The Lancang river basin is a typical area of lacking data with complicated terrain and climate characteristics. It is located in the upper reaches of Mekong river basin. There is great potential to carry out hydrological prediction in ungauged basins by using satellite estimate precipitation data. As a precipitation radar satellite, TRMM has been collecting plentiful fine temporal-spatial precipitation data, so it is significant to use the TRMM precipitation data to study hydrological and climatic characteristics in the Lancang river basin. However, it is necessary to check the accuracy of TRMM data before using it. Based on the correlation coefficients and scatter points slope methods, the accuracy of TRMM 3B43 data at monthly time scale during 1998-2009 was validated by using the 35 rain gauges data, which were distributed in the Lancang river basin and its surrounding areas. Then the influence of slope and elevation on the checking result based on Thiessen polygons and K-Means cluster methods was analyzed. Finally, principal component analysis was used to compare the differences of elevation and slope on the accuracy of TRMM 3B43. The results are obtained as follows. (1) Compared with the 35 rain gauges, TRMM 3B43 data displayed good accuracy in the whole study area at monthly time scale. (2) There were significant differences of accuracy among the 35 sites; the TRMM 3B43 data had good accuracy in the upstream and downstream of the research areas, while the middle area was poor, especially Bomi, Gongshan, Deqin and Shangrila. (3) Compared with slope, the influence of elevation on the accuracy of TRMM 3B43 was more complicated, and the accuracy showed that there was a high-low-high variation when the elevation decreased from upstream to downstream, which may be caused by strong spatial heterogeneity of precipitation in this area. (4) The slope of research area had great influence on the accuracy of TRMM 3B43 data, which decreased as the increase of slope, the middle research area has the maximum slope so the accuracy was the worst, while the upstream and downstream had relatively high accuracy due to flat terrain.
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