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Impacts of Eastern Redcedar Encroachment on Water Resources in the Nebraska Sandhills under Different Climatic Scenarios

Yaser Kishawi, University of Nebraska - Lincoln


Worldwide, shrub-dominated woodlands have been encroaching grasslands. Few studies have evaluated Eastern Redcedar encroachment on water quantity and none evaluated water quality impacts. This study evaluated both the encroachment of redcedar and projected climate change on water resources in the Upper Middle Loup River (UMLR) watershed in the Nebraska Sand Hills (NSH) using the Soil and Water Assessment Tool (SWAT). Additionally, we are evaluating coupled SWAT-MODFLOW impacts on hydrological parameters compared to SWAT alone.In Chapter 2, redcedar encroachment impacts on water quantity in NSH and water quality in the Platte River was evaluated. A calibrated SWAT was applied to evaluate impacts of 0% to 100% encroachment scenarios. With increased encroachment, discharge in the UMLR was reduced by 45.5% at full encroachment, while percolation and deep aquifer recharge increased, where nitrate and atrazine increased to 33% and 48.1% respectively due to discharge reduction.In Chapter 3, 222 climate models were ranked using the aridity index. At 5th, 50th and 95th percentiles, wet, median, and dry conditions were identified. The SWAT model was used to simulate the three identified climate-change models, with predicted CO2 concentrations and redcedar encroachment (presented in terms of percentage of land area with redcedar cover). The combined encroachment-climate-change resulted in significant discharge reduction. The discharge was reduced from a historical average of 12.9m3s-1 to 5m3s-1 for 11.6% and 2.5m3s-1 for 72% encroachment scenarios combined with the dry and wet scenarios compared to 11.5m3s-1 and 6.5m3s-1 under 11.6% and 72% without climate scenarios.In Chapter 4, SWAT-MOFLOW was calibrated and validated using discharge at outlet, 1995-water-level map, and 17 monitoring wells. Comparing simulated and measured water head R2 was 0.99, and water depth residual error was -0.91m. The estimated recharge ranged from 0.27mm yr-1 to 24.6mmyr-1. Climate scenarios showed that discharge was reduced to 12.03, 12.83, and 13.29m3s-1 for dry, wet, and median respectively. Under three climate scenarios from 2020-2035, lakes depths are predicted to decline overall, except for high precipitation years.

Subject Area

Water Resources Management|Climate Change

Recommended Citation

Kishawi, Yaser, "Impacts of Eastern Redcedar Encroachment on Water Resources in the Nebraska Sandhills under Different Climatic Scenarios" (2022). ETD collection for University of Nebraska-Lincoln. AAI29167443.