Effects of Climate Extremes on the Groundwater Recharge of the Ogallala Aquifer, USA 1950-1999

Abstract:

Climate extremes have and will continue to cause significant variations of local and regional groundwater hydrology. It is important to understand the effects of climate extremes on groundwater recharge to properly manage water resources. Using the Soil Water Balance Model (SWB) and Maurer’s 1/8-degree daily climatology datasets, this study investigates the dynamics of groundwater recharge of the Ogallala Aquifer in the second half of the 20th century relative to trends of two temperature and six precipitation extreme indices, including consecutive dry days (CDD), consecutive wet days (CWD), heavy precipitation days (ND95), annual total precipitation from heavy precipitation events (TP95), annual total precipitation from wet days (PRCPTOT), annual maximum 5-day precipitation (RX5), annual hot days (TX90) and annual hot nights (TN90). The results show that the highest recharge was about 110 mm yr^-1 in eastern Nebraska, followed by central Nebraska and western Kansas, with recharge values of 45 mm yr^-1. The range of recharge for the rest of the aquifer area was 0-20 mm yr^-1. Temporally, the overall groundwater recharge significantly (p<0.05) increased throughout the Ogallala Aquifer. Spatially, groundwater recharge significantly increased in central Nebraska, eastern Wyoming and parts of northern Texas, while it decreased from southwestern Nebraska to the northern boundary of Texas. The study area experienced enhanced temperature and precipitation extremes over the 50 year period. The changing trends of hot temperatures were not spatially uniform: increasing hot days occurred in the northwestern Ogallala, parts of the central Ogallala, and the entire southern Ogallala; while decreasing hot nights occurred in the northeastern, central, and southern Ogallala. Increases in trends of precipitation extremes were more spatially uniform. Based on spatial non-parameter correlation analysis, increasing precipitation extremes may decrease groundwater recharge in regions with less annual total precipitation, but may increase groundwater recharge in regions with sufficient precipitation. Therefore, policy-makers need to be aware of the temporal and spatial heterogeneity of extreme precipitation events, especially in arid regions.