Assessment of Climate Change Impact on Water Resources of Lesser Zab, Kurdistan, Iraq Using SWAT Model

Kurdistan in northern Iraq, a semi-arid region, predominantly a pastureland, is nourished by Lesser Zab, which is the second major tributary of Tigris River. The discharge in the tributary, in recent times, has been experiencing increasing variability contributing to more severe droughts and floods supposedly due to climate change. For a proper appreciation, SWAT model has been used to assess the impact of climate change on its hydrological components for a half-centennial lead time to 2046-2064 and a centennial lead time to 2080-2100. The suitability of the model was first evaluated, and then, outputs from six GCMs were incorporated to evaluate the impacts of climate change on water resources under three emission scenarios: A1B, A2 and B1. The results showed worsening water resources regime.

Modeling the Impact of Climate Change in A Mediterranean Catchment(Merguellil,Tunisia)

Climate change impact studies on hydrologic regime have been until recently restricted mainly because of the coarse spatial and temporal resolution of the Global Circulation Models(GCMs)outputs. Nevertheless,local meteorological variables can be derived from GCMs scenarios using downscaling techniques.In the present study,the Statistical DownScaling Model(SDSM)was selected for

Model-Based Assessment of Climate Change Impact on Isaac River Catchment, Queensland

Isaac River catchment, which is located within Fitzroy basin in Central Queensland, Australia is mostly a semi-arid region, sparsely populated, but rife with economic activities such as mining, grazing, cropping and production forestry. Hydro-meteorological data over the past several decades reveal that the catchment is experiencing increasing variability in precipitation and streamflow contributing to more severe droughts and floods supposedly due to climate change. The exposure of the economic activities in the catchment to the vagaries of nature and the possible impacts of climate change on the stream flow regime are to be analyzed. For the purpose, SWAT model was adopted to capture the dynamics of the catchment. During calibration of the model 12 parameters were found to be significant which yielded a R2 value of 0.73 for calibration and 0.66 for validation. In the next stage, six GCMs from CMIP3 namely, CGCM3.1/T47, CNRM-CM3, GFDL-CM2.1, IPSLCM4, MIROC3.2 (medres) and MRI CGCM2.3.2 were selected for climate change projections in the Fitzroy basin under a very high emissions scenario (A2), a medium emissions scenario (A1B) and a low emissions scenario (B1) for two future periods (2046-2064) and (2080-2100). All GCMs showed consistent increases in temperature, and as expected, highest rate for A2 and lowest rate for B1. Precipitation predictions were mixed-reductions in A2 and increases in A1B and B1, and more variations in distant future compared to near future. When the projected temperatures and precipitation were inputted into the SWAT model, and the model outputs were compared with the baseline period (1980-2010), the picture that emerged depicted worsening water resources variability.

Modelling Hydrological Consequences of Climate Change—Progress and Challenges

The simulation of hydrological consequences of climate change has received increasing attention from the hydrology and land-surface modelling communities. There have been many studies of climate-change effects on hydrology and water resources which usually consist of three steps： （1） use of general circulation models （GCMs） to provide future global climate scenarios under the effect of increasing greenhouse gases, （2） use of downscaling techniques （both nested regional climate models, RCMs, and statistical methods） for ＂downscaling＂ the GCM output to the scales compatible with hydrological models, and （3） use of hydrologic models to simulate the effects of climate change on hydrological regimes at various scales. Great progress has been achieved in all three steps during the past few years, however, large uncertainties still exist in every stage of such study. This paper first reviews the present achievements in this field and then discusses the challenges for future studies of the hydrological impacts of climate change.

Estimation of future water resources of Xiangjiang River Basin with VIC model under multiple climate scenarios

Variation trends of water resources in the Xiangjiang River Basin over the coming decades have been investigated using the variable infiltration capacity(VIC) model and 14 general circulation models'(GCMs') projections under the representative concentration pathway(RCP4.5) scenario. Results show that the Xiangjiang River Basin will probably experience temperature rises during the period from 2021 to2050, with precipitation decrease in the 2020 s and increase in the 2030 s. The VIC model performs well for monthly discharge simulations with better performance for hydrometric stations on the main stream of the Xiangjiang River than for tributary catchments. The simulated annual discharges are significantly correlated to the recorded annual discharges for all the eight selected target stations. The Xiangjiang River Basin may experience water shortages induced by climate change. Annual water resources of the Xiangjiang River Basin over the period from 2021 to 2050 are projected to decrease by 2.76% on average within the range from-7.81% to 7.40%. It is essential to consider the potential impact of climate change on water resources in future planning for sustainable utilization of water resources.

