A SEMIARID LONG-TERM HYDROLOGIC OBSERVATORY AT THE CONTINENTAL SCALE: THE UPPER RÍO GRANDE BASIN

Water availability is critical in arid and semiarid regions, which comprise 35% of the land area of the globe. In the Southwestern US, climate variability and landscape heterogeneity lead to strong gradients in hydrological processes, which in turn impact land-atmosphere interactions, ecological dynamics, biogeochemical cycles and geomorphic change. This complexity presents a fundamental challenge to our understanding of hydrogeology, one that is best addressed through long-term, systematic field and remote-sensing observations and numerical-model investigations. In this talk, we will present our plans to study the interaction of climate-landscape-vegetation and water using a nested set of instrumented sites within the Upper Río Grande, a continental-scale semiarid watershed. This complex watershed extends from the snow-dominated headwater basins in San Juan Mountains of southern Colorado, through the Chihuahuan Desert in New Mexico, Texas and Mexico, to the desert valley alluvial basins southeast of El Paso, Texas. As part of the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI) plan for a network of Long-Term Hydrologic Observatories (LTHOs), the Upper Río Grande would represent the combination of mountain landscapes, semiarid to arid alluvial basin aquifers and riparian corridors that are characteristic of the Western United States. We will describe existing hydrologic, ecologic and atmospheric measurement infrastructure in the watershed and discuss plans for integrating these into a coherent network that provides a core set of scientific data products for the hydrogeologic community. Data products generated by the Upper Río Grande LTHO will also aid in the testing of coupled numerical models of the atmosphere-surface-groundwater system applied at high resolution over the region. The Upper Río Grande presents a unique opportunity to test many hydrogeologic hypothesis concerning how hydrological processes, such as surface-groundwater interactions, runoff response, solute transport and reactivity, and ecological function, scale with variations in climate and landscape gradients.