Impacts of temperature and precipitation on runoff in the Tarim River during the past 50 years

The relationship between climate change and water resources in the Tarim River was analyzed by combining the temperature,precipitation and streamflow data from 1957 to 2007 from the four headstreams of the Tarim River (Aksu,Hotan,Yarkant and Kaidu rivers) in the study area.The long-term trend of the hydrological time series including temperature,precipitation and streamflow were studied using correlation analysis and partial correlations analysis.Holt double exponential smoothing was used to fit the trends between streamflow and the two climatic factors of Aksu River,Hotan River and Yarkant River.The streamflow of the main stream was forecasted by Autoregressive Integrated Moving Average Model (ARIMA) modeling by the method of time series analysis.The results show that the temperature experienced a trend of monotonic rising.The precipitation and runoff of the four headstreams of the Tarim River increased,while the inflow to the headstreams increased and the inflow into the Tarim River decreased.Changes of temperature and precipitation had a significant impact on runoff into the four headstreams of the Tarim River: the precipitation had a positive impact on water flow in the Aksu River,Hotan River and Kaidu River,while the temperature had a positive impact on water flow in the Yarkant River.The results of Holt double exponential smoothing showed that the correlation between the independent variable and dependent variable was relatively close after the model was fitted to the headstreams,of which only the runoff and temperature values of Hotan River showed a significant negative correlation.The forecasts by the ARIMA model for 50 years of annual runoff at the Allar station followed the pattern of the measured data for the same years.The short-term forecasts beyond the observed series adequately captured the pattern in the data and showed a decreasing tendency in the Tarim River flow of 3.07% every ten years.The results showed that global warming accelerated the water recharge process of the headstreams.The special hydrological characteristics of the arid area determined the significant association between streamflow and the two climatic factors studied.Strong glacier retreat is likely to bring a series of flood disasters within the study area.     

Periodical characteristics of baseflow in the source region of the Yangtze River

Baseflow,which represents the drainage of groundwater aquifers,is an essential component of runoff in hydrological basins.In the source region of the Yangtze River,the change of baseflow typically reflects the interactions between groundwater system and climatic factors in cold and arid areas.With modified Kalinen separation method,annual baseflow between 1957 and 2009 in this region was estimated and calculated.In comparison with the inner-annual variations of total streamflow,baseflow showed a weaker fluctuation.Before the 1980s,it was in a steady state;and after then,it demonstrated dramatic variations and large amplitudes.Based on the calculation results of baseflow,the real Morlet wavelet method was applied to reveal the periodical characteristics of baseflow as well as the precipitation and air temperature in the study area.It was found that annual baseflow has a 43-year trend as well as a 21-year period and a 7-year period.The 21-year period is most significant,with its wavelet coefficient having the largest fluctuation and amplitude.Summation of wavelet coefficients on these periods exhibits a similar change pattern with respect to that of annual baseflow.The summation curve takes a"W"shape,which means that the baseflow follows a four-stage sequence of descending–ascending–descending–ascending.As analyzed,the relationship among baseflow,precipitation and temperature is implied in the correlation between their normalized wavelet coefficients at different temporal scales.By the significant positive linear correlations both between precipitation and baseflow(correlation coefficient is 0.98)and between temperature and baseflow(correlation coefficient is 0.90)for the 43-year wavelet coefficients,it is suggested that the long-term increasing trends of precipitation and air temperature will lead to an increasing trend of baseflow.For wavelet coefficients of 21-year and 7-year periods,the positive linear correlation between precipitation and baseflow is significant.However,the correlation between air temperature and baseflow is not so evident,especially for the 21-year period.As a conclusion, correlation analysis with normalized wavelet coefficients showed that the change of annual baseflow was contributed mostly by the change of precipitation and secondly by the change of temperature.     

