The Willow Watershed (HUC 09010004) covers an area of approximately 2,989 square kilometers in the central part of the Sierra Nevada mountain range in California. The watershed is fed by snowpack and precipitation, with the snowpack typically accumulating from December to April. The snowpack is an important source of water for the watershed, and its melt contributes to the surface water flows in the area. The surface water in the Willow Watershed is primarily made up of streams and small rivers that eventually flow into the San Joaquin River. There are also several reservoirs in the watershed, including the Bass Lake Reservoir and the Mammoth Pool Reservoir, which provide water for irrigation, hydropower generation, and recreation. The climatic conditions in the Willow Watershed are characterized by a Mediterranean climate with hot, dry summers and cool, wet winters. Over the past few decades, the area has experienced a trend of reduced snowpack and earlier snowmelt, which has led to changes in the timing and quantity of surface water flows. Additionally, the watershed has experienced drought conditions in recent years, which has added further stress to the available water resources.