Climate transformation to warm-humid and its effect on river runoff in the source region of the Yellow River

The change characteristics and trends of the regional climate in the source region of the Yellow River, and the response of runoff to climate change, are analyzed based on observational data of air temperature, precipitation, and runoff at 10 main hydrological and weather stations in the region. Our results show that a strong signal of climate shift from warm-dry to warm-humid in the western parts of northwestern China （Xinjiang） and the western Hexi Corridor of Gansu Province occurred in the late 1980s, and a same signal of climate change occurred in the mid-2000s in the source region of the Yellow River located in the eastern part of northwestern China. This climate changeover has led to a rapid increase in rainfall and stream runoff in the latter region. In most of the years since 2004 the average annual precipitation in the source region of the Yellow River has been greater than the long-term average annual value, and after 2007 the runoff measured at all of the hydrologic sections on the main channel of the Yellow River in the source region has also consistently exceeded the long-term average annual because of rainfall increase. It is difficult to determine the prospects of future climate change until additional observations and research are conducted on the rate and temporal and spatial extents of climate change in the region. Nevertheless, we predict that the climate shift from warm-dry to warm-humid in the source region of the Yellow River is very likely to be in the decadal time scale, which means a warming and rainy climate in the source region of the Yellow River will continue in the coming decades.     

Impacts of climate change and LULC change on runoff in the Jinsha River Basin

The climate change and Land Use/Land Cover(LULC) change both have an important impact on the rainfall-runoff processes. How to quantitatively distinguish and predict the impacts of the above two factors has been a hot spot and frontier issue in the field of hydrology and water resources. In this research, the SWAT(Soil and Water Assessment Tool) model was established for the Jinsha River Basin, and the method of scenarios simulation was used to study the runoff response to climate change and LULC change. Furthermore, the climate variables exported from 7 typical General Circulation Models(GCMs) under RCP4.5 and RCP8.5 emission scenarios were bias corrected and input into the SWAT model to predict runoff in 2017–2050. Results showed that:(1) During the past 57 years, the annual average precipitation and temperature in the Jinsha River Basin both increased significantly while the rising trend of runoff was far from obvious.(2) Compared with the significant increase of temperature in the Jinsha River Basin, the LULC change was very small.(3) During the historical period, the LULC change had little effect on the hydrological processes in the basin, and climate change was one of the main factors affecting runoff.(4) In the context of global climate change, the precipitation, temperature and runoff in the Jinsha River Basin will rise in 2017–2050 compared with the historical period. This study provides significant references to the planning and management of large-scale hydroelectric bases at the source of the Yangtze River.     

Impacts of climate change on glacial water resources and hydrological cycles in the Yangtze River source region, the Qinghai-Tibetan Plateau, China: A Progress Report

The Yangtze River Source Region has an area of 137,704 km2.Its mean annual runoff of 12.52 billion m3,which was recorded by the Chumda Hydrological Station in 1961-2000,accounts for only 0.13 percent of the Yangtze River’s total annual streamflow.The extensive rivers,lakes,wetlands,glaciers,snow fields,and permafrost of the Yangtze River Source Region,as well as the region’s vast alpine grasslands,play a critical role in storing and regulating the flow of water not only in the upper Yangtze River watershed of Qinghai,Sichuan,the Tibet Autonomous Region (TAR) (Tibet) and Yunnan,but also throughout the entire lower Yangtze River basin.Climate change has been the dominant factor in recent fluctuation in the volume of the Yangtze River Source Region’s glacier resources.The Chumda Hydrological Station on the lower Tongtian River has registered a mean annual glacial meltwater of 1.13 billion m3 for the period 1961-2000,makes up 9 percent of the total annual runoff.Glacial meltwater makes up a significant percentage of streamflow in the Yangtze River Source Region,the major rivers of the upper Yangtze River Source Region:the Togto,Dam Chu,Garchu,and Bi Chu (Bu Chu) rivers all originate at large glaciers along the Tanggula Range.Glaciers in the Yangtze River Source Region are typical continental-type glaciers with most glacial meltwater flow occurring June-August;the close correlation between June-August river flows and temperature illustrates the important role of glacial meltwater in feeding rivers.Glaciers in the source region have undergone a long period of rapid ablation beginning in 1993.Examination of flow and temperature data for the 1961-2000 period shows that the annual melting period for glacial ice,snow,and frozen ground in the Yangtze River Source Region now begins earlier because of increasing spring temperatures,resulting in the reduction of summer flood season peak runoffs;meanwhile,increased rates of glacier ablation have resulted in more uneven annual distribution of runoff in the source region.T     

