Virtual water ‘flows’ of the Nile Basin, 1998–2004: A first approximation and implications for water security

This paper interprets an initial approximation of the ‘trade’ in virtual water of Nile Basin states in terms of national water security. The virtual water content (on the basis of weight) of select recorded crop and livestock trade between 1998 and 2004 is provided, and analysed for each state separately, for the Southern Nile and Eastern Nile states as groups, and for the basin states as a whole. To the extent that the datasets allow, the distinction between rainfed and irrigated production is maintained. During the period under study, Nile Basin states ‘exported’ about 14,000 Mm³ of primarily rainfed-derived virtual water outside of the basin annually and ‘imported’ roughly 41,000 Mm³/y. The ‘imports’ are considered to have played a key role in filling the freshwater deficits of Egypt and Sudan, and represent a third of the flow of the Nile River itself. Analysis of food trade within the basin shows that the equivalent of small rivers of water used to raise coffee and tea ‘flow’ from the highlands around Lake Victoria to Egypt and Sudan. Because the bulk of these ‘flows’ derive from rainfed agriculture, the virtual water ‘traded’ annually between the Nile Basin states is not considered to represent a significant demand on the water resources of the basin, nor to significantly remedy the freshwater deficits of the arid basin states. The importance of soil water and rainfed farming is in improving water security is highlighted. The limitations and merits of the inter-state basin-wide approach are also discussed. By highlighting the magnitude of water leaving and entering states in its virtual form, the approach obliges policy-makers to think beyond the basin and reconsider the concept of water security within broader political, environmental, social and economic forces.     

From headwater tributaries to international river: Observing and adapting to climate variability and change in the Nile basin

Egypt is almost totally dependent upon water that originates from the upstream headwaters of the Nile in the humid Ethiopian and East African highlands. Analysis of rainfall and river flow records during the 20th century demonstrates high levels of interannual and interdecadal variability. This is experienced locally and regionally in the headwater regions of the Nile and internationally through its effects on downstream Nile flows in Sudan and Egypt. Examples of climate variability are presented from areas in the basin where it exerts a strong influence on society; the Ethiopian highlands (links with food security), Lake Victoria (management of non-stationary lake levels) and Egypt (exposure to interdecadal variability of Nile flows). These examples reveal adaptations across various scales by individuals and institutions acting alongside other social and economic considerations.Water resources management in the downstream riparian Egypt has involved institutional level reactive adaptations to prolonged periods of low and high Nile flows. Observed responses include the establishment of more robust contingency planning and early warning systems alongside strategic assessment of water use and planning in response to low flows during the 1980s. In the 1990s high flows have enabled Egypt to pursue opportunistic policies to expand irrigation. These policies are embedded in wider socio-political and economic considerations but increase Egypt's exposure and sensitivity to climate driven fluctuations in Nile flows. Analysis of climate change projections for the region shows there is no clear indication of how Nile flows will be affected because of uncertainty about future rainfall patterns in the basin. In many instances the most appropriate entry point for adaptation to climate change will be coping with climate variability and will play out against the certainty of looming national water scarcity in Egypt due to rapid population growth and its possible exacerbation by water demands from upstream riparians.     

Sensitivity Studies of the Impacts of Climate Change on White Nile Flows

Several exploratory studies are presented on the sensitivity of the water balance of the White Nile to climate change, using both observed and stochastic time series to drive the models. Example results are presented using various assumed climate change scenarios and results from a General Circulation Model (GCM). The relative merits and shortcomings of each modelling approach are also discussed. A simple analytical model for Lake Victoria is also used to illustrate some of the overall features of the lake's likely response. Particular difficulties with the White Nile system are that, due to the huge area of open water in the basin, transient responses to short-lived events can occur over timescales comparable with those for which long term climate change impacts are being studied, and predicted changes in flows are extremely sensitive to estimates for the rainfall and evaporation at lake and swamp surfaces. Of the modelling approaches considered, the network simulation approach with stochastic inputs is recommended as a way of smoothing out these transient effects, and assessing the uncertainty in the results due to inaccuracies in the data, the model parameters and the climate change predictions. The paper concludes with a brief discussion of some other areas of uncertainty in the hydrological modelling of White Nile flows and possible alternative external forcing mechanisms for flows in the next few decades.     

