Recent fluctuations in precipitation and runoff over the Nile sub-basins and their impact on main Nile discharge

Substantial fluctuations in precipitation and runoff have occurred over the Nile Basin in recent decades. Ten-year mean flows of the Blue Nile (Khartoum gauge) during the 20th century have ranged from 42.2 to 56.7 km³ and for the White Nile (Malakal gauge) from 25.5 to 36.9 km³. These fluctuations have been responsible for changes in decade-mean Main Nile discharge of up to ± 20% which have had important consequences for water resource management in both Egypt and Sudan.This paper provides a review of the Nile Basin hydrology incorporating, for the first time, analyses of the relationships between precipitation and runoff fluctuations in the instrumental period for each of the eight major sub-basins within the Nile Basin. These sub-basins possess very different physical, climatic and hydrological characteristics. Over 90% of the Main Nile discharge originates from only four of the sub-basins; Lake Victoria, Blue Nile, Atbara, and the Sobat. Interbasin correlations of 40 y (1945-84) precipitation and runoff annual time series identify two broadly homogeneous regions; the Ethiopian highlands (Blue Nile and Atbara) and the Lake Victoria and Equatorial Lakes (White Nile). These regions posses contrasting precipitation regimes whose interannual variations are uncorrelated in time and which are therefore associated with different atmospheric circulation anomalies. The observed relationships between catchment precipitation and runoff, however, are not straightforward and the sensitivity of runoff to precipitation fluctuations varies from basin to basin. Some of the water resource management implications of these fluctuations for Egypt are discussed. With water demand in Egypt alone set to increase 17% by the year 2000, it is critical that the role of future climate change in Nile water management is thoroughly assessed based on a correct modelling of the diverse hydrological characteristics of the various Nile sub-basins.     

A numerical modelling study of coastal flooding

Summary A coastal ocean model capable of modelling tides, storm surge and the overland flow of floodwaters has been further developed to include the flux of water from tributaries and the forcing from wave breaking that leads to wave setup in the nearshore zone. The model is set up over the Gold Coast Broadwater on the east coast of Australia. This complex region features a coastal lagoon into which five tributaries flow and is subject to flooding from extreme oceanic conditions such as storm surge and wave setup as well as terrestrial runoff. Weather conditions responsible for storm surge, waves and flooding include cyclones of both tropical and mid-latitude origin. Two events are modelled. The first is an east coast low event that occurred in April 1989. This event verified well against available observations and analysis of the model simulations revealed that wave setup produced a greater contribution to the elevated water levels than the storm surge. The second case to be modelled was tropical cyclone Wanda, responsible for the 1974 floods. Modelled water levels in the Broadwater were reasonably well captured. Sensitivity experiments showed that storm surge and wave setup were only minor contributors to the elevated sea levels and their contribution was confined to the earlier stage of the event before the runoff reached its peak. The contribution due solely to runoff exhibited a tidal-like oscillation that was 180° out-of-phase with the tide and this was attributed to the greater hydraulic resistance that occurs at high tide. A simulation of this event with present day bathymetry at the Seaway produced sea levels that were 0.3–0.4 m lower than the simulation with 1974 bathymetry highlighting the effectiveness of deepened Seaway channel to reduce the impact of severe runoff events in the Broadwater. Received October 16, 2001 Revised December 28, 2001     

A PCSWMM/GIS-based water balance model for the Reesor Creek watershed

This paper presents the results of a study of a watershed experiencing the pressures of land-use change resulting from urban development. The study was undertaken to facilitate an understanding of the water balance of the watershed by developing and implementing watershed procedures that are to be addressed in a watershed plan. There were three components to the research: firstly, observation of the effects of spatially distributed rainfall measurements and their effect on modelling were assessed. Secondly, the model was then calibrated by observing how differing techniques can discretize both the landscape (e.g. land-use and soil type) and incoming precipitation. Finally, a modelling methodology was developed to integrate a Geographic Information System and a hydrologic model (e.g. Storm Water Management Model) in a water balance analysis on a watershed basis. Results show that, under certain conditions, kriging spatially distributed rainfall values can help predict rainfall at ungauged (virtual) sites. Discretization of a watershed was found to affect the differences between measured and generated runoff volumes; however, this can be refined with calibration. It was seen that a strong correlation between measured and predicted rainfall values did not always guarantee a strong relationship between measured and generated runoff Recommendations include the use of a longer time series of rainfall, streamflow and predicted rainfall to observe temporal variations, and the need to assess the differences in modelled rainfall values generated by various surface interpolation methods (e.g. Inverse Distance Weighting and other kriging options) currently available in GIS packages.     

