204 ACTA METEOROLOGICA SINICA VOL.21

Long-Term Trend and Abrupt Change for Major Climate Variables

in the Upper Yellow River Basin∗

ZHAO Fangfang†(�����

), XU Zongxue ( ����� ), and HUANG Junxiong( ��� )

Key Laboratory of Water and Sediment Sciences of the Ministry of Education, College of Water Sciences,

Beijing Normal University, Beijing 100875

(Received March 14, 2007)

ABSTRACT

On the basis of the mean air temperature, precipitation, sunshine duration, and pan evaporation from23 meteorological stations in the upper Yellow River Basin from 1960 to 2001, the feasibility of usinghypothesis test techniques to detect the long-term trend for major climate variables has been investigated.Parametric tests are limited by the assumptions such as the normality and constant variance of the errorterms. Nonparametric tests have not these additional assumptions and are better adapted to the trend testfor hydro-meteorological time series. The possible trends of annual and monthly climatic time series aredetected by using a non-parametric method and the abrupt changes have been examined in terms of 5-yrmoving averaged seasonal and annual series by using moving T-test (MTT) method, Yamamoto method,and Mann-Kendall method. The results show that the annual mean temperature has increased by 0.8◦C inthe upper Yellow River Basin during the past 42 years. The warmest center was located in the northernpart of the basin. The nonlinear tendency for annual precipitation was negative during the same period.The declining center for annual precipitation was located in the eastern part and the center of the basin.The variation of annual precipitation in the upper Yellow River Basin during the past 42 years exhibitedan increasing tendency from 1972 to 1989 and a decreasing tendency from 1990 to 2001. The nonlineartendencies for annual sunshine duration and pan evaporation were also negative. They have decreased by125.6 h and 161.3 mm during the past 42 years, respectively. The test for abrupt changes by using MTTmethod shows that an abrupt warming occurred in the late 1980s. An abrupt change of the annual meanprecipitation occurred in the middle 1980s and an abrupt change of the mean sunshine duration took place inthe early 1980s. For the annual mean pan evaporation, two abrupt changes took place in the 1980s and theearly 1990s. The test results of the Yamamoto method show that the abrupt changes mostly occurred in the1980s, and two acute abrupt changes were tested for the spring pan evaporation in 1981 and for the annualmean temperature in 1985. According to the Mann-Kendall method, the abrupt changes of the temperaturemainly occurred in the 1990s, the pan evaporation abrupt changes mostly occurred in the 1960s, and theabrupt changes of the sunshine duration primarily took place in the 1980s. Although the results obtained byusing three methods are different, it is undoubted that jumps have indeed occurred in the last four decades.

Key words: climate change, trend, abrupt change, the Yellow River

1. Introduction

The working meeting, co-organized by the Inter-

national Geosphere-Biosphere Program (IGBP) and

World Climate Research Program (WCRP), was held

at Venice City, Italy in November 1994. There were

six issues confirmed in the meeting, of which climate

abrupt dynamics and climate change evaluation were

two important issues (Wang, 1997). In recent years,

the regional climate change issues related with the

activities of people property have become one of the

most important issues (Yan et al., 2001). The cli-

mate system has typical characteristics of multi-scale

in space, multi-layer in configuration, nonlinearity in

nature, with complex mutual connection and effect

(Li, 2001). Many researchers investigated the trend

of climate variables and the characteristics of the cli-

mate abrupt changes. For example, the summer cli-

mate jumps in the Northern Hemisphere in summer of

the 1960s (Yan et al., 1990, 1992), the tendencies and

climate jumps of four main climate variables in

the Sanjiang Plain using accumulated depar-

ture, Jy parameter, Yamamoto method, and

Mann-Kendall method (Yan et al., 2001, 2003), the

∗Supported by the “Jingshi scholar” Leading Professor Program, Beijing Normal University and the National Basic ResearchProgram (973) of China under Grant No. 1999043601.

†Corresponding author: ffzhao@mail.bnu.edu.cn.

