The monthly average
“lapse rates” for Jiri-Pyramid and Doti-Simikot were calculated both for maximum and minimum
temperature separately and are shown in Table A2 in the Appendix.
20
Figure 2.2 Schematic diagram of methodology
2.2.3 Gridding and Interpolation of Temperature Data
Since APHRODITE precipitation data is DHM gauge based high resolution gridded data set, further
gridding was performed only for temperature data. After quality check procedure and filling of high
altitude missing data, the temperature daily data, from 1971 to 2014, was interpolated at grid size 1x1
Km using Co-Kriging (in R environment) developed in house by DHM with the technical assistance and
support from Finish Meteorological Institute (FMI). The script considers elevation while interpolating
the variable. This gridding method not only interpolates the temperature data where there are no
stations but also fills the missing data in all 92 stations.
2.2.4 District level and Physiographic Region Seasonal and Annual Time series
Calculation
Area averaged daily time series (i.e. for 75 districts and 5 physiographic regions for 1971-2014) of
maximum temperature, minimum temperature, and precipitation were extracted from gridded data
using publicly available GrADS (GRid Analysis and Display, http://cola.gmu.edu/grads/grads.php)
Trend analysis using Mann-Kendall & Sen’s Slope method in Microsoft excel (MAKESEN)
Extreme Indices of gridded average
Result visualization using ArcGIS software
Computation of seasonal and annual temperature and precipitation time series 1. District averaged 2. Development region averaged 3. Physiographic region averaged
Daily data of 93 stations High resolution gauge based
gridded data from APHRODITE
for precipitation
QC using RClimdex
Gap filling of missing
data using lapse rate
approach
Interpolation
using Universal
Co-Kriging in R
Language
Value extraction using GrADS at daily scale
1. District averaged
2. Development region averaged
3. Physiographic region averaged
21
software. From daily area averaged time series of corresponding districts and physiographic regions,
monthly time series (1971-2014) were calculated for each of the 75 districts and each of the 5
physiographic regions. These precipitation, maximum temperature and minimum temperature were
used to calculate seasonal normal and for trends analysis.
2.2.5 Trend Analysis
Combined Mann-Kendall test and Sen’s Slope methods were used to analyse type, magnitude and
significance of trend in timeseries data. Mann-Kendall trend test is non-parametric method that tests
the presence of monotonic positive or negative trend in a timeseries. It tests if the monotonic trend is
significant or not, whereas Sen’s Slope method estimates the magnitude of the linear trend (slope). In
this study, MS-Excel program called MAKESENS version 1.0 developed by Finish Meteorological Institute
in 2002 (Sami, 2002) was used to calculate magnitude, sign and significance of the trend. This program
incorporates both Mann-Kendall test and Sen’s Slope method for trend analysis. The detail calculation
method is explained Sami et al (2002).
A primary goal of significant test in trend analysis is to identify “signals” in change against the ‘noise’ that occur internally generated fluctuation in climate system. If the ‘signal’ is small relative to the noise, we may observe a trend in the data by chance, purely due to random fluctuations of the noise. The significance test examines if the observed trend is a signal of change or simply a random fluctuation (i.e., noise). The Man-Kendall method of significance test uses the hypothesis testing approach. It tests the null hypothesis that the monotonic trend is by chance (due to noise) in the climate data against the alternative hypothesis that there is a monotonic trend (signal) in the climate data at a certain significant level. In this study the significant test at the level of 0.001, 0.01 and 0.05 or confidence levels (CL) at 99.9%, 99% & 95% were used. Each of the significance level indicates the probability that the observed trend could have occurred by chance. Significant trend at 0.001 (at 99.9% CL) means that the probability that the null hypothesis (the trend is by chance) might be true is less than 0.1%. With such low probability the null hypothesis is likely to be incorrect and therefore the alternative hypothesis can accepted at the confidence level of 99.9%. In other words, the trend in the data can be accepted as a real signal at the confidence level of 99.9%. Similarly, significant trend at 0.01 (at 99% CL) means the trend in data can be accepted as a real signal at the confidence level of 99%. Significant trend at 0.05 (at 95% CL) means the trend in data can be accepted as a real signal at the confidence level of 95%. In this study, significance at confidence level lower than 95% is considered as insignificant and significant means significance at 95% CL.
22
2.2.6 Extreme Indices Analysis
Timeseries of extreme indices were calculated by writing a program in Fortran. Significance and the slope of the trend of output indices were estimated using Mann-Kendall and Sen’s slope method in
MS-Excel. Timeseries of extreme indices were obtained from GrADS extracted area averaged
data. Description of 11 extreme climate indices is shown in Table 2.
