Land use, climate, and water supply

A Monte Carlo simulation experiment was conducted to explore the relationships between land use, climate, and water supply yields. A watershed streamflow and sediment yield model was coupled with a reservoir model and used to estimate storage-yield relationships for otherwise identical 5,000-ha forested, agricultural, and urban watersheds using weather data from four different sections of the eastern U.S. (Georgia, Indiana, New York, and Texas). Simulation results indicated that although land use very significantly affects water supply yields, the magnitudes of the effects are quite dependent on climate. Thus the differences in yields among the three watershed types are much greater in areas such as Georgia and Texas that have high evapotranspiration than they are in Indiana and New York. For example, at the Texas and Georgia sites, urban watersheds produced more than twice the water supply yield of forests at high levels of flow regulation (large reservoir capacities) while in Indiana and New York, increases of 25-50% were obtained. Agricultural watersheds also generally provided greater yields than forests, although at smaller reservoir capacities, the loss of reservoir capacity due to sedimentation in agricultural watersheds sharply reduced yields.