NO.2 ZHAO Fangfang, XU Zongxue and HUANG Junxiong 205

climatic variation tendencies, interdecadal variations,

and climate jumps over the middle reaches of the

Yarlung Tsangpo River in the Tibetan Plateau (Zhou

et al., 2001), and the climate variations, tendencies,

and climate jumps in Xinjiang Autonomous Region

(Yang, 2003), etc. However, few studies on the cli-

mate tendencies and abrupt changes in the upper Yel-

low River Basin have been done, although Yang and

Li (2004b) analyzed the abrupt and periodic changes

of the precipitation and runoff series in this area with

EOF method and Mann-Kendall method. Therefore,

further study should be conducted. In addition, the

scarcity of water resources in the Yellow River Basin

has been paid more attention to by domestic and inter-

national experts in recent years. Headwater catchment

of the Yellow River Basin is the “water tower” of the

whole basin, in which the streamflow has reduced, and

the water level in the lakes has declined. Whether it re-

sulted from climate change or human activities should

be further studied. Therefore, on the basis of monthly

mean air temperature, precipitation, sunshine dura-

tion, and evaporation from 23 meteorological stations

in the upper Yellow River Basin (upward of Lanzhou

Station) from 1960 to 2001, the feasibility of using

hypothesis test techniques to identify the long-term

trend for major climate variables during the past 42

years has been investigated in this study. At the same

time, the abrupt changes also have been examined by

using different methods to quantitatively describe the

climate change in the study area.

2. Study area

The Yellow River Basin is located in the semi-arid

and semi-humid region with severe water scarcity, in

which the annual mean precipitation is about 200-600

mm, and the natural streamflow is about 580×108 m3

(Yang and Li, 2004b). The drainage area at upward of

Lanzhou Station is about 222551 km2. The climate be-

longs to the Qinghai-Tibetan Plateau climate system.

In cold seasons, the basin climate has the characteris-

tics of typical continental climate, which is controlled

by the high pressure of the Qinghai-Tibetan Plateau,

lasting for about seven months. In warm seasons, the

climate is affected by southwest monsoon, producing

heat low pressure, with abundant water vapor and

more precipitation, and thus forms the plateau sub-

tropical humid monsoon climate. The whole climate

characteristics of the study area are as follows: long

winter nearly without summer, spring immediatly af-

ter autumn, low heat, small annual temperature dif-

ference, large daily temperature range, long sunshine

duration, intense solar radiation, big windy storm, and

short plant growth periods. The annual air tempera-

ture is 2.68◦C, with 2554.7 h for sunshine duration,

1428.9 mm for evaporation, and 446 mm for precip-

itation. The annual precipitation shows an increas-

ing trend from northwest to southeast. The precip-

itation from June to September accounts for 75% of

the annual value. The water resources of the upper

Yellow River Basin account for 57.5% of the whole

Yellow River Basin (average of 1951-1998), in which

the spatio-temporal variations of the water resources

are very important for the whole Yellow River Basin

(Li, 2003). The variation of climate variables are

the main reasons for the water resources change (Li,

2003). Therefore, it is very important to investigate

the spatio-temporal variations of climate variables in

the upper Yellow River Basin in order to identify the

evolvement of the water resources system in the whole

Yellow River Basin.

3. Data and methodology

There are 23 meteorological stations selected in

the upper Yellow River Basin. These stations are spa-

tially well distributed, which can reflect the character-

istics of regional climate. The data of monthly mean

air temperature, precipitation, sunshine duration, and

evaporation come from the China Meteorological Ad-

ministration, which have been checked by the primary

quality control. Considered the reliability and inte-

grality, the observed data from 1960 to 2001 are se-

lected in this study. At the same time, in order to

ensure the integrality of the time series, the absent

data are interpolated by using the data from nearby

stations. From the statistical meaning, it is credible

to get the results by the use of so long time series.

The location of the study area and the meteorological

stations selected are shown in Fig.1.

206 ACTA METEOROLOGICA SINICA VOL.21

Fig.1. Location of the study area and the

meteorological stations selected.

According to the unique climate characteristics

in the upper Yellow River Basin, the seasons can

be classified as follows: March-April-May for spring,

June-July-August for summer, September-October-

November for autumn, and December-January-

Feburary (the following year) for winter (Zeng, 2004).

For the time series of each season, the data of mean air

temperature is the average of three months’ value, but

the precipitation, sunshine duration, and evaporation

are the sum of three months’ value. In order to reduce

the unilateralism of single station record, the regional

series are calculated by the spatial average of all the

stations in the whole area. When analyzing the cli-

mate abrupt changes, the 5-yr moving average series

of the regionalized data for seasonal and annual series

are estimated, which represents the long-term trends.

In this study, the climate tendencies in the study

area are analyzed by using nonparametric Mann-

Kendall method, the periodic changes are analyzed by

using departure curve method, and the climate abrupt

changes are analyzed by use of moving T method, Ya-

mamoto method, and Mann-Kendall method.

