Hydrologic Evaluation of Integrated Multi-Satellite Retrievals for GPM over Nanliu River Basin in Tropical Humid Southern China

Version 5B Integrated Multi-satellite Retrievals for GPM (IMERG) products were evaluated with rain gauge observations as reference over the Nanliu River basin in Southern China since March 2014 to December 2016 through the Xinanjiang hydrologic model. The IMERG products include the early run satellite-only IMERG product (IMERGERUncal), final run satellite-only and gauge-corrected IMERG products (IMERGFRUncal and IMERGFRCal, respectively). Direct comparison with the gauge observations indicates that both early run and final run IMERG products have good performances in capturing the precipitation at spatial and temporal characteristics. IMERGFRUncal and IMERGERUncal show compatible capabilities to detect rainfall in a daily scale with highly correlative coefficient (CC) about 0.67, relative bias (RB) about -20.79%, and root mean square error (RMSE) about 10.68 mm. IMERGFRCal performed a little better than IMERGFRUncal and IMERGERUncal with higher CC (0.7) and lower magnitude of RB (4.90%). Simulated stream flows with daily IMERG products as forcing data show a large deviation from the observed stream flows with low Nash-Sutcliffe index (NSCE) < 0.3, indicating that all of these IMERG products have limited potentials of hydrological utilization in this basin. Particularly, IMERGFRCal shows relatively poor NSCE (0.28) and underestimates the stream flow by 7.83%. IMERGFRUncal and IMERGERUncal exhibit better performance than IMERGFRCal in the hydrological simulation with higher NSCE (0.30 and 0.29, respectively) and larger deviations with RBs about -56.73% and -59.49%, respectively. This result manifests that the IMERG products users need to be cautious when using IMERG products for hydrological applications in this basin. Additionally, this study is expected to offer insights into IMERG' potentials in the hydrological utility and thus provide useful feedbacks to the IMERG algorithm developers and the users.