Investigation of the Behavior of an Agricultural-Operated Dam Reservoir Under RCP Scenarios of AR5-IPCC

In regions where the Mediterranean climate prevails, the agricultural sector and agricultural-operated dam reservoirs are threatened by climate change. In this respect, the prediction of hydro-meteorological changes that may occur in surface water resources under climate change scenarios is essential to examine the sustainability of reservoirs. In this paper, Demirköprü reservoir in the Gediz Basin/Turkey, a reservoir operated for irrigation purposes, was analyzed against the RCP4.5 and RCP 8.5 scenarios specified in the AR5 report of the IPCC. Projection period was evaluated as 2016-2050 water year period. First, statistical downscaling, Bayesian model averaging and quantile delta mapping bias correction techniques were respectively applied to monthly total precipitation and monthly average temperatures of meteorological stations in the region using 12 GCMs. According to RCP4.5 and RCP8.5, negligible reductions in precipitation are foreseen, while significant increases of 1.3 and 1.8 °C, respectively, are projected for temperatures under the same scenarios. Following the calibration of rainfall-runoff models for the sub-basins feeding the reservoir, streamflow simulations were also performed with projected precipitation and temperatures. In particular, according to the RCP 8.5 scenario, reservoir inflows during the period 2016-2050 could be reduced by 21% compared to the reference scenario results. Finally, the projected crop water demands and hydro-meteorological changes are evaluated together and the reservoir performances are examined using various indices. Assuming that the performance of the past irrigation yields will not change in the future, it is foreseen that reservoir’s sustainability will decrease by 16% under the RCP8.5 scenario. Even if the irrigation efficiency is increased by 40%, the reservoir cannot reach past sustainability characteristics.     

气候变化背景下流域生态需水预估−以好溪流域为例

为探究未来气候变化对流域生态需水量的影响,保障河流生态需水量,针对好溪流域进行生态需水量计算 及预测。基于好溪流域气象数据及下垫面条件建立流域生态需水模型,并根据 GF1-WFV 遥感影像数据订正后的 地表反射率和作物种植结构提升模型模拟精度。选择 CanESM2气候模式下的 RCP2.6、RCP4.5 和 RCP8.5 这 3 种 排放情景,建立气候变化背景下流域生态需水预测方法,计算现状年并预测未来年份的生态需水量及生态需水保 障程度。结果表明,基于光学遥感影像进行数据订正后,模型模拟精度有所提升,率定期的模型精度 R2从 0.80 提 升为 0.85,验证期的 R2从 0.75 提升至 0.78。应用提升精度后的模型进行生态需水预测,在 RCP2.6、RCP4.5 和 RCP8.5 情景下,2025—2100 年的年均生态需水分别增加了 0.27 亿、0.21 亿和 0.29 亿 m3,其中 RCP8.5 情景下生态 需水保障程度最高,RCP4.5 情景下生态需水保障程度最低。     

Effect of management strategies on reducing negative impacts of climate change on water resources of the Isfahan–Borkhar aquifer using MODFLOW

Recently, many studies have investigated the effect of climate change on groundwater resources in semiarid and arid areas and have shown adverse effects on groundwater recharge and water level. However, only a few studies have shown suitable strategies for reducing these adverse effects. In this study, climate conditions were predicted for the future period of 2020–2044, under the emission scenarios of RCP2.6, RCP4.5, and RCP8.5, for Isfahan–Borkhar aquifer, Isfahan, Iran, using MODFLOW‐2000 (MODFLOW is United States Geological Survey product). Results showed that the average groundwater level of the aquifer would decrease to 13, 15, and 16 m in 2012 to 2044 approximately under RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively. Then, three groundwater sustainability management scenarios were defined that included 10%, 30%, and 50% reduction in groundwater extraction. These strategies simulated the reduced negative effects of climate change on the aquifer. The results showed that decreases in water withdrawal rates of 10%, 30%, and 50% under RCP8.5 scenario (critical scenario) could decrease the mean groundwater level by 14, 11, and 7 m, respectively. The main result of the study showed that 50% reduction in groundwater withdrawal may increase the groundwater levels significantly in order to restore the aquifer sustainability in the study area. In this study, with assuming that the current harvest of wells in the future period is constant, so the results of studies showed that for the aquifer's sustainability management, the water abstraction from the aquifer should reduce up to 50% of the existing wells. Changing the irrigation method from surface to subdroplet irrigation plays an important role in reducing the withdrawal from the aquifer. The results of a study in Iran have shown that the change in the irrigation method from surface to subdroplet irrigation causes a 40% reduction in water use for agriculture.     