Application of the Bottom-up Method on Risk Evaluation of Climate Change in Water Resources System

Traditional approach to evaluate the impacts of climate change on the water resources systems always begins with downscaling general circulation models( GCMs) and proceeding back to the hydrological model. This approach has some distinct disadvantages: 1) GCM must be downscaled; 2) different GCMs are difficult to be reconciled for a given climate change scenario;3) the uncertainty of GCMs is far from the requirement of the evaluation of climate change impacts. To overcome these limits of the traditional method,a new method termed as "bottom-up"was used for climate risk assessment that linked vulnerability assessment with climate information to assess the risk of climate change impacts on the Quabbin Reservoir,and United States under A2 scenario.The result shows that the risks are around 20% in 2006-2035 and 2036-2055,50% in 2066-2095.

Use of SWAT to Model Impact of Climate Change on Sediment Yield and Agricultural Productivity in Western Oregon, USA

Climate change predictions for the Pacific Northwest region of the United States of America include increasing temperatures, intensification of winter precipitation, and a shift from mixed snow/rain to rain-dominant events, all of which may increase the risk of soil erosion and threaten agricultural and ecological productivity. Here we used the agricultural/environmental model SWAT with climate predictions from the Coupled Model Intercomparison Project 5 (CMIP5) “high CO2 emissions” scenario (RCP8.5) to study the impact of altered temperature and precipitation patterns on soil erosion and crop productivity in the Willamette River Basin of western Oregon. An ensemble of 10 climate models representing the full range in temperature and precipitation predictions of CIMP5 produced substantial increases in sediment yield, with differences between yearly averages for the final (2090-2099) and first (2010-2019) decades ranging from 3.9 to 15.2 MT·ha-1 among models. Sediment yield in the worst case model (CanESM2) corresponded to loss of 1.5 - 2.7 mm·soil·y-1, equivalent to potentially stripping productive topsoil from the landscape in under two centuries. Most climate models predicted only small increases in precipitation (an average of 5.8% by the end of the 21st century) combined with large increases in temperature (an average of 0.05°C·y-1). We found a strong correlation between predicted temperature increases and sediment yield, with a regression model combining both temperature and precipitation effects describing 79% of the total variation in annual sediment yield. A critical component of response to increased temperature was reduced snowfall during high precipitation events in the wintertime. SWAT characterized years with less than basin-wide averages of 20 mm of precipitation falling as snow as likely to experience severe sediment loss for multiple crops/land uses. Mid-elevation sub-basins that are projected to shift from rain-snow transition to rain-dominant appear particularly vulnerable to sediment loss. Analyses of predicted crop yields indicated declining productivity for many commonly grown grass seed and cereal crops, along with increasing productivity for certain other crops. Adaptation by agriculture and forestry to warmer, more erosive conditions may include changes in selection of crop kinds and in production management practices.

Modeling and analyzing supply-demand relationships of water resources in Xinjiang from a perspective of ecosystem services

Water shortage is one bottleneck that limits economic and social developments in arid and semi-arid areas.As the impacts of climate change and human disturbance intensify across time,uncertainties in both water resource supplies and demands increase in arid and semi-arid areas.Taking a typical arid region in China,Xinjiang Uygur Autonomous Region,as an example,water yield depth(WYD)and water utilization depth(WUD)from 2002 to 2018 were simulated using the Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)model and socioeconomic data.The supply-demand relationships of water resources were analyzed using the ecosystem service indices including water supply-demand difference(WSDD)and water supply rate(WSR).The internal factors in changes of WYD and WUD were explored using the controlled variable method.The results show that the supplydemand relationships of water resources in Xinjiang were in a slight deficit,but the deficit was alleviated due to increased precipitation and decreased WUD of irrigation.WYD generally experienced an increasing trend,and significant increase mainly occurred in the oasis areas surrounding both the Junggar Basin and Tarim Basin.WUD had a downward trend with a decline of 20.70%,especially in oasis areas.Water resources in most areas of Xinjiang were fully utilized and the utilization efficiency of water resources increased.The water yield module in the InVEST model was calibrated and validated using gauging station data in Xinjiang,and the result shows that the use of satellite-based water storage data helped to decrease the bias error of the InVEST model by 0.69×10^(8)m^(3).This study analyzed water resource supplies and demands from a perspective of ecosystem services,which expanded the scope of the application of ecosystem services and increased the research perspective of water resource evaluation.The results could provide guidance for water resource management such as spatial allocation and structural optimization of water resources in arid and semi-arid areas.