4. Climate change analysis

During the past 20 years, many researchers have

investigated the regional climate characteristics on dif-

ferent time scales in China. The results provide favor-

able basis and direction to exactly grasp the climate

characteristics on large scale and further understand

the regional climate change (Yan et al., 2001). Non-

parametric Mann-Kendall method is widely used to

analyze the trends of the environmental time series,

which is recommended by World Meteorological Or-

ganization (WMO) (Liu and Zheng, 2003, 2004; Yu et

al., 2002). It is also an efficient tool to examine the

monotonic trend of hydro-meteorological series (Xu et

al., 2002, 2003). In this study, the climate trends of

climate variables from 23 gauging stations in the up-

per Yellow River Basin for 42 yr are detected at the

95% level of significance in this study. At the same

time, the magnitude of long-term trend for climate

variables (Kendall slope) from different gauging sta-

tions are spatially interpolated in this study in the

whole basin by using Kriging method.

4.1 Temperature

Figure 2a shows the spatial distribution of non-

linear tendency for the mean air temperature in the

upper Yellow River Basin. It shows an increasing

trend in most parts of the study area. The Kendall

slopes at 21 gauging stations are positive, and only 2

stations (Zhongxin and Henan Stations) are negative.

Two warm centers are shown in the whole basin: one

is near Qiabuqia Station in the north, and the other is

near Lanzhou Station in the east, in which the Kendall

slopes are up to 0.48◦C/(10 yr) and 0.44◦C/(10 yr),

respectively. The average Kendall slope for the whole

basin is 0.18◦C/(10 yr), i.e., the mean air tempera-

ture has increased by 0.76◦C in the upper Yellow River

Basin during the past 42 years.

Figure 2b shows the departure curves of the mean

air temperature in the upper Yellow River Basin. De-

parture is the difference of climate variables for 42 yr.

It is shown in Fig.2b that there are two obvious periods

in the study area for the past 42 years. One is the cold

period of 1960-1986, in which the negative departures

account for more than 80%, and the abnormal cold

years are 1967, 1977, and 1983, respectively. The other

is the short warm period of 1987-2001, in which the

mean air temperature is 3.1◦C, 0.46◦C higher than the

average of the whole basin. In warm period, the neg-

ative departures account for more than 87%, in which

the highest temperature for 42 yr, and the temperature

in 1998 is 1.7◦C higher than that of the whole basin.

The temperature change has an obvious seasonal dif-

ference. Comparing with the departure curves, winter

temperature has major contribution to the annual

NO.2 ZHAO Fangfang, XU Zongxue and HUANG Junxiong 207

Fig.2. Distribution of nonlinear tendency for temperature: (a) spatial distribution (◦C/10 yr) and (b)

departure curves (◦C).

mean temperature. This conclusion is consistent with

the result obtained by Ding and Dai (1994).

4.2 Precipitation

Figure 3a shows the distribution of nonlinear ten-

dency for precipitation in the upper Yellow River

Basin. It shows a decreasing trend in most parts of

the basin. The Kendall slopes at 17 gauging stations

are negative. There are two decreasing centers located

near Lintao and Henan Stations along the main stem,

in which the Kendall slopes are −28.63 mm/(10 yr)

and −28.83 mm/(10 yr), respectively. The average

Kendall slope for the whole basin is −4.26 mm/(10

yr). Therefore, there is a slight dry trend in the upper

Yellow River Basin since 1960.

Figure 3b shows the departure curves of the pre-

cipitation in the upper Yellow River Basin. It is shown

that the departure curve fluctuates significantly, with

the characteristics of three increasing and three de-

creasing abrupt changes since the 1960s. The period of

more precipitation i. e., 1970-1989, lasts for long time,

in which the mean precipitation is 11.7 mm more than

that of the whole basin. The period of less precipita-

tion is from 1990 to 2001, in which the mean precip-

itation is 18.6 mm less than that of the whole basin.

The seasonal departure curves show that autumn pre-

cipitation has the greatest contribution to the annual

total.

4.3 Sunshine duration

Figure 4a shows the distribution of nonlinear ten-

dency for annual sunshine duration in the upper Yel-

low River Basin. It shows a decreasing trend in most

parts of the study area. The decreasing center is lo-

cated at Minhe and Lanzhou Stations, in which the

greatest Kendall slope is up to −104.38 h/(10 yr).

Meanwhile, the increasing area centered at Tongde

Fig.3. Distribution of nonlinear tendency for precipitation: (a) spatial distribution (mm/10 yr) and (b)

departure curves (mm).

