Assessment of Satellite Precipitation Products during Extreme Events in a Semiarid Region

Global warming is leading to an increase in the frequency and intensity of extreme weather events. In arid and semi-arid regions such as the Tensift basin in Morocco, global warming reflected in severe water shortages. In this context, it is of crucial importance to precisely quantify the amount of precipitation and its variability with respect of time and space. In the absence of adequate coverage by weather stations, it is imperative to investigate the reliability of satellite-based precipitation products in estimating observed precipitation. The objective of this study is to assess the performance of eight satellite products, namely PERSIANN, PERSIANN CDR, IMERG, ARC2, RFE2, CHIRPS, ERA5, and MSWEP in accurately estimating extreme observed precipitation within the basin. To this end, satellite precipitation products were compared to observed data collected over fourteen weather stations between 2001-2016, at various time steps (daily, monthly, seasonal, and annual). The data were analyzed using volumetric and categorical metrics. We further evaluated the estimation of the satellite products for extreme precipitation by comparing their extreme indices with those of the weather stations. In the same vein, this study examined the behavior of satellite products during droughts by comparing their SPI with the observations to determine the most accurate satellite products in determining the onset, duration, and magnitude of droughts. Finally, in order to determine whether bias correction was necessary to enhance performance and identify the most effective method, in the context of extreme events, several bias correction methods were evaluated based on the same procedures before and after bias correction. The results showed that PERSIANN CDR, IMERG, MSWEP, and ERA5 are the most accurate, with better performance at both monthly and annual time steps relative to daily time steps. Seasonally, the worse performance of all products occurs in summer and the best in autumn. Furthermore, we found out that PERSIANN CDR is the most reliable product that water managers can use for extreme events, while MSWEP, ERA5, and PERSIANN CDR are the best products that can be used to study the impact of climate change on drought. Finally, The Cumulative Distribution Function (CDF) mapping was found to be the most effective method in correcting the bias in the Tensift basin, especially for extreme events.