Synchronism of runoff response to climate change in Kaidu River Basin in Xinjiang, Northwest China

The runoff in alpine river basins where the runoff is formed in nearby mountainous areas is mainly affected by temperature and precipitation.Based on observed annual mean temperature,annual precipitation,and runoff time-series datasets during 1958–2012 within the Kaidu River Basin,the synchronism of runoff response to climate change was analyzed and identified by applying several classic methods,including standardization methods,Kendall's W test,the sequential version of the Mann-Kendall test,wavelet power spectrum analysis,and the rescaled range(R/S) approach.The concordance of the nonlinear trend variations of the annual mean temperature,annual precipitation,and runoff was tested significantly at the 0.05 level by Kendall's W method.The sequential version of the Mann-Kendall test revealed that abrupt changes in annual runoff were synchronous with those of annual mean temperature.The periodic characteristics of annual runoff were mainly consistent with annual precipitation,having synchronous 3-year significant periods and the same 6-year,10-year,and 38-year quasi-periodicities.While the periodic characteristics of annual runoff in the Kaidu River Basin tracked well with those of annual precipitation,the abrupt changes in annual runoff were synchronous with the annual mean temperature,which directly drives glacier-and snow-melt processes.R/S analysis indicated that the annual mean temperature,annual precipitation,and runoff will continue to increase and remain synchronously persistent in the future.This work can improve the understanding of runoff response to regional climate change to provide a viable reference in the management of water resources in the Kaidu River Basin,a regional sustainable socio-economic development.     

Differential changes in precipitation and runoff discharge during 1958–2017 in the headwater region of Yellow River of China

Maintenance of steady streamflow is a critical attribute of the continental river systems for safeguarding downstream ecosystems and agricultural production.Global climate change imposes a potential risk to water supply from the headwater by changing the magnitude and frequency of precipitation and evapotranspiration in the region.To determine if and to what extent the recent climate changes affected streamflow in major river systems,we examined the pattern of temporal variations in precipitation,temperature,evapotranspiration and changes in runoff discharge during 1958–2017 in the headwater region of the Yellow River in northeastern Tibetan Plateau.We identified 1989 as the turning point for a statistically significant 14% reduction in streamflow discharge(P 0.05) for the period 1989–2017 compared with 1958–1988,approximately coinciding with changes in the monthly distribution but not the interannual variations of precipitation,and detected a mismatch between precipitation and runoff after 2000.Both annual precipitation and runoff discharge displayed fourand eight-year cyclic patterns of changes for the period 1958–1988,and a six-year cyclic pattern of changes for the period 1989–2017,with two intensified two-year cyclic patterns in the changes of precipitation and a three-year cyclic pattern in the change of runoff further detected for the later period.Our results indicate that the temporal changes in runoff are not strictly consistent with the temporal variations of precipitation in the headwater region of Yellow River during the period 1958–2017.In particular,a full recovery in annual precipitation was not reflected in a full recovery in runoff toward the end of the study period.While a review of literature yielded no apparent evidence of raised evapotranspiration in the region due to recent warming,we draw attention to increased local retention of rainwater as a possible explanation of differential changes in precipitation and runoff.     

1956-2003年拉萨河流域径流变化趋势

Taking the Lhasa River Basin above Lhasa hydrological station in Tibetan Plateau as a study area, the characteristics of the annual and monthly mean runoff during 1956-2003 were analyzed, based on the hydro-data of the two hydrological stations （Lhasa and Tanggya） and the meteorological data of the three meteorological stations （Damxung, Lhasa and Tanggya）. The trends and the change points of runoff and climate from 1956 to 2003 were detected using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. The correlations between runoff and climate change were analyzed using multiple linear regression. The major results could be summarized as follows： （1） The annual mean runoff during the last 50 years is characterized by a great fluctuation and a positive trend with two change points （around 1970 and the early 1980s）, after which the runoff tended to increase and was increasing intensively in the last 20 years. Besides, the monthly mean runoff with a positive trend is centralized in winter half-year （November to April） and some other months （May, July and September）. （2） The trends of the climate change in the study area are generally consistent with the trend of the runoff, but the leading climate factors which aroused the runoff variation are distinct. Precipitation is the dominant factor influencing the annual and monthly mean runoff in summer half year, while temperature is the primary factor in winter season.     