208 ACTA METEOROLOGICA SINICA VOL.21

Dari, and Maqu Stations, with the greatest Kendall

slope up to 56.39 h/(10 yr). The average Kendall

slope for the whole basin is −29.9 h/(10 yr), i.e., the

sunshine duration decreased by 125.6 h in the upper

Yellow River Basin during the past 42 years.

Figure 4b shows the departure curves of the sun-

shine duration in the upper Yellow River Basin. There

are two obvious periods. One is the higher period from

1961 to 1980 lasting for long time, in which the sun-

shine duration is 35.4 h higher than that of the whole

basin. The other is the lower period from 1981 to

1996, in which the sunshine duration is 49.4 h lower

than that of the whole basin. In the seasonal trend

curves, the spring and winter sunshine durations make

the greatest contribution to the annual total.

4.4 Evaporation

Figure 5a shows the distribution of nonlinear ten-

dency for annual pan evaporation in the upper Yel-

low River Basin. It shows a decreasing trend in most

parts of the study area, in which the greatest Kendall

slope is −115.74 mm/(10 yr). In the eastern, southern,

and western marginal area, the evaporation shows an

increasing trend. The average Kendall slope for the

whole basin is −38.4 mm/(10 yr), i.e., the evapora-

tion decreased by 161.3 mm in the upper Yellow River

Basin during the past 42 years.

Figure 5b shows the departure curves for the pan

evaporation in the upper Yellow River Basin. There

are an obvious increasing period from 1960 to 1973

and an obvious decreasing period from 1974 to 1997.

The pan evaporation is 74 mm higher in the increasing

period and 50 mm lower in the decreasing period than

the average. In the seasonal trend curves, the spring

and summer pan evaporation has significant contribu-

tion to the annual value.

4.5 Relationship among major climate vari-

ables

The interdecadal variations for the departure time

series of the mean air temperature, precipitation, sun-

shine duration, and pan evaporation are shown in

Figs.2b, 3b, 4b, and 5b with dashed lines. It is shown

in Figs.2b and 3b that the temperature in the 1960s

and 1980s are increasing, and the precipitation is in-

creasing from the 1960s to 1980s, but deceasing in

the 1990s. The relationship between precipitation and

temperature is weak, i.e., the precipitation may be

high or low when the temperature is high. The re-

sult is similar to that obtained by Shi (1996), i.e., the

changes of temperature are not directly responsible

for the changes of precipitation. Therefore, the vari-

ations of precipitation in the future should be further

studied. The sunshine duration is one of the impor-

tant climate factors to evaluate the regional radiation

resources. In principle, decreasing of the sunshine du-

ration may result in decreasing of temperature. How-

ever, the green house effect leads to the increasing of

temperature (Yang et al., 2004). The impact of hu-

man activities in the upper Yellow River Basin is rel-

atively small. Therefore, there is inverse relationship

among sunshine duration, evaporation, and precipita-

tion. It is shown in Fig.4b that sunshine duration has

decreased since the 1960s, especially in the 1980s, and

began to increase in the 1990s. The variations of evap-

oration (Fig.5b) are the same as that of the sunshine

duration, which is opposite to the inter-decadal varia-

tions of the precipitation as shown in Fig.3b.

It is the basis of eco-environmental change in the

study area to qualitatively analyze the relationship be-

tween temperature, precipitation, sunshine duration,

and evaporation. It can help to reasonably predict the

future climate changes and establish the correspond-

ing countermeasures.

5. Abrupt changes of climatic variables

Climate system is nonlinear and discontinuous.

Therefore, it is necessary to analyze and understand

the change process of the climate system by using non-

linear theories and methods, such as theory of the

abrupt changes and the detection method (Yan et al.,

2003). Fu and Wang (1992) discussed the definition

and detection methods, which can help to understand

and detect the abrupt changes.

There are many kinds of methods to detect the

NO.2 ZHAO Fangfang, XU Zongxue and HUANG Junxiong 209

Fig.4. Distribution of nonlinear tendency for sunshine duration: (a) spatial distribution (h/10 yr) and (b)

departure curves (h).

Fig.5. Distribution of nonlinear tendency for pan evaporation: (a) spatial distribution (mm/10 yr) and (b)

departure curves (mm).

abrupt changes, such as low pass filtering method,

moving T test method (MTT method), Crammer

method, Yamamoto method, Mann-Kendall method,

Spearman method, etc. The low pass filtering method

is not applicable. MTT method, Crammer method,

and Yamamoto method are famous for intuitionistic,

simple, and convenient uses. But the results may be

different because of the artificial reasons. Therefore,

it should depend on the Mann-Kendall method and

Spearman method to accurately examine the occur-

rence of abrupt changes. These methods have merits

of broad detecting range, small artificial impact, and

high quantitative degree (Wei, 1999). Therefore, the

abrupt changes of the climate variables in the study

area are detected by using MTT method, Yamamoto

method, and Mann-Kendall method. The detailed

theories are referred to Fu and Wang (1992) and Wei

(1999).

