Watershed Modeling to Assessing Impacts of Potential Climate Change on Water Supply Availability

Climate change could have impacts on hydrologic systems threatening, availability of water supply resources. In Illinois, regional water supply planning efforts are attempting to better understand potential impacts on low flow and surface water availability through analysis of hydrologic sensitivity to a range of climate scenarios. This paper explores the development, calibration and validation of Fox River watershed model using the soil and water assessment tool (SWAT) and the model’s application to assess impacts of potential climate change. The watershed model is calibrated and validated using daily flow records at three gauging stations. Automatic model calibration followed by manual refinement of parameter values was performed. Calibration results were generally good for monthly and annual time step but only satisfactory for daily simulations. Based on simulations of global climate models produced for IPCC fourth assessment report, climate scenarios were prepared by the Illinois State Water Survey for water supply planning initiatives in north-east and east-central Illinois. These scenarios showed ranges of temperature change between 0°C to +3.3°C and annual precipitation changes between −127 to +127 mm in the next 50 years, excluding the 5% extreme ends of those climate model simulations considered. Changes in climate were reflected using adjustments to the historical record, instead of using direct outputs from individual climate models. The watershed model was used to assess the impact of potential climate change. Application results indicate that annual precipitation change of 127 mm on average increases annual water yield and 7-day low flows by 28% and 19%, respectively. In contrast, a temperature change of +3.3°C results in average reductions of annual water yield by 13% and 7-day low flows by 10%. Seasonal effects were investigated through evaluation of changes in average monthly flows. Increasing precipitation resulted in significant changes in streamflows in late summer and fall months where as increasing temperature greatly affects winter flows due to snowmelt. The key implication is that climate change-induced variability of streamflows could have major impacts on water supply availability in the Fox River watershed and in particular, increased periods of drought could result in deficit of supplies during seasons of peak water use. It must be noted that this analysis does not examine the potential impacts of population growth and water use on water supply availability, which are also expected to have substantial influences in the region.     

Future Scenarios of Surface Water Resources Availability in North African Dams

Climate change may have strong impacts on water resources in developing countries. In North Africa, many dams and reservoirs have been built to secure water availability in the context of a strong inter-annual variability of precipitation. The goal of this study is to evaluate climate change impacts on surface water resources for the largest dams in Algeria, Morocco and Tunisia using high-resolution (12 km) regional climate models (RCM) simulations. To evaluate the atmospheric demand (evapotranspiration), two approaches are compared: The direct use of actual evaporation simulated by the RCMs, or estimation of reference evapotranspiration computed with the Hargreaves-Samani (HAR) equation, relying on air temperature only, and the FAO-Penman Monteith (PM) equation, computed with temperature, wind, radiation and relative humidity. Results showed a strong convergence of the RCM simulations towards increased temperature and a decrease in precipitation, in particular during spring and the western part of North Africa. A decrease in actual evapotranspiration, highly correlated to the decrease in precipitations, is observed throughout the study area. On the opposite, an increase in reference evapotranspiration is observed, with similar changes between HAR and PM equations, indicating that the main driver of change is the temperature increase. Since the catchments are rather water-limited than energy-limited, despite opposite projections for actual and reference evapotranspiration a decrease of water availability is projected for all basins under all scenarios, with a strong east-to-west gradient. The projected decrease is stronger when considering reference evapotranspiration rather than actual evaporation. These pessimistic future projections are an incentive to adapt the current management of surface water resources to future climatic conditions.     

Impacts of Climate Change on Water Resources Availability and Agricultural Water Demand in the West Bank

Global climate change is predicted as a result of increased concentrations of greenhouse gasses in the atmosphere. It is predicted that climate change will result in increasing temperature by 2 to 6°C and a possible reduction of precipitation of up to 16% in the Mediterranean basin. In this study, the West Bank is taken as a case study from the Mediterranean basin to evaluate the effects of such climate change on water resources availability and agricultural water demands. Due to the uncertainty in climate change impacts on temperature and precipitation, a number of scenarios for these impacts were assumed within the range of predicted changes. For temperature, three scenarios of 2, 4 and 6°C increase were assumed. For precipitation, two scenarios of no change and 16% precipitation reduction were assumed. Based on these scenarios, monthly evapotranspiration and monthly precipitation excess depths were estimated at seven weather stations distributed over the different climatic and geographical areas of the West Bank. GIS spatial analyses showed that the increase in temperature predicted by climate change could potentially increase agricultural water demands by up to 17% and could also result in reducing annual groundwater recharge by up to 21% of existing values. However, the effects of reduced precipitation resulting from climate change are more enormous as a 16% reduction in precipitation could result in reducing annual groundwater recharge in the West Bank by about 30% of existing value. When this effect is combined with a 6°C increase in temperature, the reduction in groundwater recharge could reach 50%.     

