Changes in water balance variables are essential in planning and management. Two major factors affecting these variables are climate change and land use change. Few researches have been done to investigate the combined effect of the land use change and climate change using projections. In this study the hydrological processes in Upper Choctawhatchee River Watershed were modeled using the Soil and Water Assessment Tool (SWAT) to investigate the impacts of climate and land use change. We integrated land use projection based in the Shared Socioeconomic Pathways with future climate data to study the combined effects on Hydrological response of the watershed. Future rainfall and temperature, for two time periods, were obtained using General Climate Models to provide SWAT with the climatic forcing in order to project water balance variables. The simulation was carried out under two radiative forcing pathways of RCP4.5 and RCP6.0. Land use change focused on urbanization dominated the climate changes. Impacts on water balance variables differed seasonally. Results showed surface runoff experienced major changes under both emissions scenarios in some months up to 5 times increase. Among the water balance variables, evapotranspiration (ET) as the least dominant pathway for water loss showed the modest changes with the largest decrease during fall and summer. Projection indicated more frequent extreme behavior regarding water balance during midcentury. Discharge was estimated to increase through the year and the highest changes were projected during summer and fall with 186.3% increase in November under RCP6.0. Relying on rainfall for farming along with reduced agricultural landuse (11.8%) and increased urban area (47%) and population growth would likely make the water use efficiency critical. The model demonstrated satisfactory performance, capturing the hydrologic parameters. It thus can be used for further modelling of water quality to determine the sustainable conservation practices and extreme weather events such as hurricane and tropical storms.

中文翻译：

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评估美国东南部乔克塔哈奇河上游流域土地利用和气候预测下的水平衡变量

水平衡变量的变化对于规划和管理至关重要。影响这些变量的两个主要因素是气候变化和土地利用变化。很少有研究使用预测来调查土地利用变化和气候变化的综合影响。在这项研究中，使用土壤和水评估工具 (SWAT) 对上乔克塔哈奇河流域的水文过程进行了建模，以调查气候和土地利用变化的影响。我们将基于共享社会经济路径的土地利用预测与未来的气候数据相结合，以研究对流域水文响应的综合影响。使用通用气候模型获得两个时间段的未来降雨量和温度，为 SWAT 提供气候强迫，以预测水平衡变量。模拟在 RCP4.5 和 RCP6.0 两种辐射强迫路径下进行。以城市化为核心的土地利用变化主导了气候变化。对水平衡变量的影响因季节而异。结果显示，在这两种排放情景下，地表径流在几个月内发生了重大变化，增加了 5 倍。在水分平衡变量中，蒸发蒸腾（ET）作为水分流失最不显着的途径，在秋季和夏季表现出温和的变化，下降幅度最大。预测表明本世纪中叶有关水平衡的极端行为更为频繁。预计全年排放量将增加，最高变化预计在夏季和秋季，11 月份在 RCP6.0 下增加了 186.3%。依靠降雨进行农业以及减少农业用地 (11. 8%) 以及城市面积的增加 (47%) 和人口增长可能会使用水效率变得至关重要。该模型表现出令人满意的性能，捕获了水文参数。因此，它可用于进一步模拟水质，以确定可持续保护措施和极端天气事件，如飓风和热带风暴。