HR: 10:40h
AN: B31G-02    [PDF]
TI: On the Impact of Historical Land-use Changes on the Summer Climate of a Swiss Region
AU: * Schneider, N
EM: schneid@giub.unibe.ch
AF: University of Bern, Institute of Geography, Climatology \& Meteorology, Hallerstrasse 12, Bern, 3012 Switzerland
AU: Eugster, W
EM: eugster@giub.unibe.ch
AF: University of Bern, Institute of Geography, Climatology \& Meteorology, Hallerstrasse 12, Bern, 3012 Switzerland
AB: In the second half of the 19th century a major civil engineering project was initiated to adjust the lake and river system in the three-lakes region on the Swiss Plateau. The landscape was dramatically modified: the frequently inundated plains were drained and replaced by nowadays intensively used agricultural land. In this study, the impact of these historical (150 years) land-use changes on the climate of a summer month are investigated. The mesoscale dynamical Local Model of the German Weather Service is used with a very high horizontal resolution of 1.5$\times$1.5~km$^2$, nested in a coarser grid of 7$\times$7~km$^2$. In order to evaluate the influence of the land-use changes on the mesoscale climate, the same atmospheric data were used for initial and boundary conditions for all one-month long simulations with historical (circa 1850) and present (1997) conditions. For an initial assessment, a case study was conducted over three clear-sky summer days in July 1998 where detailed meteorological data are available. It could be shown that in the area of land-use changes the daily average temperature was 0.25$^\circ$C cooler for the present land-use conditions. During the day, heterogeneous changes in temperature were observed depending on the type of land-use conversion. In areas where afforestation has taken place, an average warming of more than 1.0$^\circ$C could be observed. In contrast, deforestation resulted in a cooling of up to 2.0$^\circ$C. During the night, the average temperature was up to 0.6$^\circ$C cooler for the present land-use conditions. Due to topographical effects, the nighttime cooling is mainly restricted to low-lying areas on the formerly frequently inundated plains. The diurnal temperature range in the area of land-use changes increased by 0.1--0.3$^\circ$C. With additional sensitivity experiments, it could be shown that the daytime temperature decrease caused by morphological changes dominated the temperature increase due to changed physiological properties.
DE: 0315 Biosphere/atmosphere interactions
DE: 3307 Boundary layer processes
DE: 3322 Land/atmosphere interactions
DE: 3337 Numerical modeling and data assimilation
SC: Biogeosciences [B]
MN: 2003 Fall Meeting