Global intercomparison and regional evaluation of GPM IMERG Version-03, Version-04 and its latest Version-05 precipitation products: Similarity, difference and improvements

The overarching goal of this study is to intercompare the newly released Integrated Multi-satellitE Retrievals for GPM (IMERG) Version 05 (V05) products with its former Version 04 (V04) and Version 03 (V03) products and also assess any differences and improvements, with cross-evaluation against the Global Precipitation Climatology Project (GPCP) Version 2.3, Multi-Source Weighted-Ensemble Precipitation (MSWEP) Version 2.1 and the dense gauge networks in China. Firstly, the gauge-adjusted products (Final run) of V03, V04 and V05 are compared over the globe. Then, the near-real-time products without gauge adjustments (Early and Late run) and Final run products of all versions are evaluated against ground-based observations comprised of more than 30,000 gauges over Mainland China at 0.1° × 0.1° grid and hourly and daily temporal scales. The primary conclusions are: (1) globally, both V04 and V05 Final run show significant differences and improvements from V03. Particularly, the overall mean oceanic precipitation of V04 and V05 increases by +31.36% and +28.81% respectively from that of V03 and much closer to GPCP and MSWEP; (2) over Mainland China, the Early and Late run products of the same version (V03 or V04) generally have similar performance, while V04 Early and Late run have better performance in most regions than the corresponding run of V03 except in the arid Xinjiang Province and the mountainous Tibetan Plateau; and (3) V04 and V03 Final run show comparable performance, while V05 Final run generally improves upon both V04 and V03 and has the best performance among the seven standard IMERG products. The improvement of V05 Final run is particularly evident in southeastern and western China. At a timely matter, the study provides first-hand global and regional assessment feedback to IMERG algorithm developers and also sheds insights for GPM precipitation product users across the world.