Oceanic and terrestrial origin of precipitation over 50 major world river basins: Implications for the occurrence of drought

The terrestrial and oceanic origins of precipitation over 50 major river basins worldwide were investigated for the pe-riod 1980-2018. For this purpose, we used a Lagrangian approximation that calculates the humidity that results in pre-cipitation from the entire ocean area (ocean component of the precipitation, PLO) and the entire land area (land component, PLT) as well as the sum of both components (Lagrangian precipitation, PL). PL and its components were highly correlated with precipitation over the basins, where PLT accounted for >50 % of the PL in most of them. This confirmed the importance assigned by previous studies to terrestrial recycling of precipitation and moisture transport within the continents. However, the amount of PLO in almost all North American river basins was high-lighted. The assessment of drought conditions through the Standardized Precipitation Index (SPI) at a temporal scale of 1-and 3-months revealed the number of drought episodes that affected each river basin, especially the Ama-zon, Congo, and Nile, because of the lower number of episodes but higher average severity and duration. A direct re-lationship between the severity of drought episodes and the respective severity computed on the oceanic and terrestrial SPI series was also found for the majority of basins. This highlights the influence of the severity of the SPI of oceanic origin for most basins in North America. However, for certain basins, we found an inverse relationship be-tween the severity of drought and the associated severity according to the SPI of oceanic or terrestrial origin, thus high-lighting the principal drought attribution. Additionally, a copula analysis provided new information that illustrates the estimated conditional probability of drought for each river basin in relation to the occurrence of drought conditions of oceanic or terrestrial origin, which revealed the possible main driver of drought severity in each river basin.

Automated summary

This study investigates the terrestrial and oceanic origins of precipitation in 50 major river basins worldwide from 1980 to 2018. Results show that terrestrial precipitation is the main source, confirming the importance of terrestrial recycling and moisture transport within continents. However, oceanic precipitation is also significant, especially in North American river basins. Additionally, the severity of drought episodes is directly related to the severity of the oceanic and terrestrial precipitation indices in most basins, highlighting the influence of oceanic origin in North America.