博斯腾湖流域气候变化及其对径流的影响

利用博斯腾湖流域开都河、黄水沟和清水河的出山口水文站月径流量和气象站月平均数据，开展变化特征分析和径流变化对气候因子的响应研究。结果表明，博斯腾湖流域年际气候变化以气温上升为主，降水量增加趋势不显著；域内主要河流径流量持续上升。突变检验发现，三条入湖河流90年代之前径流量增加主要是域内降水量增加的结果，随后受气温上升导致冰雪消融加快也对径流量的增加有贡献。相关分析结果显示，博斯腾湖三条入湖河流年径流量变化主要受4月和7月降水因子影响。此外，开都河的径流变化还表现出对8月气温和降水的显著响应，同时开都河流域集水区冰川的面积和占比均大于黄水沟和清水河流域，这表明冰川融水补给对开都河径流的影响大于黄水沟和清水河。所建立的气候因子-径流量多元线性回归模型，能够很好的模拟开都河、黄水沟和清水河的径流变化过程，证明了博斯腾湖流域水文变化受气候因子的显著影响。     

Long-term changes of water balance components in the basins of rivers fed by snow and ice

The variability of the main components of the annual water balance (precipitation, evaporation, glacial alimentation, and dynamic water reserves in the basin) for 1935–1990 is, for the first time, determined for the area where the Zeravshan runoff is formed, higher than hydrological post Dupuli is located. Long-term data on the annual Zeravshan River runoff from an area of 10 200 km² were derived from the measurements at Dupuli hydrological post. The other water balance components were determined with the help of computation methods. Comparison of the measured and calculated volumes of the annual runoff demonstrated that a relative difference between them is systematic, and as a whole for a computation period it is in the interval from ?0.31 to ?4.78%. The annual balance of accumulation and thawing of solid precipitation on glaciers and in the extraglacial area is also determined in the Zeravshan River basin. A new method for computing and mapping spatial variability of the maximum snowline altitude is developed.     

MACROSCALE HYDROLOGICAL MODELING OVER THE HUAIHE RIVER BASIN

The Xin'anjiang Model is used as the basic model to develop a monthly grid-based macroscalehydrological model for the assessment of the effects of climate change on water resources.Themonthly discharge from 1953 through 1985 in the Huaihe River Basin is simulated.The sensitivityanalysis on runoff is made under assumed climatic scenarios.There is a good agreement betweenthe observed and simulated runoff.Due to the increase of time interval and decrease ofprecipitation intensity on monthly time scale,there is no monthly runoff in some model girds as themomhly hydrological model is applied to the Huaihe River Basin.Two methods of downscalingmonthly precipitation to daily resolution are validated by running the Xin'anjiang model withmonthly data at a daily time step.and the model outputs are more realistic than the monthlyhydrological model.The metbods of downscaling of monthly precipitation to daily resolution mayprovide an idea in solving the problem of the shortage of daily data.In the research of the climatechange on water resources,the daily hydrological model can be used instead of the monthly one.     

Sensitivity of the Himalayan Hydrology to Land-Use and Climatic Changes

Land-use and climatic changes are ofmajor concerns in the Himalayan region because oftheir potential impacts on a predominantlyagriculture-based economy and a regional hydrologydominated by the monsoons. Such concerns are notlimited to any particular basin but exist throughoutthe region including the downstream plains. As arepresentative basin of the Himalayas, the Kosi Basin(54,000 km²) located in the mountainous area ofthe central Himalayan region was selected as a studyarea. We used water balance and distributeddeterministic modeling approaches to analyze thehydrologic sensitivity of the basin to projectedland-use, and potential climate change scenarios.Runoff increase was higher than precipitation increasein all the potential precipitation change scenariosapplying contemporary temperature. The scenario ofcontemporary precipitation and a rise in temperatureof 4 °C caused a decrease in runoff bytwo to eight percent depending upon the areasconsidered and models used. In the absence of climaticchange, the results from a distributed water balancemodel applied in the humid south of the basinindicated a reduction in runoff by 1.3% in thescenario of maximum increase in forest areas below4,000 m.     