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.

     

南水北调中线水源区和受水区干旱遭遇风险评估

基于 1961—2019 年气象观测数据和 CMIP6 模式数据,利用标准化降水蒸散指数（standardized?precipitation evapotranspiration?index,SPEI）计算南水北调中线水源区和受水区的干旱指数,并利用经验正交分析法、主成分分 析法和 Copula 函数法,对水源区与受水区的干旱演变规律进行分析,揭示干旱遭遇的联合概率分布,并对未来干 旱遭遇进行预估。研究结果表明：水源区和受水区干旱事件遭遇频繁,1965—1971 年和 1987—2005 年均出现较 为严重的干旱遭遇事件,同时在 1970 年代中后期至 1985 年前后,出现了长期明显的区域差异性;水源区和受水区 中旱和重旱的联合重现期分别约为 18 年一遇（5.51%）和 123 年一遇（0.81%）,两地同时出现极端干旱的重现期约 为 323 年一遇（0.31%）;不同气候情景下以年尺度 SPEI 指数,对南水北调中线水源区和受水区的未来干旱事件预 估表明,未来水源区和受水区在 SSP1-2.6 情景下干旱遭遇次数相对较少,而在 SSP2-4.5 情景下的 2034—2036 年、 2044—2045 年以及在 SSP5-8.5 情景下的 2032—2033 年、2068—2070 年,将有可能发生较严重的干旱遭遇事 件。     

Long-Term Climatic Variability in Calabria and Effects on Drought and Agrometeorological Parameters

In recent decades a general change in climate has been documented in several locations over the world. Such changes could have significant effects on various environmental scenarios, including water resource management, agriculture, hydrology and ecosystems. The complex topography and coastlines of Mediterranean regions influences the climatic regime exhibiting substantial fine-scale spatial variability. In Italy, the climate is generally becoming warmer and drier, with quite large differences depending on the site and data treatment. In this study a historical set of meteorological data (110 precipitation and 28 temperature series), collected over 1921–2007 in the Calabria region (Southern Italy) was analysed. Several meteorological and agrometeorological indices were selected for whether they could evaluate the potential effects of climate change on water availability for natural vegetation and cultivated plants. The significance of the analysed time series (monthly, seasonal and annual time scales) was evaluated by using statistical trend analysis (Mann-Kendall and t-test). Moreover, the intensities of drought events were determined using the Standardized Precipitation Index (SPI) for the time scales of 3 and 6 months. The analysis highlighted a general decrease in annual precipitation and an increase in drought intensity. At a regional level, yearly precipitation decreased by almost 318 mm/100 years (representing almost 30 % of the yearly mean precipitation in the region). Temperature changes were more complex. On a regional scale, yearly mean minimum temperatures increased by 0.9 °C/100 years and maximum and mean temperatures decreased by 1 °C/100 years and 0.8 °C/100 years, respectively. Due to the asymmetric behaviour of temperatures, there was a decreasing impact on evapotranspiration.     

Hydrology under climate change in a temporary river system: Potential impact on water balance and flow regime