Wei and Cao (1995) analyzed the abrupt changes

of mean air temperature in China, Northern Hemi-

sphere, and global area, and got the results that it is

creditable when 10-yr mean period is taken for the

abrupt index. Therefore, the mean period of time

n1=n2=10 is adopted in this paper, and n1=n2=14 as

the comparing period. However, only abrupt changes

occurring in 1967-1991 were detected with these two

mean periods. Based on these ideas, the abrupt

changes of climate variables are detected in terms of

5-yr moving seasonal and annual time series of tem-

perature, precipitation, sunshine duration, and pan

210 ACTA METEOROLOGICA SINICA VOL.21

evaporation in the upper Yellow River Basin.

The t statistics of mean temperature, precipita-

tion, and sunshine duration in the upper Yellow River

Basin are at the 1% level of significance in 1985, 1987,

and 1982, respectively (see Figs.6a, b, and c). It shows

that an abrupt warming occurred in the late 1980s

in the study area, which is somewhat consistent with

that obtained by You (1998). An abrupt change of

the annual precipitation occurred in the mid-1980s and

an abrupt change of the sunshine duration took place

in the early 1980s. Although the abrupt changes of

the mean temperature happened in spring of the early

1970s and winter of the late 1960s and early 1970s,

there is no statistical significance. In the same way,

the abrupt changes of precipitation occurred in sum-

mer of the 1970s and in winter of the late 1960s and

early 1970s, but it is not up to the corresponding level

of significance. Figure 6d shows that there is an obvi-

ous increasing trend for annual pan evaporation in the

1960s-1980s, and there is an abrupt change from high

value to low values in the early 1980s. In addition, the

t statistic is over 1% level of significance (negative) in

the early 1990s, i.e., there is also a significant abrupt

change from low to high values for annual evaporation

in the same period.

The abrupt changes detected by using Yamamoto

method are listed in Table 1. Two mean periods of

time n=10 and n=14 are used in this study. It is shown

that there are abrupt changes for sunshine duration in

all seasons except autumn. For other three climate

variables, the abrupt changes occurred in all four sea-

sons, especially acute jumps for annual mean tempera-

ture, winter precipitation, and spring pan evaporation.

In the 1960s, the abrupt changes occurred for the mean

air temperature, precipitation, and evaporation in the

upper Yellow River Basin, of which the abrupt changes

of the evaporation occurred in spring, winter, and the

whole year, but only in winter for the mean air temper-

ature and precipitation. It is mainly because the time

series are too short in this study. However, it can also

be understood that the abrupt changes of the climate

variables occurred in the upper Yellow River Basin in

the 1960s. In different periods of the 1970s, the abrupt

changes were detected for the mean air temperature,

precipitation, sunshine duration, and evaporation in

the upper Yellow River Basin, in which the abrupt

changes were detected in four seasons and the annual

series for evaporation, and in the summer and winter

for precipitation. One acute abrupt change was de-

tected in the winter of 1971, with signal-noise ratio

(S/N) of 2.1. In addition, some abrupt changes were

detected in the same period for spring temperature

and summer sunshine duration. Compared with the

abrupt changes in the 1960s and 1970s, the climate

jumps in the 1980s are most significant. These

results are similar to the results detected in the

Fig.6. The moving t-statistic curve of the climatic factors in the upper Yellow River Basin. (a) Temperature,

(b) precipitation, (c) sunshine duration, and (d) evaporation; dashed lines: α=0.01.

NO.2 ZHAO Fangfang, XU Zongxue and HUANG Junxiong 211

Qinghai-Tibetan Plateau (Tang et al., 1998). The

abrupt changes were examined for major climate vari-

ables in different seasons and annual series of the

1980s, except for the spring mean temperature, sum-

mer precipitation, summer sunshine duration, and

summer and winter evaporations. About 47% of the

maximum values of S/N happened in this period.

In addition, the acute abrupt changes happened for

spring evaporation in 1981 and for the annual air tem-

perature in 1985, and the values of S/N are 2.19 and

2.02, respectively.

