Uncertainty of monthly rainfall estimates from rain gauges in the Global Precipitation Climatology Project

The Global Precipitation Climatology Project (GPCP), initiated by the World Climate Research Program, has as a main objective the production of monthly global rainfall estimates on a 2.5 degrees x 2.5 degrees longitude/latitude grid by combining different sources of information such as satellite remote sensing and rain gauges. It:is important to understand the accuracy of the rain gauge estimates of mean area rainfall because these are considered the most reliable estimates for regions with high numbers of gauges. Methods to model the error resulting from using rain gauge data to estimate the spatially averaged rainfall accumulation have been developed previously. Three of these methods are investigated in this study: an empirical equation derived from rain gauge data, an analytical equation derived from statistical concepts, and an empirical equation derived from theory with parameters determined from calibration. Simulations are performed to determine the utility of these three approaches in estimating the error of the rain gauge mean in the context of the GPCP.