Contrasting hydrological regimes in the upper Indus Basin

David Archer

Jeremy Benn Associates, South Barn, Broughton Hall, Skipton, North Yorkshire BD23 3AE, UK

Received 10 December 2001; revised 24 November 2002; accepted 6 December 2002

Abstract

Since much of the flow abstracted from the River Indus for irrigation originates in the Himalayas, Karakoram and Hindu

Kush Mountains, an understanding of hydrological regimes of mountain rivers is essential for water resources management in

Pakistan. Broad characteristics of hydrological regimes are investigated using streamflow data from nineteen long-period

stations in terms of annual and seasonal runoff. Regression between climatic variables and streamflow for three key basins, the

River Hunza, River Astore and Khan Khwar have first been carried out followed by regional analysis of twelve further basins.

Analysis shows distinct hydrological regimes with summer volume governed by: melt of glaciers and permanent snow (thermal

control in the current summer), melt of seasonal snow (control by preceding winter and spring precipitation), or winter and

monsoon rainfall (precipitation control in current season). Satisfactory levels of correlation were achieved between streamflow

and measurements of temperature and precipitation at valley sites, which offer promise as a basis for assessing seasonal flow

volumes. They also suggest the possibility of extending the flow record back on the basis of historical climatic records, which

commence early in the twentieth century.

q 2003 Elsevier Science B.V. All rights reserved.

Keywords: Upper Indus Basin; Hydrological regimes; Snowmelt; Glacier melt

1. Introduction

The economic life of Pakistan depends to a large

extent on its agriculture, which in turn is dependent on

irrigation through a vast network of barrages,

diversions, and channels from the River Indus and

its tributaries. Hydropower also provides 28% of the

installed power capacity of the country most impor-

tantly from the two large dams at Tarbela on the Indus

and Mangla on the River Jhelum.

Most of the flow abstracted for irrigation from the

River Indus originates in the Karakoram, Himalaya

and Hindu Kush Mountains and is fed by

a combination of meltwater from seasonal and

permanent snow fields and glaciers, and direct runoff

from rainfall both during the winter and the monsoon

season from July to September. An understanding of

the hydrological regimes of the mountains is critical

for the management of the water resources of Pakistan

and for protection against flooding.

Previous studies have concentrated primarily on

the role of seasonal snow accumulation based

on surface measurements (De Scally, 1994) or on

remotely sensed assessments of snow covered area

(Rango et al., 1977; Dey et al., 1989). De Scally

(1994) studied the River Jhelum (Fig. 1) and obtained

high correlation coefficients between annual

maximum snowpack water storage or total winter

Journal of Hydrology 274 (2003) 198–210

www.elsevier.com/locate/jhydrol

0022-1694/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0022-1694(02)00414-6

E-mail address: davearcher@yahoo.com (D. Archer).

Fig. 1. The upper Indus Basin showing the location of streamflow gauging stations and raingauges (for key to station numbers, see Table 1).

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precipitation and annual runoff, whilst summer

precipitation was of little use in estimating annual

flow. Nevertheless, surface measurements of snow are

difficult or impracticable above 3000 m due to the

inhospitable terrain and climate and their use in

forecasting is still in its early stages.

Kolb (1994) showed, with reference to five gauged

catchments that runoff generating mechanisms and

characteristics differ between catchments which are

predominantly fed by glacial melt and those where

runoff depends mainly on the melt of a seasonal snow

pack. Further investigation of variation in runoff

regimes and the linkage between climatic variables

and river flow in northern Pakistan is needed. In

particular it is of considerable practical interest to

determine whether standard climatological measure-

ments made at lower elevations provide a suitable

basis for river flow forecasting and management. For

this purpose a general review of the streamflow

records of northern Pakistan has first been carried out.

Then three key catchments with reliable flow and

climate data have been selected for regression

analysis between climate parameters and seasonal

runoff to assess the controlling mechanisms of their

hydrological regimes. A further twelve catchments

were then studied to validate the conclusions of the

key catchments.

2. Data

Streamflow measurement in northern Pakistan is

carried out by the Water and Power Development

Authority—Surface Water Hydrology Project

(WAPDA-SWHP) with the earliest records commen-

cing in 1960. Flow at most stations is based on manual

measurements of river stage and conversion of stage

to flow using rating curves derived from current meter

measurements from cableway or bridge. The

reliability of the flow record depends on the stability

of the control, the adequacy of gauging and the quality

of level measurement. The stations all have natural

controls in gravel and boulder bed channels. The

original current meter gauging records were not

available, so the stability of the control section and

the frequency, range and variability of gaugings could

not be ascertained. Level measurement is nominally

once daily during the low flow (winter) season, hourly

during daytime hours during the high flow season, and

occasionally in flood flow for the full 24 h. The

quality of level measurement is reported to vary. The

limitations placed by physical conditions at the station

and monitoring procedures suggest that the records

are of moderate quality at best.

Daily mean flows have been published in annual

reports and have been checked and digitised in a

database prepared by the German Technical Devel-

opment Agency (GTZ) acting as advisors to WAPDA.

The full database of daily flows was made available

for this analysis but reference here is made only

to records in excess of 10 years. Station location

and catchment information is shown in Table 1 and

on Fig. 1.