Table 2: Extreme indices and their descriptions
Extreme Climate Indices
Descriptions
a. Cool nights Percentage of days when minimum temperature 90th percentile
e. Warm spell duration Annual count of days with at least 6 consecutive days when maximum temperature > 90th percentile
f. Cold spell duration
Annual count of days with at least 6 consecutive days when minimum temperature < 10th percentile
g. Very wet days Annual total precipitation when daily rainfall >95th percentile
h. Extremely Wet days Annual total precipitation when daily max rainfall >99th percentile
i. Consecutive dry days Maximum number of consecutive days with daily precipitation 1mm
2.2.7 Report preparation process
The Government constituted a Steering Committee under the coordination of the Director General of
the DHM for necessary guidance, supervision and coordination for the preparation of this report.
The DHM formed a Technical Committee under the coordination of Senior Divisional Meteorologist for
data checking, quality control, technical supervision of the work of the consultant, and finalisation of
this report.
In order to best utilise the available climate data for Nepal's NAP formulation process, the Technical
Committee organised consultations at regular basis with NAP Team and those engaged in supporting
the NAP process, in particular ICIMOD and Practical Action for sharing on approaches, data availability
and results. This report accommodates concerns and inputs of the reviewers, to the extent possible.
23
3 Climatic Normal This sections presents district and physiographic regions normal of annual and seasonal precipitation,
maximum temperature and minimum temperature. The district and physiographic regions normal
climatic values are presented in the Table A3a and Table A3b in the Appendix.
3.1 Normal Precipitation for Districts and Physiographic Regions
3.1.1 Winter Precipitation
Normal winter precipitation for districts is shown in Figure 3.1.1a. Districts in the Far Western
Development Region (FWDR) have higher normal winter rainfall than rest of the districts in the country.
The normal winter precipitation decreases eastward with lowest rainfall in the districts of Central
Development Region (CDR) and Eastern Development Region (EDR). The Figure shows lowest winter
precipitation over Mustang, Dhankuta and few Terai districts in EDR and CDR. Figure 3.1.1b shows the
normal winter precipitation for physiographic regions. It shows that the normal winter precipitation is
lowest over the High Himalayas and Terai regions.
Figure 3.1.1a: Winter precipitation normal for districts
24
Figure 3.1.1b: Winter precipitation normal for physiographic regions
3.1.2 Pre – Monsoon Precipitation
Figure 3.1.2a shows the normal pre-monsoon precipitation at district level. It shows the lowest pre-
monsoon precipitation over Mustang. Most districts in EDR and CDR, and Baitadi district receives the
highest normal rainfall during pre-monsoon. Figure 3.1.2b shows the normal pre-monsoon precipitation
for physiographic regions. It shows higher precipitation in Mid Mountains and High Mountains than in
Terai, Siwaliks and High Himalayas.
25
Figure 3.1.2a: Pre-Monsoon precipitation normal for districts
Figure 3.1.2b: Pre-Monsoon precipitation normal for physiographic regions
26
3.1.3 Monsoon Precipitation
Figure 3.1.3a shows the normal monsoon precipitation for all 75 districts. It shows that the northern
districts of the Western Development Region (WDR) and Mid-Western Development Region (MWDR) as
well as Rasuwa, Dhankuta and Tehrathum districts receive below 1000 mm of rainfall. Monsoon
precipitation is lowest over Mustang ( 2000 mm). Figure
3.1.3b shows the normal monsoon precipitation for physiographic regions. The High Himalayas receive
less than 1000mm while rest of the regions receives precipitation between 1000mm and 1500mm.
Figure 3.1.3a: Monsoon precipitation normal for districts
Figure 3.1.3b: Monsoon precipitation normal for physiographic regions.
27
3.1.4 Post-Monsoon Precipitation
Figure 3.1.4a shows the normal post-monsoon precipitation for districts. Only three districts in EDR and
Kaski in WDR receive more than 100mm rainfall whereas Mustang and Dolpa receives lowest rainfall (<
20mm). Figure 3.1.4b shows the normal post-monsoon precipitation for physiographic regions. It shows
that the High Himalayas receives below 50 mm of rain whereas the rest of the physiographic regions
receive between 50mm and 100mm of rainfall.
Figure 3.1.4a: Post-Monsoon precipitation normal for districts
Figure 3.1.4b Post-Monsoon precipitation normal for physiographic regions
28
3.1.5 Annual Precipitation
Figure 3.1.5a shows the normal annual precipitation for the districts. It shows that Mustang receives the
lowest rainfall (
29
3.2 Normal Maximum Temperature
3.2.1 Winter maximum temperature
Figure 3.2.1a shows normal winter maximum temperature for the districts. Manang has the lowest
(
30
Figure 3.2.1b: Winter maximum temperature normal for physiographic regions
3.2.2 Pre – Monsoon maximum temperature
Figure 3.2.2a shows the normal pre-monsoon maximum temperature for the districts. Manang, Mustang
and Dolpa have the lowest (30oC) normal pre-monsoon maximum temperature. Figure 3.2.2b shows the
normal pre-monsoon maximum temperature for the physiographic regions. The High Himalayas and
High Mountains have the lowest pre-monsoon maximum temperature (0oC-5oC) whereas the Siwalik
and the Terai regions have the highest pre-monsoon maximum temperature (30oC-35oC).