Response of vegetation to temperature and precipitation in Xinjiang during the period of 1998-2009

In this paper,10-day spatio-temporal response of vegetation to the change of temperature and precipitation in spring,summer,autumn and whole year during the period of 1998―2009 was analyzed based on the data of SPOT VEGETATION-NDVI and 10-day average temperature or precipitation from 54 meteorological stations in Xinjiang.The results show that the response of 10-day NDVI to temperature was more significant than that to precipitation,and the maximal response of vegetation to temperature and precipitation lagged for two 10-day periods.Seasonally,the effect of temperature and precipitation on vegetation NDVI was most marked in autumn,then in spring,and it was not significant in summer.The response of vegetation to 10-day change of meteorological factors was positive with a long affecting duration in spring,and it had a relatively short affecting duration in autumn and summer.Spatially,the 10-day maximal response of NDVI to temperature in northern Xinjiang was higher than that in southern Xinjiang.The correlation between the 10-day NDVI in whole year and the temperature in the 0-8th 10-day period was significantly higher than that between the annual NDVI and the annual temperature at all meteorological stations;the interannual change of NDVI was accordant well with the change of annual precipitation.However,the effect of precipitation within a year on NDVI was not strong.The results indicated that interannual change of temperature was not the dominant factor affecting the change of vegetation NDVI in Xinjiang,but the decrease of annual precipitation was the main factor resulting in the fluctuation of vegetation coverage.Ten-day average temperature was an important factor to promote vegetation growth in Xinjiang within a year,but the effect of precipitation on vegetation growth within a year was not strong.     

Effects of irrigation on precipitation in the arid regions of Xinjiang,China

Soil moisture is an important parameter for the interaction between soil and atmosphere.It is the second important factor that influences climate change,next to sea surface temperature(SST).Most previous studies focused on the monsoon regions in East China,and only a few laid emphases on arid environments.In Xinjiang, which is located in Northwest China,the climate is typically arid and semi-arid.During the past 20 years,the precipitation in Xinjiang has shown a significant increasing trend,and it is closely related to oasis irrigation.This paper aims at discussing whether abnormal soil moisture in spring can be the signal to forecast summer precipitation.The effects of abnormal soil moisture due to farm irrigation in spring in arid environments on regional climate are investigated by using a regional climate model(RegCM3).The results indicate that positive soil moisture anomaly in irrigated cropland surface in May led to an increase in precipitation in spring as well as across the whole summer. The impact could last for about four months.The effects of soil moisture on the surface air temperature showed a time-lagging trend.The summer air temperature declined by a maximum amplitude of 0.8oC.The increased soil moisture could enhance evaporation and ascending motion in the low troposphere,which brought in more precipitation.The soil moisture affected regional weather and climate mainly by altering the surface sensible and latent heat fluxes.     

Long-term variations in runoff of the Syr Darya River Basin under climate change and human activities

In this study,we analyzed the hydrological and meteorological data from the Syr Darya River Basin during the period of 1930–2015 to investigate variations in river runoff and the impacts of climate change and human activities on river runoff.The Syr Darya River,which is supplied by snow and glacier meltwater upstream,is an important freshwater source for Central Asia,as nearly half of the population is concentrated in this area.River runoff in this arid region is sensitive to climate change and human activities.Therefore,estimation of the climatic and hydrological changes and the quantification of the impacts of climate change and human activities on river runoff are of great concern and important for regional water resources management.The long-term trends of hydrological time series from the selected 11 hydrological stations in the Syr Darya River Basin were examined by non-parametric methods,including the Pettitt change point test and Mann-Kendall trend tests.It was found that 8 out of 11 hydrological stations showed significant downward trends in river runof f.Change of river runoff variations occurred in the year around 1960.Moreover,during the study period(1930–2015),annual mean temperature,annual precipitation,and annual potential evapotranspiration in the river basin increased substantially.We employed hydrological sensitivity method to evaluate the impacts of climate change and human activities on river runoff based on precipitation and potential evapotranspiration.It was estimated that human activities accounted for over 82.6%–98.7%of the reduction in river runoff,mainly owing to water withdrawal for irrigation purpose.The observed variations in river runoff can subsequently lead to adverse ecological consequences from an ecological and regional water resources management perspective.     

