Declining terrestrial water storage is associated with changes in effective hydrological memory and drought buffering

Abstract

Drought impacts in large river basins depend not only on precipitation deficits but also on how terrestrial water storage (TWS) buffers climate anomalies through hydrological memory, which is the persistence of past storage conditions. In this study, we quantify this as the “effective hydrological memory,” measured as the e-folding decay time of the low-frequency TWS (periods over 12 months) autocorrelation function, since it integrates climate signals and basin physical properties. Using observations from the Gravity Recovery and Climate Experiment (GRACE) satellite missions from 2002 to 2025, we show that quasi-global TWS is decreasing at -172.62 ± 0.77 km 3 /year, driven by concentrated drying hotspots that outweigh regional gains. Across 50 major river basins, the average effective hydrological memory ranges from 4 to 16 months, with many regions showing significant trends. We found that 55% of basins experiencing storage depletion also exhibit a decline in drought buffering capacity. Notably, the lengthening of memory in several arid basins (up to +1.0 months/year) may reflect fossilized persistence linked to impaired recovery rather than increased resilience. Conversely, semi-arid systems with rapidly shortening memory (as low as -1.0 months/year) experience quicker drought onset and weaker buffering. These results reveal a transition from dynamically buffered systems toward regimes that are either too flashy to resist or too stagnant to recover. Our study suggests that storage-memory metrics may help assess basin resilience, although further proof-of-concept studies are still needed.