Climatological measurement is primarily the

responsibility of the Pakistan Meteorological Depart-

ment (PMD), which maintains stations with standard

measurements including temperature, precipitation

(daily and recording), humidity and wind speed. Such

stations are mainly located at lower elevations in

valleys. WAPDA also maintain a network of clima-

tological stations but with shorter runs of record and

of lower reliability. Daily precipitation and tempera-

ture records were digitised for selected stations,

especially Gilgit and Skardu where the records

commence in the early twentieth century. Monthly

mean temperature and precipitation were digitised for

all PMD stations in northern Pakistan. The main

emphasis in this analysis is on those stations that were

suitably located and of sufficient record length for use

in correlation and regression analysis with river

runoff. They are listed in Table 2 and shown in Fig. 1.

3. Influences on river flow in the upper Indus basin

The ultimate source of river flow in any river basin

is the occurrence of precipitation. However, the time

distribution and magnitude of river flow is greatly

modified by storage within the catchment. In the

Karakoram Himalaya the most critical storages are in

the seasonal and perennial snowpack and in glacier

ice. Thus, the occurrence of flow and particularly of

peak seasonal and daily flow does not necessarily

coincide with the occurrence of precipitation (with

appropriate catchment lag) but with the combined

availability of heat energy to melt the snowpack

D. Archer / Journal of Hydrology 274 (2003) 198–210200

and the availability of water stored in the form of

snow and ice.

Storages and energy availability differ between

basins in the region and these influence the hydro-

logical regime of rivers. Two particular factors affect

storages within a basin,

† the elevation range and the distribution of areas

within each elevation band in the catchment (the

hypsometric curve). Elevation influences the occur-

rence and magnitude of precipitation and the

proportion that is stored in the form of snow. It is

also closely linked to available energy inputs for

melting snow and ice. Thus snowmelt runoff only

occurs from that portion of the basin that is above

the snow line and below the freezing level. The

lower the catchment elevation, the greater the

proportion of precipitation that falls as rain and

the closer the time distribution of precipitation and

runoff. In addition any snow that occurs at lower

elevations is melted at an earlier date than at higher

altitudes. In contrast at the highest levels, where

there is permanent snow and ice, the runoff is linked

entirely to energy availability and not to precipi-

tation occurrence. No gauged catchments fall

entirely within this category but it is postulated

that basins draining the highest gauged catchments

will show the greatest influence of energy inputs and

their variability. Hypsometric curves were available

for all gauged catchments (Hormann, 1990).

Table 1

Station location and catchment information for gauging stations in northern Pakistan

No River Station Latitude Longitude Period of

record

Years of

record

Basin area

(km2)

Mean elevation

metres

% area above

5000 m

1 Shyok Yogo 35 11 76 06 73–97 24 65,025 4900 46.2

2 Indus Kharmong 34 56 76 13 82–97 15 72,500 4755 36.7

3 Shigar Shigar 35 20 75 45 85–97 12 6650 4401 31.2

4 Indus Kachura 35 27 75 25 70–97 28 146,100 4789 40.2

5 Hunza Dainyor 35 56 74 23 66–97 31 13,925 4472 35.8

6 Gilgit Gilgit 35 56 74 18 60–98 39 12,800 3740 2.9

7 Gilgit Alam Br. 35 46 74 36 66–97 31 27,525 4094 18.1

8 Indus Partab Br. 35 43 74 38 62–96 35 176,775 4656 36.2

9 Chitral Chitral 35 52 71 47 64–96 33 12,425 3794 8.1

10 Astore Doyian 35 33 74 42 74–97 24 3750 3921 2.8

11 Swat Kalam 35 28 72 36 61–97 37 2025 3300 0.3

12 Swat Chakdara 34 39 72 01 61–97 37 5400 2499 0.14

13 Kunhar Naran 34 54 73 39 60–98 39 1175 3700 0.0

14 Kunhar Garhi Habibullah 34 27 73 22 60–98 39 2400 3061 0.0

15 Khan Khwar Karora 34 54 72 46 75–96 22 625 1906 0.0

16 Siran Phulra 34 19 73 05 69–96 28 975 1550 0.0

17 Brandu Daggar 34 30 72 28 69–96 27 725 1171 0.0

18 Indus Shatial Br. 35 32 73 34 83–97 13 187,275 4579 34.3

19 Indus Besham 34 56 72 53 69–97 32 196,425 4505 32.6

Table 2

Location and elevation of utilised climate stations in Northern Pakistan

Station Latitude Longitude Period of record Years of record Elevation (m)

Astore 35 22 74 54 1954–97 44 2394

Gilgit 35 55 74 20 1903–99 80a 1460

Skardu 35 18 75 41 1900–99 80a 2210

Besham 34 55 72 53 1970–97 28 480

Drosh 35 34 71 47 1931–97 66 1465

a Records intermittent 1935–1958.

D. Archer / Journal of Hydrology 274 (2003) 198–210 201

† The glacierised proportion of the catchment.

Glaciers and permanent snowfields provide a

long-term storage which enables melt to con-

tinue beyond the precipitation that has accumu-

lated during the immediate past season and thus

provide a buffer against the variability of annual

precipitation. Data on glacierised area in each

basin was not available, but the percentage area

of the basin above 5000 m (Table 1) gives a

broad indication of the permanent snow cover.