CLIMATE CHANGE HYDROLOGY AND WATER RESOURCES IMPACT AND ADAPTATION FOR SELECTED RIVER BASINS IN THE CZECH REPUBLIC

The Czech Republic has a northern hemisphere Atlantic-continental type of moderate climate. Mean annual temperature ranges between 1.0 and 9.4 °C (between 8.8 and 18.5 °C in summer and between –6.8 and 0.2 °C in winter). Annual precipitation ranges between 450 mm in dry regions and 1300 mm in mountainous regions of the country. With its 2000 m³ per capita fresh water availability, the Czech Republic is slightly below average. Occasional water shortages do not usually result from general unavailability of water resources but rather from time or space variability of water supply/demand and high degree of water resources exploitation. To study potential impacts of climate change on hydrological system and water resources, four river basins have been selected in the territory of the Czech Republic: the Elbe River at Decin (50761.7 km²), the Zelivka River at Soutice (1188.6 km²), the Upa River at Ceska Skalice (460.7 km²) and the Metuje River at Marsov n. M. (93.9 km²). To simulate potential changes in runoff, three hydrological models have been applied using incremental and GCM (GISS, GFDL and CCCM) scenarios: the BILAN water balance model, the SACRAMENTO (SAC-SMA) conceptual model and the CLIRUN water balance model. The paper reviews methods applied in the study, results of the assessments and concludes with suggestions for possible general adaptation policy options where the preference is for nonstructural measures such as water conservation, efficient water demand management and protection of water resources.     

基于SWAT模型的洪湖流域供水资源模拟研究

利用SWAT分布式水文模型,对洪湖流域1961—2011年供水资源变化情况进行模拟。结果表明:SWAT模型对洪湖流域供水资源模拟适用性良好。近51 a流域年平均地表径流和降水量增加趋势相当,且降水量峰值对应地表径流和地下径流均较高。流域在1960s、1970s相对偏枯,1980s后降水相对丰沛,流域呈现由干转湿的变化。进入21世纪后,流域又趋于偏枯。流域季节降水量、地表径流、地下径流、蒸散发量及土壤含水量变化最大值均出现在夏季,最小值均出现在冬季,但丰、枯年季节分配不同,各要素月季节分布差异较大。洪湖年均入湖水量呈略增加趋势,春、夏季增加趋势较为明显。     

基于不同降水产品的WRF-Hydro模式径流模拟——以漳河流域为例

以漳河流域为研究区域,以CMORPH卫星-地面自动站-雷达三源降水融合数据和ERA5再分析降水资料为WRF-Hydro模式的输入,进行径流模拟,对比分析模拟径流与实测径流的差异,探讨基于两种降水数据的WRF-Hydro模式在漳河流域的径流模拟效果。结果表明:三源降水融合数据的径流模拟效果较优,纳什系数均达到0.7以上,模拟径流与实测径流过程吻合较好;采用三源降水融合数据和ERA5再分析降水资料率定WRF-Hydro模式,以ERA5再分析降水资料为输入,径流模拟结果都不佳;总体而言,三源降水融合数据与WRF-Hydro模式耦合能够较好地模拟漳河流域径流过程。      

未来气候变化对淮河流域径流的可能影响

采用新安江月分布式水文模型, 结合1961—2000年历史月气候资料和4个CGCMs的3个SRES排放情景下 (B1, A 2, A 1B) 未来降水和气温情景模拟结果, 对过去淮河流域的径流进行模拟检验并对未来2011—2040年的径流影响进行评估, 为水资源管理和规划提供依据。结果表明:水文模型能较好地反映年、月流量以及多年平均值和季节的变化; 年流量模拟一般好于月流量, 淮河干流主要控制水文站如王家坝、鲁台子、蚌埠的年流量模型效率系数均在80%以上; 多年平均值模拟效果好, 平均绝对相对误差为10%。多数CGCMs不同排放情景下气候模拟结果表明:未来2011—2040年, 淮河流域气候将趋于暖湿, 但年径流量将可能以减少趋势为主。这对淮河地区水资源的可持续发展以及东线调水工程水资源统一调配和管理提出了较大的挑战。淮河流域大部分区域2011—2040年月径流量减少将主要发生在1月和7—12月, 变化趋势较为确定; 4—6月, 径流量将以增加趋势为主, 不确定性较大; 2—3月, 径流具有增加趋势的地区多分布在淮河以北地区, 具有减少趋势的地区则多分布在淮河干流及以南地区和洪泽湖、平原区, 这些地区增加或减少趋势的不确定性较大。     

