Effect of landuse and landcover change and climate change on the hydrological response and water quality of Big Creek Lake Watershed South Alabama USA

Abstract

Land use and climate are the two key factors affecting the hydrological processes of a watershed. This research aimed to evaluate the impact of changing land use and land cover (LULC) and climate change on hydrological responses and water quality by applying the Soil and Water Assessment Tool (SWAT) to Big Creek Lake watershed located in Mobile County, South Alabama. Digital elevation model (DEM), LULC data, weather data, soil data, observed streamflow, nitrogen, and phosphors data were input files used to calibrate and validate the SWAT model. Downscaled and bias-corrected daily projected climate data were used under moderate (Representative Concentrative Pathways4.5) and extreme (Representative Concentrative Pathways8.5) scenarios. These data were used as inputs of a calibrated SWAT model of the watershed in order to determine the effects of climate change and LULC on streamflow and total nitrogen and phosphorus in the watershed from 2020 to 2050. The SWAT model was calibrated and validated using the SUFI-2 algorithm in the SWAT Calibration Uncertainties Program (SWAT-CUP) software. LULC changes and climate changes were investigated to quantify the effects of the major hydrological components such as actual evapotranspiration, percolation, lateral flow, surface runoff, groundwater and water yield. About 11,045 acres of agricultural land and 3,350 acres of urban area has been increased and 11,482 acres of forest area has been decreased between 1991 and 2020. This changing scenario of LULC has increased not only the stream flow but also the total nitrogen and phosphorus. The average annual total precipitation would increase about 4874 mm (RCP4.5) and 5357 (RCP8.5) mm in future thirty years compare to the last three decades (1991-2020). Moreover, the temperature will also increase at about 1.80C and 1.70C for RCP4.5 and RCP8.5 scenario respectively. This increasing precipitation and temperature lead to the increasing stream flow and total nitrogen and phosphorus of the watershed. But, the impact of climate variability on the streamflow and nitrogen and phosphorus would be more profound in RCP8.5 than RCP4.5. The results obtained in this study are able to provide guidance to water resource management and plan to policy makers and water managers in the Mobile County.