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.     

目标函数对滦河流域SWAT模型径流模拟不确定性的影响

针对水文模型参数和径流模拟结果不确定性问题,选取2Nash-Sutcliffe效率系数(NSE)、改进的决定系数(R_m²)、相对误差(PBIAS)、Kling-Gupta效率系数(KGE)4种目标函数,对构建的滦河流域潘家口水库上游SWAT模型进行参数率定及验证,分析了不同目标函数下模型参数的敏感性差异及径流模拟的不确定性。结果表明：参数敏感性会随迭代次数增加和抽样范围变化发生改变,不同目标函数下率定的参数范围和最优值显著不同;NSE和KGE作为目标函数在各站点径流模拟中更稳健,分别表现出较高的模拟精度和较低的模拟不确定性。     

Comparative Simulation of GIS-Based Rainwater Management Solutions

Rain Water Harvesting (RWH) as a solution for sustainable rainwater management is the focus of this research. To locate the potential sites for RWH, multi-criteria analysis following analytical hierarchy process using land-use/landcover, slope, drainage density, and runoff depth has been performed. By introducing continuous soil moisture accounting procedure in the globally used SCS-CN method, discrepancies in computed runoff values have been assessed. To appraise the usefulness of revised Soil Moisture Accounting (SMA) -enhanced SCS-CN models, a number of modifications have been compared. The models’ performance has been evaluated using R², Root Mean Square Error (RMSE), Nash Sutcliffe Efficiency (NSE), Percent BIAS (PBIAS) statistical indicators, and Rank Grading System (RGS) and the best has been selected to calculate the runoff depth for RWH potential zones. The resultant suitability map classifies Gurriala catchment into three suitability zones. 33.8% of the total area has been found as least suitable, comprised mainly of forest, residential land, and water bodies, while 46.8% and 19.4% of the area is recognized as moderately suitable and high suitable respectively. Selected suitable sites have been further classified into suitability zones for enhanced RWH structures and runoff volume contributed by each RWH structure has been computed. The total runoff potential of the area is 22.47 MCM that is enough to fulfill the water demands of suburban areas as a most inexpensive solution.

     

Modelling the Effects of Climate Change on Water Resources in Central Sweden

This article describes investigationsinto the effects of climate change on flow regimes oftwenty-five catchments (from 6 to 1293 km²) incentral Sweden. Hydrological responses of fifteenhypothetical climate change scenarios (e.g.combinations of T = +1, +2 and +4 °C andP = 0, ± 10%, ± 20%) were simulated by a conceptual monthly water balance model. The results suggest thatall the hypothetical climate change scenarios wouldcause major decreases in winter snow accumulation.Significant increase of winter flow and decrease ofspring and summer runoff were resulted from mostscenarios. Attendant changes in actualevapotranspiration were also examined for all climatechange scenarios. Despite the changes in seasonaldistribution of evapotranspiration, the change inannual total evapotranspiration was relatively smallwith the maximum change of 23% compared with the 76%for mean annual snow water equivalent changes and 52%for mean annual runoff changes. Such hydrologicresults would have significant implications on futurewater resources design and management.     

Evaluating the SWAT Model for Hydrological Modeling in the Xixian Watershed and a Comparison with the XAJ Model

Already declining water availability in Huaihe River, the 6th largest river in China, is further stressed by climate change and intense human activities. There is a pressing need for a watershed model to better understand the interaction between land use activities and hydrologic processes and to support sustainable water use planning. In this study, we evaluated the performance of SWAT for hydrologic modeling in the Xixian River Basin, located at the headwaters of the Huaihe River, and compared its performance with the Xinanjiang (XAJ) model that has been widely used in China. Due to the lack of publicly available data, emphasis has been put on geospatial data collection and processing, especially on developing land use-land cover maps for the study area based on ground-truth information sampling. Ten-year daily runoff data (1987?C1996) from four stream stations were used to calibrate SWAT and XAJ. Daily runoff data from the same four stations were applied to validate model performance from 1997 to 2005. The results show that both SWAT and XAJ perform well in the Xixian River Basin, with percentage of bias (PBIAS) less than 15%, Nash-Sutcliffe efficiency (NSE) larger than 0.69 and coefficient of determination (R²) larger than 0.72 for both calibration and validation periods at the four stream stations. Both SWAT and XAJ can reasonably simulate surface runoff and baseflow contributions. Comparison between SWAT and XAJ shows that model performances are comparable for hydrologic modeling. For the purposes of flood forecasting and runoff simulation, XAJ requires minimum input data preparation and is preferred to SWAT. The complex, processes-based SWAT can simultaneously simulate water quantity and quality and evaluate the effects of land use change and human activities, which makes it preferable for sustainable water resource management in the Xixian watershed where agricultural activities are intensive.     