Climate change impacts on the streamflow of Zarrineh River,Iran

Zarrineh River is located in the northwest of Iran,providing more than 40%of the total inflow into the Lake Urmia that is one of the largest saltwater lakes on the earth.Lake Urmia is a highly endangered ecosystem on the brink of desiccation.This paper studied the impacts of climate change on the streamflow of Zarrineh River.The streamflow was simulated and projected for the period 1992-2050 through seven CMIP5(coupled model intercomparison project phase 5)data series(namely,BCC-CSM1-1,BNU-ESM,CSIRO-Mk3-6-0,GFDL-ESM2G,IPSL-CM5A-LR,MIROC-ESM and MIROC-ESM-CHEM)under RCP2.6(RCP,representative concentration pathways)and RCP8.5.The model data series were statistically downscaled and bias corrected using an artificial neural network(ANN)technique and a Gamma based quantile mapping bias correction method.The best model(CSIRO-Mk3-6-0)was chosen by the TOPSIS(technique for order of preference by similarity to ideal solution)method from seven CMIP5 models based on statistical indices.For simulation of streamflow,a rainfall-runoff model,the hydrologiska byrans vattenavdelning(HBV-Light)model,was utilized.Results on hydro-climatological changes in Zarrineh River basin showed that the mean daily precipitation is expected to decrease from 0.94 and 0.96 mm in 2015 to 0.65 and 0.68 mm in 2050 under RCP2.6 and RCP8.5,respectively.In the case of temperature,the numbers change from 12.33℃ and 12.37℃ in 2015 to 14.28℃ and 14.32℃ in 2050.Corresponding to these climate scenarios,this study projected a decrease of the annual streamflow of Zarrineh River by half from 2015 to 2050 as the results of climatic changes will lead to a decrease in the annual streamflow of Zarrineh River from 59.49 m^(3)/s in 2015 to 22.61 and 23.19 m^(3)/s in 2050.The finding is of important meaning for water resources planning purposes,management programs and strategies of the Lake's endangered ecosystem.

Response of water resources to climate change and its future trend in the source region of the Yangtze River

In this paper, variations of surface water flow and its climatic causes in China are analyzed using hydrological and meteorological observational data, as well as the impact data set （version 2.0） published by the National Climate Center in November 2009. The results indicate that surface water resources showed an increasing trend in the source region of the Yangtze River over the past 51 years, especially after 2004. The trend was very clearly shown, and there were quasi-periods of 9 years and 22 years, where the Tibetan Plateau heating field enhanced the effect, and the plateau monsoon entered a strong period. Precipitation notably increased, and glacier melt water increased due to climate change, all of which are the main climatic causes for increases in water resources in the source region. Based on global climate model prediction, in the SRESA1B climate change scenarios, water resources are likely to increase in this region for the next 20 years.

Climate change impacts on streamflow,water quality,and best management practices for the Shell and Logan Creek Watersheds in Nebraska,USA

Improvements in the management of water,sediment,and nutrients under future climatic conditions are needed to ensure increased crop and livestock production to meet greater global needs and the future availability of water for competing demands and protection against adverse water quality impairments.This study determined the impacts of future climate change scenarios on streamflow,water quality,and best management practices(BMPs)for two watersheds in Nebraska,USA.The Soil and Water Assessment Tool(SWAT)was employed to simulate streamflow,sediment,total nitrogen(N)and total phosphorus(P)from the Shell Creek Watershed near Columbus,Nebraska and the Logan Creek Watershed near Sioux City,Iowa.Available streamflow and water quality records for the two watersheds were used to calibrate model parameters that govern streamflow,sediment,and nutrient responses in SWAT.For each watershed,precipitation,air temperature,and CO2 concentrations were input to SWAT for four climatic conditions:a baseline condition for the 1980 to 2000 period and the SRES A2,A1B,and B1 climate scenarios for a future period from 2040 to 2059.Findings from this study suggest that under the three future climate change scenarios,sediment losses are expected to be about 1.2 to 1.5 times greater than the baseline condition for Shell Creek and 2 to 2.5 times greater for Logan Creek;total N losses are expected to be about 1.2 to 1.4 times greater for Shell Creek and 1.7 to 1.9 times greater for Logan Creek.Relative to the baseline,total P losses under the future climate scenarios are projected to be about the same for Shell Creek and 1.5 to 1.7 times greater for Logan Creek.Findings from this study also suggest that future projected increases in both precipitation and CO2 concentration account for net increases in streamflow,but in different ways on each watershed.