31
Figure 3.2.2a: Pre-Monsoon maximum temperature normal for districts
32
Figure 3.2.2b Pre-Monsoon maximum temperature normal for physiographic regions
3.2.3 Monsoon maximum temperature
Figure 3.2.3a shows the normal monsoon maximum temperature for the districts. Manang has
the lowest (30oC) normal monsoon maximum temperature. Figure 3.2.3b
shows the normal monsoon maximum temperature for the physiographic regions. The High
Himalayas has the lowest monsoon maximum temperature (10oC-15oC) whereas the Siwalik and
the Terai regions have the highest monsoon maximum temperature (30oC-35oC).
33
Figure 3.2.3a Monsoon maximum temperature normal for districts
Figure 3.2.3b Monsoon maximum temperature normal for districts
34
3.2.4 Monsoon maximum temperature
Figure 3.2.4a shows the normal post-monsoon maximum temperature for districts. Mustang and
Manang have the lowest ( 30oC). Figure 3.2.4b shows the normal post-
monsoon maximum temperature for the physiographic regions. The High Himalayas has the lowest post
monsoon maximum temperature (0oC-5oC) whereas the Terai region has the highest post monsoon
maximum temperature (30oC-35oC).
Figure 3.2.4a Post Monsoon maximum temperature normal for districts
35
Figure 3.2.4b: Post Monsoon maximum temperature normal for districts
3.2.5 Annual maximum temperature
Figure 3.2.5a shows the normal annual maximum temperature for the districts. Manang has the
lowest (30oC).
36
Figure 3.2.5a: Annual maximum temperature normal for districts
Figure 3.2.5b: Annual maximum temperature normal for physiographic regions
37
3.3 Normal Minimum Temperature
3.3.1 Winter minimum temperature
Figure 3.3.1a shows the normal winter minimum temperature for the districts. The northern
districts of MWDR, WDR and Solukhumbu have the lowest (
38
Figure 3.3.1b: Winter minimum temperature normal for physiographic regions
3.3.2 Pre – Monsoon minimum temperature
Figure 3.3.2a shows the normal pre-monsoon minimum temperature for the districts. Manang
has the lowest (
39
have the highest normal pre-monsoon minimum temperature (15oC-20oC).
Figure 3.3.2a: Pre-Monsoon minimum temperature normal for districts
40
Figure 3.3.2b: Pre-Monsoon minimum temperature normal for physiographic regions
3.3.3 Monsoon minimum temperature
Figure 3.3.3a shows the normal monsoon minimum temperature for the districts. Humla, Dolpa,
Mustang and Manang districts have the lowest (
41
Figure 3.3.3a Monsoon minimum temperature normal for districts
Figure 3.3.3b Monsoon minimum temperature normal for districts
42
3.3.4 Post-Monsoon minimum temperature
Figure 3.3.4a shows the normal post monsoon minimum temperature for the districts. Dolpa,
Mustang and Manang districts have the lowest (
43
Figure 3.3.4b Post Monsoon minimum temperature normal for districts
3.3.5 Annual minimum temperature
Figure 3.3.5a shows the normal annual minimum temperature for the districts. Humla, Mugu,
Dolpa, Mustang and Manang districts have the lowest (
44
Figure 3.3.5a Annual minimum temperature normal for districts
Figure 3.3.5b Annual minimum temperature normal for districts
45
4 All Nepal Climatic Trends Seasonal and annual climatic trends represent Nepal’s averaged precipitation, maximum temperature
and minimum temperature trends (Table 4).
Table 4: Climatic Trend of Nepal
Seasons Precipitation
(mm/yr)
Maximum Temperature
(oC/yr)
Minimum Temperature
(oC/yr)
α Q α Q α Q
Winter 0 -0.072 *** 0.054 0 -0.009
Pre-monsoon 0 -0.081 *** 0.051 0 -0.003
Monsoon 0 -0.085 *** 0.058 * 0.014
Post-monsoon 0 -0.324 *** 0.056 0 -0.005
Annual 0 -1.333 *** 0.056 0 0.002
4.1 All Nepal Maximum Temperature Trend
All Nepal maximum temperature trend is positive and significant at 99.9% annually and for all
the seasons. Monsoon season has the highest positive trend of 0.058oC/yrear and pre-
monsoon has the lowest trend of 0.051oC/yrear. The average annual maximum temperature
trend is 0.056oC/yrear for the period of 1971-2014. Seasonal and annual timeseries of
maximum temperature of Nepal is illustrated in Figure 4.1a which shows increasing trend with
inter-annual variability in all seasons.
