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Mid-Century Ensemble Regional Climate Change Scenarios for the Western United States

机译：美国西部世纪中叶整体区域气候变化方案

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To study the impacts of climate change on water resources in the western U.S., global climate simulations were produced using the National Center for Atmospheric Research/Department of Energy (NCAR/DOE) Parallel Climate Model (PCM). The Penn State/NCAR Mesoscale Model (MM5) was used to downscale the PCM control (20 years) and three future(2040–2060) climate simulations to yield ensemble regional climate simulations at 40 km spatial resolution for the western U.S. This paper describes the regional simulations and focuses on the hydroclimate conditions in the Columbia River Basin (CRB) and Sacramento-San Joaquin River (SSJ) Basin. Results based on global and regional simulations show that by mid-century, the average regional warming of 1 to 2.5 °C strongly affects snowpack in the western U.S. Along coastal mountains, reduction in annual snowpack was about70% as indicated by the regional simulations. Besides changes in mean temperature, precipitation, and snowpack, cold season extreme daily precipitation increased by 5 to 15 mm/day (15–20%) along theCascades and the Sierra. The warming resulted in increased rainfall at the expense of reduced snowfall, and reduced snow accumulation (or earlier snowmelt) during the cold season. In the CRB, these changes were accompanied by more frequent rain-on-snow events. Overall, they induced higher likelihood of wintertime flooding and reduced runoff and soil moisture in the summer. Changes in surface water and energy budgets in the CRB and SSJ basin were affected mainly by changes in surface temperature, which were statistically significant at the 0.95 confidence level. Changes in precipitation, while spatially incoherent, were not statistically significant except for the drying trend during summer. Because snow and runoff are highly sensitive tospatial distributions of temperature and precipitation, this study shows that (1) downscaling provides more realistic estimates of hydrologic impacts in mountainous regions such as the western U.S., and (2) despite relatively small changes in temperature and precipitation, changes in snowpack and runoff can be much larger on monthly to seasonal time scales because the effects of temperature and precipitation are integrated over time and space through various surface hydrological and land-atmosphere feedback processes. Although the results reported in this study were derived from an ensemble of regional climate simulations driven by a global climate model that displays low climate sensitivity compared with most other models, climate change was found to significantly affect water resources in the western U.S. by the mid twenty-first century.
机译：为了研究气候变化对美国西部水资源的影响，使用国家大气研究/能源部（NCAR / DOE）并行气候模型（PCM）进行了全球气候模拟。宾州州立大学/ NCAR中尺度模型（MM5）用于缩减PCM控制（20年）和三个未来（2040-2060年）气候模拟的规模，以产生美国西部40 km空间分辨率的整体区域气候模拟。区域模拟，重点关注哥伦比亚河盆地（CRB）和萨克拉曼多-圣华金河（SSJ）盆地的水文气候条件。根据全球和区域模拟得出的结果表明，到本世纪中叶，平均温度升高1至2.5°C会对美国西部的积雪产生严重影响。沿沿海山区，年度积雪减少约70％，如区域模拟所示。除了平均温度，降水和积雪的变化以外，沿着喀斯喀特山脉和山脉，寒冷季节的极端每日降水量增加了5至15毫米/天（15-20％）。变暖导致降雨量增加，但降雪量减少，并且在寒冷季节降雪量减少（或更早融雪）。在CRB中，这些变化伴随着更频繁的雪上降雨事件。总体而言，它们引起了冬季洪水泛滥的可能性更高，并在夏季减少了径流和土壤湿度。 CRB和SSJ盆地地表水和能源收支的变化主要受地表温度变化的影响，在0.95的置信度上具有统计学意义。降水的变化，尽管在空间上是不连贯的，但除了夏季的干燥趋势外，没有统计学意义。由于降雪和径流对温度和降水的空间分布高度敏感，因此该研究表明（1）降尺度提供了对美国西部山区的水文影响的更实际估计，以及（2）尽管温度和降水的变化相对较小，积雪和径流的变化在月度到季节时间尺度上可能更大，这是因为温度和降水的影响是通过各种地表水文和陆地-大气反馈过程随时间和空间进行整合的。尽管本研究报告的结果来自由全球气候模型驱动的区域气候模拟整体，该模型显示出与大多数其他模型相比较低的气候敏感性，但到20世纪中期，气候变化已被发现对美国西部的水资源产生了重大影响-一世纪。

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