A long-term trend observed in TRMM/PR monthly rainfall products and an evaluation of sampling error by a bootstrap method

This study examines the trend in the 7-year monthly rainfall amounts (September 2001-August 2008) observed by the TRMM Precipitation Radar (PR). It is shown that the monthly rainfall amounts averaged in the range of 35°S to 35°N (PR observation range) tend to increase slightly over this period. This tendency can be considered to be affected by sampling errors due to the narrow observation swaths of the PR, in addition to natural variations. Therefore, this study developed the method of evaluating the sampling errors by a bootstrap method using the actual data observed by the PR. We examined the trend in the averaged rainfall amounts during 7 years considering the simulated sampling errors. As a result, the positive trend was significantly detected, even when sampling error was removed. From this, it can be concluded that this positive trend is highly likely to be due to natural variations.