Temperature is the only widely available measure

of energy input and, although it is an imperfect

measure of total radiant heat input, it has the

advantage of being spatially conservative. Regression

analysis of seasonal and annual temperatures of nine

Karakoram stations ranging in elevation from 1000 to

4700 m give correlation coefficients greater than 0.98

and lapse rates ranging from 0.65 to 0.75 8C/100 m

(Archer, 2001).

There is greater uncertainty about seasonality and

magnitude of precipitation input and how representa-

tive climate stations at low elevations are of more

active hydrological zones at higher elevations.

Similarly there is uncertainty as to whether the

seasonal proportion changes with elevation. Wake

(1989) suggests the possibility that a higher pro-

portion of annual precipitation occurs during the

monsoon season at higher elevations. However,

regression analysis of seasonal and annual precipi-

tation between Karakoram stations shows universally

positive correlation coefficients (Archer, 2001). Cor-

relation coefficients of over 0.60 between seasonal

precipitation at valley stations separated by major

topographic barriers suggest that valley stations can

give a reasonable representation of the year-to-year

changes in precipitation over the region as a whole

including higher elevations.

4. Characteristics of hydrological regimes

There is a wide range of response between basins

in the region as shown by monthly and annual runoff

(Table 3). Highest annual runoffs are exhibited in

catchments in the south—the Rivers Swat, Astore and

Kunhar with annual runoff of 1000 to 1400 mm.

These are catchments with significant winter rainfall

at low levels and snow at higher levels to sustain river

flows by melt through the summer months. Very low

annual runoff is experienced at opposite extremes of

the region. The upper Indus and the River Shyok have

low annual runoff but totals gradually increase

downstream with the receipt of tributary flows with

higher runoff. The Hunza and Gilgit rivers contribute

runoffs between 700 and 800 mm and nearly double

the runoff rate in the overall Indus catchment below

the confluence. Further high runoff enters from the

Astore and from the neighbouring tributaries. The

lowland Bara (108 mm) and Brandu (298 mm) rivers

present a strong contrast to the neighbouring River

Swat, with lower rainfall, higher evaporation and a

very small or non-existent contribution from melting

snow and ice during the summer.

There is considerable variation in the monthly

and annual runoff even where there a single runoff

mechanism predominates. Thus in the high moun-

tain catchments dominated by glacier melt there is

a range from 168 mm for the Shyok to 974 mm for

the neighbouring Shigar. The individual behaviour

of catchments depends on local exposure to

precipitation-bearing winds

Where monthly runoff is considered as a percen-

tage of annual runoff, the contrast between catch-

ments at high altitudes and with large glacier cover

and those with lower mean elevations is emphasised.

Thus the Shyok and Hunza have the lowest

percentages of annual flow occurring during the

winter months and the slowest arrival of the spring

melt. However, in contrast they have the greatest

concentration of their annual flow in the two summer

months of July and August with approximately 60%

during these two months. There is a progressive

decrease to below 50% in these two months down

river to Besham and concomitant increases in

percentage in late spring and early summer.

Rivers Swat and Astore have further summer

percentage decreases to around 40% of annual total in

July and August and much greater sustained flow

during the winter months.

Low-level stations of Bara, Siran and Brandu have

a seasonal distribution that more closely reflects the

seasonal distribution of rainfall, with highest percen-

tages during the spring months.

Consideration of the regional variation in runoff

and its seasonal distribution suggests strong contrasts

D. Archer / Journal of Hydrology 274 (2003) 198–210202

between high altitude basins dominated by melt from

glaciers and permanent snowfields and those of lower

mean altitude where runoff is predominantly from

melt of seasonal snowpacks. The regime of foothill

catchments is also clearly influenced by both winter

and monsoon precipitation.

5. Analysis

The primary objective of this study is to assess the

existence and strength of linkages between seasonal

climate and streamflow parameters and whether they

vary systematically through the region. Of critical

practical importance is whether precipitation and

energy inputs at valley locations can reasonably

represent and predict runoff from large basins at

higher elevation and at some considerable distance

from the climate station. In the first instance three key

catchments have been chosen for analysis on the basis

of the reported reliability of the flow record and

the proximity of a climate station with a record

coinciding in time with the streamflow record.

Analysis is then repeated for other gauged catchments

for which climate station is more distant, to confirm

the relationships established for the key catchments

and to aid interpretation of regional patterns of flow

regime. Further regression analysis is then carried out

between current monthly runoff and precipitation and

temperature and monthly serial correlation within the

runoff record

5.1. Three key catchments

The three catchments chosen for exploratory

analysis are the River Astore at Doyien, the River

Hunza at Dainyor Bridge and the River Khan Khwar

at Karora (Table 1 and Fig. 1). The River Hunza at

Dainyor Bridge represents the moderately high runoff

catchments in the centre of the Karakoram where a

significant proportion of the flow is derived from

glacier melt. It has good and lengthy records of

streamflow and the temperature and rainfall record at

Gilgit just outside the basin has been used for testing

runoff controls. The River Astore at Doyien represents

the high runoff catchments on the southern margin of

the Karakoram Himalaya and has coincident records

of temperature and rainfall from the town of Astore

within the catchment. The River Khan Khwar

represents catchments of the southern margins of

Table 3

Monthly runoff (mm) for gauging stations in northern Pakistan

River Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

Shyok Yugo 2.2 1.9 1.8 1.8 3.9 18.1 51.0 54.0 21.0 6.4 3.6 2.7 168.3

Indus Kharmong 3.8 3.2 3.7 5.4 17.8 42.7 48.5 41.8 20.2 8.3 5.2 4.4 204.9

Shigar Shigar 10.5 10.1 11.5 12.4 30.8 124.5 293.7 286.0 133.9 31.7 17.2 11.7 973.9