Precipitation changes in the mid-latitudes of the Chinese mainland during 1960–2014

Based on daily precipitation data from 163 meteorological stations, this study investigated precipitation changes in the mid-latitudes of the Chinese mainland(MCM) during 1960–2014 using the climatic trend coefficient, least-squared regression analysis, and a non-parametric Mann-Kendall test.According to the effects of the East Asian summer monsoon on the MCM and the climatic trend coefficient of annual precipitation during 1960–2014, we divided the MCM into the western MCM and eastern MCM. The western MCM was further divided into the western MCM1 and western MCM2 in terms of the effects of the East Asian summer monsoon. The main results were as follows:(1) During the last four decades of the 20~(th) century, the area-averaged annual precipitation presented a significant increasing trend in the western MCM, but there was a slight decreasing trend in the eastern MCM, where a seesaw pattern was apparent. However, in the 21~(st) century, the area-averaged annual precipitation displayed a significant increasing trend in both the western and eastern MCM.(2) The trend in area-averaged seasonal precipitation during 1960–2014 in the western MCM was consistent with that in the eastern MCM in winter and spring. However, the trend in area-averaged summer precipitation during1960–2014 displayed a seesaw pattern between the western and eastern MCM.(3) On an annual basis,both the trend in rainstorms and heavy rain displayed a seesaw pattern between the western and eastern MCM.(4) The precipitation intensity in rainstorms, heavy rain, and moderate rain made a greater contribution to changes in the total precipitation than precipitation frequency. The results of this study will improve our understanding of the trends and differences in precipitation changes in different areas of the MCM. This is not only useful for the management and mitigation of flood disasters, but is also beneficial to the protection of water resources across the MCM.     

Spatial distribution of δ~2H and δ~18O values in the hydrologic cycle of the Nile Basin

Existing δ2H and δ18O values for precipitation and surface water in the Nile Basin were used to analyze precipitation inputs and the influence of evaporation on the isotopic signal of the Nile River and its tributaries. The goal of the data analysis was to better understand basin processes that influence seasonal streamflow for the source waters of the Nile River, because climate and hydrologic models have continued to produce high uncertainty in the prediction of precipitation and streamflow in the Nile Basin. An evaluation of differences in precipitation δ2H and δ18O values through linear regression and distribution analysis indicate variation by region and season in the isotopic signal of precipitation across the Nile Basin. The White Nile Basin receives precipitation with a more depleted isotopic signal compared to the Blue Nile Basin. The hot temperatures of the Sahelian spring produce a greater evaporation signal in the precipitation isotope distribution compared to precipitation in the Sahara/Mediterranean region, which can be influenced by storms moving in from the Mediterranean Sea. The larger evaporative effect is reversed for the two regions in summer because of the cooling of the Sahel from inflow of Indian Ocean monsoon moisture that predominantly influences the climate of the Blue Nile Basin. The regional precipitation isotopic signals convey to each region's streamflow, which is further modified by additional evaporation according to the local climate. Isotope ratios for White Nile streamflow are significantly altered by evaporation in the Sudd, but this isotopic signal is minimized for streamflow in the Nile River during the winter, spring and summer seasons because of the flow dominance of the Blue Nile. During fall, the contribution from the White Nile may exceed that of the Blue Nile, and the heavier isotopic signal of the White Nile becomes apparent. The variation in climatic conditions of the Nile River Basin provides a means of identifying mechanistic processes through changes in isotope ratios of hydrogen and oxygen, which have utility for separating precipitation origin and the effect of evaporation during seasonal periods. The existing isotope record for precipitation and streamflow in the Nile Basin can be used to evaluate predicted streamflow in the Nile River from a changing climate that is expected to induce further changes in precipitation patterns across the Nile Basin.     