Response of runoff to climate change and its future tendency in the source region of Yellow River

This study examines the hydrological and meteorological data of the source region of the Yellow River from 1956 to 2010 and future climate scenarios from regional climate model （PRECIS） during 2010-2020. Through analyzing the flow variations and revealing the climate causes, it predicts the variation trend for future flows. It is found that the annual mean flow showed a decreasing trend in recent 50 years in the source region of the Yellow River with quasi-periods of 5a, 8a, 15a, 22a and 42a; the weakened South China Sea summer monsoon induced precipitation decrease, as well as evaporation increase and frozen soil degeneration in the scenario of global warming are the climate factors, which have caused flow decrease. Based on the regional climate model PRECIS prediction, the flows in the source region of the Yellow River are likely to decrease generally in the next 20 years.

Fine-scale hydrologic modeling for regional landscape applications:the California Basin Characterization Model development and performance

Introduction:Resource managers need spatially explicit models of hydrologic response to changes in key climatic drivers across variable landscape conditions.We demonstrate the utility of a Basin Characterization Model for California(CA-BCM)to integrate high-resolution data on physical watershed characteristics with historical or projected climate data to predict watershed-specific hydrologic responses.Methods:The CA-BCM applies a monthly regional water-balance model to simulate hydrologic responses to climate at the spatial resolution of a 270-m grid.The model has been calibrated using a total of 159 relatively unimpaired watersheds for the California region.Results:As a result of calibration,predicted basin discharge closely matches measured data for validation watersheds.The CA-BCM recharge and runoff estimates,combined with estimates of snowpack and timing of snowmelt,provide a basis for assessing variations in water availability.Another important output variable,climatic water deficit,integrates the combined effects of temperature and rainfall on site-specific soil moisture,a factor that plants may respond to more directly than air temperature and precipitation alone.Model outputs are calculated for each grid cell,allowing results to be summarized for a variety of planning units including hillslopes,watersheds,ecoregions,or political boundaries.Conclusions:The ability to confidently calculate hydrologic outputs at fine spatial scales provides a new suite of hydrologic predictor variables that can be used for a variety of purposes,such as projections of changes in water availability,environmental demand,or distribution of plants and habitats.Here we present the framework of the CA-BCM model for the California hydrologic region,a test of model performance on 159 watersheds,summary results for the region for the 1981–2010 time period,and changes since the 1951–1980 time period.

气候变化对南方典型小水电站入库径流及发电的影响

在全球气候变化不断加剧的背景下,降水、气温、蒸发等气象要素的变化对流域水文和水力发电产生重要影响;中国作为水能资源丰富的国家,水力发电在能源结构中具有重要地位,研究气候变化对入库径流和水力发电的影响,对实现水资源和水电能源的可持续开发利用具有重要意义。以位于北江支流的官溪水电站为研究对象,基于19个CMIP6全球气候模式数据,利用RCCC-WBM模型分析了未来气候变化对官溪水电站入库径流和发电量的影响。结果表明:(1)在SSP2-4.5情景下,官溪水电站以上流域的气温、降水均呈现上升趋势;(2)尽管不同GCMs模式预估结果存在一定差异,从19个模式集合平均结果看,官溪水电站未来入库径流和水力发电量将有所增加;(3)与基准期(1981—2020年)相比,2031—2060年和2061—2090年官溪水电站入库流量将增加3.55%[−34.14%,39.84%]和5.66%[−32.27%,41.96%],发电量将可能增加5.87%[−29.3%,50.1%]和8.03%[−27.3%,52.4%]。未来径流和发电潜能的增加为官溪水电站的扩容改造提供了一定的科学依据。

基于VAR模型的气候变化对水资源的影响研究

气候变化已成为一个全球重点关注的问题,对各个领域影响愈加显著。水资源作为生态系统和人类社会发展的重要基础,同样不可避免地受气候变化的影响。本文利用向量自回归(VAR)模型,研究气候变化对水资源的影响。基于贵州省1995年至2021年的年平均气温、年降水量、年日照时数和水资源量的数据,建立VAR模型进行分析。研究结果表明,气候变化对水资源产生重要的影响,特别是年平均气温的变化对水资源量的影响更为显著。这为制定针对性的水资源管理政策提供了一定的理论基础。同时,本文也为进一步研究气候变化对水资源的影响提供了一种有效的方法。

