Similarity of Microclimate as Simulated in Response to Landscapes of the 1930s and the 1980s

Abstract

In the time between the 1930s and the 1980s land use was modified by deforestation, urbanization, afforestation and recultivation of open-pit mines, further installation of open-pit mines, and drainage in about 46% of a 30?000 km2 area in the south Brandenburg/north Saxony region of Germany (51°00?N, 11°58?E; 52°17?N, 11°53?E; 51°00?N, 14°54?E; 52°17?N, 14°49?E). This study evaluates the short-term (1 day) impacts of these land use changes assuming the same typical day in May for both landscapes. In so doing, a state-of-the-art, meso-?-scale atmospheric model is applied with a resolution of 5 km ? 5 km on the coarse grid and 1 km ? 1 km on the subgrid. Under the land use of the 1980s, the simulated atmospheric boundary layer (ABL) is slightly warmer and drier than it was in the 1930s. The sensitivity of the ABL to the changes in land use varies with time. The calculated probability density functions show that the partitioning of incoming energy between sensible and latent heat and the partitioning of cloud microphysical processes between the warm and cold paths of precipitation formation differ appreciably. The cloud and precipitation distributions are affected the most of all the variables examined here. For precipitation, simply changing coniferous forest to its full extent in the 1980s may provide results even more dissimilar when compared with results provided by a 1930s landscape than does a simulation with a 1980s landscape. Deviations from the principle of superposition of the responses of the simple land use changes can be induced by primary (land use changes) and secondary (e.g., altered cloud distributions as a response to the land use modifications) differences. Diminution or enhancement of the atmospheric response depends on 1) the size of the resulting new patch as well as the uniformity of its land use, 2) the kind of change in the hydrologic and thermal characteristics, and 3) the type of land use prevailing in the environments of land use conversion. According to the results of this case study, areas dominated by grassland and forests are more sensitive to concurrent land use changes than are prevailingly agriculturally used areas.