A paleo-hydrological simulation experiment and its verification in an inland basin

Hydrological circulation, as the most basic material cycle and active natural phenomenon on earth, exerts a significant influence on climate change. The mid-Holocene is an important period to better understand modern environmental change;however, little research has focused on its quantitative simulation of paleo-hydrological process. In this research, we first collected chronological evidence and sediment records from six Holocene sedimentary sections in the Shiyang River Basin to reconstruct the mid-Holocene environment and terminal paleo-lake area. Secondly, we comprehensively analyzed modern pollen combinations and their propagation characteristics in surface soil, air, river and lacustrine sediments in the Shiyang River Basin, and combined the pollen records, as well as quantitatively reconstructed the millennial-scale vegetation zones. Finally, based on the land-cover adjustment results during the mid-Holocene, we successfully used the Soil and Water Assessment Tool(SWAT) model, a modern distributed hydrological watershed model, to simulate mid-Holocene runoff in the basin. Results show that the reconstructed climate in the basin was warmer and moister than that in recent times. Vegetation types in the mid-Holocene mainly consisted of sub-alpine shrub distributed between 2,550 m and 2,750 m,forest at an elevation of 2,550-2,750 m, steppe at an elevation of 1,550-2,150 m and desert steppe below 1,550 m. The upstream, midstream, downstream and average annual runoff of the mid-Holocene in the basin were 16.76×10~8 m~3, 22.86×10~8 m~3, 9.00×10~8 m~3 and 16.20×10~8 m~3 respectively, compared to 15.61×10~8 m~3 of modern annual runoff. Also, the area of terminal paleo-lake in the mid-Holocene was 628 km~2. Thus, this study provides a new quantitative method for paleo-hydrological simulation.     

基于小波分析的江河源区汛期和枯水期径流特征(英文)

By decomposing and reconstructing the runoff information from 1965 to 2007 of the hydrologic stations of Tuotuo River and Zhimenda in the source region of the Yangtze River, and Jimai and Tangnaihai in the source region of the Yellow River with db3 wavelet, runoff of different hydrologic stations tends to be declining in the seasons of spring flood, summer flood and dry ones except for that in Tuotuo River. The declining flood/dry seasons series was summer > spring > dry; while runoff of Tuotuo River was always increasing in different stages from 1965 to 2007 with a higher increase rate in summer flood seasons than that in spring ones. Complex Morlet wavelet was selected to detect runoff periodicity of the four hydrologic stations mentioned above. Over all seasons the periodicity was 11-12 years in the source region of the Yellow River. For the source region of the Yangtze River the periodicity was 4-6 years in the spring flood seasons and 13-14 years in the summer flood seasons. The differences of variations of flow periodicity between the upper catchment areas of the Yellow River and the Yangtze River and between seasons were considered in relation to glacial melt and annual snowfall and rainfall as providers of water for runoff.     

三江源地区气候变化及其对径流的驱动分析(英文)

Based on the precipitation and temperature data of the 12 meteorological stations in the "Three-River Headwaters" region and the observed runoff data of Zhimenda in the headwater sub-region of the Yangtze River, Tangnaihai in the headwater sub-region of the Yellow River and Changdu in the headwater sub-region of the Lancang River during the period 1965-2004, this paper analyses the trends of precipitation, temperature, runoff depth and carries out significance tests by means of Mann-Kendall-Sneyers sequential trend test. Makkink model is applied to calculate the potential evaporation. The runoff model driven by precipitation and potential evaporation is developed and the influence on runoff by climate change is simulated under different scenarios. Results show that during the period 1965-2004 the temperature of the "Three-River Headwaters" region is increasing, the runoff of the three hydrological stations is decreasing and both of them had abrupt changes in 1994, while no significant trend changes happen to the precipitation. The runoff model suggests that the precipitation has a positive effect on the runoff depth, while the potential evaporation plays a negative role. The influence of the potential evaporation on the runoff depth of the Lancang River is found to be the significant in the three rivers; and that of the Yellow River is the least. The result of the scenarios analysis indicates that although the precipitation and the potential evaporation have positive and negative effects on runoff relatively, fluctuated characteristics of individual effect on the runoff depth in specific situations are represented.     

The response of annual runoff to the height change of the summertime 0℃ level over Xinjiang

According to climate features and river runoff conditions, Xinjiang could be divided into three research areas: The Altay-Tacheng region, the Tianshan Mountain region and the northern slope of the Kunlun Mountains. Utilizing daily observations from 12 sounding stations and the annual runoff dataset from 34 hydrographical stations in Xinjiang for the period 1960–2002, the variance of the summertime 0℃ level height and the changing trends of river runoff are analyzed both qualitatively and quantitatively, through trend contrast of curves processed by a 5-point smoothing procedure and linear correlation. The variance of the summertime 0℃ level height in Xinjiang correlates well with that of the annual river runoff, especially since the early 1990s, but it differs from region to region, with both the average height of the 0℃ level and runoff quantity significantly increasing over time in the Altay- Tacheng and Tianshan Mountain regions but decreasing on the northern slope of the Kunlun Mountains. The correlation holds for the whole of Xinjiang as well as the three individual regions, with a 0.01 significance level. This indicates that in recent years, climate change in Xinjiang has affected not only the surface layer but also the upper levels of the atmosphere, and this raising and lowering of the summertime 0℃ level has a direct impact on the warming and wetting process in Xinjiang and the amount of river runoff. Warming due to climate change increases the height of the 0℃ level, but also speeds up, ice-snow melting in mountain regions, which in turn increases river runoff, leading to a season of plentiful water instead of the more normal low flow period.     

