CPC unified gauge-based analysis of global daily precipitation

A new project has been launched at NOAA Climate Prediction Center (CPC) to create a unified suite of precipitation analysis products with improved quantitative accuracy and inter-products consistency. The primary goal of this project is to collect and quality control information from all available sources, including in situ measurements and satellite estimates, and to integrate them into a consistent suite of precipitation products for a wide range of applications covering the research, operations, and services activities in the fields of atmospheric, oceanic, and hydrological sciences.

As a first step of this project, a gauge-based analysis of daily precipitation has been constructed over the global land areas. Gauge reports from over 30,000 stations are collected from multiple sources including GTS, COOP, and other national and international agencies. Quality control is performed through comparisons with historical records and independent information from measurements at nearby stations, concurrent radar / satellite observations, as well as numerical model forecasts. Quality controlled station reports are then interpolated to create analyzed fields of daily precipitation with consideration of orographic effects (Xie et al. 2007). The daily analysis is constructed on a 0.125olat/lon grid over the entire global land areas, and released on a 0.5olat/lon grid over the global domain for a period from 1979, and on its original resolution over CONUS for a period from 1948 to the present.

Quality of the new CPC unified daily gauge analysis is examined through comparisons with existing CPC products and with other similar gauge-based analyses. The results showed improved quality of our analysis in representing the spatial distribution patterns and temporal changes of precipitation. Uncertainties, however, exist in the analysis, especially in reproducing the long-term homogeneity of precipitation over regions with changing station networks and substantial spatial variability in precipitation (e.g. western US mountainous regions). A detailed analysis of the problems will be reported at the meeting. Discussions with our potential users in the hydrology community are expected for the further improvements of this product.