Figure 4.1: Seasonal and annual maximum temperature time series of Nepal
Note: DJF means months of December, January and February; MAM is for March, April and May; JJAS
is for June, July, August and September; and ON denotes for October and November.
5
10
15
20
25
30
19
71
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73
19
75
19
77
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79
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81
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83
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85
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87
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89
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91
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93
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95
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97
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99
20
01
20
03
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05
20
07
20
09
20
11
20
13
Tem
pe
ratu
re (
oC
)
DJF MAM JJAS ON Annual
46
4.2 All Nepal Minimum Temperature Trend
Magnitude and the significance of the seasonal and annual minimum temperature trend is given in Table
4 and it shows increasing minimum trend only annually and in the monsoon season but only monsoon
trend is significant at 95% CL. During other seasons minimum temperatures are in decreasing trends and
they are insignificant at 95% or higher CL. Seasonal and annual timeseries of all Nepal averaged minimum
temperature is shown in the Figure 4.2.
Figure 4.2: Seasonal and annual minimum temperature trend of Nepal
4.3 All Nepal Precipitation Trend
Seasonal and annual all Nepal precipitation trends are shown in Table 4. It shows precipitation in all
season is decreasing with the highest decreasing trend (-0.3 mm/yr) in the post-monsoon season. Annual
decrease in precipitation in Nepal is -1.3 mm/yr. However, all the decreasing trends are insignificant.
Figure 4.3 shows the Nepal averaged precipitation timeseries.
0
2
4
6
8
10
12
14
16
18
Tem
pe
ratu
re (
oC
)
DJF MAM JJAS ON Annual
47
Figure 4.3 Precipitation time series of Nepal (a) Pre-Monsoon (b) Monsoon (c) Post-Monsoon (d) Winter (e) Annual
4.4 Summary of All Nepal Climate Trends
Among three All Nepal climatic trends, only Nepal maximum temperature trend shows
significantly increasing trend annually and in all seasons. All Nepal minimum temperature
show significant positive trend only in monsoon season, while no significant trends are found
in precipitation trends. Previous studies have found slightly lower positive trend (0.05 oC/yr)
of all Nepal averaged maximum temperature (PAN, 2009; Shrestha et al., 1999) than this
study (0.058oC/yr).
0
50
100
150
200
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71
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Rai
nfa
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m/y
r)
Year
Post-Monsoon
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Rai
nfa
ll(m
m/y
r)
Year
Winter
0
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400
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71
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Rai
nfa
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m/y
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Year
Pre-Monsoon
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Rai
nfa
ll(m
m/y
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Year
Monsoon
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Rai
nfa
ll(m
m/y
r)
Year
Annual
(a) (b)
(c) (d)
(e)
48
5 Precipitation Trends for Districts and Physiographic Regions The annual and seasonal precipitation trends for districts and physiographic regions are discussed in this chapter. District level precipitation trends are shown in Table A5 in the Appendix. The summary of number of districts with positive and negative trends of seasonal and annual precipitation is shown in Table 5.1 below. Physiographic precipitation trends are shown in Table 5.2 below.
Table 5.1: Summary of number of districts with positive and negative trends in seasonal and annual
precipitation
Winter Pre-monsoon
Monsoon Post-monsoon
Annual
Number of districts with negative trend
42 (0) 35 (3) 47 (5) 73 (2) 47 (8)
Number of districts with positive trend
33 (0) 40 (4) 28 (2) 2(0) 28(3)
Note: Number in parenthesis indicates number of districts with significant trend at 95% or higher confidence level (Table A5 in Appendix)
Table 5.2: Seasonal and annual Precipitation trends in physiographic regions of Nepal
Physiographic Regions
Winter Pre-monsoon Monsoon Post-monsoon Annual
α Trend
(mm/yr) α Trend
(mm/yr) α Trend
(mm/yr) α Trend
(mm/yr) α Trend
(mm/yr)
Terai 0 0.09 + 1.24 0 0.51 0 -0.26 0 0.49
Siwaliks 0 0.08 0 0.75 0 -0.60 0 -0.38 0 -1.48
Mid Mountain 0 0.03 0 0.03 0 -0.45 0 -0.43 0 -1.58
High Mountains 0 -0.06 0 -0.82 0 -1.19 0 -0.50 + -3.17
High Himalayas 0 -0.03 * -0.74 0 -0.21 0 -0.32 + -1.46
Note: Significant: * 95% CL, ** 99% CL and *** 99.9% CL ; insignificant at 95% CL : + , 0
5.1 Winter Precipitation Trend
Winter precipitation trend for the districts is shown in Figure 5.1a and summary of number of districts with negative and positive winter precipitation trends is shown in Table 5.1. The Table shows 42 districts have negative trends and 33 districts have positive trends in winter precipitation but these trends are insignificant in all the districts. The positive trends are observed in the northern districts of MDR, WDR and EDR and southern districts of FDR, MDR, and WDR and in few districts of CDR. Rest of the districts, mainly southern districts in Central and Eastern Development regions, have negative trends. However, none of districts show significant trend. The trend values of each district along with significance level are presented in Table A5 in the Appendix. The magnitude of the trend is also very small, between ± 2 mm/yr. Though insignificant, the highest increasing trend (0.51mm/yr) is observed in Humla while highest decreasing trend (-0.60mm/yr) is detected in Rasuwa (Table A5, Appendix).