2020年8月黄河中游致洪暴雨气象水文特征

利用ECMWF提供的ERA5再分析资料(分辨率0.25°×0.25°)和黄河流域加密的气象水文实况资料,分析了降水集中期的气象水文特征。结果表明:平均中纬度低槽、南亚高压和阻塞高压偏强,副热带高压位置偏西、偏北,且异常偏强是造成2020年8月黄河中游持续性强降水的主要环流背景;水汽输送较常年同期偏多,来自东海和孟加拉湾的东南和西南暖湿气流沿副热带高压边缘不断输送到黄河中游地区,并和中纬度低槽携带的冷空气在此交汇形成持续性的强降水。水文特征分析表明,导致潼关水文站出现3次洪水的较大面雨量,主要来源于潼关以上的8个子流域;2020年8月的洪水超过2011年9月的,为潼关站近20 a来的最大的洪水过程;5号和6号洪水连续超过编号标准的时长,为120 h和44 h,最大流量达6 300 m³·s^-1;流量开始增加的时间落后降水开始的时间12 h~3 d,峰值落后降水结束的时间12 h~4 d;黄河支流水文站的流量峰值与水文站所在子流域降水范围、量级呈正相关,流入潼关站的流量从大到小依次为龙门站、华县站、状头站和河津站。历史对比表明,2020年8月黄河中游累积面雨量为近30 a来最大,北部6个子流域面雨量表现更为极端,降水持续时间更长。     

RCP情景下内蒙古黄河流域径流预估及其对水资源的影响

根据内蒙古黄河流域内72个国家气象站观测的1961—2005年和区域气候模式CCLM模拟的1961—2100年的气温和降水数据,采用BP人工神经网络模型,预估分析3种RCP情景下头道拐水文站2011—2100年流量变化,评估未来气候变化对流域水资源的可能影响。结果表明:①2011—2100年内蒙古黄河流域气温升高,降水变化不明显,年平均流量呈减少趋势,RCP2.6、RCP4.5和RCP8.5情景分别减少3.6%、2.7%和23.4%。②未来春季流量以增加为主;夏季在不同情景的变化趋势不一致;秋季在21世纪50年代前以增加为主,之后以减少为主;冬季则以减少为主。③未来流域可利用水资源呈减少趋势,尤其夏季水资源的供需矛盾加剧,以及径流季节分配发生变化,可能产生更大的春季径流。     

呼伦湖湿地消长对气象水文因子变化的响应

利用1961—2005年呼伦湖湿地的气象及水文资料,基于灰色关联度分析、Mann-Kendall检验及小波分析、回归统计等方法,分析了湿地消长对气象水文因子变化的响应特征。结果表明:年与夏季气候在湿地消长中起主导作用。区域年降水量每增加10 mm,年降水量的直接作用是使湿地水域面积和水位深度分别增加2.6 km2和1.6 cm;年径流量每增加1×108 m3,湿地水域面积和水位深度分别增加4.8 km2和3.0 cm。45年来,湿地消长对影响因子连续变化过程的响应特征具有一致性,特别在20世纪90年代后响应更显著,湿地萎缩加快;气温与降水量变化在湿地水域面积、水位深度消长中的贡献率分别为33.1%与66.9%,22.5%与77.5%,降水量变化起主导作用。湿地消长对影响因子的多时间尺度周期性具有很好的响应。在27年的年代际尺度主周期与11~16年次周期、2~10年年际尺度准周期的叠加作用下,45年来,湿地消长出现了2次减少、1次增加的周期过程,并呈现短周期波动特征。     

