Abstract
Greenhouse gas (GHG) emissions affect precipitation worldwide. The response is commonly described by two timescales linked to different processes: a rapid adjustment to radiative forcing, followed by a slower response to surface warming. However, additional timescales exist in the surface-warming response, tied to the time evolution of the sea-surface-temperature (SST) response. Here, we show that in climate model projections, the rapid adjustment and surface mean warming are insufficient to explain the time evolution of the hydro-climate response in three key Mediterranean-like areas-namely, California, Chile, and the Mediterranean. The time evolution of those responses critically depends on distinct shifts in the regional atmospheric circulation associated with the existence of distinct fast and slow SST warming patterns. As a result, Mediterranean and Chilean drying are in quasiequilibrium with GHG concentrations, meaning that the drying will not continue after GHG concentrations are stabilized, whereas California wetting will largely emerge only after GHG concentrations are stabilized. The rapid adjustment contributes to a reduction in precipitation, but has a limited impact on the balance between precipitation and evaporation. In these Mediterranean-like regions, future hydro-climate-related impacts will be substantially modulated by the time evolution of the pattern of SST warming that is realized in the real world.
Highlights
Greenhouse gas (GHG) emissions affect precipitation worldwide
In the Mediterranean, Chile, and California, the regional hydro-climate response to GHGs is strongly modulated by the time evolution in the SST warming patterns, via the impact it exerts on the midlatitude atmospheric circulation
The rapid adjustment to GHGs contributes to the precipitation response via a suppression of the local hydrological cycle, but, with the exception of Chile, it plays a negligible role in the response of the water balance (P – E), which is controlled by circulation changes rather than by energetic constraints
Summary
Greenhouse gas (GHG) emissions affect precipitation worldwide. The response is commonly described by two timescales linked to different processes: a rapid adjustment to radiative forcing, followed by a slower response to surface warming. It is a standard approach to consider the climate response as the sum of a rapid adjustment proportional to the radiative forcing and a slower response proportional to surface warming [7] The presence of such distinct timescales is evident in coupled experiments forced by abrupt increases in greenhouse gas (GHG) concentrations, so that the climate impacts of radiative forcing and warming are well separated. For hydrological changes, this framework has successfully explained the time evolution of the global-mean precipitation response to GHG increases, which drops (rapidly) due to changes in the atmospheric radiative absorption, before increasing (slowly) with global surface warming [7,8,9]. This two-timescale decomposition has been recently extended to understand the response of regional precipitation to GHG
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