EFFECTS OF URBANIZATION AND LAND USE CHANGE ON HYDROLOGIC FLOW REGIME

Population growth and urbanization are major threats to the sustainability of water resources systems. This process increases impervious surfaces of watersheds which results in more surface runoff and less infiltration, increasing risk of floods during storm events, and also reduce the base flow of rivers and the recharge of aquifers. One of the elements that plays a key role in this process is land use. Most of the models consider land use as a static parameter. However, land use in fast growing cities is dynamic and have profound impacts in the main hydrologic processes. This study proposes the use of a Cellular Automata (CA) to represent land use change and its interactions with the hydrologic cycle. The CA land use change model represents urban sprawl by calculating the likelihood of changing the state of an undeveloped cell to urban based on spatial factors such as number of developed neighbors, distance to roads and central areas. The CA model is connected to a hydrologic model, Soil and Water Assessment Tool (SWAT), to assess impacts of land use change on streamflow and also observe how much dynamic land use change incorporation within watershed modeling improve model simulations by considering different criteria such as NSE, PBIAS, and RSR. This method was applied in two urban watersheds in San Antonio, TX (Salado Creek and Leon Creek) which is experiencing one of the highest rates of population growth in the US and faces tremendous stormwater and drought challenges.