Non-Amazonian South America has one of the highest rates of conversion of native ecosystems globally. Most of the studies investigating the climate impacts of these changes focus on the Amazon while the possible influences that these changes may have on climate of non-Amazonian regions have received less attention. The aim of this thesis was to evaluate the impacts of land use and land cover on the mean and extreme climate of non-Amazonian South America by conducting modelling experiments for pre-clearing (before year 1500) and present (year 2005) land covers. It develops new data sets of changes in land surface characteristics for this period and applies a high resolution regional climate model to simulate the potential impacts of changes in natural vegetation cover.The thesis begins by providing a theoretical framework of land-atmosphere interactions. It then reviews the process of land use and land cover change and subsequent climatic consequences in non-Amazonian South America and identifies those ecosystems most affected and least studied. Nature Geoscience Letters.