全球变化下澜沧江-湄公河流域水量平衡模拟

流域水文模型是区域水资源评价的重要工具,基于普林斯顿全球气象驱动数据集和澜沧江-湄公河流域（简称：澜湄流域）八个水文站实测资料,分析了澜湄流域不同区间的水文特性,采用RCCC-WBM模型（Water Balance Model developed by Research Center for Climate Change,RCCC-WBM）开展了区间径流及水量平衡模拟研究。结果表明：1）澜湄流域不同区间气候水文差异显著,上游气温低且年内变幅大,下游气温高年内变幅小;尽管不同区间降水、径流的年内分配特征总体一致,但径流的年内分布峰值大多滞后降水峰值一个时段。2）RCCC-WBM模型能够较好地模拟出澜湄流域不同区间的径流过程,率定期和验证期的月径流模拟效率系数（Nash-Sutcliffe Efficiency,NSE）均在60%以上,总量模拟误差（Relative Error,RE）也均控制在±10%以内,模型具有较好的区域适应性。3）模拟的土壤含水量都具有先衰减后增加再衰减的年内分配特征;不同季节径流和蒸发耗散的水源不同,降水是汛期水分耗散的主要来源,而土壤含水量是非汛期径流和蒸发消耗的主要水源。     

气候变化对长江上游径流影响预估

利用第五次国际耦合模式比较计划(CMIP5)中5个气候模式在3种典型浓度路径(RCPs)下的预估结果驱动SWAT水文模型,预估了21世纪气候变化对长江上游年径流量、季节分配以及极端径流的影响。结果表明：预估的长江上游平均气温呈显著上升趋势,21世纪末较当前(1986—2005年)升高1.5~5.5℃,降水总体呈增加趋势,在21世纪30年代后高于当前气候平均值,21世纪末相对于当前增加5%~15%。流域内气候变化存在明显空间差异,金沙江和岷沱江流域气温升高和降水增加幅度均大于流域平均值。预估的长江上游年径流量及各月平均径流均有增加趋势,在21世纪30年代后高于当前多年平均值,21世纪中期增加4%~8%,21世纪末增加10%~15%。预估的径流年内分布的均匀性有所增加,但年际变化明显增大,极端旱涝事件的频率和强度明显增加。预估的各子流域径流变化对气候变化的响应也存在差异,金沙江和岷沱江流域年径流量、年际变化和年内分布变化小,对气候变化的响应表现为低敏感;嘉陵江流域、乌江流域和长江上游干流径流增加幅度大,同时极端丰枯出现的频率和程度增加显著,是气候变化响应的敏感区域。     

博斯腾湖流域气候变化对开都河径流量的影响

利用线性回归分析法、突变检验法等分析博斯腾湖流域1980～2018年的年均气温、年降水量、年蒸发量等气候因子变化趋势和突变现象及其对开都河径流量的影响.结果表明:1980～2018年博斯腾湖流域年均气温呈波动中上升趋势,其变化速率为0.15℃(10a)-1,年降水量则以0.765mm(10a)-1的速率增加,而年蒸发量...     

Using the SWAT Model for Studying the Hydrological Regime of a Small River Basin (the Komarovka River,Primorsky Krai)

The research describes the experience of using digital models (of terrain, soil, and vegetation) for the underlying surface of the catchment for developing the spatial structure of the open-source SWAT (Soil and Water Assessment Tool) hydrological model. The hydrological regime for the Komarovka River basin (616 km²) is simulated with a daily resolution using the data of Primorskaya water balance station and the modern observation network of Primorye Administration for Hydrometeorology and Environmental Monitoring. It is found that the calculated and measured runoff hydrographs are generally in good agreement, and the model is suitable for describing the hydrological regime of mid-latitude rivers where rainfall floods prevail. The model well reproduces average water years, underestimates the peaks caused by intense rainfall of the typhoon origin and overestimates baseflow.     

博斯腾湖水位变化特征及其可能影响机制分析

应用开都河下游大山口水文站径流和博斯腾湖1956-2009年的逐月水位数据和流域内各气象站的气象数据,通过模糊聚类等统计方法,分析了博斯腾湖水位变化趋势及其可能影响因子.结果表明:博斯腾湖的水位年际变化受开都河流域径流的影响很大,当开都河流域径流量大时博湖水位较高,且开都河径流与其上、下游气温和降水关系密切.博斯腾湖水位逐年的月变化基本上可以分为5类,其中最主要的为第一类型和第二类型:第一类为递减型,特征为季节变化不明显,水位在春季较高,以后逐渐降低;第二类为递增型,特点是季节变化较第一大类明显,水位在夏末秋初的时候较高,整体呈现上升趋势.递增、递减型出现的主要原因是受上下游降水和大山口径流的影响,当上下游降水和径流偏多时水位月际变化出现递增型,反之易出现递减型.