Spatio-temporal patterns of drought in North Xinjiang,China, 1961–2012 based on meteorological drought index

Drought, which is one of the most frequently occurring severe hazards with long time scales and covering wide geographical areas, is a natural phenomenon resulting in significant economic losses in agriculture and industry. Drought is caused by an imbalance between the inputs of and the demand for water which is insufficient to meet the demands of human activities and the eco-environment. As a major arid and semi-arid area and an important agricultural region in Northwest China, North Xinjiang(NX) shows great vulnerability to drought. In this paper, the characteristics of inter-annual and seasonal drought were analyzed in terms of drought occurrence and drought coverage, by using the composite index of meteorological drought and the data of daily precipitation, air temperature, wind speed, relative humidity and sunshine duration from 38 meteorological stations during the period 1961–2012. Trend analysis, wavelet analysis and empirical orthogonal function were also applied to investigate change trend, period and regional characteristics, respectively. In NX, annual and seasonal drought occurrence and drought coverage all showed a decreasing trend that was most significant in winter(with rates of –0.26 month/10 a and –15.46%, respectively), and drought occurrence in spring and summer were more frequent than that in autumn and winter. Spatially, drought was severe in eastern regions but mild in western regions of NX. Annual and seasonal drought occurrence at 38 meteorological stations displayed decreasing trends and were most significant in "Shihezi-Urumqi-Changji", which can help to alleviate severe drought hazards for local agricultural production and improve human livelihood. NX can be approximately classified into three sub-regions(severe drought region, moderate drought region and mild drought region), which were calculated from annual drought frequencies. The cross wavelet transform suggested that SOI(Southern Oscillation Index), AOI(Arctic Oscillation Index), AAOI(Antarctic Oscillation Index), PAOI(Pacific/North American Oscillation Index) and NAOI(North Atlantic Oscillation Index) have significant correlation with the variation of drought occurrence in NX. To prevent and mitigate the occurrence of drought disasters in NX, agricultural and government managers should pay more attention to those drought events that occur in spring and summer.     

Spatio-temporal variation of hydrological drought under climate change during the period 1960–2013 in the Hexi Corridor,China

In recent years, climate change has been aggravated in many regions of the world. The Hexi Corridor is located in the semiarid climate zone of Northwest China, which is particularly affected by climate change. Climate change has led to the spatial and temporal variations of temperature and precipitation, which may result in hydrological drought and water shortage. Thus, it is necessary to explore and assess the drought characteristics of river systems in this area. The patterns of hydrological drought in the Hexi Corridor were identified using the streamflow drought index(SDI) and standardized precipitation index at 12-month timescale(SPI12) from 1960 to 2013. The evolution of drought was obtained by the Mann–Kendall test and wavelet transform method. The results showed that both the mean annual SDI and SPI12 series in the Hexi Corridor exhibited an increasing trend during the study period. According to the results of wavelet analysis, we divided the study period into two segments, i.e. before and after 1990. Before 1990, the occurrence of droughts showing decreased SDI and SPI12 was concentrated in the northern part of the corridor and shifted to the eastern part of the corridor after 1990. The probability of drought after 1990 in Shule River basin decreased while increased in Shiyang River basin. The wavelet analysis results showed that Shiyang River basin will be the first area to go through the next drought period. Additionally, the relationships between drought pattern and climate indices were analyzed. The enhanced westerly winds and increased precipitation and glacier runoff were the main reasons of wet trend in the Hexi Corridor. However, the uneven spatial variations of precipitation, temperature and glacier runoff led to the difference of hydrological drought variations between the Shule, Heihe and Shiyang River basins.     

