| 英文摘要: | To the Editor —
Projected changes in precipitation are generally assumed to be monotonic with respect to global temperature changes: rainfall will either increase or decrease as the climate warms. However, using an example in South America, we demonstrate that, under a high emissions scenario, rainfall changes in some regions can actually be non-monotonic, which has important implications for biodiversity, the carbon cycle and long-term climate policy.
The latitudinal position of the Intertropical Convergence Zone (ITCZ) is projected to move equatorwards in response to a warming climate1, 2, 3, although there is uncertainty as to how far and how fast. As it moves, some low-latitude regions may find that the rainfall they receive first increases in accordance with the 'wet get wetter' paradigm, but then decreases as the ITCZ moves over and past them; such regions will experience non-monotonic changes in precipitation with time. We examine this phenomenon using multi-centennial projections of precipitation from different global climate models (GCMs) (see Supplementary Information).
According to the models, non-monotonic changes in precipitation are pronounced over the oceans after the year 2100 — especially in the tropical Atlantic (Supplementary Fig. 1) and Pacific — but they also occur over land regions where impacts on infrastructure and ecosystems will be far more significant. As an example, several GCMs display evidence of non-monotonic changes for tropical South America (Fig. 1). Specifically, several simulations suggest an increase in precipitation near latitude 5° N until the year 2100, followed by a decrease. In contrast, temperatures exhibit a monotonic increase in this region (Supplementary Fig. 2). |