Evaluating Factors that Control Diffuse and Irrigation Recharge in Thick Vadose Zones Under Climate Variability and Change

Understanding the potential effects of climate variability and change on groundwater recharge is crucial for the development and implementation of groundwater sustainability management plans. This project aims to understand the factors that control diffuse and irrigation recharge through a thick vadose zone under rangeland, irrigated, and non-irrigated corn crop land cover in response to climate change and variability. Six research sites of varying land use and land cover (LULC) located in Nebraska's Central Platte Natural Resources District (CPNRD) overlying the northern High Plains aquifer are modeled using Hydrus-1D numerical modelling software to simulate flux in the vadose zone. Soil profile information for the six vadose zone sites was gathered and provided by the U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS) and United States Geological Survey (USGS) and range from 14 to 40 m thick. Nine Global Climate Models (GCMs), each with relative concentration pathway (RCP) scenarios of 4.5 and 8.5, give projection estimates of air temperature and precipitation for the years 1950 to 2100 and are used as inputs in each Hydrus-1D model to create outputs of recharge rate and total potential profile timeseries. Estimates of total potential profiles in the vadose zone indicate the direction of flow, upward or downward flux, in response to LULC and GCM climate inputs, which can affect the rate of recharge into the underlying aquifer. Particular attention is given to periods of recent drought to understand the aquifer's resilience to such events in the future. Analysis of recharge rates and total potential profiles of these sites during the 150-year time period will be presented to give an understanding of vadose zone recharge mechanism, diffuse and irrigation recharge, responses to potential climate variability and change, which can be valuable for quantifying the recharge component of water budgets for groundwater sustainability and management plans in similar semi-arid agricultural areas.