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
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We assess the correspondence between precipitation products from atmospheric reanalyses (ERA40, NCEP1, and NCEP2), the Climate Prediction Center (CPC) Merged Analyses of Precipitation (CMAP1 and CMAP2), and the Global Precipitation Climatology Project Version 2 (GPCP2) with adjusted observational precipitation (AOP) from China for 19792001 and also for ERA40 and NCEP1 over 19581978. In general, we conclude that CMAP1 and GPCP2 agree more closely with AOP than the reanalysis products do, although ERA40 data agree more closely with AOP than NCEP data. The percentages of precipitation differences (PPDs) across China between annual ERA40, NCEP1, NCEP2, CMAP1, CMAP2, and GPCP2 data and AOP are 12, 22, 14, 8, 7, and 15%, respectively, for 19792001. Although relatively small biases are evident for China as a whole, maximum PPDs, usually occurring around the QinghaiTibetan Plateau, can exceed 1000%, indicating a strong terrain dependence of gridded precipitation data. GPCP2, although characterized by greater underestimation for most of China compared with CMAP1, exhibits a smaller biases range and hence may be better than CMAP1. Compared with the NCEP1 system, NCEP2 represents an improvement as NCEP2 precipitation agrees more closely with AOP than NCEP1 data. However, the coherence of NCEP2 precipitation needs further improvement. In addition, we find worse consistency and accuracy and larger positive biases in some parts of China for CMAP2 versus CMAP1, illustrating an advantage of including reanalysis data in CMAP, as CMAP1 does. CMAP1 could be further improved if they used the more skillful ERA40 precipitation instead of the NCEP/NCAR data.
