Effect of various crops on the spatial variability of temperatures over the Alpilles-Reseda experiment analyzed by the 3d atmospheric model MESONH
Abstract
Numerous papers using mesoscale climate models have shown that local landuse practices influence significantly regional climate. But most of these studies dealt with large spatial scale and a grid mesh around 1km. The aim of our paper is to analyse the effect of various crops described at a finer scale (50m) on the spatial variability of temperatures and fluxes with the 3D atmospheric model called MESONH. We simulated a small agricultural region of 5x5km in the SE of France, the Alpilles -Reseda experiment site, where a lot of data characterizing soil, vegetation and atmosphere were acquired in 1997. The main surface parameters necessary to the surface schema ISBA were derived from remote sensing or airborne data. Albedo, LAI and vegetation fraction were computed from the POLDER images. We chose to simulate two different periods for crop development (mainly wheat and sunflower) in April and June. The results showed that the fluxes were strongly correlated to the surface parameters, as expected, and that there was a large variability on the whole area for the two periods due to high hydric contrasts between the crop types. The surface temperatures simulated were in good agreement with the thermal infrared images measured by a airborne camera and were well correlated with soil moisture of the different fields. On the other hand, instantaneous air temperature values simulated at 2m above the surface showed spatial variations less affected by the crops and more dependant on turbulence phenomenons. Coherent structures appeared between 100 and 1500m in the surface boundary layer with a wave length in the order of magnitude of the simulated area. More investigations are now necessary to analyse these convective cells observed for the first time at this scale.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....14644C