Temporal and spatial variation of annual mean air temperature in arid and semiarid region in northwest China over a recent 46 year period

We analyzed the 1961-2006 mean surface air temperature data of 138 stations in China’s northwest arid and semi-arid areas(CNASA),to measure climate change in terms of annual mean air temperature changes.We used methods of linear regression analysis,multinomial fitting,Empirical Or-thogonal Function(EOF),Rotated Empirical Orthogonal Function(REOF),Mann-Kendall,Glide T-examination,wavelet analysis and power spectrum analysis.The results show that(1) the warming rate of the annual mean air temperature in CNASA was 0.35oC/10a during the 1961-2006 study period.Some places in the west part of Xinjiang and east part of the Qinghai plateau,which is impacted by the terrain of leeward slope,exhibit smaller increasing trends.However,the majority of region has shown distinct warming in line with general global warming;(2) The standard deviation of the annual mean temperature distribution is non-uniform.The south Xinjiang and east Qinghai-south Gansu areas show relatively small standard deviations,but the inter-annual variation in annual mean air temperature in the greater part of the region is high;(3) Inner Mongolia,Shaanxi,Gansu,Ningxia and Tarim Basin are the areas where the temperature changes are most sensitive to the environment.The degree of uniformity in annual mean air temperature increase is higher in the arid and semi-arid area.From the early 1970s,the trend in tempera-ture changed from a decrease to an increase,and there was a marked increase in mean temperature in 1986.After that mean temperature went through a period of rapid increase.The entire area’s 10 hottest years all occurred in or since the 1990s,and 90% of various sub-districts’ hottest years also occurred after 1990.The process of temperature change appears to have a roughly 5-year and a 10-year cycle;(4) An-nual mean air temperature variation has regional differences.In Inner Mongolia-Xinjiang and Shaanxi-Gansu-Ningxia-Qinghai areas,the temperature variation in their northern areas was very different from that in their southern areas;(5) Using     

近50年来喀什噶尔河流域气温、降水及径流的变化趋势

应用喀什噶尔河流域内7个气象站、3个水文站的观测资料,分析了全流域、平原区和帕米尔高原的气温、降水以及出山口控制站年径流量的变化特征.结果显示:①从20世纪90年代开始,喀什噶尔河全流域以及平原区和帕米尔高原的年以及冬、秋季明显增暖,近5年春季迅速增温.从90年代起,全流域与高原区的年降水量明显增加,近5年平原区也明显增加;自90年代起全流域的春季、夏季降水明显增加,而近5年秋、冬季增湿迅速;近5年平原区的秋、春季以及冬季降水增加明显,高原区却以夏、秋季增湿最明显.②喀什噶尔河全流域以及平原区和帕米尔高原的年气温与降水量都呈显著的线性增加趋势.平原区的秋、冬季气温显著上升,冬季最明显,夏季呈不显著的下降趋势;平原区的四季降水呈不显著的上升趋势.帕米尔高原的夏、秋、冬季气温呈显著的上升趋势,秋季最明显;帕米尔高原的四季降水呈上升趋势,只有夏季的增湿趋势较显著.③喀什噶尔河年径流量(3站合计)近47年来呈显著的线性上升趋势,以3.0%·(10 a)-1的速率增加.流域内3条河流情况有所不同,克孜河径流量的线性增加趋势最明显,而盖孜河呈不显著的下降趋势.     

开都河源区径流变化的气候响应

气候变化下的山区径流时空变异特征是干旱区水文水资源研究的热点之一。本研究选择天山南坡开都河流域源区为典型研究区,基于1958-2017年大山口水文站和巴音布鲁克水文站径流数据,及巴音布鲁克气象观测数据,采用TFPW-MK趋势检验、小波分析与小波相干等方法分析径流序列的趋势、突变和周期特征及其对气候变化的响应。结果表明:近60 a来,开都河源区径流、降水、气温呈显著增加趋势,并且径流量、降水量与最高气温的增率在加快,而平均气温与最低气温的增率减缓;径流量、降水与平均气温的突变年份集中在20世纪90年代,并且均存在28 a的周期;夏季径流量增加主要受夏季升温的影响,而早春径流量增加主要与冬季降水增加、早春升温有关;在年尺度上,降水是影响开都河径流变化的主要因素,气温主要以积温形式影响着径流的变化;在月尺度上,积温与降水均与径流呈显著正相关关系,且源区上游径流较下游径流对气温变化更为敏感。     