三江源区径流演变及其对气候变化的响应

利用水循环模型、统计检测、对比分析等手段对三江源区水循环过程进行了分析,模拟和检测了1958-2005 年黄河源区出口唐乃亥站、长江源区直门达站、澜沧江源区昌都站汛期、非汛期和年径流过程的变化趋势。在此基础上,检测CSIRO和NCAR两种气候模式A1B和B1 排放情景下未来2010-2039 年源区出口断面的径流演变趋势,对比分析了气候变化的影响。研究表明过去48 年三江源区出口唐乃亥站年径流和非汛期径流过程呈显著减少趋势,而直门达和昌都站径流过程变化趋势并不显著。这将导致对黄河中下游地区的水资源补给显著减少,加剧黄河流域水资源短缺。气候变化背景下,未来30 年黄河源区径流量与现状相比有所减少,尤其是在非汛期,将持续加剧黄河中下游流域水资源短缺的现象。长江源区径流量将呈增加趋势,而且远远高于现状流量,尤其是在汛期,长江中下游地区防洪形势严峻。而澜沧江源区未来30 年径流量均高于现状流量,但汛期和年径流变化并不显著,而非汛期径流变化存在不确定性,CSIRO模式B1 情景显著减小,而NCAR模式B1 情景显著增加。气候变化对长江源区径流影响最显著,黄河源区其次,而澜沧江源区最小。     

1960-2015年青海三江源地区降水时空特征

青海三江源地区是中国生态系统最为敏感和脆弱的地区,其降水特别是生长季降水的波动,是影响本区及江河中下游水资源安全、生态系统可持续发展的关键因素。综合线性趋势、Mann-Kendall检验、BG分割算法、R/S、EEMD等多方法细致辨识了1960-2015年研究区降水量序列的时空特征。结果显示：① 三江源降水量总体呈现弱增趋势,21世纪以来降水量显著增加,各子源区气候倾向率不尽相同;② 年、季降水量自东南向西北递减,澜沧江源区夏季降水和黄河源区秋季降水呈弱减趋势,雨量弱减区在空间上呈斑块状分布;③ 年、季降水量年代际变化和增湿率的空间差异较明显,春夏季降水气候倾向率与经纬度、海拔的复相关性显著高于冬季;④ 20世纪90年代中后期,各子源区降水总体显现增强信号,并于2002年前后发生突变;⑤ 年际和低值年代际显著周期是造成降水量变动的主要因素;⑥ 除澜沧江源区夏季降水趋于减少外,其他年、季降水量变化呈现增幅不一的转湿趋势;⑦ 横向比较各子源区可见,长江源区降水变化更能表征高原气候变化。研究结果显示,研究区降水时空序列变化具有明显的区域和季节差异性特征,与以往类似研究存在些许差异,可见为有效提高气候序列演变过程及突变诊断的准确性,仍需进一步融合多方法实施集成分析。     

三江源气候变化及其对径流的驱动分析

以1965-2004 年三江源地区12 个气象台站的降水和气温资料以及长江源区直门达、黄河源区唐乃亥和澜沧江源区昌都水文站的径流资料为基础,分析三江源地区的降水、气温和径流的变化趋势,并采用Mann-Kendall-Sneyers 方法进行趋势显著性检验;采用Makkink 公式计算三江源区12 个气象站点的潜在蒸发,建立三江源区降水和潜在蒸发对径流的驱动模型,并对气候变化(降水和气温的变化) 对径流的驱动进行情景分析。研究表明：1965-2004 年三江源区气温升高,径流减少,并且气温和径流都在1994 年发生突变,但降水的变化趋势不明显。降水和潜在蒸发对径流深的驱动模型表明三江源区降水对径流起正向的驱动作用,潜在蒸发对径流起负向的驱动作用,具体来说,澜沧江源区潜在蒸发对径流的驱动力最大,长江源区次之,黄河源区最小。借助驱动模型对三江源气候变化(降水和气温的变化) 对径流的影响进行情景分析,结果显示,降水和气温对径流的驱动在总体上虽然分别是正、负方向上的驱动,但在具体情景下其各自的驱动作用又呈现出波动的特征。     