Indus Kachura 3.4 2.9 3.2 4.3 13.4 35.1 56.9 54.2 24.6 8.9 5.4 4.2 216.3

Hunza Dainyor 9.2 7.6 7.8 10.5 32.0 110.1 224.2 219.6 91.9 29.3 13.9 10.6 766.7

Gilgit Gilgit 13.0 10.3 10.2 12.1 43.6 143.0 189.0 142.6 69.9 30.8 19.3 15.5 694.7

Gilgit Alam Br 11.4 9.0 9.4 12.0 38.4 125.4 205.7 183.5 81.2 31.0 17.2 13.5 737.9

Indus Partab Br 6.3 5.2 5.7 7.1 20.6 63.4 103.0 97.5 42.3 15.5 9.2 7.4 383.3

Chitral Chitral 16.4 13.3 14.6 19.4 40.1 101.0 172.5 158.4 77.2 34.9 23.0 19.2 690.0

Astore Doyian 22.1 18.2 20.1 37.0 124.1 257.0 292.5 186.9 89.3 45.8 31.5 25.6 1150.0

Swat Kalam 20.1 16.5 21.6 57.3 164.0 323.1 353.2 234.0 105.7 47.6 29.5 23.5 1395.9

Swat Chakdara 19.7 21.6 51.3 96.2 143.9 205.4 211.6 147.6 66.1 35.8 23.9 21.7 1044.8

Kunhar Naran 25.2 19.1 20.0 28.5 90.4 271.5 396.8 228.7 102.2 52.4 35.2 28.6 1290.4

Kunhar Garhi HK 26.0 25.4 46.5 103.1 201.0 307.6 274.0 166.4 81.6 47.8 34.2 29.1 1337.4

Khan K Karora 30.5 44.7 142.5 189.1 136.7 87.7 134.7 131.2 66.2 47.2 31.9 29.1 1071.6

Siran Phulra 24.5 36.5 86.9 93.2 65.1 36.5 82.2 86.1 43.1 28.0 18.3 21.2 621.6

Brandu Daggar 17.6 18.6 35.0 25.2 18.0 16.1 36.1 49.6 29.1 21.8 17.2 16.6 298.2

Indus Shatial Br 5.7 4.7 4.9 6.7 20.7 58.0 90.1 78.0 38.6 14.2 8.4 6.6 338.4

Indus Besham 6.1 5.3 6.9 11.3 28.5 67.9 101.5 89.6 39.1 15.0 8.9 7.1 387.3

Bara Jhansi Post 5.6 3.8 8.4 21.4 19.5 10.2 9.7 9.8 6.6 5.2 3.9 3.8 107.8

D. Archer / Journal of Hydrology 274 (2003) 198–210 203

the Karakorams without glaciers and with limited

snow cover in winter and with flow predominantly

dependent on winter and monsoon rainfall. It has a

streamflow record at Karora from 1975 to 1995 and a

nearby rainfall record at Besham. The nearest

available temperature record is from Astore.

Regression analysis has been performed between

annual and seasonal streamflow and annual and

seasonal rainfall and temperature to establish what

are the main controlling factors in runoff. Correlation

coefficients between annual seasonal and monthly

streamflow and seasonal precipitation and temperature

are shown in Table 4 for the three catchments.

Significance levels are shown as italic (0.05) and

bold (0.01)

Inspection of these tables shows strong contrasts

between the catchments:

1. Annual runoff is significantly correlated with

annual precipitation for the Astore (r ¼ 0.75) and

for the Khan Khwar (r ¼ 0.59) but not for the

Hunza (r ¼ 20.17) which, in contrast, shows

significant positive correlation with both winter

and summer temperature.

2. There is significant correlation between summer

(July to September) mean temperature and stream-

flow (highest r is 0.70) for the Hunza at Dainyor. In

contrast for the Astore there is no significant

correlation between summer temperature and

streamflow (highest r is 0.24 and negative).

Similarly as anticipated, there is no significant

correlation between seasonal temperature and

streamflow for Khan Khwar.

3. A quite different pattern emerges for rainfall. At

Astore summer runoff is well predicted by

precipitation over the full winter accumulation

period (Oct to Jun: r ¼ 0.88) or by component

parts of the season; maximum monthly and even

maximum daily flow have a significant positive

correlation with winter precipitation. In contrast

at Dainyor there is no significant correlation

between winter and spring precipitation and

runoff. The Khan Khwar shows positive corre-

lation between winter precipitation and annual

runoff and with spring runoff. Although October

to March precipitation and April to September

runoff are significantly correlated (r ¼ 0.53),

linkages to summer months are weak, indicating

little persistence of snowmelt into these months.