青海湖水位波动对气候暖湿化情景的响应及其机理研究

利用1961—2015年青海湖水位资料及其流域气温、降水量、蒸发量等气象观测资料,高原季风、西风环流气候等指数及植被数据,分析青海湖水位波动的基本特征,揭示高原季风、西风环流、植被覆盖、径流以及冻土退化对湖泊水位波动的影响机理,建立基于水量平衡的青海湖水位变化的定量评估模型。研究表明：2004年前后,青海湖水位出现由降到升的突变,自2005年以来持续回升;水位波动具有8 a和21 a的显著性周期;全球变暖背景下高原季风增强、西风环流趋弱、气候趋于暖湿、流域植被恢复、冻土退化和径流量显著增大,引起了2005年以来青海湖水位的持续回升。基于湖泊水量平衡原理建立的气候变化对青海湖水位影响定量评估模型,能够客观反映青海湖流域上年及当年降水量、流量和蒸发量对湖泊水位的效应。     

沁河流域实测径流对环境变化的定量响应分析

根据1956-2000年沁河流域降水、耗水量和入黄武陟站实测径流资料,采用趋势分析、Mann-Kendall法和滑动t检验法分析了武陟站实测径流变化的事实,辨析了影响实测径流变化的原因,并在确定基准期的基础上,建立了降水径流双累积曲线关系,分离出了由降水、人类活动中引耗水及下垫面条件变化引起的实测径流变化量。分析结果表明：沁河入黄实测径流减少趋势明显,1972年为突变年份,且降水的减少、人类活动引耗水的增加和流域煤矿开采、地下水超采和水土保持措施等综合作用致使实测径流减少。人类引耗水、气候变化及下垫面条件变化对径流的影响总量为70.6 mm,其中,引耗水致使实测径流减少为17.6 mm,贡献率为24.9%;气候变化影响量为35.6 mm,贡献率为50.4%;下垫面条件变化影响量为17.5 mm,贡献率为24.7%。     

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.     

不同气候情景下华北平原蒸发与径流时空变化分析

基于中国气象局国家气候中心生成的IPCC第四次评估报告中23种气候模式的情景集成数据,采用Schreiber公式和Thornthwaite方法计算实际蒸发和径流,分析了2001-2060年SRES A1B、A2和 B1这3种情景下,华北平原气温、降水、蒸发与径流的时空变化。结果表明：未来华北平原气温呈升高趋势,且冬半年升温幅度大于夏半年;降水亦呈增加趋势,而冬半年降水增加幅度小于夏半年;与此相应,华北平原蒸发和年径流呈增加趋势,增幅和空间差异随时间推移而增大,到2041-2060年蒸发将上升7.1%～9.4%,径流将增加8.7%～10.7%。     

山东水资源分析及趋势预测

通过分析近３９年山东省水资源的历史倾向性、阶段性、周期性,研究了水资源总量及径流量和地下水位的变化特征。结果表明,山东水资源量的年际变化大且呈快速下降态势,其中,地表径流量的下降尤为明显;水资源的变化存在一定的阶段性和周期性。通过分析降水与水资源的关系,发现两者的变化规律一致,但降水对水资源,特别是对地下水分量的影响有一定的持续性。建立均生函数预测模型,对未来水资源总量进行预测显示,１９９８￣２０     

1955-2002年气候因子对鄱阳湖流域径流系数的影响

1955-2002年间,鄱阳湖流域径流系数均呈现显著上升趋势,有较明显的突变性和阶段性,突变主要发生在20世纪60年代末和90年代初。径流系数的趋势及突变与该时期降水量的变化吻合较好;气温和蒸发量的变化趋势及突变点也与径流系数基本吻合;季节变化中,7-9月的径流系数与气候因子的变化趋势最为吻合。气候因子的变化与鄱阳湖流域径流系数变化的一致性,说明48 a来气候变化对径流系数的影响非常显著。尽管鄱阳湖流域的径流系数还受到土地利用变化、水土流失和地形等因素叠加效应的影响,但是气候变化仍然是其主要影响因素。     

1961—2018年中国主要江河枯季径流演变特征与成因

枯季是水旱、水生态和水资源问题的重要时期,枯季径流的变化直接影响着河流生态和流域水资源管理.基于中国网格气象数据和主要江河枯季径流资料,初步分析了1961—2018年中国气候变化趋势和主要江河枯季径流演变特征与成因.结果表明,全国枯季平均气温显著上升,北方地区升温较早,南方地区2001—2018年升温明显.全国约84％...     