Assessment of Water Resources Development Projects under Conditions of Climate Change Using Efficiency Indexes (EIs)

The purpose of this study is to evaluate Gharanghu multi-purpose reservoir system (East Azerbaijan, Iran) using efficiency indexes (EIs) affected by climate change. At first, the effects of climate change on inflow to the reservoir, as well as changes in the demand volume over a time interval of 30 years (2040–2069) are reviewed. Simulation results show that inflow to the reservoir is decreased in climate change interval compared to the baseline interval (1971–2000), so that comparison of long-term average monthly inflow to the reservoir in climate change interval is reduced about 25% compared to the baseline. Also, water demand in climate change interval will increase, namely volume of water demand for agricultural, drinking and industrial, and environmental in climate change interval is expected to increase by 20%. The simulation results of the water evaluation and planning (WEAP) model is used to determine EIs of multi-purpose reservoir system. Next, three scenarios of water supply for climate change interval are introduced to WEAP model, keeping variable of parameter related to water demand volume (based on different percentages of supply) and keeping constant of the parameter related to the volume of inflow to the reservoir. Results show that system EIs in climate change interval will have a disadvantage compared to the baseline. So that, reliability, vulnerability, resiliency and flexibility indexes in climate change interval based on 100% of water supply compared to the baseline will decrease 18%, increase 150%, decrease 33%, and decrease 47%, respectively. These indexes based on 85% of supply compared to the baseline will decrease 12%, increase 75%, decrease 30%, and decrease 39%, respectively. Also, those based on 70% of supply compared to the baseline will decrease 1%, will be without change, decrease 18%, and decrease 18%, respectively. Changes in indexes in future interval indicate the need to manage water resource development projects in the basin.     

Evaluation of Adaptation Scenarios for Climate Change Impacts on Agricultural Water Allocation Using Fuzzy MCDM Methods

Due to the impacts of climate change on agriculture and water allocation, an investigation of the farmers’ perceptions and stakeholders’ views on the adaptation strategies to climate change has a great of importance for sustainable development in the future. In this study, a fuzzy based decision support system has been developed to evaluate and rank the proposed adaptation scenarios to climate change in the Jarreh agricultural water resources system in southwest of Iran. Using output of ten coupled models inter comparison project phase 5 (CMIP5) under two representative concentration pathway scenarios (RCP 4.5, and RCP 8.5), the results indicated an increasing the annual mean temperature (1.64–1.84 °C under RCP 4.5, and 1.85–2.1 °C under RCP 8.5), reducing the amount of runoff into the reservoir (17.83–46.24% under RCP 4.5, and 21.54–50.91%under RCP 8.5), as well as increasing the amount of agricultural water requirement. Also, the results showed decreasing in reliability of system (12–53% under RCP 4.5, and 23–63% under RCP 8.5). Following, due to the main purpose of the system, six adaptation scenarios by using a questionnaire and stakeholders’ opinions are proposed to mitigate the effects of climate change. In the next step, by fuzzy mode of the technique for order of preference by similarity to ideal solution (TOPSIS) and fuzzy preference ranking organization method for enrichment of evaluations (PROMETHEE II), the proposed scenarios have been ranked according to the performance criteria. The final results of this study indicated the superiority of improving the irrigation efficiency and decreasing the area under cultivation among other proposed scenarios.

