5.
Title: On the Causes of Recent Trends in
Precipitation over La Plata Basin and Their Impact on the Basin's
Hydrology
PI, CoPI: Ernesto H. Berbery, Dennis L. Lettenmaier
Period: 1-Jun-2005 to 31-May-2009
Total budget: USD 192,004
Funding Agency: NSF
Summary:
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. However, it is
generally believed that they may be the result of (a) changes in the
large scale circulation (e.g., more frequent/stronger El Niños)
and (b) local changes in land use and land cover mostly due to
deforestation and agricultural practices, or (c) a combination of
both.
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 relative importance of local effects and remote impacts as
related to observed interannual-to-decadal scale changes in La Plata
Basin precipitation and streamflow?”
Specifically, it will be sought to: a) Determine the modes of interannual variability of precipitation within La Plata basin and adjacent land areas;
b) Assess the degree to which regional climate simulations capture the precipitation changes in the 1970’s over La Plata Basin;
c) Estimate the effects of local
forcings (e.g., soil moisture, vegetation) on the precipitation and
surface hydrology of La Plata Basin; and
d) Identify links between remote
climate variability and interannual-to-decadal scale precipitation
variability in the basin, and the relative role of local effects.
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 remote effects affect 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.