49
Figure 5.1a: Winter precipitation trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank means insignificant at 95% CL)
Figure 5.1b shows winter precipitation trend in 5 physiographic regions of Nepal. Terai, Siwaliks and
Mid-Mountains show slightly increasing winter precipitation trend but trends are not significant at 95%.
The High Mountains and High Himalayas showed slightly decreasing winter precipitation tendency, and
these negative trends are also insignificant. It is noteworthy that both negative and positive trend values
are less than 0.1mm/yr. Though insignificant, winter precipitation trend is increasing at lower elevation
and decreasing in higher elevation. The highest decreasing trend is in High Mountain region and the
highest increasing trend is in Terai. (Table 5.2)
50
Figure 5.1b: Winter precipitation trend for physiographic regions. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank
means insignificant at 95% CL)
5.2 Pre-Monsoon Precipitation Trend
District level pre-monsoon precipitation trend is shown in Figure 5.2a and a number of districts with
positive and negative trends are shown in Table 5.1 above. Forty districts show positive trend, with trend
significant in 4 districts and 35 districts have negative trend, with trend significant in 3 districts (Table
5.1). Figure 5.2a shows positive trends in the southern districts of all the Development regions, while
northern districts in all the Development regions have negative pre-monsoon rainfall trends. The
significant positive trends are observed mainly in the Eastern and Central Development regions.
The district level trend values along with significance level are shown in Table A5 in the Appendix. The
highest significant increase trend (2.2mm/yr) is observed in Sunsari and the highest significant negative
trend (1.3mm/yr) is observed in Rasuwa. It is noteworthy that both winter and pre-monsoon
precipitation trends in the southern districts in FWDR, MWDR and WDR are in increasing trend.
51
Figure 5.2a: Pre-Monsoon precipitation trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank means insignificant at 95% CL)
Increasing trend of pre-monsoon precipitation is observed in Terai, Siwaliks and Mid Mountains, while
it shows decreasing trend in High Mountains and High Himalayas physiographic regions (Figure 5.2b).
These trends are insignificant, except significant negative trend in the High Himalayan region at 95% CL.
Though insignificant, the highest trend value (1.24mm/yr) is found in Terai. It is noteworthy that at lower
elevation pre-monsoon precipitation is increasing and at higher elevation it is decreasing, with highest
decrease in High Mountains (Table 5.2). This pattern is similar to winter precipitation trend (Figure 5.1b).
52
Figure 5.2b: Pre-Monsoon precipitation trend for physiographic regions. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL;
blank means insignificant at 95% CL)
5.3 Monsoon Precipitation Trend
Monsoon precipitation trends in the districts of Nepal are presented in Figure 5.3a and distribution of positive and negative trend in the districts is shown in Table 5.1. Monsoon precipitation trends are positive in 28 districts, out of which only two districts have significant trend, and trends are negative in 47 districts, out of which 5 district have significant trend. Figure 5.3a shows increasing monsoon precipitation in all the districts of FWDR and southwestern and northeastern districts in MWDR and central districts in the WDR, among which only Parbat and Syangja of WDR show significance at 95% CL. The figure shows decreasing monsoon precipitation in large parts of EDR,CDR and northern part of WDR. Among these districts with negative trend, only 5 districts (Manang, Dolakha, Ramechhap, Sindhuli and Ilam) have significance at 95% or higher CL. The southern districts of FWDR have positive precipitation trend, which is also observed in winter (Figure 5.1a) and pre-monsoon (Figure 5.2a) seasons. The monsoon precipitation trend values are shown in Table A5 in the appendix. The highest significant increasing trend (9.04mm/yr) is found in Syangja and the highest significant decreasing trend value (-7.5 mm/yr) is observed in Ilam district.