     

Application of the Grasshopper Optimization Algorithm (GOA) to the Optimal Operation of Hydropower Reservoir Systems Under Climate Change

Hydropower is a low-carbon energy source, which may be adversely impacted by climate change. This work applies the Grasshopper Optimization Algorithm (GOA) to optimize hydropower multi-reservoir systems. Performance of GOA is compared with that of particle swarm optimization (PSO). GOA is applied to hydropower, three-reservoir system (Seymareh, Sazbon, and Karkheh), located in the Karkheh basin (Iran) for baseline period 1976–2005 and two future periods (2040–2069) and (2070–2099) under greenhouse gases pathway scenarios RCP2.6, RCP4.5, and RCP8.5. GOA minimizes the shortage of hydropower energy generation. Results from GOA optimization of Seymareh reservoir show that average objective function in baseline is 85 and minimum value of average objective function in 2040–2069 would be under RCP2.6 (equal to 0.278). Optimization of Seymareh-reservoir based on PSO shows that average value of objective function in baseline is less (that is, better) than value obtained with GOA (10.953). Optimization results for two-reservoir system (Sazbon and Karkheh) based on GOA optimization show that objective function in baseline is 5.44 times corresponding value obtained with PSO, standard deviation is 2.3 times that calculated with PSO, and run-time is 1.5 times PSO’s. Concerning three-reservoir systems it was determined that objective function based on PSO had the best value (the lowest energy deficit), especially in future. GOA converges close to the best objective function, especially in future-periods optimization, and convergence to solutions is more stable than PSO’s. A comparison of performance of GOA and PSO indicates PSO converges faster to optimal solution, and produces better objective function than GOA.

     

Climate Change Impacts on Water Resources and Reservoir Management: Uncertainty and Adaptation for a Mountain Catchment in Northeast Portugal

Reservoirs often play an important role in mitigating water supply problems. However, the implications of climate change are not always considered in reservoir planning and management. This study aimed to address this challenge in the Alto Sabor watershed, northeast Portugal. The study analysed whether or not the shortage of water supply can be effectively addressed through the construction of a new reservoir (two-reservoir system) by considering future climate projections. The hydrological model Soil and Water Assessment Tool (SWAT) was calibrated and validated against daily-observed discharge and reservoir volume, with a good agreement between model predictions and observations. Outputs from four General Circulation Models (GCM) for two scenarios (RCP 4.5 and 8.5) were statistically downscaled and bias-corrected with ground observations. A general increase in temperature is expected in the future while the change in precipitation is more uncertain as per the differences among climatic models. In general, annual precipitation would slightly decrease while seasonal changes would be more significant, with more precipitation in winter and much less in spring and summer. SWAT simulations suggest that the existence of two-reservoir will better solve the water supply problems under current climate conditions compared to a single-reservoir system. However in the future, the reliability of this solution will decrease, especially due to the variability of projections from the different climatic models. The solution to water supply problems in this region, adopted taking only present-day climate into account, will likely be inefficient for water supply management under future climate conditions.     

基于新型综合干旱指数的珠江流域未来干旱变化特征研究

综合干旱指数构建及评估未来综合干旱特征变化具有重要的理论价值和现实意义。本文基于Copula函数,联合降水及VIC模型模拟的蒸散发、径流和土壤水等水文气象要素,构建了一种能综合表征气象-水文-农业干旱特征的新型综合干旱指数(CSDI),并以珠江流域为例进行应用,分析了未来气候变化情景下研究区综合干旱的变化特征。结果表明:(1)CSDI指数综合考虑了与干旱发生、演变密切相关的水文气象要素,能很好地监测到干旱的发生、发展过程,可综合从气象、水文与农业等角度刻画干旱特征。(2)RCP2.6情景下,流域下游综合干旱严重性降低且历时减少,而RCP4.5和RCP8.5情景下,全流域则均增加,严重性和历时分别至少平均增加14.8%和11.5%。(3)RCP2.6情景下,流域上下游超阈联合重现期100年的同频设计严重性和历时值均大幅降低,而RCP4.5、RCP8.5情景下,流域大部分地区则均呈升高。本研究可为研究区防旱抗旱提供新的参考。     

