Evaluation of precipitation from the ERA-40, NCEP-1, and NCEP-2 reanalyses and CMAP-1, CMAP-2, and GPCP-2 with ground-based measurements in China

Abstract

[1] We assess the correspondence between precipitation products from atmospheric reanalyses (ERA-40, NCEP-1, and NCEP-2), the Climate Prediction Center (CPC) Merged Analyses of Precipitation (CMAP-1 and CMAP-2), and the Global Precipitation Climatology Project Version 2 (GPCP-2) with adjusted observational precipitation (AOP) from China for 1979-2001 and also for ERA-40 and NCEP-1 over 1958-1978. In general, we conclude that CMAP-1 and GPCP-2 agree more closely with AOP than the reanalysis products do, although ERA-40 data agree more closely with AOP than NCEP data. The percentages of precipitation differences (PPDs) across China between annual ERA-40, NCEP-1, NCEP-2, CMAP-1, CMAP-2, and GPCP-2 data and AOP are -12, 22, 14, - 8, - 7, and - 15%, respectively, for 1979-2001. Although relatively small biases are evident for China as a whole, maximum PPDs, usually occurring around the Qinghai-Tibetan Plateau, can exceed 1000%, indicating a strong terrain dependence of gridded precipitation data. GPCP-2, although characterized by greater underestimation for most of China compared with CMAP-1, exhibits a smaller biases range and hence may be better than CMAP-1. Compared with the NCEP-1 system, NCEP-2 represents an improvement as NCEP-2 precipitation agrees more closely with AOP than NCEP-1 data. However, the coherence of NCEP-2 precipitation needs further improvement. In addition, we find worse consistency and accuracy and larger positive biases in some parts of China for CMAP-2 versus CMAP-1, illustrating an advantage of including reanalysis data in CMAP, as CMAP-1 does. CMAP-1 could be further improved if they used the more skillful ERA-40 precipitation instead of the NCEP/NCAR data. Copyright 2009 by the American Geophysical Union.