Impact of Climate Change on Mediterranean Irrigation Demand: Historical Dynamics of Climate and Future Projections

Global warming is causing important changes in climate conditions, which must be studied in detail and locally in those zones where irrigated agriculture is developed—the major consumer of water worldwide. This study proposes the climatic characterization of a historical series (1971–2000) and its future projections (2011–2099) for an Irrigation District located in the Middle Ebro Valley (Spain), for three different scenarios: low, medium, and high global emission levels of greenhouse gases. Analysis of historical series reveals a significant increase in reference evapotranspiration (3.3 mm/year²; 2.4 ‰) along with a decrease in precipitation (2.5 mm/year²; 5.6 ‰). A comparison was carried out between real historical data and the scenarios produced by the climate models and it was observed that the most adequate climate model to predict climate in the study zone is MPI-ECHAM5. For the XXI century, MPI-ECHAM5 predicts cyclic climate trends but with a general increment in aridity, which intensifies according to the scenario chosen. Changes in climate are affecting agriculture doubly, since evapotranspiration requirements increase at the same time that water resources decrease. These effects are felt especially in irrigated agriculture, since the growing cycles of the main crops coincide with the months most affected by climate change.     

系统微分响应参数率定方法在建阳流域SWAT模型中的应用

利用基于系统微分响应理论的参数率定方法率定闽江建阳流域SWAT模型,通过流域1992—2000年日资料验证了该方法的实际应用效果,采用纳什效率系数(NSE)、偏差百分比(PBIAS)和相关系数r作为评价指标对率定后的SWAT模型模拟精度进行评价,并与传统利用SUFI-2方法率定得到的SWAT模型模拟结果进行对比分析。结果表明：系统微分响应方法率定的参数在建阳流域的日径流模拟中表现较好,率定期和检验期NSE均为0.65以上,径流量PBIAS在5%以内,r在0.65以上;利用系统微分响应率定参数方法率定SWAT模型参数在实际应用中可行,且效率与精度均高于传统的SUFI-2方法。     

土地利用变化情景下牧羊河水文响应研究

土地利用方式变化影响水量平衡各要素的分配,进而导致流域水源涵养能力发生变化。本研究选用长江流域金沙江水系下段牧羊河小流域内及周边气象站气象资料,植被、土壤以及地形数据,构建了研究区SWAT水文模型,并分析其在牧羊河适用性后,结合1986—2009年的土地利用以及设置的人类活动增强和生态环境改善的4种土地利用变化情景,用SWAT模型分析了土地利用变化下牧羊河水文响应。结果表明,径流依次按1986、2000、2009、1995年土地利用方式减小,而蒸散依次按2009、1986、2000、1995年土地利用方式减小,土地利用对径流和蒸散的影响在汛期大于非汛期,随着林地面积的增加径流将减小;将现有耕地变为林地或变为草地都有助于减少径流,从流域水源水量涵养角度出发,构建适宜的生态系统将有助于减少径流和蒸散,而增加入渗。这一结果为牧羊河水源涵养林建设提供科学依据。     

Assessing the Impacts of Climate Change on Hydrology of the Upper Reach of the Spree River: Germany

The aim of this study was to assess the potential impacts of future climate change on the hydrological response in the upper reach of the Spree River catchment using the Soil and Water Assessment Tool (SWAT). The model was calibrated for ten years (1997–2006) and validated with the data from four years (2007–2010) using average monthly stream flow. The impact of future climate change on precipitation, temperature, evapotranspiration and stream flow was then investigated from two different downscaled climate models (CLM and WETTREG2010) under SRES A1B scenarios for two future periods (2021–2030 and 2041–2050). Besides that, sensitivity analysis was carried out with and without observations, to test robustness of the sensitivity algorithm used in the model. Results of the determination coefficient R² and Nasch-Sutcliff efficiency E_NC were 0.81 and 0.80, respectively, during the calibration; 0.71 and 0.70, respectively, during the validation. Although some parameters were changed their sensitiveness ranking when the model run with observations, the SWAT model was, however, able to predict the top influential parameters without observations. According to 12 realizations from the two downscaled climate models, annual stream flow from 2021–2030 (2041–2050) is predicted to decrease by 39 % (43 %). This corresponds to an increase in annual evapotranspiration from 2021–2030 (2041–2050) of 36 % (38 %). The upper reach of the Spree River catchment will likely experience a significant decrease in stream flow due to the increasing in the evapotranspiration rates. This study could be of use for providing insight into the availability of future stream flow, and to provide a planning tool for this area.     