4. For the Hunza there is a significant inverse

relationship between summer (Jul–Sep) precipi-

tation and annual, seasonal and maximum

monthly streamflow (highest r value is 20.49).

This is presumably because summer precipi-

tation and associated cloudiness at high altitudes

reduces energy input for ablation and sub-

sequently increases albedo from new snow. For

the Khan Khwar in contrast the correlation

coefficients are positive but of low significance,

in this case from the direct influence of

monsoon rainfall on summer flow. Summer

precipitation and runoff appear unrelated for

the River Astore.

5. Strong and somewhat puzzling contrasts occur in

the association between winter and spring

temperature (Jan–Jun) and summer runoff. For

the Astore the relationship is inverse

(r ¼ 20.60) whilst for the Hunza it is positive

(r ¼ 0.48).

It is concluded that for the River Astore, summer

flow from July to September when more than 40% of

the annual flow occurs, as well as the longer ablation

season from April to September, is predetermined by

conditions during the preceding winter. Not only is it

positively related to the winter precipitation but

inversely related to the winter temperature. Conver-

sely, neither the monsoon precipitation nor the

temperature appears to have any impact on the flow

during that season. Although the rainfall station at

Astore is only at 2400 m altitude it appears to give a

satisfactory representation of the amount and seasonal

variation over the whole catchment, which ranges up

to over 8000 m in Nanga Parbat.

For the River Hunza with a higher mean elevation

and with a greater proportional contribution of glacier

melt to runoff than the River Astore, summer runoff is

unrelated to winter precipitation but depends largely

on the energy input, represented by temperature, for

the current season. Although the Gilgit climate station

is at an elevation of only 1460 m and at the boundary

of the catchment, the level of correlation suggest that

it gives a reasonable representation of the temperature

conditions over higher elevations where ablation

occurs and most runoff originates. Its representation

of catchment precipitation is more open to question.

D. Archer / Journal of Hydrology 274 (2003) 198–210204

The much lower levels of correlation for the Khan

Khwar with respect to temperature indicate the much

smaller contribution to runoff from melting snow.

However, the annual runoff is more influenced by

winter and spring precipitation than by monsoon

rainfall.

5.2. Regional regression analysis

Regression analysis has been repeated for catch-

ments covering a wider range of size and orientation,

to establish to what extent the pattern of relationships

in the three key catchments represents broader

Table 4

Annual and seasonal correlation coefficients between streamflow. a. River Hunza (1980–98) and rainfall and temperature (Gilgit). b. River

Astore (1982–97) and rainfall and temperature (Astore). c. Khan Khwar (1976–95) and rainfall (Besham) and temperature (Astore)

Climate period Flow period

Jan–Dec Apr–Sep Jul–Sep Max month Max day

a. River Hunza at Dainyor Bridge

Precipitation at Gilgit

Jan–Dec 20.17 20.18 20.28 20.25 20.21

Oct–Jun 0.06 0.07 0.04 0.11 20.02

Oct–Mar 0.03 0.05 0.03 0.09 20.06

Jan–Mar 0.15 0.16 0.13 0.15 20.04

Jan–Jun 0.03 0.04 0.01 0.06 20.06

Jul–Sep 20.47 20.49 20.49 20.47 20.07

Temperature at Gilgit

Jan–Jun 0.59 0.58 0.48 0.46 0.28

Jul–Sep 0.62 0.64 0.70 0.67 0.44

Apr–Sep 0.63 0.64 0.64 0.65 0.44

b. River Astore at Doyien

Precipitation at Astore

Jan–Dec 0.75 0.76 0.74 0.73 0.49

Oct–Jun 0.79 0.81 0.88 0.80 0.55

Oct–Mar 0.66 0.66 0.75 0.58 0.38

Jan–Mar 0.71 0.71 0.70 0.59 0.34

Jan–Jun 0.78 0.80 0.80 0.77 0.51

Jul–Sep 0.04 20.02 20.12 20.03 20.10

Temperature at Astore

Jan–Jun 20.39 20.39 20.60 20.47 20.43

Jul–Sep 20.12 20.12 20.17 20.17 20.24

Apr–Sep 20.23 20.23 20.37 20.30 20.32

c. Khan Khwar at Karora

Precipitation at Besham

Jan–Dec 0.59 0.36 20.07 0.35

Oct–Jun 0.59 0.31 20.21 0.40

Oct–Mar 0.54 0.53 0.30 0.35

Jan–Mar 0.57 0.32 20.20 0.28

Jan–Jun 0.61 0.36 20.15 0.34

Jul–Sep 0.29 0.42 0.39 0.35

Temperature at Astore

Jan–Jun 20.29 20.16 0.21 20.01

Jul–Sep 20.02 0.01 0.22 0.13

Apr–Sep 20.10 20.02 0.27 0.12

Bold figures: significance 0.01. Italic: significance 0.05.

