Forest favours conditions for convective precipitation in the Mediterranean Basin

The Mediterranean Basin is identified as a climate change hotspot and prone to future drying. Through carbon sequestration, forests may mitigate climate change and reduce future drying. Nevertheless, the effect of forests on freshwater availability in the Mediterranean Basin is uncertain. Trees contribute to enhanced evapotranspiration, which may enhance drying; the resulting impact on precipitation in the Mediterranean Basin, however, remains unclear. Here we use a simple model to simulate the development of the atmospheric boundary layer (ABL) to determine the impact of forest on convective rainfall potential. There is convective rainfall potential when (1) the ABL reaches the lifting condensation level, and (2) there is sufficient convective available potential energy. We model the ABL development over the Mediterranean Basin for a bare soil scenario (covered fully with bare soil) and a forest scenario (covered fully with forest) to determine its land cover sensitivity. In addition, we examine the sensitivity of the ABL to variations in soil moisture for the forest scenario specifically. We identify two distinct responses to forest in the Mediterranean Basin dependent on soil moisture content. Forest contributes to warming and drying in relatively dry regions (low soil moisture content) and to cooling and wetting in relatively wet regions (high soil moisture content). We find that both forest cover and soil moisture contribute to convective rainfall potential. In regions with a relatively high soil moisture content, forest cover positively influences both the convective available potential energy, and the crossing of the ABL and lifting condensation level. The results suggest that forestation in the Mediterranean Basin may contribute to local precipitation in relatively wet regions and reduce local precipitation in relatively dry regions.