全球气候变化对黄河流域天然径流量影响的情景分析

本文从干旱指数蒸发率函数出发,以HadCM3 GCM对降水和温度的模拟结果为基础,在IPCC不同发展情景下,分析了未来近100年内黄河流域天然径流量的变化趋势。研究结果表明,在不同气候变化情景下,多年平均年径流量的变化随着区域的不同而有显著差异,其变化幅度在-48.0%²03.0%之间。全球气候变化引起的多年平均天然径流量的变化从东向西逐渐减小。就黄河流域而言,2006²035年、2036²065年、2066²095年A2情景下（人口快速增长、经济发展缓慢）多年平均天然径流量的变化量分别为5.0%、11.7%、8.1%,B2情景下（强调社会技术创新）相应的变化分别为7.2%、-3.1%、2.6%。     

潮河流域降水-径流关系变化及驱动因子识别

基于1973-2010年长系列日降水、径流数据,利用降水径流双累积曲线、M-K统计检验和降水集中度等方法,结合HIMS模型模拟结果,分析了潮河流域降水-径流关系的变化及其原因。得到的主要结论如下：（1）近38年来,潮河流域降水变化较小,但径流下降趋势显著,降水-径流关系发生了两次突变,即在1973-1983年、1984-1998年和1999-2010年三个阶段降水-径流关系存在明显差异;（2）大雨日降水总和（P_≥20）与径流深关系较为密切,其变化是导致降水-径流关系在1983年发生突变的主要驱动因子;（3）HIMS模型模拟结果显示,1999-2010年潮河流域下垫面条件较前两阶段变化明显,人类活动引起的减水效应由第二阶段的14.93%增加至第三阶段的25.78%,人类活动是导致降水-径流关系在1998年发生突变的主要驱动因子。     

2000-2011 年三江源区植被覆盖时空变化特征

基于MODIS-NDVI 数据,辅以线性趋势分析、Hurst 指数及偏相关系数等方法,本文从三个尺度分析了近12 年三江源区植被覆盖时空变化特征、未来趋势及其驱动因素。结果表明:(1) 近12 年三江源区植被覆盖呈现增加趋势,增速为1.2%/10a,其中长江源区、黄河源区植被均呈增加趋势,而澜沧江源区植被呈下降趋势。(2) 三江源区植被覆盖具有显著的区域差异,且NDVI频度呈现“双峰”结构。(3) 近12 年三江源区植被覆盖呈增加趋势和减少趋势的面积分别占64.06%和35.94%,且表现为源区北部增加、南部减少的空间格局。(4) 三江源区植被变化的反向特征显著,植被变化由改善趋势转为退化趋势的区域主要分布在长江源区和黄河源区的北部,而由退化趋势转为改善趋势的区域主要分布在澜沧江源区。(5) 三江源区植被对降水和潜在蒸散的响应存在时滞现象,而对气温的响应不存在时滞现象。(6) 三江源区植被覆盖的增加主要归因于气候暖湿化以及生态保护工程的实施。     

黄河流域NDVI时空变化及其与降水/径流关系

NDVI是表征区域植被覆盖的重要指标。本文把黄河流域划分为 16个区域 ,利用Pathfinder (探路者 )的AVHRR NDVI资料 ,得到各区域 1982～ 1998年NDVI统计序列 ,详细分析了各区域NDVI时空变化特征。研究表明 ,17年来黄河流域各分区年平均NDVI都呈增加趋势 ,说明植被覆盖增加 ,生态环境好转 ,但是 8月份龙羊峡以上和兰河干流区间NDVI则有所下降 ,生态环境有局部恶化趋势。最后研究各区域NDVI与降水、径流和径流系数的年内、年际相关关系 ,结果表明 :从年内变化看 ,黄河流域各区域NDVI变化与降水、径流变化呈明显的正相关 ;从年际变化看 ,黄河流域各区域NDVI波动趋势与降水具有一定的相关性 ,但与径流、径流系数变化的关系相对复杂 ,不具有明显的相关性     

黄河流域坡高地系统最小生态需水研究

以保护和恢复流域坡高地生态系统为目的，对坡高地最小生态需水问题进行研究，提出了坡高地生态需水和生态缺水的计算方法。以黄河流域为实例，在GIS和遥感技术支持下对坡高地最小生态需水量和缺水量进行了计算，并从时空两个尺度揭示了黄河流域坡高地生态系统最小生态需水的变化规律，研究成果可为流域生态环境建设和水资源合理配置提供依据。