The change and prediction of temperature and precipitation in the Dawen River basin using the statistical downscaling model (SDSM)

In order to explore the climate change in the Dawen River basin,based on the data of six weather stations in the Dawen River basin from 1966 to 2017,Mann Kendall test and wavelet analysis were used to study the temperature and precipitation trends,mutations and cycles in the region.In addition,based on the three scenarios of RCP2.6,RCP4.5,and RCP8.5 under the CanESM2 model,SDSM was used to compare and analyze the future climate change of the Dawen River basin.The results revealed that:the annual mean temperature of the Dawen River basin had increased significantly since 1966 (p<0.01);in different scenarios,the spatial distribution of the projected maximum temperature,minimum temperature and precipitation will hardly change compared with that in history;the temperature and precipitation in the Dawen River basin will generally increase in the future.The rising trend of maximum and minimum temperature under the three scenarios is in the EP相似文献   

Assessing Adaptability of Cyclic and Non-Cyclic Approach to Conjunctive use of Groundwater and Surface water for Sustainable Management Plans under Climate Change

Groundwater overdraft in many regions throughout the world has been threatening the sustainability of this valuable resource. It has been argued that climate change may contribute to the severity of the issue; hence “impact assessment” is being replaced by “adaptation,” which explores more adapting scenarios and approaches. This study explores the adaptability of the proposed cyclic and non-cyclic conjunctive use of groundwater and surface water resources in increasing groundwater sustainability while increasing the sustainability of water allocation to the agricultural sector under possible climate change scenarios. To simulate climate change in the study area, precipitation and temperature variables are extracted from the results of three global atmospheric circulation models (Ensemble, CMCC-CMS, MRI-CGCM3) under RCP2.6 and RCP8.5 greenhouse gas emission scenarios in the period of 2021–2031. Spatial downscaling is performed using the M5 decision tree algorithm. The Wavelet-M5 hybrid model is used to predict runoff values as a rainfall-runoff model. Also, the Kharrufa method is applied to calculate evaporation in the future seasons. The system's adaptability to climate change is examined using the multi-objective cyclic and non-cyclic conjunctive use of surface and groundwater models. The study reveals that cyclic operation strategy improves the conjunctive use system adaptability compared to the optimal operation strategy that employs the non-cyclic approach. In this study's case study, the improvement in groundwater sustainability index exceeds 27 percent over the non-cyclic conjunctive use strategy.

     

Assessing Impacts of Conservation Measures on Watershed Hydrology Using MIKE SHE Model in the Face of Climate Change

Climate change triggers changes in temperature, precipitation, evapotranspiration, etc. and has a significant impact on water resources in many regions. Considering the increasing scarcity of water as a result of climate change, conservation of water and groundwater recharge have become crucial factors for water resources planning and management. In this paper, an attempt is made to study the detailed hydrological behaviour of a treated watershed using physically based distributed hydrological modelling system MIKE SHE to assess the impact of conservation measures on watershed hydrology considering future climate change. Three hypothetical management scenarios are simulated for the period 2010–2040. RegCM4 regional climate model is used in the study for RCP 4.5 and RCP 8.5 scenarios. Detailed hydrological water balance is extracted for individual years from 1979 to 2009 to compare relevant components. The evaluation for base period shows 10.06% reduction in surface runoff and 11.33% enhancement in groundwater recharge. Further simulation with RCP 4.5 and RCP 8.5 scenarios show notable reduction in surface runoff and increase in groundwater recharge. The structures in the micro-watershed influence the surface runoff and increase infiltration into the soil, resulting in higher groundwater recharge. MIKE SHE simulations for various structures management scenarios establish the role of conservation measures in reducing surface runoff and enhancing groundwater recharge under substantial effect of climate change. The results will assist in decision-making on watershed development plans in quantitative terms, including planning for water conservation measures in the face of climate change.

