Assessing drought risk in the Northern Hemisphere under weakened AMOC

Droughts are complex and far-reaching natural hazards, with cascading impacts that span ecosystems, agriculture, water security, and socio-economic stability. Unlike sudden-onset disasters, droughts develop across multiple spatial and temporal scales, often persisting for months to years, and their full consequences may only emerge long after the onset. This complex spatiotemporal dynamic hinders both early warning systems and risk management efforts, particularly as climate change alters the frequency, intensity, and spatial distribution of drought events. A critical uncertainty lies in how drought hazard and risk may evolve under extreme climate scenarios, such as in response to potential disruptions of the Atlantic Meridional Overturning Circulation (AMOC). Given the AMOC’s established influence on Northern Hemisphere precipitation patterns, its weakening under anthropogenic forcing could affect future drought dynamics. To address this, we analyse four pairs of model experiments. Each pair compares the weakening of AMOC against their respective control simulation, which has a stronger AMOC. Three pairs of experiments were conducted with the EC-EARTH3.3 climate model, where the AMOC is artificially weakened by introducing freshwater anomalies into the North Atlantic high-latitude ocean, under fixed radiative forcing respectively at pre-industrial, 2025, and 2050 (SSP5-8.5) conditions. The fourth pair of experiments was conducted with the NASA GISS ModelE climate model, in which the AMOC strength stochastically bifurcates (i.e., between 'on' and 'off' states) under identical SSP2-4.5 extended scenario and without artificial freshwater forcing. We evaluate changes in drought persistence and intensity by using an innovative approach based on Meteorological Drought Tracking built on the Standardized Precipitation Index (SPI).