18 February, 2021
Accurate precipitation measurement has always been a major challenge in Nepal because of its nature of the topography. The existing surface precipitation measurement network is sparse, and detailed information on precipitation characteristics is lacking. With the development of remote sensing technology, Satellite Based Rainfall Estimates products have been a potential alternative to surface measurement. Since the lunch of TRMM, many such products are available at various spatial and temporal resolutions. Multiple studies have been conducted to evaluate such products around the globe including Nepal.
A recent collaborative study conducted by CDHM faculties and alumni in collaboration with researchers from DHM, ICIMOD and WFP has indicated the potential of SRE’s on extreme precipitation events study over Nepal. Two recent satellite rainfall estimates (SREs) from Global Precipitation Measurement (GPM)-era—Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG-V06) and gauge calibrated Global Satellite Mapping of Precipitation (GSMaP-V07) were evaluated for their spatiotemporal accuracy and ability to capture extreme precipitation events using 279-gauge stations from southern slope of central Himalaya, Nepal, between 2014 and 2019.
Study suggested that both SREs can capture the spatiotemporal precipitation variability, although both underestimated the observed precipitation amount. Among the two products, the IMERG product shows a more consistent performance with a higher correlation coefficient (0.52) and smaller bias (−2.49 mm/day) than the GSMaP product. The monthly gauge-calibrated IMERG product yields better detection capability (higher probability of detection (POD) values) of daily precipitation events than the daily gauge calibrated GSMaP product; however, they both show similar performance in terms of false alarm ratio (FAR) and critical success index (CSI).
Assessment based on extreme precipitation indices revealed that the IMERG product outperforms GSMaP in capturing daily precipitation extremes (RX1Day and RX5Day). In contrast, the GSMaP product tends to be more consistent in capturing the duration and threshold-based precipitation extremes (consecutive dry days (CDD), consecutive wet days (CWD), number of heavy precipitation days (R10mm), and number of extreme precipitation days (R25mm)). Study suggested that the IMERG product can be a good alternative for monitoring daily extremes; meanwhile, GSMaP could be a better option for duration-based extremes in the mountainous region.
Link: https://www.mdpi.com/2073-4433/12/2/254