53
Figure 5.3a Monsoon Precipitation trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank means
insignificant at 95% CL)
Figure 5.3b presents monsoon precipitation trends in the physiographic regions. Terai has increasing trend while the rest of the physiographic regions have decreasing trend, but these trends are insignificant. Though insignificant, monsoon precipitation trend is positive in lower elevation and negative in the higher elevations, with highest decreasing trend in High Mountains (Table 5.2). This pattern is similar to winter (Figure 5.1b) and pre-monsoon (Figure 5.2b) precipitation trends.
54
Figure 5.3b Monsoon Precipitation trend for physiographic regions. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL;
blank means insignificant at 95% CL)
5.4 Post-monsoon Precipitation Trend
Figure 5.4a shows post-monsoon precipitation trend in districts of Nepal. Only two districts (Humla and Mugu) show positive trend and 72 districts show negative trend (Table 5.1). However, only two districts (Rasuwa and Solukhumbu) show significant negative trend, rest of the districts did not show any significant positive or negative trends. The post-monsoon trend pattern is totally different from previous three seasons (Figure 5.1a-Figure 5.3a). The districtwise trend values are presented in Table A5 in the Appendix. Significant highest decreasing trend (-1.1mm/yr) is found in Rasuwa district.
55
Figure 5.4a Post-Monsoon Precipitation trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank means
insignificant at 95% CL)
Post-monsoon precipitation trend in five physiographic regions are shown in Figure 5.4b. It shows
insignificant decreasing trend (0 to -1.9 mm/yr) in all five regions. Though insignificant, highest
decreasing trend is found in High Mountains (Table 5.1b)
Figure 5.4b Post-Monsoon Precipitation trend for physiographic regions. (Significance: * 95% CL, ** 99% CL, *** is 99.9%
CL; blank means insignificant at 95% CL)
56
5.5 Annual Precipitation
Figure 5.5a shows the annual precipitation trends along with their respective significance levels in 75 districts of Nepal. Twenty eight districts show increasing annual precipitation trend and 47 districts show decreasing annual precipitation trend (Table 5.1). Figure 5.5a shows that the annual precipitation trend pattern is almost similar to the monsoon precipitation trend pattern. Most of the districts in EDR and CDR and northern parts of WDR region show decreasing annual precipitation whereas most of districts in the FWDR and central districts of WDR show increasing trend. The districtwise trend values of annual precipitation are listed in Table A5 in the Appendix. Significantly highest decreasing annual precipitation trend is observed in Kaski and the significantly highest increasing trend (9.0mm/yr) is in Syangja.
Figure 5.5a Annual Precipitation trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank means insignificant at 95% CL)
Annual precipitation trend in 5 physiographic regions are shown in Figure 5.5b. Except Terai, all the physiographic regions show decreasing annual rainfall trend. As in seasonal precipitation trends, highest negative trend (-2 to -3 mm/yr) is found in High Mountain region. The pattern of decreasing rainfall trend with elevation is also found in annual precipitation trend.
57
Figure 5.5b Annual Precipitation trend for physiographic regions. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank
means insignificant at 95% CL)
5.6 Summary of Precipitation Trend
At district level, winter and post-monsoon precipitation trends are insignificant (Figure 5.1a and Figure
5.4). Pre-monsoon and monsoon precipitation shows both significant positive and negative trends in
few districts (Humla, Rasuwa, Ramechhap, Mahottari, Saptari, Sunsari and Morang in Figure 5.2a and
(Syangja, Parbat, Manang in Figure 5.3a).
Though insignificant, the southern districts of FWDR show positive precipitation trend persistent in three
seasons: winter, pre-monsoon and monsoon. It is also noteworthy that monsoon precipitation is
increasing in all the districts in FWDR and central part of WDR and is decreasing in majority of districts
east of 83E. Positive monsoon trend in all districts in FWDR might be a reflection of the rise in damage
due to extreme weather and flood events in FWDR in recent years. Similar might be the case in central
part of WDR where daily maximum precipitation is highest. Decreasing monsoon rainfall in the east,
where monsoon is most influential might be an indication of weakening of monsoon in the east. The
highest significant positive rainfall trend is observed in Syangja and Parbat districts in monsoon season.
In physiographic regions, only pre-monsoon precipitation shows significant trend (positive) in the High-
Himalayan region. In other seasons precipitation trends are insignificant in all the physiographic regions.
Though insignificant, the High Mountain region shows highest decreasing rainfall trend in all the seasons
and Terai region shows positive trend in all the season, except in post-monsoon.
