Wetlands and Forests Regulate Climate via Evapotranspiration

The role of wetlands and forests in climate and climate change is usually considered as a part of their functions as source or sink of greenhouse gases. However, the permanent vegetation in these systems is an active factor that, through the process of evapotranspiration, directly influences climate as well. Wet vegetation transforms solar radiation into the latent heat of water vapour. Evapotranspiration is a powerful tool that has, due to the phase change of water, a double air-conditioning effect in the landscape. In addition, it reduces thermal gradients, mitigates temperature extremes and closes water and mass cycles. Evapotranspiration-condensation processes slow down where there is a lack of water and permanent vegetation. Solar radiation is then transformed into sensible heat. The overheated surfaces warm the adjacent air layer. Warm air rises turbulently upwards and is capable of absorbing higher amounts of water vapour, which is then transmitted to higher levels of the atmosphere where condensation occurs. These processes significantly dry out the landscape. The Intergovernmental Panel on Climate Change (IPCC) reports, however, do not take into account this direct effect of water and vegetation on climate. This chapter explains the direct function of wetlands and the air-conditioning effect of evapotranspiration, which is also illustrated with thermal ground images. The role of forest and wetlands in transport of water from ocean into continents in terms of a biotic pump is discussed on the basis of the literature.