POTENTIAL ADVANCES IN QUANTIFYING THE WATER CYCLE IN KARST SYSTEMS USING HYDROLOGIC OBSERVATORY APPROACH

Karst systems supply about 40% of the groundwater for drinking in the US and about 25% globally. Developing sustainable water resources for human and ecosystem needs is extremely difficult because of the dynamic nature of karst systems and their rapid response to climate variability and land use change. Karst systems are ideal settings for evaluating land atmosphere interactions because of tight coupling between atmospheric forcing and surface and subsurface hydrology. Our understanding of fluxes of water and related nutrients in these systems would greatly benefit from multiscaled, intensive monitoring programs proposed for hydrologic observatories. The Edwards Aquifer in central Texas is used as an example to show how a detailed monitoring program would further our predictive understanding of these systems. Improved precipitation monitoring at high spatial and temporal resolution would be used to ground reference NEXRAD data to more accurately quantify precipitation input to the system. Precipitation monitoring, combined with detailed Lidar topographic mapping and improved runoff modeling would provide better predictions of flooding in these regions with longer lead times. This region is particularly susceptible to flooding and has suffered large numbers of fatalities (e.g. 39 in 1998) and property damage related to flooding. Quantifying surface runoff in these regions would also benefit groundwater recharge estimation because 85% of the recharge in this region is derived from surface water. These karst systems directly link surface water and groundwater. Recharge is critical because these systems are extremely vulnerable to droughts and maintaining spring flow is essential for endangered species. Increased monitoring of evapotranspiration (ET) using micrometeorologic approaches and relating ET to land use would allow evaluation of potential impacts of land use change on the water cycle. An improved ET monitoring network would also provide ground referencing of satellite based estimates of ET. The proposed integrated, multidisciplinary approach to quantifying various components of the water cycle would provide valuable information to optimize management of water resources in these systems to meet human and ecosystem needs.