The potential impacts of future climate scenarios on water balance and flow regime are presented and discussed for a temporary river system in southern Italy. Different climate projections for the future (2030–2059) and the recent conditions (1980–2009) were investigated. A hydrological model (Soil and Water Assessment Tool) was used to simulate water balance at the basin scale and streamflow in a number of river sections under various climate change scenarios, based on different combinations of global and regional models (global circulation models and regional climate models). The impact on water balance components was quantified at the basin and subbasin levels as deviation from the baseline (1980–2009), and the flow regime alteration under changing climate was estimated using a number of hydrological indicators. An increase in mean temperature for all months between 0.5–2.4 °C and a reduction in precipitation (by 4–7%) was predicted for the future. As a consequence, a decline of blue water (7–18%) and total water yield (11–28%) was estimated. Although the river type classification remains unvaried, the flow regime distinctly moves towards drier conditions and the divergence from the current status increases in future scenarios, especially for those reaches classified as I‐D (ie, intermittent‐dry) and E (ephemeral). Hydrological indicators showed a decrease in both high flow and low flow magnitudes for various time durations, an extension of the dry season and an exacerbation of extreme low flow conditions. A reduction of snowfall in the mountainous part of the basin and an increase in potential evapotranspiration was also estimated (4–4.4%). Finally, the paper analyses the implications of the climate change for river ecosystems and for River Basin Management Planning. The defined quantitative estimates of water balance alteration could support the identification of priorities that should be addressed in upcoming years to set water‐saving actions.     

Flood Vulnerability to Climate Change through Hydrological Modeling

Abstract

Determination of flood vulnerability to climate change is one of the most critical issues for regional water management. Most of the previous studies related to system vulnerabilities to climate change were either a qualitative assessment without the support of hydrological modeling or too complex to apply them to real-world systems. In this study, a modeling and assessment system is proposed to tackle flood vulnerability to the climate change through the incorporation of future climate change scenarios, rainfall-runoff simulation, and vulnerability estimation within an integrated frame. The developed approach is applied to provide decision support for flood management of the Swift Current Creek watershed in Western Canada. The approach not only is useful to determine relative flood vulnerabilities to climate change for supporting flood control planning in the watershed, but also can be extended to estimate vulnerabilities of water quality and water supply to climate change.     

Assessment of Water Resources Availability and Groundwater Salinization in Future Climate and Land use Change Scenarios: A Case Study from a Coastal Drainage Basin in Italy

The joint effect of changes in climate and land use on the future availability of water resources was assessed under the SRES A1B and A2 climate scenarios as well as five land use scenarios for the 2080–2100 time-frame in an Italian coastal watershed. The study area is a small coastal polder (100 km²) characterized by irrigated agriculture, urban expansion, drainage, quarrying and sensitivity to salt-water intrusion. The hydroclimatic budget and the GALDIT index have been computed for assessing water resources availability and groundwater vulnerability to salinization, respectively. The methodology developed is integrated into a tool based on Excel?, which supported the development of scenarios in participatory processes. The conclusions emerged from the analysis are the following: (1) climate change is more effective than land use change in controlling future freshwater availability and amplifies the imbalance between winter surplus and summer deficits, (2) freshwater availability in the summer will likely be affected by an increase in evaporation from open water surfaces due to increased temperature, whereas winter surplus would increase, (3) the vulnerability of the coastal aquifer to salinization will probably moderately increase but an inherent limitation of the GALDIT index to land use change parameters prevents a sound assessment. Strategies that may be proposed to administrators and stakeholders are based on increasing storage of seasonal water surplus.     

Vulnerability of Korean water resources to climate change and population growth.

Freshwater availability is affected by changes in climate and growth. We assessed the freshwater vulnerability for five major Korean river basins for 2015 and 2030. We used a regional climate model based on the IPCC SRES A2 scenario, US Geological Survey's Precipitation Rainfall Simulation Model, and population and industrial growth scenarios for impact assessment. The model simulation results suggest increasing spatial and temporal variations of water stress for the basins that are already developed. While freshwater is more vulnerable to growth scenarios than the climate change scenario, climate change alone could decrease mean annual runoff by 10% in four major river basins by 2030. As the first national assessment of climate change, we suggest possible adaptive water resource management and policy strategies for reducing climate related risks in Korea.     

