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Estimation of precipitation climatographies using atmospheric models

IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Author(s): Scott Swerdlin
Thomas Warner
National Center for Atmospheric Research Boulder, Colorado, USA

Keyword(s): precipitation, climatography, downscaling, water cycle, climatology

AbstractHigh horizontal-resolution estimates of precipitation characteristics in data-sparse regions are necessary for understanding the details of the hydrologic cycle and for formulating water- resources-management policy. Even though satellite data are sometimes available for providing information, model- based estimates are complementary and sometimes better. This paper describes a method for dynamically downscaling with atmospheric models to provide fine-scale, gridded estimates of precipitation for areas with poor conventional data coverage. The Penn State/National Center for Atmospheric Research community mesoscale model, MM5, has been adapted so that it can provide high-resolution depictions of the regional precipitation climate, as well as soil moisture and evaporation rate. The geographic focus area of the case to be reported on here is the eastern Mediterranean and the adjacent countries of the Middle East, where the Mediterranean Sea and some areas of the Middle East represent large voids in terms of conventional data. Even though satellite estimates of rainfall are themselves imperfect, they are used to infer that the model is reasonably replicating the small-scale aspects of the precipitation climate. For this test, the model has been run for six Januaries (2001-2006) using NCAR-NCEP Reanalysis Project archived global analyses for lateral- boundary conditions. Surface and upper-air observations are assimilated on the model grids to provide the best possible model climatography of the region. Based on the model, significant precipitation maxima are seen along the coastlines of the Levant, Turkey, and Greece. There is also considerable precipitation over the Mediterranean to the south of Greece. The precipitation gradient is very large along the North African coastline. The gradient is somewhat less along the Levant and Turkey coasts, but it is still large. Estimates from the Tropical Rainfall Measurements Mission satellite are consistent with the model estimates, showing the greatest amounts along the coasts of the Levant, Turkey and Greece, with large coastal gradients. But, there is less precipitation estimated by the model over the central and southern Mediterranean Sea. In summary, this modeling system enables the generation of high-resolution, 4-dimensional gridded analyses of the atmospheric and surface hydrologic cycle for use in water-resource analyses, flood potential, and physical-process studies. The study described here demonstrates the success of the modeling system, which can be re-applied for any area of the world.
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