La Plata is the second largest river in South America and its tributaries are the life blood of the southern part of the continent. La Plata has an annual-mean discharge at its mouth near Buenos Aires larger than that of the Mississippi. The installed hydropower generating capacity (mostly in the Parana, a major subbasin) exceeds 20,000 MW, almost double that of the Columbia River basin, which by far has the largest hydropower production among U.S. rivers. On the other hand, the region is vulnerable to large scale floods with losses of life and damages to property. Precipitation and other land surface water cycle variables have undergone very large decadal scale changes over the last century in much of the southern part of South America, and within La Plata Basin in particular. In the last thirty years, precipitation increased up to 30-40% over the central La Plata basin, and important scientific questions have emerged: what are the reasons for these changes, and how are variations in precipitation linked to streamflow changes? Up to now, no certain evidence has been offered to explain the reasons for such changes. A team of North and South American hydrologists and atmospheric scientists has been assembled to address this crucial and unique aspect of the basin's regional water cycle. The overarching scientific question to be addressed by this research is: "What is the importance of local effects in the observed interannual-to-decadal scale changes in La Plata Basin precipitation and streamflow?" Specifically, it will be sought to: (a) Assess the degree to which regional climate simulations capture the precipitation changes in the 1970's over La Plata Basin; (b) Estimate the effects of local forcings (e.g., soil moisture, vegetation) on the precipitation and surface hydrology of La Plata Basin; (c) Identify the role of local effects and large scale precipitation variability in the basin. The research strategy outlined in this proposal is based on diagnosis analysis and numerical experiments with the atmospheric regional mesoscale Eta model and the VIC hydrologic model, in coupled and uncoupled mode. The Eta model, coupled with VIC and a river routing scheme, will be employed to describe the pathways from remote and/or local forcings to the changes in river discharge. Experiments are designed to understand the impacts of land use changes on the longer term climate and the feedbacks between land use/land cover and precipitation and river discharge. Experiments will also focus on the mechanisms by which large scale variability affects the regional precipitation. The relevance of this research is not only due to the yet unanswered scientific questions it will address, but also because it is a defined application for water resources of a region of the developing world. The approach aims at having the atmospheric and hydrologic problems treated in a consistent manner. The proposal has a strong educational component. Students will be directly involved in the research; scientists from Universities of South America will participate adding regional expertise but also enhancing the educational component. Plans are in place for exchanges with students of South America, and one or two related courses at the University of Buenos Aires are planned (at no cost to this project). This proposal takes advantage of available infrastructure both at the University of Maryland and the University of Washington. Computer systems are already in place and needed upgrades will be ready by the time this project starts.