58
6 Maximum Temperature Trend for Districts and Physiographic Regions The annual and seasonal maximum temperature trends for districts and physiographic regions are
discussed in this chapter. Districtwise maximum temperature trends along with significance levels are
listed in Table A6in the Appendix. The summary of number of districts with positive and negative
seasonal and annual maximum temperature is listed in Table 6.1 below. Physiographic maximum
temperature trends are shown in Table 6.2 below.
Table 6.1: Summary of number of districts with positive and negative trends in seasonal and annual
maximum temperatures
Winter Pre-monsoon
Monsoon Post-monsoon
Annual
Number of districts with negative trend
11(0) 1(0) 0 (0) 0 (0) 0 (0)
Number of districts with positive trend
64(59) 74(62) 75 (75) 75 (71) 75 (72)
Note: Number in parenthesis indicates number of districts with significant trend at 95% or higher confidence level (Table A6 in Appendix)
Table 6.2: Seasonal and Annual Maximum Temperature Trends in the Physiographic Regions
Physiographic Regions
Winter Pre-monsoon Monsoon Post-monsoon Annual
α Trend (oC/yr) α
Trend (oC/yr) α
Trend (oC/yr) α
Trend (oC/yr) α
Trend (oC/yr)
Terai 0 -0.004 0 0.018 *** 0.036 ** 0.028 *** 0.021
Siwaliks 0 0.010 * 0.031 *** 0.040 *** 0.033 *** 0.030
Mid Mountain *** 0.046 *** 0.049 *** 0.055 *** 0.052 *** 0.052
High Mountains *** 0.070 *** 0.062 *** 0.064 *** 0.064 *** 0.068
High Himalayas *** 0.101 *** 0.076 *** 0.072 *** 0.085 *** 0.086
Note: Significant: * 95% CL, ** 99% CL and *** 99.9% CL ; insignificant at 95% CL : + , 0
6.1 Winter Maximum Temperature Trend
Figure 6.1a shows winter maximum temperature trend in the districts of Nepal. It shows positive trend at significant at 99% or higher CL in majority of the districts, except in most of the Terai districts. All the Terai districts, west of Mahottari district show slightly decreasing trend, but are insignificant. Whereas eastern districts including Mohottari show increasing winter maximum temperature trend, among which only three districts (Jhapa, Morang and Sunsari) have significant positive trend at 95% or higher CL. The negative trends of Terai districts might be due to the long episode of fog events in winter since last decade. Moreover, the magnitude of winter maximum temperature trend is negative or lowest positive in the southernmost districts (Terai districts) and the magnitude increases towards north with elevation. It is interesting to note that 59 districts show significant positive trend at 95% or higher while 56 districts has significant positive trend at 99% or higher CL. All the significant trends are positive trend. No significant negative trend is recorded in any district. The highest positive
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trend (0.118oC/yr) is observed in Manang district and lowest positive trend (0.016oC/yr) is found in Makwanpur district (Table A6 in the Appendix).
Figure 6.1a Winter Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank means insignificant at 95% CL)
Figure 6.1b shows winter maximum temperature trend in five physiographic regions. It shows positive temperature trend significant at 99.9% CL in Mid Mountain, High Mountain and High Himalayan regions. Siwalik and Terai shows insignificant positive and insignificant negative winter maximum temperature trends respectively. The highest positive trend (0.101oC/yr) is in High Himalayas and the lowest positive trend (0.010oC/yr) in the Siwaliks (Table 6.2). Moreover the magnitude of the winter maximum temperature trend is negative in Terai and lowest positive in the Siwaliks and positive trend magnitude increases with altitude which is similar to winter maximum temperature trend for districts (Figure 6.1a)
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Figure 6.1b Winter Maximum Temperature trend for physiographic regions.(Significance: * 95% CL, ** 99% CL, *** is 99.9%
CL; blank means insignificant at 95% CL)
6.2 Pre-monsoon Maximum Temperature Trend
Pre-monsoon maximum temperature trend in districts of Nepal is shown in Figure 6.2a. It shows increasing trend in most of the districts except in Rautahat, which has negative trend. Most of the districts with positive trend are significant at 95% or higher CL, except in the districts in Terai.Positive trends in Terai districts are significant only in four eastern districts (Jhapa, Morang, Sunsari and Siraha) at 95% CL and the positive trends in rest of the Terai districts are not significant.Positive temperature trend in the districts increases towards north with the elevation. The pre-monsoon maximum temperature values are listed in Table A6 in the Appendix. This table shows, the highest significant positive trend (0.086oC/yr) is found in Darchula district and the lowest (0.024oC/yr) is found in Siraha district.
