Evaluation of the GPM IMERG satellite-based precipitation products and the hydrological utility

Pre-occupation evaluation of latest generation satellite-based precipitation products (SPPs) is an essential step before the massive scale use. Taking the Beijiang River Basin as the case study, we used nine statistical evaluation indices and the Variable Infiltration Capacity (VIC) distributed hydrological model to quantitatively evaluate the performance and the hydrological utility of three Global Precipitation Measurement (GPM) Integrated Multi-satellitE Retrievals for GPM (IMERG) products: the near-real-time "Early" run and "Late" run IMERG products (IMERG-E and IMERG-L), and the post-real-time "Final" run IMERG product (IMERG-F) over south China during 2014-2015, with the last-generation Tropical Rainfall Measurement Mission (TRMM) Multi satellite Precipitation Analysis (TMPA) 3B42-V7 product as comparison. The IMERG-F presents satisfactory accuracy with high correlation coefficient (CC = 0.63) and low relative bias (0.92%), while the IMERG-E and IMERG-L performs relatively poorly featuring low correlation (with CC of 0.49 and 0.52 respectively) with the ground observations. All of the three IMERG products present apparently higher probability of detection (POD, 0.64-0.67) but have higher false alarm ratio (FAR,>= 0.14) than the 3B42-V7. The hydrological simulation under scenario I (model calibrated by the gauge observations) shows that, the IMERG-F, with a high Nash-Sutcliffe coefficient of efficiency (NSCE) of 0.742, presents better hydrological performance than the 3B42-V7; the IMERG-E and IMERG-L perform poorly for the whole simulation period with NSCE lower than 0.35 and relative bias higher than 28% while perform satisfactorily during the flood season with apparently higher NSCE of 0.750 and 0.733 respectively. The hydrological simulation under scenario II (model calibrated by the 3B42-V7) shows that the performance of all the IMERG products was significantly improved. Generally, the IMERG-F has high accuracy and good hydrological utility, while the IMERG-E and IMERG-L products have satisfactory hydrological utility during the flood season and thus have great potential for the real-time application such as flood forecasting. The late-run IMERG-L presents little improvement in performance comparing with the early-run IMERGE, therefore, the timelier IMERG-E is recommended to be firstly considered.