The Upper Frio Watershed, located in south-central Texas, encompasses an area of approximately 938 square miles. The area is characterized by steep terrain, and the hydrology of the region is dominated by the Frio River, which runs through the watershed. The region receives relatively low levels of precipitation, with an average annual rainfall of around 25 inches. Snowfall is uncommon in the area. Surface water resources in the Upper Frio Watershed are primarily derived from the Frio River, which provides water for irrigation, recreation, and municipal uses. The region is also home to several reservoirs, including the Choke Canyon Reservoir, which serves as a major source of water for the city of San Antonio. In recent years, the Upper Frio Watershed has experienced a trend of increasing temperatures and decreasing rainfall, which has led to concerns about the long-term sustainability of the region's water resources. Additionally, the area is prone to flooding during periods of heavy rainfall.