The Impacts of Climate Variability and Future Climate Change in the Nile Basin on Water Resources in Egypt

This paper describes the application of hydrologic models of the Blue Nile and Lake Victoria sub-basins to assess the magnitude of potential impacts of climate change on Main Nile discharge. The models are calibrated to simulate historical observed runoff and then driven with the temperature and precipitation changes from three general circulation model (GCM) climate scenarios. The differences in the resulting magnitude and direction of changes in runoff highlight the inter-model differences in future climate change scenarios. A 'wet' case, 'dry' case and composite case produced +15 (+12), -9 (-9) and + 1(+7) per cent changes in mean annual Blue Nile (Lake Victoria) runoff for 2025, respectively. These figures are used to estimate changes in the availability of Nile water in Egypt by making assumptions about the runoff response in the other Nile sub-basins and the continued use of the Nile Waters Agreement. Comparison of these availability scenarios with demand projections for Egypt show a slight surplus of water in 2025 with and without climate change. If, however, water demand for desert reclamation is taken into account then water deficits occur for the present-day situation and also 2025 with ('dry' case GCM only) and without climate change. A revision of Egypt's allocation of Nile water based on the recent low-flow decade-mean flows of the Nile (1981-90) shows that during this period Egypt's water use actually exceeded availability. The magnitude of 'natural' fluctuations in discharge therefore has very important consequences for water resource management regardless of future climate change.     

Effects of Land-Use and Climate Change on Hydrological Processes in the Upstream of Huai River, China

Land use/land cover and climate change can significantly alter water cycle at local and regional scales. Xixian Watershed, an important agricultural area in the upper reach of the Huaihe River, has undergone a dramatic change of cultivation style, and consequently substantial land use change, during the past three decades. A marked increase in temperature was also observed. A significant monotonic increasing trend of annual temperature was observed, while annual rainfall did not change significantly. To better support decision making and policy analysis relevant to land management under climate change, it is important to separate and quantify the effect of each factor on water availability. We used the Soil and Water Assessment Tool (SWAT), a physically based distributed hydrologic model, to assess the impact of Land use and climate changes separately. The SWAT model was calibrated and validated for monthly streamflow. Nash-Sutcliff efficiency (NSE), percentage bias (PBIAS), and coefficient of determination (R ²) were 0.90, 6.3 %, and 0.91 for calibration period and 0.91, 6.9 %, and 0.911 for validation period, respectively. To assess the separate effect of land use and climate change, we simulated streamflow under four scenarios with different combinations of two-period climate data and land use maps. The joint effect of land use and climate change increased surface flow, evapotranspiration, and streamflow. Climate variability increased the surface water and stream-flow and decreased actual evapotranspiration; and land use change played a counteractive role. Climate variability played a dominant role in this watershed. The differentiated impacts of land-use/climate variabilities on hydrological processes revealed that the unapparent change in stream-flow is implicitly because the effects of climate variability on hydrological processes were offset by the effects of land use change.     

基于SWAT模型的秦淮河流域气候变化水文响应研究

为了解气候变化对水文水资源的影响机理,以秦淮河流域为研究区构建SWAT模型,使用SWAT-CUP对模型进行参数敏感性分析、率定及验证,并采用任意假设法设计未来气候情景,分析温度及降雨变化对流域径流及实际蒸散发量的影响。结果表明:模型在月径流模拟中具有较高的精度,适用于秦淮河流域气候变化下的水文响应研究;气温降低或降雨量上升都会引起流域径流量增加,反之则减少;实际蒸散发量与降雨量正相关,而实际蒸散发量对气温变化的响应不明显;平水年径流量对降雨量变化的响应较强,枯水年径流量对温度变化的响应较强;枯水年实际蒸散发量对降雨量变化的响应较强。     

Impact of Climate Change on the Hydrology of Upper Tiber River Basin Using Bias Corrected Regional Climate Model

The use of regional climate model (RCM) outputs has been getting due attention in most European River basins because of the availability of large number of the models and modelling institutes in the continent; and the relative robustness the models to represent local climate. This paper presents the hydrological responses to climate change in the Upper Tiber River basin (Central Italy) using bias corrected daily regional climate model outputs. The hydrological analysis include both control (1961–1990) and future (2071–2100) climate scenarios. Three RCMs (RegCM, RCAO, and PROMES) that were forced by the same lateral boundary condition under A2 and B2 emission scenarios were used in this study. The projected climate variables from bias corrected models have shown that the precipitation and temperature tends to decrease and increase in summer season, respectively. The impact of climate change on the hydrology of the river basin was predicted using physically based Soil and Water Assessment Tool (SWAT). The SWAT model was first calibrated and validated using observed datasets at the sub-basin outlet. A total of six simulations were performed under each scenario and RCM combinations. The simulated result indicated that there is a significant annual and seasonal change in the hydrological water balance components. The annual water balance of the study area showed a decrease in surface runoff, aquifer recharge and total basin water yield under A2 scenario for RegCM and RCAO RCMs and an increase in PROMES RCM under B2 scenario. The overall hydrological behaviour of the basin indicated that there will be a reduction of water yield in the basin due to projected changes in temperature and precipitation. The changes in all other hydrological components are in agreement with the change in projected precipitation and temperature.     