     

Optimal water allocation at different levels of climate change to minimize water shortage in arid regions (Case Study: Zayandeh-Rud River Basin,Iran)

Climate change is one of the most important factors influencing the future of the world's environment. The most important impacts of climate change are changes in water supply and demand in different regions of the world. In this study, different climate change patterns in two RCP4.5 and RCP8.5 emission scenarios (RCP: Representative Concentration Pathway), were adopted for the Zayandeh-Rud River Basin, Iran, through weighting of GCMs (General Circulation Models). These climate change patterns are including ideal, medium, and critical patterns. Using the LARS-WG model (Long Ashton Research Station Weather Generator), the outputs of the GCMs were downscaled statistically and the daily temperature and precipitation time series were generated from 2020 to 2044. Then, based on this information, the inflow volume into the Zayandeh-Rud Reservoir was predicted by the IHACRES model (Identification of unit Hydrograph and Component flows from Rainfall, Evaporation and Streamflow) and the agricultural water demand was also estimated based on future evapotranspiration. Finally, using GAMS (General Algebraic Modeling System) software, water resources in this basin were allocated based on the basic management scenario (B) and the water demand management scenario (D). The results showed that the average monthly temperature will increase by 0.6 to 1.3 °C under different climate change patterns. On the other hand, on the annual basis, precipitation will decrease by 6.5 to 31% and inflow volume to the Zayandeh-Rud Reservoir will decrease by 21 to 38%. The results also showed that the water shortages based on the baseline management scenario (B) will be between 334 and 805 MCM (Million Cubic Meters). These range of values varies between 252 and 787 MCM in the water demand management scenario (D). In general, the water shortage can be reduced in the Zayandeh-Rud River Basin with water demand control, but complete resolution of this problem in this region requires more integrated strategies based on a sustainable development, such as a fundamental change in the cropping pattern, prevention of population growth and industrial development.     

Impacts of climate change on water provisional services in Tungabhadra basin using InVEST Model

Water is one of the most important ecosystem services because it is essential for food and energy production. The Tungabhadra basin, located in peninsular India, has a variety of challenges, including inter-basin water-sharing issues, low agricultural productivity and value, and rising need for renewable energy production. The Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) water yield model is used to analyze the consequences of climate change on water related services such as water yield and hydropower generation in the densely populated Tungabhadra basin. The impact of climate change on water supply services is studied for the period 1971–2000 as well as the future period 2021–2040. The model is calibrated using streamflow data collected at the Bawapuram gauge station in Telangana and there is a strong correlation between observed and simulated flow. The water yield for the entire basin declined by 33 and 50% under the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios, respectively. The RCP 4.5 scenario reduces hydropower production and its Net Present Value (NPV) by 41 to 59%, whereas the RCP 8.5 scenario reduces production and NPV by 56 to 67%. The assessment of ecosystem services at the catchment scale revealed that the basin could be vulnerable to climate change due to a dramatic drop in ecosystem services. The methodology developed in this study can be applied to other river basins where quantifying ecosystem services is critical.     

新安江流域气候变化及径流响应研究

针对新安江流域新安江水库控制区域,构建新安江月水文模型,利用1979-2005年实测水文资料对模型进行率定和验证,并以CMIP5大气环流模式输出驱动水文模型,生成2006-2099年该流域在RCP2.6、RCP4.5和RCP8.5情景下的逐月径流过程。在此基础上,研究气候变化背景下流域气温、降雨、蒸发和径流的变化趋势,并对其不确定性进行分析。结果表明:2006-2099年该流域年均气温与年蒸发深度均呈上升趋势,且对于辐射强度变化较敏感,呈显著正相关关系。流域年降雨量与径流深呈波动上升趋势,对于辐射强度变化敏感性并不显著。年径流深在丰水年和平水年相对基准期有所减少,而在枯水年和特枯水年则呈增加趋势。月径流深在秋、冬季呈上升趋势,在春、夏季则呈下降趋势。     

