Drivers of dry day sensitivity to increased CO2

Abstract

Persistent precipitation deficits are among the most impactful consequences of global warming. Here we focus on changes in the annual mean number of dry days (NDD) and in the annual maximum length of dry spells due to a quadrupling of atmospheric CO2. We use atmosphere only simulations to break down the changes into additive contributions. A fast radiative and vegetation adjustment to increased CO2 leads to a global increase in NDD, although the picture is more complex over land with notable regional exceptions (e.g., South Asia and Sahel). The effect of the uniform component of the surface ocean warming is model-dependent but shapes the spatial distribution of the NDD response in each model. Finally, the SST warming pattern also contributes to large uncertainties, likely through contrasting changes in large-scale circulation. Our results thus highlight the complexity of the NDD response, with policy-relevant practical implications for the use of global projections.