Sensitivity of runoff to climatic variability in the northern and southern slopes of the Middle Tianshan Mountains,China

Temperature and precipitation play an important role in the distribution of intra-annual runoff by influencing the timing and contribution of different water sources.In the northern and southern slopes of the Middle Tianshan Mountains in China,the water sources of rivers are similar;however,the proportion and dominance of water sources contributing to runoff are different.Using the Manas River watershed in the northern slope and the Kaidu River watershed in the southern slope of the Middle Tianshan Mountains as case studies,we investigated the changes in annual runoff under climate change.A modified hydrological model was used to simulate runoff in the Kaidu River and Manas River watersheds.The results indicated that runoff was sensitive to precipitation variation in the southern slope and to temperature variation in the northern slope of the Middle Tianshan Mountains.Variations in temperature and precipitation substantially influence annual and seasonal runoff.An increase in temperature did not influence the volume of spring runoff;but it resulted in earlier spring peaks with higher levels of peak flow.Damages caused by spring peak flow from both slopes of the Middle Tianshan Mountains should be given more attention in future studies.     

近30 a来开都河上游径流量变化的气候响应

利用巴音布鲁克水文站1980-2010年逐日径流量观测资料,采用线性趋势分析、多元回归分析等方法,研究了近30 a来开都河上游4-9月径流量的变化特征。同时,基于同期巴音布鲁克气象站气温、降水资料,探讨开都河上游气温与降水变化对春季径流量的影响。结果显示：开都河上游年径流量在过去30 a呈明显增加趋势。其中4-6月月平均径流量没有明显变化趋势,7-9月径流量增加明显。虽然年径流量主要分布在夏季,但年最大日径流量大多发生在春季4、5月份。进一步分析表明,前期冬季降水量与当年春季增温均对春季径流量有极显著的影响。     

1960—2019年黄河源区气候变化时空规律研究

黄河源区是气候变化敏感区及生态环境脆弱区,也是黄河的主要产流区,其气候变化问题备受关注。利用黄河源区均一化气温和降水观测数据,系统分析了近60 a黄河源区平均气候与极端气候事件的变化特征。结果表明:1960—2019年黄河源区年平均气温、平均最高及最低气温表现出增温趋势的一致性,且源区东部增温幅度高于西部;黄河源区年均气温在2000年前后发生突变转折,转折后升温速率达0.61℃·(10a)^-1,高于1960—2019年的增温率0.37℃·(10a)^-1。1960—2019年黄河源区年降水量总体呈微弱增加趋势[7.6 mm·(10a)^-1],2003年后进入降水偏多阶段,近10 a(2010—2019年)源区平均年降水量达到610 mm;春、夏、冬季降水增多,秋季降水减少;其中源区东部夏、秋季降水减少明显,阶段性干旱风险加剧。近10 a源区平均气温、降水量均为60 a来最高值,总体处于最暖湿阶段。受持续暖湿化影响,1960—2019年黄河源区平均极端气温阈值呈显著的增大趋势,而霜冻日数减少;年最大3日降水量和强降水日数增多,降水强度增大,其中尤以夏季最为显著,对源区生态保护和水资源利用乃至黄河全流域高质量发展均可能带来风险挑战。     

