Climate variability in a simple model of land-atmosphere interaction

A simple model is developed to describe land-atmosphere interaction processes important for long-term climate variation. It includes bulk soil hydrology, simple dynamic vegetation, and simple land-atmosphere interaction processes. An idealized seasonal cycle is prescribed to describe the variations related to heat and temperature. The model can simulate the basic features of land surface control on evapotranspiration (ET) at seasonal timescales as well as biosphere-atmosphere interaction processes at interannual to interdecadal timescales. The model is used to study several problems in the long-term land-atmosphere interaction with a series of sensitivity experiments. It is found that the initial land cover has much influence on the local long-term climate only when the outside forcing is small, enough outside forcing can shift the climate between dry and wet equilibriums. Modeling of human managed cropland compared with natural vegetation shows that croplands are vulnerable to drought in both dry and wet climates if irrigation is not sufficient. If well irrigated, the croplands can change the local dry climate by bringing more rainfall, but if irrigation is not sufficient, the croplands can change the local wet climate by decreasing the rainfall.