Updated Understanding of Continental Precipitation Recycling Using Global 3-D Lagrangian Tracking

Water is crucial for human health, food and industrial production, ecosystem services, and climate and weather systems. As a major contributor of renewable freshwater over land, humans have been studying the origin of continental precipitation for nearly a century. From the moisture budget perspective, local evapotranspiration in a vast part of the Earth’s surface is effectively smaller than local precipitation. This entails the role of moisture advection in sustaining continental precipitation. However, previous trajectory-based quantification appeared to underestimate the global “continental precipitation recycling (CPR)” ratio –– that is, the fraction of continental precipitation originating from evapotranspiration. To this end, the present study completed a 40-year (1971-2010) tracking of moisture from continental precipitation using a three-dimensional Lagrangian tracking model and optimized water accounting diagnostics. Our Lagrangian tracking confirms that 62% of continental precipitation stems from evapotranspiration, aligning well with the water budget-based estimates in the literature. Across the globe, non-local terrestrial sources dominate 1˚-scale precipitation in nearly 70% of the land areas, together with the greatest continental moisture feedback in the interior of South America, Africa and Eurasia. Seasonally, the CPR ratio anomalies are markedly different between the mid-to-high latitudes and monsoon regions worldwide, from which two kinds of moisture source-regulated hydroclimate are generalized. For transboundary water governance, perennial source hotspots for continental precipitation are identified, including the biome-rich Amazon and Congo rainforests and other major watersheds within 30˚ equatorward. Leveraging the backward “WaterSip” and the forward “WaterDrip” algorithms, we propose two ubiquitous processes of cascading moisture recycling (CMR) that formulate a cascade of regional water cycles. The watershed-scale CMR metrics quantify the hidden interdependence between the regional water cycles through moisture recycling. Overall, by closing the gap in the estimate of the CPR ratio, this work updates the understanding of the moisture recycling, feedback and cascading characteristics of the continental atmospheric water cycle. The outcome sheds light on the potential vulnerability of local precipitation in response to the modification of non-local land surface fluxes by human activities.