The hydrological sensitivity to global warming and solar geoengineering derived from thermodynamic constraints

We derive analytic expressions of the response of the hydrological cycle to surface warming from the surface energy balance in which turbulent heat fluxes are constrained by the thermodynamic limit of maximum power. For a given steady state temperature change, this approach predicts the transient and steady state response of surface energy partitioning and the hydrologic cycle. We show that the predicted hydrological sensitivities to greenhouse warming and solar geoengineering are comparable to the results from climate model simulations of the Geoengineering Model Intercomparison Project. Although not all effects can be explained, our approach nevertheless predicts the general trend as well as the magnitude of the changes in the global-scale hydrological cycle surprisingly well. This implies that much of the global-scale changes in the hydrologic cycle can be robustly predicted by the response of the thermodynamically constrained surface energy balance to altered radiative forcing.