Figure 7 shows the S/N values of annual time

series for four climatic factors. The phases of S/N

values for the pan evaporation abrupt changes are ob-

viously ahead of other climate factors. The abrupt

changes of the evaporation mainly occurred in the

1970s. However, the phases of S/N values for other

factors mainly occurred in the 1980s. Different climate

factors were detected with different S/N values of the

abrupt changes. The abrupt changes can be detected

in 1971-1987 simultaneously using the two mean pe-

riods of time, with the similar results. However, the

abrupt changes of climate factors can not be detected

before 1971 and after 1987 when n=14 because of the

limited time series.

For the upper Yellow River Basin, the abrupt

changes of four climate factors did not exhibit con-

sistent rules. This is mainly due to the different sea-

sonal changes for four climate factors. For example,

the abrupt changes of the precipitation, sunshine du-

ration, and evaporation showed better association in

the mid-1970s, i.e., the summer precipitation increased

and the summer sunshine duration and evaporation

decreased.

Table 2 lists the abrupt changes for regional an-

nual and seasonal time series detected by using Mann-

Kendall method for four climate factors in the up-

per Yellow River Basin, with the corresponding years

shown in Fig.8. It is shown that the abrupt changes of

mean air temperature mainly occurred in the 1990s,

which is corresponding to the results for global warm-

ing period of 1990-1991 (Wei et al., 1995). The abrupt

changes of autumn precipitation were detected in 1986,

which is similar to the results obtained by Yang and

Li (2004a). In addition, the abrupt changes of evap-

oration mostly occurred in the 1960s and the abrupt

changes of the sunshine duration primarily took place

in the 1980s.

Table 1. Climate jumps detected by using Yamamoto method in the upper Yellow River Basin during the period

of 1960-2001

Time n valuesMean temperature Precipitation Sunshine duration Pan evaporation

n=10 n=14 n=10 n=14 n=10 n=14 n=10 n=14

Periods1973-1974 1973-1975 1981-1983 1982-1986 1981-1985 1967-1968,1971 1971-1974

1989-1991 1991 1979-1983,1991 1978-1983Spring

Years of 1.14(1974) 1.39(1974) 1.4(1982) 1.71(1984) 1.62(1983) 1.54(1967), 1.04(1971) 1.22(1971)

max.S/N 1.89(1991) 1.14(1991) 2.19(1981), 1.53(1991) 1.66(1981)

Periods 1985-1991 1986-1987 1972-1976 1973-1974 1973-1979 1976-1980 1972-1981, 1989-1991 1971-1980

Summer Years of 1.37(1987) 1.37(1987) 1.28(1973) 1.06(1974) 1.23(1973) 1.15(1979) 1.7(1973), 1.22(1991) 1.7(1973)

max.S/N 1.7(1974)

Periods1984-1988 1979-1987 1983-1988 1983-1986 1972,1984-1985 1971-1972

1991 1990-1991 1985-1987Autumn

Years of 1.65(1986) 1.45(1987) 1.75(1984) 1.42(1985) 1.03(1972),1.13(1984) 1.09(1971)

max.S/N 1.10(1991) 1.15(1991) 1.13(1987)

Periods1969-1970 1983-1987 1969-1974 1972-1974 1982-1986 1982 1967-1974 1971-1973

1983-1986 1985-1988 1986Winter

Years of 1.27(1970) 1.61(1985) 2.1(1971) 1.37(1973) 1.48(1985) 1.01(1982) 1.33(1971) 1.44(1971)

max.S/N 1.65(1985) 1.85(1986) 1.00(1986)

Periods1984-1988 1984-1987 1985-1991 1986-1987 1981-1985 1980-1983 1967,1971-1975 1971-1981

1991 1978-1982,1990-1991Annual

Years of 2.02(1985) 1.43(1987) 1.59(1987) 1.68(1987) 1.32(1982) 1.45(1981) 1.12(1967), 1.33(1973) 1.45(1973)

max.S/N 1.03(1991) 1.61(1981), 1.61(1991) 1.45(1980)

212 ACTA METEOROLOGICA SINICA VOL.21

Fig.7. S/N values of annual time series for four climatic factors for (a) n=10 and (b) n=14.

The comparison of the results obtained by Ya-

mamoto method with those obtained by Mann-

Kendall method exhibited that some of the abrupt

changes detected by using two methods were quite

similar, especially the sunshine duration in the 1980s.