Optimizing the Runoff Estimation with HEC-HMS Model Using Spatial Evapotranspiration by the SEBS Model

Most of the commonly used hydrological models do not account for the actual evapotranspiration (ETa) as a key contributor to water loss in semi-arid/arid regions. In this study, the HEC-HMS (Hydrologic Engineering Center Hydrologic Modeling System) model was calibrated, modified, and its performance in simulating runoff resulting from short-duration rainfall events was evaluated. The model modifications included integrating spatially distributed ETa, calculated using the surface energy balance system (SEBS), into the model. Evaluating the model’s performance in simulating runoff showed that the default HEC-HMS model underestimated the runoff with root mean squared error (RMSE) of 0.14 m³/s (R²?=?0.92) while incorporating SEBS ETa into the model reduced RMSE to 0.01 m³/s (R²?=?0.99). The integration of HECHMS and SEBS resulted in smaller and more realistic latent heat flux estimates translated into a lower water loss rate and a higher magnitude of runoff simulated by the HECHMS model. The difference between runoff simulations using the default and modified model translated into an average of 95,000 m³ runoff per rainfall event (equal to seasonal water requirement of ten-hectare winter wheat) that could be planned and triggered for agricultural purposes, flood harvesting, and groundwater recharge in the region. The effect of ETa on the simulated runoff volume is expected to be more pronounced during high evaporative demand periods, longer rainfall events, and larger catchments. The outcome of this study signifies the importance of implementing accurate estimates of evapotranspiration into a hydrological model.

     

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.

     

Development of a New Integrated Framework for Improved Rainfall-Runoff Modeling under Climate Variability and Human Activities

The relationship between rainfall and runoff is a complex phenomenon and understanding the physical processes, hydrological components and their impacts on response of watershed to precipitation is one of the challenging issues in watershed hydrology and planning. There is still a need to improve conceptual hydrological models in water scarce regions, such as Iran mainly because in many cases there is not enough data to fully describe this phenomenon. In this research, we aimed to present an improved and parsimonious framework that increases the performance of a conceptual model in water balance and discharge modeling for Delichay watershed located in Hablehroud basin, Iran as one of the main source of water supply for downstream fertile agricultural areas that produce a considerable amount of cereals and play a major role for food and water security of the region. In areas where data for water cycle components are not available or limited, it is recommended to use parsimonious approach in order to have an acceptable level of understanding of the system with minimum possible predictor variables. The Salas model used in current research to model water balance over the period 1983–2012 and evaluation of the results indicated an unsatisfactory performance when the entire period was modeled altogether (NSE?=?0.35, d?=?0.70, R²?=?0.63, RSR?=?0.80, PBIAS?=?4.96 and RMSE?=?41.87). A key reason is that this watershed is intensively impacted by human activities and homogeneity analysis confirmed a sudden shift in runoff data during 1998–1999. Such a sudden shift reveals the role of human activities impacts on the watershed with a total reduction of 58 mm of runoff per year while the climate variability has not occurred in the region. Thus, the entire period (i.e. 1983–2012) was divided into two homogenous sub-periods of before and after the change point (i.e., pre-change and post-change periods). The results indicated that modeling performance in the sub-periods improved (e.g. the NSE was 0.77 and 0.66 for pre-change and post-change, respectively, vs. 0.35 for entire period). Meanwhile, it is revealed that water balance affected by human activities over the time and application of historical data for water balance modeling cannot be reliable without considering the homogeneous data. Since, many watersheds in the world have been affected by human activities or climate variability, it is recommended to consider the homogeneity of observed data before any application.

