The Upper Gila San Carlos Reservoir Watershed (HUC 15040005) covers an area of approximately 2,306 square miles in southeastern Arizona. The hydrology of the area is characterized by a dry desert climate with low annual precipitation, typically ranging from 10 to 15 inches per year. Snowpack is relatively rare in this region, and surface water sources are limited. The San Carlos Reservoir, which is the primary water source for the region, is fed by the Gila River and serves as a critical source of water for irrigation, domestic use, and power generation. The reservoir is subject to water quality concerns due to elevated levels of nutrients and sedimentation. The region experiences high temperatures during summer months, often reaching over 100°F, and is prone to droughts. Increased warming and drying trends in the area may lead to more frequent and severe droughts, potentially impacting water availability and quality.