HR: 0800h
AN: H31D-0447    [Abstracts]
TI: Sensitivity of Groundwater Recharge to Variations of Climate, Soils, and Vegetation Based on Unsaturated-Flow Modeling
AU: * Keese, K E
EM: keese@mail.utexas.edu
AF: Jackson School of Geosciences, Dept. of Geol. Sciences, Univ. of Texas at Austin, C1140, Austin, TX 78712
AU: Scanlon, B R
EM: bridget.scanlon@beg.utexas.edu
AF: Jackson School of Geosciences, Bur. of Econ. Geol, Univ. of Texas at Austin, 10100 Burnet Rd, Austin, TX 78758
AU: Reedy, R C
EM: bob.reedy@beg.utexas.edu
AF: Jackson School of Geosciences, Bur. of Econ. Geol, Univ. of Texas at Austin, 10100 Burnet Rd, Austin, TX 78758
AB: Understanding the relative importance of climate, vegetation, and soils in controlling groundwater recharge is important for estimating effects of climate variability and land use/land cover change on recharge/water resources. The purpose of this study was to evaluate the sensitivity of groundwater recharge to variations in climate, soil type, and vegetation type using unsaturated-flow modeling and to further assess the sensitivity of the model to variations in parameterization and design. More detailed sensitivity analyses were conducted at representative sites to evaluate the impact of vegetation parameters (percent bare area, leaf area index, and root depth), and other parameters on simulated recharge by generally increasing and decreasing parameters by 50%. One dimensional unsaturated flow models were developed for 13 sites (county areas) that represented a range of climate (arid - humid), vegetation (shrub, grass, forest, crops), and soil (fine to coarse grained, monolithic and layered) conditions based on readily available online data from Texas, US. Spatially and temporally averaged recharge rates are more appropriate for water resources management than point estimates at a single time; therefore, simulated long-term (1961 - 1990) average recharge for each combination of vegetation type and soil profile layering was regionalized to the site area (county) for this analysis using Geographic Information Systems (GIS). Simulated 30 yr average recharge rates for nonvegetated monolithic sand profiles ranged from 54 mm/yr in arid regions to 720 mm/yr in humid regions, correlating positively with precipitation (r=0.99). Adding vegetation to the monolithic sand profiles had a similar effect on recharge as soil profile layering; both reduced recharge relative to that in monolithic sand profiles by factors ranging from 2 to 10. Vegetation and soil-profile layering both resulted in high local variability in recharge within each site (county); however, spatially-weighted long-term average recharge rates were much less variable and were positively correlated with precipitation (r=0.79 to 0.96). The most realistic simulations included vegetation and layered soil profiles, which resulted in a range of recharge rates from 0 to 114 mm/yr and correlated with precipitation (r=0.95). Including bare area up to 50% greatly increased recharge. Decreasing LAI and root depth also had great impacts on recharge. Simulated recharge was more sensitive to PET rates in the humid setting relative to the arid setting. These detailed sensitivity analysis provide more in depth understanding of specific controls on recharge. The general analysis indicates that strong relationships between climate, vegetation and simulated recharge should be useful in assessing potential impacts of climate variability and land use change on recharge.
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting