Guiding the Improvement of the Global Precipitation Measurement Mission (GPM) with Radar Networks over France and USA Mountainous Regions

Orographic precipitation is a critical driver of Earth’s water budget at various time scales. At longer time scales, it affects the amount and distribution of snowpack, which impacts freshwater supply and water security; at shorter time scales it generates floods, landslides, and avalanches. These mechanisms shape local climates, ecosystems, and societies. A better understanding of the distribution of orographic precipitation is a critical topic for fundamental research. Yet the spatial and temporal variability of rainfall in complex terrain remains challenging to capture from ground-based observations. This promotes integrated satellite-based precipitation products (SPPs) with quasi-global coverage. The Integrated Multi-Satellite Retrievals for GPM (IMERG) algorithm intercalibrates, merges and interpolates all available PMW retrievals, microwave-calibrated IR satellite estimates, and rain gauges. Yet, multiple uncertainties are associated with Level-2 PMW, and IR precipitation retrievals and Level-3 merged SPPs. Despite extensive IMERG validation over many areas around the globe, precipitation estimation over mountainous regions remains a challenge and validation is uncommon. There is a need to document the performance and error characteristics of the retrievals and how they relate to orographic processes. Therefore, precipitation mechanisms that are driven by environmental and physical parameters are considered for a detailed uncertainty analysis.

This study promotes the use of global radar-gauge references to evaluate satellite precipitation products over diverse climatologies. GPM-era IMERGV07 and its components (PMW, IR and morph) are evaluated over USA and France mountainous areas. Over the USA, the Ground Validation Multi-Radar Multi-Sensor (GV-MRMS) radar-based Quantitative Precipitation Estimation (QPE) is used as a reference at 0.1deg and half hourly spatiotemporal resolution. Over France, the similar Ground Validation PANTHERE (GV-PANTHERE) rain gauge corrected radar-based QPE is used as a reference at the same resolution. It aims to understand the uncertainties of IMERG due to topographically induced rainfall processes.