Deforestation decreases resistance of simulated Easter Island climate to drought

Abstract. Easter Island underwent a rapid deforestation several hundred years ago. The causes have been discussed in depth. However, the effect of the deforestation on the near-surface climate of Easter Island and possible feedbacks have not yet been studied. Here we use the limited-area model COSMO to simulate a series of typical weather situations for a fully tree-covered, grass-covered and a bare soil Easter Island, respectively. We find that the top soil layer of the deforested island becomes much warmer and the wind speed roughly doubles, thereby enhancing the erosion on the deforested island. During a drought spell, evapotranspiration decreases much more slowly over a forested area. If the soil has become dry, then the tree-covered island triggers convective precipitation much more efficiently than the bare-soil or grass-covered island could do. This is caused by the higher surface roughness and stronger sensible heat flux which lead to a deeper boundary layer and an enhanced moisture flux convergence over the forested island. Hence, the climate of a deforested Easter Island appears to be significantly less resistant to drought than a forested island and thus, deforestation has probably exacerbated the effects of past climate drought spells on Easter Island socio-ecological systems.