Understanding Drought Risk in the Northern Hemisphere under AMOC weakening

The collapse of the Atlantic Meridional Overturning Circulation (AMOC) has long been classified as a low-probability, high-impact event. However, recent evidence suggests the probability of such a collapse may be significantly higher than previously estimated. From a disaster and risk management perspective, this shift calls for a re-evaluation of preparedness strategies and a deeper inquiry into how a drastic weakening or a complete shutdown would reshape the global risk landscape.

Central to these concerns is the role of AMOC in modulating Northern Hemisphere precipitation. An anthropogenic weakening could significantly alter future drought dynamics, further complicating the management of drought risk, a hazard already characterised by extensive socio-economic impacts.

To address these changing dynamics, we examine four sets of paired climate model simulations, each comparing a weakened AMOC state with a control run featuring a stable, stronger AMOC. Three of these experiment pairs employ the EC-EARTH3.3 model, where freshwater perturbations in the North Atlantic induce an artificial AMOC slowdown under fixed pre-industrial, present-day (2025), and future (2050, SSP5-8.5) forcing. The fourth pair employs the NASA GISS ModelE, simulating a spontaneous AMOC collapse under an extended SSP2-4.5 scenario without external freshwater forcing. Using an advanced Meteorological Drought Tracking approach based on the Standardized Precipitation Index (SPI) we quantify shifts in drought duration, severity, and spatial coherence, highlighting where significant changes would be expected.