However, some abrupt changes detected by using

Mann-Kendall method, including pan evaporation in

the 1960s and mean temperature and precipitation in

the 1990s, could not be detected by Yamamoto method

because of the limited data. The abrupt changes de-

tected by using Mann-Kendall method are only 50% of

those detected by using Yamamoto method, in which

the abrupt changes could not be detected by using

Mann-Kendall method for mean air temperature in the

1980s, sunshine duration in the 1970s, and pan evap-

oration in the 1970s and 1980s. Different detection

methods may get different results, and each method

has its own virtues and shortages (Fu et al., 1992; Yan

et al., 2001). Figure 8 shows the abrupt changes of cli-

matic factors detected by using Mann-Kendall method

at a significance level of 5% in the study area.

Table 2. The years with climate jump detected by using Mann-Kendall method in the upper Yellow River Basin

Time Mean temperature Precipitation Pan evaporation Sunshine duration

Spring 1998 - 1968 1984

Summer 1997 - 1965 1977

Autumn 1995 1986 - -

Winter 1986 1975 1969 1982

Annual 1994 1994 1965 1981

Fig.8. Jump of climatic factors detected by using Mann-Kendall method in the upper Yellow River Basin.

(a) Temperature, (b) precipitation, (c) sunshine duration, and (d) evaporation; dashed lines: α=0.05.

NO.2 ZHAO Fangfang, XU Zongxue and HUANG Junxiong 213

6. Discussions and conclusions

Some conclusions can be drawn by analyzing the

climate data in the upper Yellow River Basin from

1960 to 2001.

(1) Mean air temperature: There are two increas-

ing centers in the study area: one is near Qiabuqia

Station in the north, and the other is near Lanzhou

Station in the east. The Kendall slope of the mean

air temperature is 0.18◦C/(10 yr) in the whole area,

increasing by 0.76◦ for 42 yr. The winter temperature

has the greatest contribution to the annual total. The

detection results show that there is an obvious abrupt

warming occurring in the late 1980s. An acute abrupt

change was detected by using Yamamoto method in

1985.

(2) Precipitation: The climate exhibits a dry

tendency in the upper Yellow River Basin since the

1960s. The mean Kendall slope of precipitation is

−4.26 mm/(10 yr) for the whole basin. The winter

precipitation has the greatest contribution to the an-

nual total. The detecting results show that there is an

obvious abrupt change for precipitation in the mid-

1980s, changing from wet to dry.

(3) Sunshine duration: The Kendall slope of an-

nual sunshine duration is −29.9 h/(10 yr). There are

two obvious periods: one is the high period of 1961-

1980, and the other is the low period of 1981-1996.

An obvious abrupt change occurred in the early 1980s,

changing from high to low value.

(4) Pan evaporation: The annual evaporation de-

creased by 161.3 mm for the past 42 years, in which

the spring and summer evaporation have great con-

tribution to the annual evaporation. In the results

obtained by using MTT method, two abrupt changes

occurred in the 1980s and the early 1990s. The test re-

sults obtained by using the Yamamoto method show

that the abrupt changes of evaporation mainly oc-

curred in the 1970s. According to the Mann-Kendall

method, the abrupt changes mostly occurred in the

1960s.

In conclusion, there is a warm and dry tendency

in the upper Yellow River Basin for the past 42 years,

i.e., increasing temperature and decreasing precipi-

tation. One interesting phenomenon is that there is

a decreasing trend for evaporation in the study area

during the past 42 years, although the temperature

is increasing. This may result from possible climate

change or the impact of human activities. It should

be pointed out that it is not easy to distinguish from

abrupt changes and monotonic trends, and thus fur-

ther investigation is required to identify these trends

more precisely. However, it is confident that the ap-

proaches presented in this paper may be useful tools

for further examining the impact of climate change on

hydrological processes.

REFERENCES

Ding Yihui and Dai Xiaosu, 1994: Temperature variation

in China during the last 100 years. Meteorological

Monthly, 20(12), 19-26. (in Chinese)

Fu Congbin and Wang Qiang, 1992: The definition and

detection of the abrupt climatic change. Scientia

Atmospherica Sinica, 16(4), 482-493. (in Chinese)

Li Chunhui, 2003: The reproducible evaluation of the

surface water resources in the Yellow River Basin.

Dissertation, Beijing Normal University. (in Chi-

nese)

Li Daofeng, 2003: Impact of climate and land-cover

change on runoff of the source regions of the Yellow

River. Dissertation, Beijing Normal University. (in

Chinese)

Li Yueqing, 2001: A phase space EOF method and its

application to climate diagnosis. Plateau Meteorol-

ogy, 20(1), 88-93. (in Chinese)

Liu Changming and Zheng Hongxing, 2004: Changes in

components of the hydrological cycle in the Yellow

River Basin during the second half of the 20th cen-

tury. Hydrological Processes, 18, 2337-2345.