     

Adaptation Strategy to Mitigate the Impact of Climate Change on Water Resources in Arid and Semi-Arid Regions: a Case Study

Climate change and drought phenomena impacts have become a growing concern for water resources engineers and policy makers, mainly in arid and semi-arid areas. This study aims to contribute to the development of a decision support tool to prepare water resources managers and planners for climate change adaptation. The Hydrologiska Byråns Vattenbalansavdelning (The Water Balance Department of the Hydrological Bureau) hydrologic model was used to define the boundary conditions for the reservoir capacity yield model comprising daily reservoir inflow from a representative example watershed with the size of 14,924 km² into a reservoir with the capacity of 6.80 Gm³. The reservoir capacity yield model was used to simulate variability in climate change-induced differences in reservoir capacity needs and performance (operational probability of failure, resilience, and vulnerability). Owing to the future precipitation reduction and potential evapotranspiration increase during the worst case scenario (?40% precipitation and +30% potential evapotranspiration), substantial reductions in streamflow of between ?56% and ?58% are anticipated for the dry and wet seasons, respectively. Furthermore, model simulations recommend that as a result of future climatic conditions, the reservoir operational probability of failure would generally increase due to declined reservoir inflow. The study developed preparedness plans to combat the consequences of climate change and drought.     

Spatiotemporal Modelling of Water Balance Components in Response to Climate and Landuse Changes in a Heterogeneous Mountainous Catchment

Landuse change and climate change are the main drivers of hydrological processes. The purpose of this study was to analyse the separate and combined future effects of climate and landuse changes on water balance components on different spatial and temporal scales using the integrated hydrological Soil and Water Assessment Tool model. The study focused on the changes and relationship between water yield (WYLD) and sediment yield (SYLD) in the heterogeneous Taleghan Catchment in Iran. For future climate scenarios, RCP 4.5 and RCP 8.5 of GFDL-ESM2M GCM were used for 2020–2040. A Markov chain model was used to predict landuse change in the catchment. The results indicated an increase in precipitation and evapotranspiration. The findings also showed that the relationship between WYLD and SYLD is direct and synergic. Climate change has a stronger effect on WYLD than landuse change, whereas landuse change has a stronger effect on SYLD. The conversion of rangelands to barren land is the most critical landuse change that could increase SYLD. The highest increase in WYLD and SYLD in scenario RCP4.5 resulted from the combined effects of climate and landuse change. We estimated WYLD of about 295 mm and SYLD of around 17 t/ha. The proposed methodology is universal and can be applied to similar settings to identify the most vulnerable regions. This can help prioritize management strategies to improve water and soil management in watersheds.

     

An Integrated Approach for Partitioning the Effect of Climate Change and Human Activities on Surface Runoff

Climate change and human activities have been identified as the two main reasons for the change in runoff. To better understand the factors causing runoff change, this paper develops an integrated approach which combined the elasticity coefficient approach (including a non-parametric model and six Budyko framework based models) and the hydrological modelling approach (using SIMHYD models) for partitioning the impacts of climate change and human activities on surface runoff. The Guanzhong River Basin(GRB), which is the sub-basin of the Wei River basin in China is chosen as the study area. In this study, trends in runoff, rainfall and potential evapotranspiration (PET) from 1958 to 2008 are analyzed using the Mann-Kendall test and change-points in the annual runoff from 1958 to 2008 are sought using the Fu formula, Mann-Kendall test and double mass curve. The calibrated and validated rainfall-runoff model SIMHYD is used to simulate the runoff in the GRB during 1958–2008. Seven different methods are used to calculate the elasticity coefficient and then the elasticity coefficient methods are used to evaluate the contribution of climate change and human activities. Combining all these results, the contribution of climate change and human activities to runoff change is 34.1?~?47.3 and 52.7?~?65.9 %, respectively. The study provides scientific foundation for understanding the causes of water resources decrease and significant information for water resources management under the influence of climate change and human activities.     

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.     