珠江河口风暴潮对径流的敏感性研究:以台风“山竹”为例

径流-风暴潮相互作用可增大河口区风暴潮增水,增加风暴潮灾害风险。基于SCHISM模式建立了珠江河口风暴潮数值模型,以台风“山竹”为例,采用实测资料对模型计算结果进行验证,最高潮位相对误差在9%以内。设计了台风“山竹”实测径流与5年一遇洪水的对比试验,讨论了径流变化对河口风暴潮增水的影响,结果表明:河口口门站位风暴潮增水随径流量的增大而增大。径流增加对泗盛围、南沙等站位的风暴潮影响较大,在风暴潮增水达到最大值时影响最为显著。以径流动力作用为主的区域,当上游径流量增大时,对风暴潮增水起到负影响作用:如磨刀门水道,随着径流的增加,沿河道上溯的风暴潮增水逐渐减小,由灯笼山站3.22 m减小至马口站1.12 m。以潮汐动力作用为主的区域,当上游径流量增大时,对风暴潮增水起到正影响作用:如珠江干流,随着径流的增加,沿河道上溯的风暴潮增水逐渐增大,大虎站的最大增水值为3.44 m,中大站为4.24 m,从口门至后航道区域增大了0.8 m。      

GRAPES NOAH-LSM陆面模式水文过程的改进及试验研究

土壤含水量的计算影响着陆面过程的能量平衡和水量平衡,是陆面模式的核心计算要素之一。目前,GRAPES_Meso模式采用的NOAH-LSM(Noah-Land Surface Model)陆面模式既不能有效地表达径流产源面积的变动情况,也不能完整描述水文循环过程。本次试验针对以上问题对其进行了改进:(1)加入蓄水容量曲线,考虑网格内产流面积的变化及土壤含水量的不均匀性;(2)加入汇流模式,以考虑水平二维水分再分配,提高模式对径流和流量模拟能力。选取2008年8月至9月降水进行模拟试验,研究陆面水循环过程对近地面气象要素的影响。结果表明:改进后的模式模拟土壤湿度、2 m温度等近地面气象要素更接近观测值,并最终对降水量以及降水落区也产生了一定的影响。     

基于CMADS驱动SWAT模型的富春江水库控制流域水量平衡模拟

以富春江水库控制流域为研究区域,利用中国大气同化驱动数据集（CMADS V1.1）驱动SWAT水文模型,对富春江水库控制流域进行了逐日径流模拟,探讨了流域2008-2016年径流变化及水量平衡过程。结果表明：CMADS V1.1数据集驱动SWAT模型对研究区域的径流变化具有较好的模拟效果,在验证期,逐日模拟的效率系数大于0.70,决定系数大于0.75,达到了模型评价标准。在流域水量平衡各项中,地表径流和蒸散发为主要的输出项,分别占降水量的57.2%和36.2%,其中蒸散发量年际变化较为平稳。降水量、地表径流量、土壤对地下水补给、地下侧流量、蒸散发量最大值均出现在6月,最小值均出现在1月。流域径流量以地表径流为主,其在各个月份与月降水变化趋势基本一致。而基流量较小,且各月基流量对降水量的响应并不显著。     

乌鲁木齐河山区冰雪水资源及径流量丰枯频率

乌鲁木齐河山区冰和雪资源，对径流补给，其量不很大，但对河水稳定起着很大作用和影响，冰川近几十年来一直退缩，冰川厚度冰薄，但冰川和融雪对乌鲁木齐河径流一直起着调剂和“保证”作用，山区冰川水（补给11．3％），融雪水（36．1％），降水是其必要的补给。从360年重建年径流可知，平水年频率57．7％，偏丰和特丰年较少（17．4％，1．7％），偏枯年23．2％特枯年为0。     

我国西南地区年径流变异及变化趋势研究

用寸滩与梧州水文站上百年长系列径流资料,分析研究了由于气候均值变化引起的年径流均值、表征年径流年际变化幅度的变差系数Cv及表征其分布偏态特征的偏差系数Cs的变化.并研究了仅由均值变化引起的这两个流域丰水、平水及枯水年出现的概率变化.所得结果对气候变化影响下水资源管理中的适应对策问题有一定的参考价值.为了得到气候变化引起的年径流均值和Cv、Cs值的变化,除了应给出未来30年气候均值变化情景外,还应给出气候系列变异的可能变化,以修正原水文-气候基准系列的自然波动.     

