Potential impacts of land use/cover and climate changes on ecologically relevant flows

Abstract

This study explored the sensitivity of ecologically relevant flows to individual and combined impacts of climate and land use/cover (LULC) change as well as to their synergistic impacts (combined effect minus sum of individual effects) in a rapidly urbanizing watershed in Alabama, USA. The Soil and Water Assessment Tool (SWAT) was first calibrated (1988–1993) and validated (2008–2013) at daily time scale for streamflow. Then, bias-corrected and downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) climate data from 2035 to 2060 with eleven climate models under two different representative concentration pathways (RCP 2.6 and RCP 8.5) were fed into SWAT to quantify the effects of future climate. Watershed LULC change was represented in SWAT via a future projected dataset developed by the United States Geological Survey (USGS). Past, present, and future potential streamflow responses to LULC and climate changes were analyzed for various ecologically relevant flow parameters. A total of 38 key flow parameters known to have significant impacts on aquatic flora and fauna were examined including high, low, and median flows, as well as flashiness. Increased summer temperature and decreased fall precipitation are expected in the study region accompanied by rapid urbanization. Climate change is expected to increase maximum monthly streamflows, especially in June-September potentially altering habitat availability for aquatic organisms. When climate change was combined with LULC change, more frequent drought and flood events are expected, which may negatively affect many fish species. Significant shifts in the timing of annual extreme streamflow conditions were also predicted in the future, which may adversely impact the life cycle of various aquatic species.