Responses of soil moisture to climate change based on projections by the end of the 21st century under the high emission scenario in the ‘Huang–Huai–Hai Plain’ region of China

Based on the future potential projections in the late 21st century under the Representative Concentration Pathway (RCP) 8.5 scenario, the maximal responses of surface soil moisture (SSM) to an extreme climate change are exhibited in the ‘Huang–Huai–Hai Plain’ (‘3H’) region of China. The Common Land Model (CoLM) and the approach of conditional nonlinear optimal perturbation related to parameters (CNOP-P) are employed to explore the above issue. Three climate change scenarios, associated with temperature change, precipitation change and changes in both temperature and precipitation, are provided by applying the CNOP-P approach and denoted as the CNOP-P-type temperature change scenario, the CNOP-P-type precipitation change scenario and the CNOP-P-type climate change scenario, respectively. For the CNOP-P-type scenarios, the changes in both climatology and climate variability relative to the reference climate condition are included. To explore the different responses of SSM to different types of climate scenarios, the hypothesized climate change scenarios are examined as well, in which only the change in climatology is considered. Numerical results have suggested that the CNOP-P-type scenario induces greater SSM responses in terms of variation magnitudes than the hypothesized climate change does, especially in the semi-arid regions north of 35°N. For the two types of climate change scenarios, the differences about precipitation and soil ice changes result in the difference about SSM changes in the northern region, though the difference about evapotranspiration variations helps to narrow the difference about SSM. The above results imply that climate variability is important to SSM in the semi-arid region.     

基于Budyko弹性系数法的佳芦河流域径流变化归因识别

气候变化和人类活动对径流的影响是一个综合过程,因此径流动态变化及其归因识别和定量表征对区域水资源开发管理至关重要。以佳芦河流域为研究区,选用Mann-Kendall趋势检验法、有序聚类法等分析了研究区水文要素的主要变化特征;采用基于Budyko水热耦合平衡理论的弹性系数法,定量分析了径流深变化对各驱动因素的响应程度。结果表明:研究时段内,降水量和潜在蒸散发量均无明显变化,但径流深呈显著减少趋势且在1978年发生突变,相比基准期,径流深相对变化率为-58.5%;人类活动和气候变化共同作用于该流域导致径流深锐减,其中人类活动、降水量和潜在蒸散发量对径流深变化的贡献率分别是77.54%、21.31%和1.15%。     

An Assessment of Climate Change,Water Resources,and Policy Research

ABSTRACT

A significant climate change can affect water resources and result in social and/or environmental impacts that can become policy issues. Review of the research in this emerging field of climate, water and policy reveals certain key issues that affect the transfer of information to policymakers. It also reveals the necessity for interdisciplinary analyses, a lack of information about parts of the hydrologic cycle, and the limited views many hydrologists have about climate changes and how to deal with them. The emphasis of recent research has been on effects on precipitation of CO, induced global warming on how climate changes might alter extreme events (droughts and floods), the relationship of climate alterations and water quality, and development of methods to better ascertain linkages of climate, water, and society. Policymakers attempting to address the effects of climate change on water resources generally ask six questions including: (1) the type of climate change apt to occur; 2) the changes beyond our recent (100-year) experience; 3) whether the changes can be predicted; 4) the certainty of change/s predicted; 5) the effects (social and environmental) that will occur; and (6) the potential adjustments needed.

Efforts to address adequately these questions are often hindered by four problem areas that need attention. First, climate impacts research is still in the developmental stage. Second, knowledge about certain hydrologic cycle variables is lacking and in particular, the interactions between climate and water quality. Third, many hydrologists assume stationarity in climate and find it difficult to accept and utilize climate change concepts. Finally, the impact of information on climate-water issues on the policy process is less than adequate often because scientists poorly understand the policy process.     

