Influence of Atmospheric Rivers in Extra-Tropical Patterns of Hydrological Extremes

Past research on atmospheric rivers (ARs) highlights their significant contribution to total precipitation, with most focus on western North America and West Europe. However, the influence of ARs on global surface hydrology and water resources remains to be characterized and quantified. This is of particular relevance as a global AR detection and climatology study by Guan and Waliser (2015) led to the identification of considerable AR landfalls (and inland penetration) and fractional annual precipitation in areas with traditionally less scientific attention on ARs, such as South-East Asia, western Africa, Australia and South America.  In this study we look at the way overland ARs alter hydrological extremes patterns across the globe. In particular, we identify the global catchments and regions where: a) the presence of ARs intensify high flows, and b) the absence of ARs lead to the prevalence of low flows. We perform a sensitivity experiment with a standard offline version of JULES Land Surface Model and CaMa-Flood Model in order to detect daily states of global river flow. So first we run a control simulation with standard meteorological conditions (obtained from the latest WFDEI global gridded reanalyses product). Second, we run a no-AR simulation by removing the precipitation corresponding from ARs as detected by Guan and Waliser (2015) from the total precipitation. Daily output runoff values from JULES (from the control and no-AR simulations) were provided to the CaMa-Flood model in order to obtain river discharge values and quantify AR impacts on river dynamics. Our results identify the regions of the globe where AR tend to play a major role in flood risk and hydrological drought, and help to provide water managers and flood forecasters/relief planners a scientific framework that may aid in their decision process.