The oceanic and terrestrial origin of precipitation in the great world river basins: their role in drought severity


Recommended citation: Sorí, R.; Gimeno-Sotelo, L.; Stojanovic, M.; Fernández-Alvarez, J.C.; Pérez-Alarcón, A.; Nieto, R.; Gimeno, L. (2022). The oceanic and terrestrial origin of precipitation in the great world river basins: their role in drought severity. XXXVIII Reunión Bienal de la Real Sociedad Española de Física . Murcia, 11-15 July 2022.


In this study, we initially investigated the origin of the precipitation over 50 major world river basins. For this aim, the global monthly outputs from the Lagrangian Particle Dispersion Model (FLEXPART), considering a forward in time experiment from the entire oceans and continents were used. The horizontal resolution was 0.25º and the period of study is from 1980 to 2018. These outputs permitted to estimate a “Lagrangian precipitation” from the oceanic (PLO) and terrestrial (PLT) origin, which sum is close to the precipitation over the basins. Following this approach, the percentage of precipitation from oceanic and terrestrial origin was determined for each river basin, and compared with the precipitation from the MultiSource Weighted-Ensemble Precipitation (PMSWEP). The results show a great amount of PLT over the major number of river basins, confirming the importance of terrestrial recycling and moisture export across the continents. However, the influence of PLO seems to be dominant over a great part of the western North American river basins, and some basins located in western Eurasia and Southeast Asia. The multivariate Standardised Precipitation Index (SPI) was utilised to assess the temporal evolution of dry/wet conditions in the river basins. It was calculated at 1- and 3-months temporal scales using the PMSWEP as well as PLO and PLT series, resulting in the series of SPIMSWEP, SPIPLO, and SPIPLT. Afterwards, was calculated the number of drought episodes that affected each river basin. The results showed that at the 1-month temporal scale the number of drought episodes is larger than at 3-month, due to the greater variability of the SPIMSWEP, which result in a major number of flash droughts. Those basins more (less) affected by drought episodes according to the SPIMSWEP at a 1-month temporal scale are located in northern Eurasia and North America (tropical South America and Africa). In addition, we present the relationship between the severity of drought episodes and the correspondent severity computed with the SPIPLO, and SPIPLT. Finally, a copula analysis revealed the conditional probability of occurrence of drought, severe and extreme drought, and extreme drought conditions according to the SPIMSWEP with the SPIPLO and SPIPLT, confirming the crucial role of PLO (PLT) deficit in North America (Eurasian) river basins.