Exploring and contrasting the impact of changes in land surface properties to changes in atmospheric CO2 on the global hydrologic cycle.

Abstract:

In this study, we contrast the response of precipitation over terrestrial regions to two distinct forcing mechanisms: changes in atmospheric CO₂ and changes in physical land surface properties associated with vegetation change, both of which have exhibited large changes over Earth’s history. We use an idealized climate model framework to evaluate the response of precipitation patterns to large-scale decreases in land surface albedo, reductions in terrestrial evaporation, and increases in atmospheric CO₂. We find that while there are some similarities, particularly in the tropics, of the pattern of response of precipitation to both changes in land albedo and changes in atmospheric CO₂, changes in terrestrial albedo generate much stronger changes in precipitation over land than do changes in atmospheric CO₂. Precipitation over terrestrial regions can be modulated by large-scale circulation and local land-atmosphere interactions. Both the large-scale atmospheric circulation and the strength of local land-atmosphere coupling can be modified by changes in the physical properties of the land surface associated with vegetation change (e.g. albedo, aerodynamic roughness, resistance to evaporation). Changes in land surface properties are a fundamentally non-uniform forcing on the Earth system, due to the non-uniform distribution of land; these properties modulate fluxes of water and energy into the base of the atmospheric column. Changes in atmospheric CO₂ not only lead to global-scale warming, with associated changes in precipitation, but can also modify local land-atmosphere coupling by inducing vegetation responses to higher CO₂.