The fate of the City of Mutare's urban water supply as changing climate impacts on its source in the Pungwe sub-catchment

Sustaining a steady supply of water to urban communities is of importance in a period that is characterised by rapid urban population growth, a global pandemic, and a changing climate that threatens the availability of the resource from its sources. Water supply to the City of Mutare is from three sources, Small Bridge Dam, Odzani, and the Pungwe River. The Pungwe source provides better quality water resources equivalent to the combined quantity supplied by the other two. It becomes an important source for the city, but climate change threatens the availability of water resources in the southern African region. Thus, it is imperative to quantitatively assess the impacts of a changing climate on water resources to enable the development of sustainable management alternatives. Using two carbon emission scenarios Representative Concentration Pathways (RCPs) 4.5 and 8.5, the study assesses the future availability of water resources from the Pungwe River to the City of Mutare using the Pitman hydrological model applied in an uncertainty framework. Available historical streamflow observations at gauging station F14 indicate a Q₉₅ flow of about 2 Mm³/year. Projected future water resources at the end of the 21st century show a slight increase of up to 2.38% under the low carbon emission scenario (RCP4.5) and a decrease of up to 9.73%under the high carbon emission scenario (RCP8.5). These model-generated results are useful to water managers to plan for catchment management strategies that would ensure continuous urban water supply, and the identification and development of possible future alternative water sources.     

基于Copula函数的气候变化下洪水峰量联合分析

为研究气候变化对北江流域洪水特征发生频率的影响,采用分位数映射(Quantile Mapping,QM)后处理方法校正BCC_CSM1.1气候模式2种情景(RCP4.5和RCP8.5)下的气候数据,用于SWAT模型模拟历史(1965—2010年)和未来(2030—2064年、2065—2099年)的北江流域径流量,并采用单变量分析法和基于Copula函数的双变量联合分析法分别对各时期年最大洪峰流量Q和年最大7 d洪量W进行对比分析。结果表明:除RCP8.5下2065—2099年的W外,重现期(T≥50 a)越大,气候变化对Q和W的影响越大; RCP4.5下气候变化对Q和W的影响较RCP8.5下大;2种未来情景下,气候变化对Q的影响均大于对W的影响;对于同一重现期,双变量联合分析法推求的洪水特征设计值较单变量分析法的偏安全。该研究结合了气候变化和双变量联合分析,对变化环境下的洪水风险评价与管理具有一定的参考价值。     

Selecting the Best Approach to Modeling the Performance of Water Supply System Using the Combination of Rough Set Theory with Multi-Criteria Decision Making

The purpose of this study is to select the best modeling approach (simulation or optimization) for operation the water supply system using multi-criteria decision-making method. For this purpose, the Geophysical Fluid Dynamics Laboratory-Earth System Models (GFDL-ESM2M) and the Model for Interdisciplinary Research on Climate-ESM (MIROC-ESM) models were selected to predict the changing trend of the climatic variables of rainfall and temperature, respectively. Then Artificial Neural Network (ANN) model and a decision support system tool named Cropwat were used to simulate water resources and consumption; and to model the behavior of the water supply system, the MODified SYMyld (MODSIM) (as simulator) and the modeling language and optimizer LINGO 18 (as optimizer) were used in the future time period (2026–2039) and the results were compared with the baseline period (1987–2000) for the Idoghmush reservoir (Iran). The results of MODSIM simulation model show that the indexes of reliability, vulnerability, reseiliency and flexibility in the future time period under the RCP2.6 emission scenario compared to the baseline time period decreased by 9%, decreased by 22%, increased by 4%, and decreased by 2%, respectively. The results of the LINGO 18 optimization model show that the reliability, vulnerability, resiliency and flexibility indexes in the future time period under the RCP2.6 emission scenario compared to the baseline time period decreased by 13%, decreased by 17%, increased by 14% and increased by 3%, respectively. Due to the different results obtained from optimization and simulation approaches for the study area, the Multi-Attributive Ideal-Real Comparative Analysis (MAIRCA) multi-criteria decision-making method was used to select a more appropriate approach. The results show that for water resources management planning, the simulation approach is given priority over the optimization approach due to its characteristics.

