Decoupling climate variability and terrestrial water storage anomalies in global endorheic basins

Spatiotemporal dynamics of the terrestrial water storage (TWS), an integration of all water masses on and below the continental surface, are intricately linked to the natural variability of the climate system. Tracking TWS dynamics, particularly at large geographic scales, has been unprecedentedly facilitated by the Gravity Recovery and Climate Experiment (GRACE) and the GRACE Follow-On (GRACE-FO) satellite missions. One of the prominent findings from GRACE observations is that TWS in the global endorheic (hydrologically landlocked) system, which spatially concurs with arid or semiarid regions, experienced a substantial decline (about 100 Gt per year) since about the start of this century. If excluding the contributions of ice sheets and glaciers, this endorheic water loss dominated the TWS trend in the entire continental surface, which exacerbated the water stress in the already arid regions of the world. However, the primary drivers of this endorheic TWS loss, particularly the contributions of climate variability versus secular forces (e.g., climate change and direct human water management), are still poorly understood. This study aims to improve this understanding by diagnosing the possible associations between climate variability and the endorheic TWS anomalies. Our considered climate variability includes primary oscillatory teleconnections at inter-annual to inter-decadal timescales, such as the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multi-Decadal Oscillation (AMO). Time series of each of the climate variability indices were acquired mainly from the NOAA Earth System Research Laboratories, and the time series of TWS anomalies were retrieved from multiple GRACE mascon solutions. A variety of statistical methods, such as multivariate analysis, cross correlation, and the Empirical Orthogonal Function analysis, will be explored to reveal how endorheic TWS may respond to climate variability across space and time. The diagnosed relations will also be contrasted with those between climate variability and TWS anomalies in the exorheic basins, in order to better understand the causation of the recent endorheic water loss in a global context.