Liu Changming and Zheng Hongxing, 2003: Trend anal-

ysis of hydrological components in the Yellow River

Basin. Journal of Natural Resources, 18(2), 129-

135. (in Chinese)

Shi Yafeng, 1996: Chinese Historical Climatic Changes.

Shandong Science & Technology Press, 443-467. (in

Chinese)

Tang Maocang, Bai Chongyuan, Feng Song, and Caiy-

ing, 1998: Climate abrupt change in the Qinghai-

Tibetan Plateau in recent century and its relation

to astronomical factors. Plateau Meteorology, 17(3),

250-257. (in Chinese)

Wang Shaowu, 1997: Scientific intersection of PAGES

and CLIVAR. Acta Meteorologica Sinica, 55(6),

214 ACTA METEOROLOGICA SINICA VOL.21

662-669. (in Chinese)

Wei Fengying and Cao Hongxing, 1995: Detection of

abrupt changes and trend prediction of the air tem-

perature in China, the Northern Hemisphere and

the globe. Scientia Atmospherica Sinica, 19(2),

140-148. (in Chinese)

Wei Fengying, 1999: Modern Technology of Statistics,

Diagnosis and Forecast for Climate. China Meteo-

rological Press, 62-76. (in Chinese)

Xu Z. X., K. Takeuchi, and H. Ishidaira, 2002: Long-term

trends of annual temperature and precipitation time

series in Japan. Journal of Hydroscience and Hy-

draulic Engineering, 20(2), 11-26.

Xu Z. X., K. Takeuchi, and H. Ishidaira, 2003: Monotonic

trend and step changes in Japanese precipitation.

Journal of Hydrology, 279, 144-150.

Yan Minhua, Deng Wei, and Chen Panqin, 2003: Analy-

sis of climate jumps in the Sanjiang Plain. Scientia

Geographica Sinica, 23(6), 661-667. (in Chinese)

Yan Minhua, Deng Wei, and Ma Xuehui, 2001: Climate

variation in the Sanjiang Plain disturbed by large

scale reclamation during the past 45 years. Acta

Geographica Sinica, 56(2), 159-170. (in Chinese)

Yan Zhongwei, Ji Jinjun, and Ye Duzheng, 1990a: The

climatic jump of the Northern Hemisphere in sum-

mer during the 1960s. I: Precipitation and temper-

ature change. Chinese Science (B), 1, 97-103. (in

Chinese)

Yan Zhongwei, Ji Jinjun, and Ye Duzheng, 1990b: The

climatic jump of the Northern Hemisphere in sum-

mer during the 1960s. II: Sea level pressure and 500

hPa height change. Chinese Science (B), 8, 879-885.

(in Chinese)

Yan Zhongwei, 1992: A primary analysis of the process

of the 1960s Northern Hemispheric summer climatic

jump. Scientia Atmospherica Sinica, 16(1), 111-

119. (in Chinese)

Yang Lianmei, 2003: Climate change of extreme precipi-

tation in Xinjiang. Acta Geographica Sinica, 58(4),

577-583. (in Chinese)

Yang Yanwu, Yu Qiang, and Wang Jing, 2004: Spatio-

temporal variations of principal climatic factors in

North China and part of East China within the past

40 years. Resources Science, 26(4), 45-50. (in Chi-

nese)

Yang Zhifeng and Li Chunhui, 2004a: Abrupt and pe-

riodic changes of the annual natural runoff in the

subregions of the Yellow River. Journal of Mountain

Science, 22(2), 140-146. (in Chinese)

Yang Zhifeng and Li Chunhui, 2004b: The spatial and

temporal structure of precipitation in the Yellow

River Basin. Progress in Geography, 23(2), 27-33.

(in Chinese)

You Weihong, 1998: Multi-scale Diagnosis of Climatic

Change and Some Technologies and Methods for Its

Forecast. China Meteorological Press, 1-17. (in Chi-

nese)

Yu, P. S., T. C. Yang, and C. K. Wu, 2002: Impact of

climate change on water resources in southern Tai-

wan. Journal of Hydrology, 260, 161-175.

Zeng Yan, 2004: Distributed modeling of actual evapo-

transpiration over rugged terrain of the Yellow River

Basin. Dissertation, Chinese Academy of Sciences.

(in Chinese)

Zhou Shunwu, Jia La, and Du Jun, 2001: Analyses of

climatic trend and jump over the middle reaches of

Yarlung Tsangpo River in the Tibetan Plateau in

recent 42 years. Plateau Meteorology, 20(1), 71-75.

(in Chinese)