The Critical Effect of Subgrid-Scale Scheme on Simulating the Climate Impacts of Deforestation

Land surface schemes (LSSs) in Earth System Models simulate how vegetation regulates land-atmosphere fluxes of heat, water, carbon, and momentum. Despite advances in the spatial resolution of regional climate modeling, significant land cover changes occured at sub-grid scale still not properly treated. Here, we investigate the response of evapotranspiration, representing the fluxes of heat and water, to deforestation in Southeast Asian Massif by employing three LSSs (Noah mosaic, Noah-MP and Community Land Model (CLM)) with different approaches in representing sub-grid variability, implemented in the Weather Research and Forecasting model. Two experiments, with and without satellite-observed deforestation, were performed for each scheme. Results show that the simulations are highly sensitive to the subgrid-scale approaches embedded in the LSSs. Compared with the observed historical climate, CLM outperforms other schemes and Noah mosaic shows the largest bias. However, if we target the simulation of the climate impacts of land cover change, the Noah mosaic scheme taking the sub-grid approach can better capture the response of evapotranspiration to deforestation. The NoahMP and CLM schemes underestimate the evapotranspiration response in the grid cells where the dominant land cover type has not changed, but overestimate the response in those grid cells with dominant type changed, which is a characteristic of dominant-grid approach. To improve our understanding of climate impacts induced by fine-scale land cover change, future efforts to better represent subgrid-scale variability and land-atmosphere flux exchange in climate models are desirable.