D. Archer / Journal of Hydrology 274 (2003) 198–210 205

regional patterns of runoff regime. A selection of

results is presented in Fig. 2 with respect to (a) the

relationship between winter precipitation (Oct–Mar)

and summer runoff (Jul–Sep) and (b) between

summer temperature and runoff. Because of the

greater distance between climate stations and the

catchments, relationships were tested for different

climate records and the best selected. The emphasis is

on regression and prediction of summer runoff

because of its practical significance for water resource

use in the lower Indus. Three distinct groupings of

catchments emerge that largely correspond with the

key catchments above.

1. High elevation catchments where the summer

runoff is predominantly influenced by summer energy

input. Three catchments fall distinctly into this group-

ing, the contiguous Karakoram catchments of Hunza,

Shyok and Shigar with significant correlation coeffi-

cients greater than 0.65 between summer temperature

and runoff. The Indus at Kachura, which is below the

confluence with Shyok and Shigar, shows less strongly

the influence of summer energy inputs (r ¼ 0.48); flow

in the upper Indus falls in a quite different regime. The

two gauging stations on the River Swat at Kalam and

Chakdara also have moderate correlation levels

between summer temperature and runoff.

2. Catchments where summer runoff is predomi-

nantly conditioned by winter and spring precipitation.

The Kunhar adjacent to the Astore shows a similar

runoff regime in spite of its opposite orientation to the

Astore. Both gauged catchments at Naran and Ghari

Habibullah have correlation coefficients between

winter precipitation and summer runoff greater than

0.65. For the southward flowing Swat the correlation

for October to March is moderate but where the spring

months are included (Oct– Jun) the correlation

coefficients rise above 0.60. Perhaps most surprising

in this group is the Upper Indus at Kharmong with

Fig. 2. Correlation between runoff (July to September) and (a) rainfall (October to March) and (b) temperature (July to September).

D. Archer / Journal of Hydrology 274 (2003) 198–210206

a catchment area of 72,500 km2 and a very high mean

elevation, where the relationship with a precipitation

record outside its boundary is as strong as for the

River Astore. Although the river rises far to the east

on the Tibetan Plateau and drains the eastern

Karakoram and Zanskar and Ladakh Ranges, the

southern part of the catchment drains the northern

slopes of the Greater Himalaya and this appears to

exert the strongest influence on the runoff regime. In

spite of draining the western Karakoram adjacent to

the Hunza, the Gilgit River also falls in this group and

shows little influence of summer temperature. All

these stations (like the Astore) show negative

correlations between winter temperature and summer

runoff, the highest for the Kunhar at Naran

(r ¼ 20.79) and no significant correlation between

summer precipitation and runoff.

3. Southern foothill catchments influenced directly

by winter and monsoon rainfall. The Siran River, like

the Khan Khwar, has a moderate correlation coeffi-

cient between summer precipitation and runoff but

otherwise the only significant correlations are

between winter and annual rainfall and annual runoff.

The neighbouring River Brandu at Daggar has no

significant correlation for any period and data error is

strongly suspected. Similarly no significant corre-

lation was found for the River Chitral.

5.3. Monthly correlation of runoff with rainfall

and temperature

The variation in streamflow regimes is further

investigated with reference to the relationship

between runoff and the precipitation and temperature

for the current month. Analysis is again limited to the

three key stations. Results are shown in Table 5.

This table shows again the striking contrast

amongst the three hydrological regimes. For the

River Hunza for the ablation period, April to

September, each month (with the surprising exception

of June) shows strong correlation with temperature.

The equivalent relationships for the River Astore and

Khan Khwar are poor or non-existent. For the River

Astore neither current precipitation nor temperature

has good correlation with the exception of May

for temperature when snow at lower levels is melted.

For the Khan Khwar there is a moderate positive

correlation between precipitation and runoff through

the year and a weak negative correlation with

temperature.

5.4. Serial correlation

Where climate provides a limited guide to future

runoff, the internal statistical properties of the runoff

series may be used as a basis for prediction and as a

further means of distinguishing flow regimes. Serial

correlation establishes the relationship (if any)

between runoff in the current month and runoff in

the previous month (Lag 1) or in n months previous

(Lag n). Monthly serial correlation coefficients are

shown in Table 6 for Lag 1–Lag 3 again for the three

key catchments.

For the River Astore serial correlation is very high

for Lag 1–Lag 3 through the winter months from

October to March with recession dependent on storage

Table 5

Correlation between streamflow and temperature and precipitation for the current month for the Rivers Hunza, Astore and Khan Khwar

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr

River Hunza

Rain 20.22 0.27 20.25 0.04 20.27 0.19 20.13 20.33 20.16 0.05 0.14 0.01 20.17

Temp 0.44 20.14 0.01 0.63 0.75 0.15 0.78 0.81 0.52 0.24 0.11 0.38 0.69

River Astore

Rain 0.26 0.09 0.26 0.21 20.26 0.26 0.01 20.22 0.39 20.05 20.04 0.25 0.70

Temp 20.15 20.11 0.05 0.14 0.61 0.28 20.25 20.04 0.36 20.23 0.46 0.41 20.23

Khan Khwar

Rain 0.31 0.56 0.61 0.32 0.44 0.33 0.33 0.40 0.58 0.72 0.04 0.29 0.59

Temp 20.44 0.20 20.52 20.18 20.16 20.41 0.42 20.06 20.12 20.59 0.08 20.15 20.07

Bold figures: significance 0.01. Italic: significance 0.05.

