A comprehensive assessment of satellite precipitation products over a semi-arid region: focus on extreme events

Global warming has increased the frequency and intensity of extreme weather events worldwide. Arid and semi-arid regions, such as the Tensift basin in Morocco, have experienced severe water shortages as a result. The unavailability of quality data limits our understanding of the occurrence of extreme events and their associated impacts. This study assesses the accuracy of eight satellite, reanalysis, and merged precipitation products (SRMP): PERSIANN, PERSIANN CDR, IMERG, ARC2, RFE2, CHIRPS, ERA5, and MSWEP, in estimating extreme precipitation in the Tensift basin. The datasets were assessed against observed data from fourteen weather stations for the period 2001-2016 at daily, monthly, seasonal, and annual time scales. Volumetric and categorical metrics were used for analysis, along with evaluation of extreme precipitation indices (EPI) and drought characterization. The ability of SRMP to characterize meteorological drought using Standardized Precipitation Index (SPI) was also examined. A complementary analysis is carried out by comparing all the SRMPs to reproduce the precipitation of November 2014 event. Cumulative Distribution Function (CDF) mapping bias correction method was employed to enhance the performance of the SRMP, with particular focus on improving the extreme events. Results showed that PERSIANN CDR, IMERG, MSWEP, and ERA5 exhibit the highest accuracy, performing relatively well at monthly and annual time scales (correlation > 0.7, Rbias < 0.4). The weakest seasonal performance for all products was evident in summer while autumn showed the best results. PERSIANN CDR emerged as the most reliable product for reproducing extreme precipitation events over Tensift region, while MSWEP, ERA5, and PERSIANN CDR were the most suitable products for studying drought events. The CDF performs well as a bias correction technique in the Tensift basin, particularly for extreme events. In conclusion, PERSIANN CDR, IMERG, MSWEP, and ERA5 demonstrated high accuracy in estimating extreme precipitation in the Tensift basin. These findings have implications for water managers in the region, providing valuable information to address water shortages during extreme events, as well as for studying the effects of climate change on drought conditions.