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Figure 6.2aPre-Monsoon Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL;
blank means insignificant at 95% CL)
Figure 6.2b shows pre-monsoon maximum temperature trend in five physiographic regions. It shows significant positive temperature trend in all the regions at 95% or higher CL, except in Terai. The trend values are shown in Table 6.2 above. This table shows that the Terai has lowest and insignificant positive trend and the High Himalayan region has the highest increasing trend (0.076oC/yr) with significance at 99.9% CL. Siwaliks has the lowest positive trend (0.031oC/yr) with significance at 95% CL. This is consistent with the pattern of pre-monsoon maximum temperature trend in districts of Nepal (Figure 6.2a). As in winter season (Figure 6.1b) the magnitude of positive pre-monsoon temperature trend increases with altitude.
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Figure 6.2bPre-Monsoon Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL;
blank means insignificant at 95% CL)
6.3 Monsoon Maximum Temperature Trend
Figure 6.3a shows monsoon maximum temperature trend for 75 districts of Nepal. Interestingly, it shows positive trend significant at 99.9% CL in all the districts. Except in Sarlahi and Rautahat, all the districts show positive trends higher than 0.04oC/yr. Most of the districts in the northwestern and northeastern parts of Nepal show higher positive trends. The monsoon maximum temperature trends are shown in Table A6 in the Appendix. This table shows that the highest positive trend in monsoon maximum temperature trend (0.090oC/yr) is observed in Dolpa district and the lowest positive trend (0.026oc/yr) in Rautahat district.
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Figure 6.3aMonsoon Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank
means insignificant at 95% CL)
Monsoon maximum temperature trend in five physiographic regions is shown in Figure 6.3b. It shows
significant positive temperature trend at 99.9% CL in all five regions. The Terai has lowest positive trend
(0.036oC/yr) and the magnitude increases northward with elevation and the High Himalayas has the
highest positive trend (0.072oC/yr) (Table 6.2). This is consistent with the distribution of monsoonal
maximum temperature trend in districts of Nepal and also follows increase in maximum temperature
trend with elevation as in winter (Figure 6.1b) and pre-monsoon (Figure 6.2b) seasons.
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Figure 6.3bMonsoon Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank
means insignificant at 95% CL)
6.4 Post-monsoon Maximum Temperature Trend
Figure 6.4a shows post-monsoon maximum temperature trend in the districts of Nepal. It shows
increasing trend at significant level 95% or higher CL in most of the districts, and insignificant positive
trend in Nawalparasi, Bara, Rautahat and Sarlahi. No negative maximum temperature trend is found in
any districts in this season. In post-monsoon season also the magnitude of the positive temperature
trend increases from south to north with the altitude.
The trend values of post-monsoon maximum temperature are shown in Table A6 in the Appendix. It
shows that the highest positive trend (0.094oC/yr) is observed in Taplejung district and lowest positive
trend (0.021oC/yr) is observed in Parsa district with significance higher than 95% CL.
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Figure 6.4aPost-Monsoon Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL;
blank means insignificant at 95% CL)
Figure 6.4b shows post-monsoon maximum temperature trend in five physiographic regions. It shows significant positive temperature trend at 99% CL in all five regions. The High Mountains and High Himalayan regions show highest increasing post-monsoon maximum temperature trend. The trend values for each region are shown in Table 6.2. It shows the lowest positive trend (0.028oC/yr) in Terai and the highest positive trend (0.085oC/yr) in High Himalayas. There is increase in temperature trend with the elevation from south to north which is consistent with the distribution of post-monsoon maximum temperature trend in districts.
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Figure 6.4bPost Monsoon Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL;
blank means insignificant at 95% CL)
6.5 Annual Maximum Temperature Trend
Figure 6.5a shows annual maximum temperature trend in districts. It shows significantly increasing trend at 99% or higher CL in all the districts, with insignificant positive trends in Bara, Rautahat and Sarlahi districts. The Figure shows increase in temperature trend with altitude from south to north. This pattern is consistent with the seasonal maximum temperature trend patterns. The annual maximum temperature trend values are listed in Table A6 in the Appendix. The highest significant positive trend (0.092oC/yr) is observed in Manang and lowest positive trend (0.017oC/yr) is observed in Parsa.
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Figure 6.5a Annual Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank
means insignificant at 95% CL)
Figure 6.5b shows annual maximum temperature trend in five physiographic regions. It shows positive
temperature trend significant at 99.9% CL in all five regions. The temperature trend increases northward
with elevation. This pattern is consistent with the distribution of annual maximum temperature trend in
districts and in physiographic regions in other seasons. The trend values along with significance level are
shown in Table 6.2 above. Terai has the lowest positive trend (0.021oC/yr) while High Himalayan region
has the highest increasing trend (0.086oC/yr).
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Figure 6.5b Annual Maximum Temperature trend for districts. (Significance: * 95% CL, ** 99% CL, *** is 99.9% CL; blank
means insignificant at 95% CL)
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