Effect of land use/cover changes on runoff in the Min River watershed

Quantifying and interpreting the impacts that land use/cover change (LUCC) have on hydrology at basin scales are of great significance for the sustainable development of watershed ecosystems, water resources, and land management. The Soil and Water Assessment Tool was used to establish the regional model. The Min River watershed was divided into 236 sub‐basins, and simulations showed the spatial distribution of runoff in each sub‐basin with GIS‐based image displays. We set five scenarios to investigate the negative hydrological effects characterized by reductions in the water yield. From 1995 to 2004, the effect of simulated mean annual runoff caused by LUCC was ?12.61 m³/s and the climate variability caused ?67.61 m³/s. From 2005 to 2014, the hydrological effect caused by LUCC was ?2.38 m³/s and the climate variability caused ?58.53 m³/s. The elevation, Shannon's diversity index, largest patch index, and interspersion and juxtaposition index were all characterized by strong relationships with the sub‐basin outlet flows (adjusted R² = 0.572) using multivariate stepwise regression analysis. Redundancy analysis further proved that the reduction in grassland has led to a decrease in vegetation dominance while large increase in cultivated and residential lands has led to a higher degree of landscape richness and fragmentation, which has caused the reduced water yield. The restoration of grassland vegetation, as well as urban and agricultural water usage should be the primary focus of flow recovery.     

北庙水源地土地利用变化对水文要素影响的研究

选用保山市日气象观测数据和北庙水源地水库坝上径流资料,结合北庙水源地内的土地利用数据、土壤数据和DEM数据,构建其SWAT分布式水文模型,研究水源地三期不同土地利用方式变化对水文要素的影响。结果表明:在模型率定期和验证期,R2数分别为0.70和0.72,模型效率系数均大于0.55,径流模拟值与实测值相对误差在15%以内,SWAT水文模型在北庙水源地有较好的适用性。1986-2009年,北庙水源地土地利用类型以林地、耕地、草地为主;草地面积减少,耕地、未利用土地和居民用地增加是这一时期土地利用方式变化的主要特征。水源地水文要素发生相应的变化主要表现为坡面径流深、径流深和土壤侵蚀模数增加,而实际蒸散减少。     

Evaluation of the Best Management Practices at the Watershed Scale to Attenuate Peak Streamflow Under Climate Change Scenarios

The objectives of this study are (1) to develop a calibrated and validated model for streamflow using the Soil and Water Assessment Tool (SWAT) for the Lower Pearl River Watershed (LPRW) located in southern Mississippi, and (2) to assess the performance of parallel terraces, grassed waterways, and detention pond BMPs at attenuating peakflows at the watershed-scale under changes in precipitation, temperature, and CO₂ concentrations. The model was calibrated and validated for streamflow at 4 USGS gauge stations at the daily scale from 1994 to 2003 using the Sequential Uncertainty Fitting (SUFI-2) optimization algorithm in SWAT-CUP. The model demonstrated good to very good performance (R²?=?0.49 to 0.90 and NSE?=?0.49 to 0.84) between the observed and simulated daily streamflows at all 4 USGS gauge stations. This study found that grassed waterways had the highest peak flow reduction (?8.4 %), followed by detention ponds (?6.0 %), and then parallel terraces (?3.1 %) during the baseline climate scenario. Combining the different BMPs yielded greater reduction in average peak flow compared to implementing each BMP individually in both the current and changing climate scenarios. This study also found that the effectiveness of BMPs to reduce peakflows decreases significantly when increased rainfall or increased CO₂ concentrations are introduced in the watershed model. When increasing temperatures or decreasing rainfall is incorporated in the model, the peakflow reductions caused by BMPs generally does not change significantly.     

气候变化对嘉陵江流域水资源量的影响分析

 嘉陵江是长江的最大支流,流域面积约16万km2。针对2050,2100年不同的气候变化情景,选取较为不利的参数组合,根据降水、气温、湿度、风速、日照等气候要素的变化,建立潜在蒸发量模型计算流域的潜在蒸发量（ET0）,再根据流域内植被的蒸散发系数（Kc）,计算流域的面平均蒸散发量（ETc）。并利用流域面平均降水量减去径流深得到流域的实际蒸散发量,对计算的流域面平均蒸散发量进行验证。对不同的水平年利用降水的预测成果（气候变化情景不同具有不同的降水量预测成果）及计算流域的面平均蒸散发量,根据水量平衡模型分析计算气候变化对嘉陵江流域水量的影响。结果表明：不利条件下2050年年径流将减少23.0%～27.9%;2100将减少28.2%～35.2%;2050,2100年平均年径流分别相当于目前7年一遇和12年一遇的干旱年。由此说明,气候变化对流域内的水资源量影响十分显著。 