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。     

Human implication of changes in the hydrological regime due to climate change in Northern Greece

This paper examines the impacts of climate change on various forms of water resources and on some critical water management issues. The study area is the Aliakmon river basin including three subbasins of hydrological interest located in northern Greece. A monthly conceptual water balance model was calibrated for each subbasin separately, using historical hydrometeorological data. This model was applied to estimate runoff values at the outlet of each subbasin under different climate change scenarios. Two equilibrium scenarios (UKHI, CCC) referring to years 2020, 2050 and 2100 and one transient scenario (UKTR) referring to years 2032 and 2080 were implied. It was found that reduction of the mean annual runoff and mean winter runoff values, as well as serious reduction of the summer runoff values would occur in all cases and basins. However, the runoff values for November, December and January were increased, whereas the spring runoff values were decreased, leading to a shifting of the wet period towards December and severe prolongation of the dry period. Moreover, the results indicate that all subbasins exhibit almost the same behavior under the different climate change scenarios, while the equilibrium scenarios (UKHI, CCC) seem to give more reasonable and consistent results than the transient scenario (UKTR). Finally, the negative effects of the climatically induced changes on the hydroelectric production and the water use for agricultural purposes in the study basin were assessed.     

A study of photochemical air pollutants in the urban Airsheds of Edmonton and Calgary

Abstract

A small catchment in south‐central Ontario was divided into two zones to evaluate the effect of a small wetland on runoff response during spring snowmelt in 1980. Runoff from the downstream side‐slope zone was produced by a combination of saturation overland flow and subsurface flow. The response to individual snowmelt and rainfall events varied according to antecedent wetness conditions. Runoff delivery from the wetland zone was affected even more by antecedent conditions. For the first and largest event, the response of the wetland was very similar to that of the side‐slope zone, but as the runoff season progressed, the increasing storage capacity of the wetland resulted in more marked contrasts. Quickflow yields and peak flows were much lower from the wetland and response times were longer. Over the whole runoff season, the wetland yielded substantially less runoff mainly because the perched ground water system that sustained it became isolated from the regional ground water system, and this limited the extent of the runoff contributing area in the wetland zone.     

黄河上游和源区气候、水文的年代际变化及其对华北水资源的影响

利用我国气象观测站1951~2000年降水、气温资料以及黄河上游有关水文测站1960~2003年的径流资料,分析了黄河上游和源区气候的年代际变化及其对径流变化的影响,并分析了黄河上游径流变化对华北水资源的影响。分析结果表明:黄河上游和源区降水从20世纪90年代有所减少,气温明显上升,导致了黄河源区和上游径流量锐减。黄河上游径流的减少是90年代黄河下游流量锐减、黄河断流天数增多的重要原因,并表明了黄河上游来水量的多少是影响华北地区水资源的重要原因。     

冬半年南支槽与乌江流域汛期径流的关系探讨

基于1954—2014年乌江流域站点的逐月径流与NCEP/NCAR的逐月位势高度、风矢量资料、比湿及垂直速度资料,采用相关分析、回归分析、合成分析等方法,研究了冬半年南支槽与汛期乌江流域径流的关系,并探讨了其对乌江流域径流影响的可能机制。结果表明,冬半年各月南支槽强度指数(Southern Branch Trough Index,SBTI)与5月乌江流域径流有着稳定且显著的负相关关系,且基于冬半年月份SBTI构建的线性回归模型可以很好地预测5月径流;因此,冬半年南支槽指数可以作为乌江流域5月径流的预报因子。合成分析表明,南支槽强年,青藏高原南侧西风带波动强烈,且槽前风场差值呈气旋性异常,伴随着乌江流域的南风矢量,为槽前暖湿气流向乌江流域的输送提供了水平动力;副热带高压强度的减弱可能使得来自西太平洋的水汽流向乌江流域,强化了水汽向乌江的输送;南支槽强年乌江流域低层到高层水汽含量显著增加,垂直上升运动可持续到300 h Pa,加强了乌江流域的水汽辐合和对流运动,有利于该流域降水的产生,进而使得径流量显著增加。