基于SSP情景的黄河源区未来径流模拟预估

受全球气候变化影响,黄河源区的水文情势发生了较大改变,预估气候变化情景下未来流域径流变化趋势对区域水资源利用具有重要意义。利用气候模式数据驱动长短期记忆网络(LSTM)模型,研究了未来近期(2030—2059年)和未来远期(2060—2099年)不同气候变化情景下黄河源区降水和气温的变化趋势,预估了相应径流过程的系统性变化趋势,并采用气候弹性系数法定量分析了气候变化对区域水资源的影响。结果表明:①LSTM模型在黄河源区径流模拟中具有良好的适用性,修正后的模型在训练期和验证期的纳什效率系数分别达到0.84和0.87。②2030—2099年黄河源区的气温呈持续升高态势,年均降水量呈轻微增长趋势,其中汛期降水量减少,非汛期降水量增加。③未来研究区年均径流量呈轻微减少趋势,其中非汛期径流量呈增长趋势,增长幅度大多在30%左右;汛期径流量呈减少趋势,减少幅度为30%~40%。④黄河源区水资源对降水和气温的弹性系数分别为0.392和-0.085,水资源量对降水变化的敏感性高于对气温变化的敏感性。预计降水量变化-15%~25%时,水资源量变化-5.87%~9.79%;气温升高1.0~3.0℃时,水资源量变化-7.29%~-2.42%。

气候变化下水文模拟不确定性若干问题讨论

在阐释水文不确定性定义的基础上,根据气候变化下水文模拟不确定性的分类,总结了气候变化情景、水文模型和评估过程方面不确定性研究的基本范式,概述了每种不确定性的来源及影响,综述了气候变化下水文模拟不确定性研究进展。指出了未来水文系统模拟不确定性研究的重点和方向:结合复杂网络,增强对极端气候事件预估的可靠性;科学处理数据时间窗问题和冗余性,为无资料地区径流预测提供支撑;揭示变化环境下非平稳异方差性水文序列的发生规律。

基于RBF-SWAT的气候变化下汉江上游流域径流预测及特征分析

为研究气候变化下汉江上游流域的径流响应,基于RBF神经网络降尺度模型,利用2020—2099年CanESM2模式下RCP8.5(高温室气体排放)和RCP2.6(低温室气体排放)两种气候情景,生成未来气温与降水数据;耦合SWAT水文模型,模拟分析流域2020—2099年径流变化对不同气候情景的响应特征。结果表明,汉江上游年径流量均呈不明显增加趋势,RCP8.5情景下的径流增加趋势比RCP2.6情景稍小,径流量年内分配与基准期大致相同,两种情景下汛期径流量稍有减小,可能是降尺度模型生成的降水量极大值偏小导致的。研究结果可为汉江流域水文气象综合管理提供一定的科学依据。

基于CMIP6的通州区未来地表水资源量估算

为探究气候变化对未来地表水资源量的影响,以南通市通州区为研究区,选用CMIP6中的气候模式数据,驱动平原河网产流模型,计算未来地表水资源量。结果表明,平原河网产流模型在通州区径流过程的模拟有较好适用性,率定期月地表径流深模拟R^(2)、NSE分别为0.89、0.88,验证期月地表径流深模拟R^(2)、NSE分别为0.92、0.92;未来区域降雨量、气温较基准期呈增加趋势;相较于基准期,通州区未来地表水资源量总体呈增加趋势,SSP126、SSP245、SSP585情景下,地表径流深分别增加了2.7%、11.1%、15.9%。研究成果揭示了通州区地表水资源量变化趋势与气温、降水之间的相互关系,可为通州区水资源规划提供科学理论依据。

1960~2020年千岛湖流域水资源情势演变分析

针对气候变化条件下千岛湖流域水资源演变情势,建立WEP-L分布式水文模型模拟流域1960~2020年水循环过程,采用Mann-Kendall非参数检验法和Hurst指数法分析流域水资源总量年际变化、年内分配特征,评价了千岛湖流域水资源量时空分布与演变趋势。结果表明,WEP-L模型在千岛湖流域模拟结果较好,率定期的Nash系数在0.83以上,验证期的Nash系数在0.85以上;全流域产水系数在0.436~0.630之间,多年平均水资源总量122.5×10^(8)m^(3),折合产水深1176.4 mm,年内分配过程呈单峰型结构,各子流域产水深范围在742~1266 mm,空间分布呈西高东低;流域年水资源总量系列呈不显著上升趋势,Hurst指数0.86,存在上升的持续性;从月度水资源量来看,1、2月显著增加,其余月份变化均不显著。