Operational 24-hour accumulated rainfall dataset over Indian region by merging rain gauge and multi-satellite estimate from 'Global Precipitation Measurement' mission

A hierarchy of numerical global/regional models is being run operationally in India for weather forecasting at short-to-medium range, sub-seasonal, and seasonal scales. Many researchers also use these models for development purposes. These numerical model outputs need proper verification with high-resolution observed rainfall data. The observed gridded rainfall data are also required for process studies along with the use of global and regional numerical models. A high-resolution multi-satellite rainfall product became available after the launch of the Global Precipitation Measurement (GPM) satellite in 2014. This led to the development of a realistic 24-hour accumulated gridded higher resolution merged rainfall data for the Indian region on an operational basis by merging it with available rain gauge observations from the India Meteorological Department (IMD). This merged rainfall dataset is freely available from IMD, Pune website on a near real-time basis since 1st October 2015. The procedures for the development of this operational daily gridded rainfall dataset jointly by the National Centre for Medium Range Weather Forecasting (NCMRWF) and IMD at 0.25 degrees spatial resolution are presented in this study. The new GPM-based merged rainfall dataset has also been compared with the Tropical Rainfall Measuring Mission (TRMM) satellite-based merged rainfall product available at 0.5 degrees latitude/longitude grid for July 2014. The new rainfall data represents finer spatial features of the southwest monsoon rainfall more realistically as compared to the TRMM-based merged rainfall. The error in the new rainfall product has reduced at all-India and sub-regional scales after merging it with rain gauge observations. Improvement in categorical skills has also been found in the new rainfall data after merging rain gauge observations. This merged satellite-gauge rainfall dataset considers updated versions of the GPM-based near real-time rainfall product when newer versions get released, along with a higher number of rain gauges available from IMD. This new rainfall data at 0.25 degrees spatial resolution for the Indian region will continue to be useful for rainfall diagnostics in higher-resolution numerical models at scales from days-to-season and for hydro-meteorological applications.