Anthropic land use causes summer cooling in ­Central Europe

Abstract

The diagnostic potential natural vegetation (PNV) model, VERDE (Vegetation Recon- struction by Diagnostic Equilibrium), recently developed by the authors, is coupled to the Italian regional climate model (RegCM) ICTP, and is implemented in the European and Mediterranean regions. This study assesses the effect of anthropic land use on the present-day climate in these regions, and computes the climate associated with the PNV through iteration of a 2-step procedure, composed of a multi-annual model simulation and subsequent computation by VERDE of the PNV corresponding to the simulated climate. In the first iteration, RegCM adopts the present land use (which over Europe is dominated by crops and farming, with very little natural vegetation). The pro- cedure is iterated until there is no appreciable difference between the PNV used by RegCM, and that associated with the climate that it produces, so that the PNV and model climate are consistent. The equilibrium PNV consists mainly of shrubs in the Mediterranean and deciduous broadleaf forest in central Europe. The effect of anthropic land use on climate is assessed by analyzing the difference between the simulated present-day anthropic land use and PNV climates, which is given by the dif- ference between the first and the last iterations of the procedure. We found that anthropic land use produces cooler summers, and identified 2 different mechanisms: (1) over the Balkan Peninsula, anthropic land use modifies the surface energy balance by increasing evapotranspiration; (2) over central-western Europe, cooling is mostly due to cloudier sky conditions. These results show: (1) that reforestation may not be appropriate as a tool for climate change mitigation at the regional scale, and (2) expansion of agricultural land use may have reduced past warming signals at the regional scale, though historical records of land-use evolution suggest that this effect is probably small for Europe during the 20th century.