D. Archer / Journal of Hydrology 274 (2003) 198–210 207

at the end of the previous summer. There is a

discontinuity in April and May in the changeover

period from accumulation to ablation (though coeffi-

cients remain positive). Then moderately high serial

correlation coefficients are re-established during the

melt period and persist into the subsequent recession.

High summer serial correlation seems to imply a

greater dependence on initial snow cover than on the

prevailing temperatures for melt during the summer

months.

Monthly serial correlation coefficients are not

nearly so high on the River Hunza as they are on

the River Astore but they are with one exception

positive for all months for Lag 1–Lag 3. Again for

Lag 1 the best serial correlation is during the winter

recession period from November to March and then

during the summer from June to August. However,

the correlation weakens sharply at Lag 2 and 3. Again

there are sharp discontinuities in correlation in the

change over months from accumulation to

ablation (May) and from ablation to accumulation

(September).

Monthly serial correlation coefficients are gener-

ally lower for Khan Khwar than for either the River

Hunza or Astore. The best serial correlation is again

during the recession period from November extend-

ing to June but also affected by snow melt from

higher parts of the catchment. There is a sharp break

with negative correlations between June and July and

there is little serial correlation during the summer

monsoon period.

In general, correlation is high between sequences

of months where the controlling factor on runoff

remains unchanged, for example during periods of

recession, when the relationship depends on ground-

water and glacier storage decay. Similarly during a

summer melt season where the flow depends on the

initial catchment snow water equivalent available for

melt, reasonable serial correlation may be expected.

Where runoff is driven entirely by liquid precipitation

on the catchment, the serial correlation can be

expected to be low. Serial correlation in the driving

factors of precipitation and temperature was not

investigated.

6. Discussion and conclusions

High mountain regions are characterised by

altitudinal variations in the contribution of rainfall,

snowmelt and glacier melt to runoff (Wohl, 2000),

resulting in quite different hydrological regimes.

Collins and Taylor (1990) note that for alpine

catchments the ratio of summer to annual runoff

increases, the occurrence of maximum monthly runoff

is delayed and inter-annual variability is reduced

with increasing glacierised proportion of the catch-

ment. These are also features of the Upper Indus.

Table 6

Monthly serial correlation coefficients for lag 1 to lag 3 (a) River Hunza, (b) River Astore, (c) Khan Khwar

Lag Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr

River Hunza

1 0.57 0.93 0.76 0.45 0.16 0.60 0.63 0.68 0.24 0.42 0.57 0.62 0.29

2 0.54 0.36 0.70 0.40 0.01 0.10 0.33 0.55 0.01 0.03 0.14 0.22

3 0.18 0.09 0.24 0.47 0.19 0.15 0.18 0.18 0.29 0.24 20.04 0.01

River Astore

1 0.98 0.98 0.91 0.39 0.65 0.33 0.64 0.79 0.63 0.86 0.93 0.96 0.33

2 0.91 0.83 0.88 0.44 0.25 0.10 0.10 0.57 0.56 0.49 0.80 0.87

3 0.84 0.89 0.85 0.44 0.33 0.52 0.15 20.08 0.52 0.68 0.44 0.82

Khan Khwar

1 0.59 0.77 0.67 0.65 0.72 0.76 20.18 0.34 0.21 0.35 0.59 0.80 0.56

2 0.47 0.19 0.75 0.50 0.40 0.68 20.10 20.05 0.30 20.36 0.33 0.52

3 0.33 0.46 0.46 0.52 0.28 0.42 20.07 0.08 0.59 20.07 20.32 0.37

Bold figures: significance 0.01. Italic: significance 0.05.

D. Archer / Journal of Hydrology 274 (2003) 198–210208

Alford (1992) suggests that annual variations in runoff

in the Karakoram probably depend primarily on

melting rates in summer and that a sunny summer

can be expected to give higher runoff at the expense of

glacier storage. In contrast he indicates that runoff

from the sub-alpine zone south of the Karakoram

Range ought to be bigger after an unusually snowy

winter. However, the level and spatial variation of the

climate runoff relationships have not previously been

defined.

In this analysis simple linear regression for the

three key catchments indicates the different controls

on seasonal river flow, whilst regional application of

the same procedures permits the broad spatial

definition of the catchments over which given climatic

controls predominate.

1. High altitude Karakoram catchments with large

glacierised proportion (Hunza, Shigar and Shyok)

have summer and annual runoff that is strongly

dependent on concurrent energy input represented

by seasonal temperature.

2. Middle altitude catchments south of the Kara-

koram (Astore, Kunhar and Swat) have summer

flow predominantly defined by preceding winter

precipitation. However, the Gilgit and the Indus

above the Shyok confluence also show the same

winter precipitation control.

3. Foothill catchments (Khan Khwar and Siran)

have a runoff regime that is controlled mainly

by liquid precipitation, predominantly in winter

but also during the monsoon.

