(The) impacts of land surface changes on climate simulation over East Asia

Abstract

Although on a global scale, the radiative forcing estimates of landscape alteration appear to be small (about -0.2±0.2 Wm-2), in East Asia where the landscape changes have been intensive, the impact of land use and land cover change (LULCC) is comparable to those of greenhouse gases and sea surface temperatures. In order to better understand the historical climate changes, impact of land cover change on climate has been widely investigated. But in East Asia, there are few studies to assess effects of cropland management within existing croplands and impacts of land cover change and its accompanying dust aerosol. In this study, it will be proposed regional climate responses to land surface changes after harvest in the North China Plain of a double cropping region and the impacts of land cover generated by dynamic vegetation model on East Asian climate. In the relation to the cropland management, this study reports the impacts of land use alterations from harvesting practices on the regional surface climate over the North China Plain. Observational analysis and modeling results showed that the land surface was warmer and drier after harvest. The bare soil surface after harvest in June has biophysical impacts on the surface climate that were mediated by decreasing evapotranspiration and latent heat flux effects, which increased surface temperatures and decreased surface humidity. Under two Representative Concentration Pathways (RCP) scenarios, land conversion induced additional warming in addition to greenhouse gases induced global warming. In the relation to the land cover generated by dynamic vegetation model, it was investigated the impacts of land cover change, as simulated by a dynamic vegetation model, on the summertime climatology over Asia. The climate model used in this study has systematic biases of underestimated rainfall around Korea and overestimation over the South China Sea. When coupled to a dynamic vegetation model, the resulting change in land cover is accompanied by an additional direct radiative effect over dust-producing regions. The direct radiative effect of the additional dust contributes to increasing the rainfall biases, while the land surface physical processes are related to local temperature biases such as warm biases over North China. In time-slice runs for future climate, as the dust loading changes, anomalous anticyclonic flows are simulated over South China Sea, resulting in reduced rainfall over the South China Sea and more rainfall toward around Korea and South China. In contrast with the rainfall changes, the influence of land cover change and the associated dust radiative effects are very small for future projection of temperature, which is dominated by atmospheric CO2 increase. The results suggest that the land cover simulated by a dynamic vegetation model can affect, and be affected by, model systematic biases on regional scales over dust emission source regions such as Asia. In particular, analysis of the radiative effects of dust changes associated with land cover change is important in order to understand future changes of regional precipitation in global warming.