Comprehensive validation of the latest IMERG V06 precipitation estimates over a basin coupled with coastal locations, tropical climate and hill-karst combined landform

The version 6 (V06) of Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) provides three products and their Satellite Estimates (SE) has three different temporal resolution. As the study area, the Nanliujiang River Basin (NRB) located in the coastal tropics of southern China has a hill-karst combined landform. Based on the Ground Observations (GO) from 14 gauges of NRB, the SE of three IMERG products with the highest resolution of 0.5 h are evaluated under 12 days. Then, by selecting daily SE, IMERG V06 is compared with its previous version (i.e., V05) from December 2016 to November 2017 while monthly SE of IMERG V06 are compared with that of TMPA 3B43 from 2008 to 2014. Besides the ordinary evaluation of the detection capability, correlation and error, a metric called Comprehensive Performance Index (CPI) is introduced to show the overall performance of the products. The main results of the comprehensive validation are that (1) IMERG keeps higher detection capability under low precipitation thresholds at the basin- or grid-scale. The diurnal variation of three 0.5 h products' rainfall detection becomes obvious with threshold increasing. The advantage of IMERG V06 products over V05 in rainfall detection is small. (2) IMERG Final Run (IMERG-F) half-hourly product of V06 shows a high correlation with GO than the two near-real-time products at the partial gauges and dates. IMERG V06 outperforms than V05 or TMPA 3B43 on correlation at the basin-scale and partial gauges. (3) Main form of the biases presented in the validation of three IMERG products at 0.5 h resolution and the comparison of IMERG V06 to other daily or monthly satellite products are reflected as rainfall overestimation and underestimation, respectively. Compared with V05 and 3B43, biases in the relatively cold and dry season are significantly improved by V06. (4) IMERG cannot reflect the spatial distribution of average precipitation with high values. The performance of SE changing between different gauges, which is shown as the spatial variability. (5) The number of gauges where IMERG-F of V06 has higher (or the highest) CPI values is the largest among each product combination of validation.

Automated summary

The study evaluated different versions of the Global Precipitation Measurement (IMERG) products using various performance metrics. It found that IMERG V06 has advantages in rainfall detection, but still needs improvement in rainfall overestimation and underestimation.