All the gauged catchments are large and cover a

wide altitudinal range. Whilst local runoff controls

must vary within such catchments, most catchments

as a whole show strong predominance of a single

control. However, the Indus at Kachura below the

Shyok and Shigar confluences shows the joint

influences of winter precipitation and summer tribu-

taries characterised by its tributaries. Subsequent

downstream stations on the main Indus stem were

not analysed but are expected to show the same mixed

relationships. The two River Swat gauging stations

also show the mixed control of summer energy input

and winter precipitation. This analysis suggests

that seasonal forecasts of Indus inflow to Tarbela

Reservoir can be achieved by multiple regression or a

more detailed modelling approach.

De Scally (1994) found that in the Kunhar basin

low elevation snow courses were as useful for

forecasting as data from remote high elevation sites.

These results also suggest that standard measurements

of temperature and predominantly liquid precipitation

made at low level valley stations can provide a basis

for forecasting seasonal runoff even when they are at

some distance from the catchment being modelled.

However, it is noted that the station at Astore which is

higher in elevation sometimes provide marginally

better correlations than stations at Gilgit and Skardu

even when these are in closer proximity to the

catchment. A network of more than 20 automatic

weather stations established in the 1990s at elevations

ranging up to 4700 m (Kunjerab Pass) may ultimately

prove more effective for seasonal forecasting (Hewitt

and Young, 1993). Nevertheless problems remain

with the reliability of automatic measurement of snow

(as opposed to liquid precipitation at lower

elevations).

The results have practical consequences for flow

forecasting on the River Indus. They show that

precipitation measurements at standard valley climate

stations can be used as a basis for forecasting the

volume of flow originating in the upper Indus and the

Rivers Astore, Swat and Jhelum with a lead-time of

three months or more. However, flow originating in

high altitude snowfields and glaciers of the Kara-

koram is little dependent on snow-covered area.

Control of runoff by the energy balance as indexed

by temperature of the current season implies that

seasonal flow forecasting from this region will be

more appropriately based on statistical properties of

the time series including serial correlation. The strong

serial correlation during the seasonal hydrograph

recession in winter may be used as a basis for low

flow forecasting. Differing hydrological regimes over

the mountains of northern Pakistan must be taken into

account in the planning, design, management and

operation of water resources of the River Indus.

The availability of daily temperature and precipi-

tation from the early twentieth century for Gilgit and

Skardu and other stations further south suggests that

generation of historic flow records for major Indus

tributaries may be possible.

D. Archer / Journal of Hydrology 274 (2003) 198–210 209

Acknowledgements

The work was carried out whilst the author was a

volunteer with Voluntary Service Overseas (VSO)

and employed by the German Agency for Technical

Development (GTZ). The author wishes to thank

colleagues of both agencies for the opportunity and

their support. Particular thanks are due to GTZ

counterpart Dr Juan Jose Victoria, and to Messrs

Numan and Ahsan for their careful digitisation of

hardcopy daily records.

References

Alford, D., 1992. Hydrological aspects of the Himalayan Region.

ICIMOD (International Centre for Integrated Mountain Devel-

opment) Occasional Paper No 18, Kathmandu.

Archer, D.R., 2001. The climate and hydrology of northern Pakistan

with respect to the assessment of flood risk to hydropower

schemes. Unpublished Report, GTZ/WAPDA, Lahore.

Collins, D.N., Taylor, D.P., 1990. Variability of runoff from

partially glacierised Alpine Basins. In: Lang, H., Musy, A.

(Eds.), Hydrology in mountainous regions, I Hydrological

measurements, the water-cycle, IAHS Publication 193,

pp. 365–372, Wallingford, UK.

De Scally, F.A., 1994. Relative importance of snow accumu-

lation and monsoon rainfall for estimating the annual runoff,

Jhelum basin, Pakistan. Hydrological Sciences Journal 39,

199–216.

Dey, B., Sharma, V.K., Rango, A., 1989. A test of snowmelt-runoff

model for a major river basin in the western Himalayas. Nordic

Hydrology 20, 167–178.

Hewitt, K., Young, G.J., 1993. The snow and ice hydrology project:

a Pakistan–Canada research and training programme. Snow and

Glacier Hydrology (Proceedings of a Kathmandu Symposium)

IAHS Publication 218, 49–58.

Hormann, K., 1990. River runoff in the high mountain areas of

northern Pakistan. Analysis of the WAPDA discharge measure-

ments since 1960 and elaboration of foundations of statistical

runoff forecasts, Pakistan German Technical Co-operation,

SHYDO-GTZ.

Kolb, H., 1994. Abflussverhalten von flussen in hochgebirgen

Nordpakistans (Runoff characteristics in rivers in high moun-

tainous areas of northern Pakistan). (in German with English

Summary), Beitrage und Materialen zur. Regionalen Geogra-

phie, 7, pp. 21–l14, Institut fur Geographie der Technischen

Universitat Berlin.

Rango, A., Salomonson, V.V., Foster, J.L., 1977. Seasonal stream-

flow estimation in the Himalayan region employing meteor-

ological snow cover observations. Water Resources Research

13, 109–l12.

Wake, C.P., 1989. Glaciochemical investigations as a tool to

determine the spatial variation of snow accumulation in the

Central Karakoram, Northern Pakistan. Annals of Glaciology

13, 279–284.

Wohl, E., 2000. Mountain Rivers, Water Resources Monograph 14,

American Geophysical Union, Washington, DC.

D. Archer / Journal of Hydrology 274 (2003) 198–210210