黄土高塬沟壑区砚瓦川流域近60年降水时空变化特征

采用气候趋势倾向率、小波变换、Mann-Kendall突变检验等方法,对黄土高原砚瓦川流域1951-2009年近60年的降水进行时空特征分析。结果表明：从时间过程上看,该流域春、秋季降水量明显趋于减少,而夏、冬季则稍有增加,年降水量在波动中呈下降趋势;年降水量最显著的振荡周期为32年,经历高-低-高3个循环交替,夏、秋季的周期变化对年降水量的影响较大;该流域50年一遇的年降水量和最大日降水量分别是815．3 mm和111．5 mm;降水年内分布主要集中在6-9月,占全年的68％。年降水量没有明显的突变现象,但在50年代有两次降水转折,80年代后期以来出现七次降水转折。从空间分布上看,流域年降水呈西高、东低的态势,其中东北部年降水量近60年来下降幅度较大,西部年降水量下降幅度较小。     

阿克苏河流域近46年气候变化研究

利用线性回归、突变分析和小波分析方法,分析了阿克苏河流域1961-2006年6个地面台站的平均气温和降水量的变化。结果表明:1)46 a来阿克苏河流域气温呈上升趋势,气候倾向率为0.18℃/10 a;2)阿克苏河流域46 a来年降水量以13.1mm/10 a的变化倾向率呈增加趋势;3)阿克苏河流域的年平均气温在1993年发生了由低向高的突变,降水在1987年发生了由低向高的突变;4)阿克苏河流域年降水量较大尺度12-16 a和8-12 a左右的振荡周期非常明显。     

玛纳斯河流域绿洲区气候变化特征分析与预测

利用1964～2007年玛纳斯河流域绿洲区5个气象台站逐月气温、降水数据,建立玛河流域绿洲区年均气温、降水序列,利用一元线性回归、Mann-Kendall等方法分析研究区44年来气温、降水的变化特征.并利用均生函数预测模型对研究区未来5年气温、降水变化进行预测.结果表明:1)玛河流域绿洲区近44a来气温呈显著上升趋势,...     

三江平原挠力河流域近50年降水时空分布特征

通过非参数检验法(Mann-Kendall)分析三江平原挠力河流域19个气象站点近50年(1956-2004)降水序列的变化趋势,并利用Surfer8.0做出流域降水量及倾斜度β值等值线图,研究该流域降水的时空分布特征。结果表明:时间上,总体上挠力河流域降水以年均1.500mm/a的幅度逐渐减少,其中9月份降幅最大,为-0.439mm/a;同时,夏秋两季(6～11月)降水都是减少的,特别是夏季(6～9月),降幅达-1.485mm/a;此外,流域降水年内分布不均,其中夏季降水最多,占全年降水总量的69.8%。空间上,对于年序列而言,降水大致以七星河流域为中心向下游逐渐增加,同时,龙头站附近出现了降水减少的低值中心;对于季序列而言,挠力河流域春季降水逐渐增加,最大值为0.338mm/a(八五三),而夏、秋、冬季降水逐渐减少,其中夏季降水变化较复杂,秋季降幅均值最大,冬季降幅最小。     

西北干旱区近50年气候变化对出山径流的影响分析——以黑河流域为例

对黑河上游山区1956—2004a祁连站气温与降水数据、莺落峡水文站出山径流进行各季年均值变化分析、基于MathCAD对气温和降水分别与出山径流的关系进行相关分析,发现近50a黑河流域气温与降水的变化没有显著的相关性,降水变化与径流的变化表现出正相关,而气温与径流则没有相关性。近50a降水各季变化没有一致性,却出现一定的规律,即春季持平,夏秋下降,而冬季增加。相对于降水而言,气温变化则表现出各季之间的一致性趋势,即近10a表现出明显的增温趋势,而且增温幅度相似,都在2℃左右。另外对气温与降水对出山径流的影响做了量化,降水与径流的相关系数为0.557,而气温与径流的相关系数只有0.045左右;根据影响径流的气候因子所占权重,集成气候(无量纲)变化曲线,显示出与径流变化的一致性,即气候变化对径流变化有明显的影响;依据本文分析和总结,预计今后10—20a气温、降水都将有升高或增加趋势,届时出山径流将相应增加。