     

Downscaling Monsoon Rainfall over River Godavari Basin under Different Climate-Change Scenarios

Evaluating the impact of climate change at river basin level has become essential for proper management of the water resources. In the present study, Godavari River basin in India is taken as study area to project the monthly monsoon precipitation using statistical downscaling. The downscaling method used is a regression based downscaling termed as fuzzy clustering with multiple regression. Among the atmospheric variables simulated by global circulation/climate model (GCM) mean sea level pressure, specific humidity and 500 hPa geopotential height are used as predictors. 1^o × 1^o gridded rainfall data over Godavari river basin are collected from India Meteorological Department (IMD). A statistical relationship is established between the predictors and predictand (monsoon rainfall) to project the monsoon rainfall for the future using the Canadian Earth System Model (CanESM2) over IMD grid points under the Representative Concentration Pathways 2.6, 4.5 and 8.5 (RCP 2.6, 4.5, 8.5) scenarios of Fifth Coupled Model Inter-Comparison Project (CMIP 5). Downscaling procedure is applied to all 25 IMD grid points over the basin to find out the spatial distribution of monsoon rainfall for the future scenarios. For 2.6 and 4.5 scenarios results show an increasing trend. For scenario 8.5 rainfall showed a mixed trend with rainfall decreasing in the first thirty years of prediction and then increasing gradually over the next sixty years.     

Climate change impact on water quality in the integrated Mahabad Dam watershed-reservoir system

Climate change, besides global warming, is expected to intensify the hydrological cycle, which can impact watershed nutrient yields and affect water quality in the receiving water bodies. The Mahabad Dam Reservoir in northwest Iran is a eutrophic reservoir due to excessive watershed nutrient input, which could be exacerbated due to climate change. In this regard, a holistic approach was employed by linking a climate model (CanESM2), watershed-scale model (SWAT), and reservoir water quality model (CE-QUAL-W2). The triple model investigates the cumulative climate change effects on hydrological parameters, watershed yields, and the reservoir’s water quality. The SDSM model downscaled the output of the climate model under moderate (RCP4.5) and extreme (RCP8.5) scenarios for the periods of 2021–2040 and 2041–2060. The impact of future climate conditions was investigated on the watershed runoff and total phosphorus (TP) load, and consequently, water quality status in the dam’s reservoir. The results of comparing future conditions (2021–2060) with observed present values under moderate to extreme climate scenarios showed a 4–7% temperature increase and a 6–11% precipitation decrease. Moreover, the SWAT model showed a 9–16% decline in streamflow and a 12–18% decline in the watershed TP load for the same comparative period. Finally, CE-QUAL-W2 model results showed a 3–8% increase in the reservoir water temperature and a 10–16% increase in TP concentration. It indicates that climate change would intensify the thermal stratification and eutrophication level in the reservoir, especially during the year’s warm months. This finding specifies an alarming condition that demands serious preventive and corrective measures.     

From Natural to Reclaimed Land

ABSTRACT

The Aral Sea, a huge saline lake located in the arid south-central region of the former U.S.S.R., is vanishing because the inflows from its two feed rivers, the Amudar'ya and Syrdar'ya, have diminished radically over the past three decades. The loss of river flow is the result of massive increases in river withdrawals, primarily for cotton irrigation in the basins. A microcomputer model, the Water Evaluation and Planning System (WEAP), has been developed for simulating current water balances and evaluating water management strategies in the Aral Sea region. WEAP treats water demand and supply issues in a comprehensive and integrated fashion. The scenario approach allows flexible representation of the consequences of alternative development patterns and supply dynamics. For the Aral region's complex water systems, a detailed water demand and supply simulation was performed for the 1987–2020 period, assuming that the current practices continue. The analysis provides a picture of an unfolding and deepening crisis. Policy scenarios incorporating remedial actions will be reported in a separate paper