Assessing The Hydrologic Impacts Of Extreme Rainfall And Land Use Change On A Semiarid Watershed

Abstract: Intense precipitation events increase the risk of flash floods in the New Mexico-Texas-Mexico border region. Compounding effects of changing land use and precipitation pattern can influence rainfall-runoff processes that govern flash flooding. Paradoxically, this southwestern semiarid watershed has substantial water conflict that may get worse by 2025 due to changing climate and increasingly competitive demands for over-appropriated water resources. Using Soil and Water Assessment Tool (SWAT), we investigate the impact of changes in precipitation intensity and land use on runoff and arroyo flows in the dry, mountainous terrains. The baseline watershed simulation model shows that for a statistically insignificant change in the precipitation from 1996-2005 to 2006-2015, the water balance components (e.g. evapotranspiration, surface runoff, soil water content and water yield) showed a statistically significant decrease. Three extreme precipitation scenarios - largest 24-hr rainfall event in 1994-2015 period, 24-hr precipitation with 100-year and 200-year recurrence intervals-were modeled using NOAA precipitation frequency estimation data. The effect of these precipitation scenarios was also assessed under future land use/land cover scenarios using the USGS FOREcasting-SCEnarios (FORE-SCE) 2050 land use maps under A1B, A2 and B1 storylines developed by the Intergovernmental Panel on Climate Change (IPCC), representing different economic growth paths. The study identified the spatial location of sub-basins that are vulnerable to surface runoff and demonstrated that both extreme rainfall event and land use land cover change affect the hydrology of the watershed. Surface runoff is mostly governed by extreme rainfall events, but it shows spatial variability under future land use land cover scenarios. Results improve understanding of spatial and temporal variation of runoff associated with precipitation and land use patterns, which has important implications for planning watershed management practices that mitigate flash flooding and sediment transport