California's interconnected water system is one of the most advanced water management systems in the world, and understanding of long-term trends in atmospheric and hydrologic behavior has increasingly being seen as vital to its future well-being. Knowledge of such trends is hampered by the lack of long-period observation data and the uncertainty surrounding future projections of atmospheric models. This study examines historical precipitation trends over the Shasta Dam Watershed (SDW), which lies downstream of one of the most important aspects of California's water system, Shasta Dam, using a dynamic downscaling methodology that can obtain reconstructed climate data at fine time-space scales. The methodology for reconstructing historical precipitation data over SDW started with the coarse-resolution historical 2.5 degrees Twentieth Century Reanalysis Version 2c (20CRv2c) dataset. The weather research and forecasting (WRF) model was then used to produce 159 years of long-term reconstructed hourly precipitation data at a 3 km spatial resolution over SDW. Trend analysis on this data indicated an increase in total precipitation over the study period as well as a growing intensity of extreme events such as 6, 12, 24, 48, and 72-hour storms. These results both inform long-term planning decisions regarding the future of Shasta Dam and California's water system and validate a methodology that can be used in data-sparse basins around the world.
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