P3.2
Correction of global precipitation products for orographic effects
Jennifer C Adam, University of Washington, Seattle, WA; and D. P. Lettenmaier and E. F. Wood
Underestimation of precipitation in topographically complex regions is a problem with most gage-based gridded precipitation data sets. Gage locations tend to be in or near population centers, which usually lie at low elevations relative to the surrounding region. For example, past modeling studies have found that simulated mean annual Columbia River streamflows using gridded precipitation based on Global Precipitation Climatology Center (GPCC) precipitation products is about one-third of the observed discharge. In an attempt to develop a globally consistent correction for the underestimation of gridded precipitation in mountainous regions, we used a hydrologic water balance approach. The precipitation in orographically-influenced drainage basins was adjusted using a combination of water balance and variations of the Budyko ET/P vs. PET/P curve. The method is similar to other methods in which streamflow measurements are distributed back onto the watershed and a water balance is performed to determine "true" precipitation; but instead of relying on a modeled runoff ratio, evaporation is estimated using the ET/P vs. PET/P curves. This approach requires annual time-series of hundreds of historical discharge records world-wide which were obtained from the Global Runoff Data Center (GRDC) and the Global River Discharge Database (RivDIS v1.1). The correction ratios from each of the basins were interpolated and used to scale monthly precipitation from an existing monthly global data set (1979 through 1999, half-degree resolution), following application of adjustments for precipitation catch deficiencies. Comparisons are made to other data sets, including the Parameter-elevation Regressions on Independent Slopes Model (PRISM) precipitation products.
Poster Session 3, Hydrometeorology Posters (Including Orographic and Scale Issues) (Hall 4AB)
Thursday, 15 January 2004, 9:45 AM-11:00 AM, Hall 4AB
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