Evaluation of IMERG Over CONUS Complex Terrain Using Environmental Variables

Abstract

Satellite-based precipitation products (SPPs) provide extensive spatial and temporal coverage globally but are challenged in complex terrain. This study aims at understanding uncertainties of SPP estimation due to topographically induced rainfall. Environmental and physical parameters, that is, orographically forced upward motion and horizontal moisture flux convergence, are considered to condition precipitation mechanisms for a detailed uncertainty analysis. The Global Precipitation Measurement (GPM) precipitation product Integrated Multi-Satellite Retrievals for GPM (IMERG) is compared at its native resolution against a high quality and accurate radar and rain gauge precipitation reference Ground Validation Multi-Radar Multi-Sensor (GV-MRMS). Conditional analysis of IMERG using environmental parameters is conducted over mountainous terrain. The highest GV-MRMS mean rainfall rate is found to be associated with positive high Q and moderate w values, confirming that vigorous moisture flux convergence is a strong condition for heavy rainfall. IMERG shows over- and underestimation for positive w and Q when GV-MRMS rainfall magnitudes between 0.8 and 13 mm h−1.