Drought evolution in North American river basins: attribution analysis through a Lagrangian approach

Drought events have become more frequent and severe across North America, threatening water availability in river basins and thus ecosystem and socio-economic development. This is why in this study, we investigate the occurrence, evolution, and attribution of drought conditions in nine major North American river basins, the Colorado, Columbia, Fraser, Mackenzie, Mississippi, Rio Grande, Saskatchewan-Nelson, St. Lawrence, and Yukon. The analysis was performed on a spatio-temporal scale for the period 1980-2018. Precipitation data from MSWEP and CRU were used, as well as terrestrial water storage from GRACE. In addition, the Lagrangian moisture contribution from oceanic and terrestrial origin to precipitation over the basins, named PLO and PLT, respectively, were used. Drought indices such as the Standardised Precipitation Index (SPI), Standardised Precipitation-Evapotranspiration Index (SPEI), and Drought Severity Index (DSI) were used to assess the occurrence of dry conditions at various temporal scales. In addition to the attribution of the occurrence and severity of drought extremes due to PLO and PLT deficits, the trend was assessed. The results show that despite the differentiated nature of precipitation origin between the western and eastern basins, in most of them, a joint coupling prevails in the occurrence of positive or negative trends of dry/wet conditions of oceanic and terrestrial origin, which ultimately modulate the evolution of dry/wet conditions in the basins.