Climate Variability Impact on the Spatiotemporal Characteristics of Drought and Aridityin Arid and Semi-Arid Regions

Investigating the spatiotemporal distribution of climate data and their impact on the allocation of the regional aridity and meteorological drought, particularly in semi-arid and arid climate, it is critical to evaluate the climate variability effect and propose sufficient adaptation strategies. The coefficient of variation, precipitation concentration index and anomaly index were used to evaluate the climate variability, while the Mann-Kendall and Sen’s slope were applied for trend analysis, together with homogeneity tests. The aridity was evaluated using the alpha form of the reconnaissance drought index (Mohammed & Scholz, Water Resour Manag 31(1):531–538, 2017c), whereas drought episodes were predicted by applying three of the commonly used meteorological drought indices, which are the standardised reconnaissance drought index, standardized precipitation index and standardized precipitation evapotranspiration index. The Upper Zab River Basin (UZRB), which is located in the northern part of Iraq and covers a high range of climate variability, has been considered as an illustrative basin for arid and semi-arid climatic conditions. There were general increasing trends in average temperature and potential evapotranspiration and decreasing trends in precipitation from the upstream to the downstream of the UZRB. The long-term analysis of climate data indicates that the number of dry years has temporally risen and the basin has experienced succeeding years of drought, particularly after 1994/1995. There was a potential link between drought, aridity and climate variability. Pettitt’s, SNHT, Buishand’s and von Neumann’s homogeneity test results demonstrated that there is an evident alteration in the mean of the drought and aridity between the pre- and post-alteration point (1994).

     

Drought variability and its connection with large-scale atmospheric circulations in Haihe River Basin

Drought is one of the most widespread and devastating extreme climate events when water availability is significantly below normal levels for a long period. In recent years, the Haihe River Basin has been threatened by intensified droughts. Therefore, characterization of droughts in the basin is of great importance for sustainable water resources management. In this study, two multi-scalar drought indices, the standardized precipitation evapotranspiration index(SPEI) with potential evapotranspiration calculated by the Penmane Monteith equation and the standardized precipitation index(SPI), were used to evaluate the spatiotemporal variations of drought characteristics from 1961 to 2017 in the Haihe River Basin. In addition, the large-scale atmospheric circulation patterns were used to further explore the potential links between drought trends and climatic anomalies. An increasing tendency in drought duration was detected over the Haihe River Basin with frequent drought events occurring in the period from 1997 to 2003. The results derived from both SPEI and SPI demonstrated that summer droughts were significantly intensified. The analysis of large-scale atmospheric circulation patterns indicated that the intensified summer droughts could be attributed to the positive geopotential height anomalies in Asian mid-high latitudes and the insufficient water vapor fluxes transported from the south.     

Water Resource Availability in Three Catchments of Swaziland under Expected Climate Change

Abstract

The greenhouse gases (CO₂, CH₄, N₂O, HFCs, PFCs, and SF₆) concentrations in the atmosphere have increased very much since the industrial revolution. The greenhouse gas effect has been projected to cause a global average temperature increase on the order of 1.4 to 5.8°C over the period of 1990 to 2100. The global average annual precipitation is projected to increase during the 21^st century due to the greenhouse effect. The impact of climate change on hydrology and water resources in the three catchments of Swaziland (Komati, Mbuluzi and Ngwavuma) has been evaluated using General Circulation Model results (rainfall, potential evapotranspiration, air temperature etc.) as inputs to a rainfall runoff model. Three General Circulation Models (GCMs) namely: Canadian Climate Change Equilibrium (CCC-EQ); Geophysical Fluid Dynamics Laboratory (GFDL) and United Kingdom Transient Resilient (UKTR) were found appropriate for use to project the temperature and precipitation changes for Swaziland for year 2075. This information was used to generate the temperature, precipitation and potential evapotranspiration values for the three catchments for year 2075 which was input into a calibrated WatBall rainfall runoff model. Simulation results without taking into consideration of water use projections show that there will be high flows during the summer months but low flows during the winter months. Simulation results after taking into consideration of water use projections show a water deficit from June to September in both the Komati, and Ngwavuma catchments and a water deficit from May to September in the Mbuluzi catchment. This means that the environmental water needs and Swaziland's water release obligation in the three catchments to South Africa and Mozambique will not be met during the winter months under expected climate change conditions.