ON THE VARIATION OF THE ENERGY-BALANCE COMPONENTS WITH OROGRAPHY IN THE UPPER RHINE VALLEY

Within the framework of REKLIP (Regio-Klima-Projekt) performed in the Upper Rhine Valley and the surrounding mountains 36 meteorological sta tions have been installed at different altitudes, in order to investig ate the climatic state and the energy balance with high temporal and s patial resolutions. Here a one year data set will be investigated to l ook at two different characteristic features in more detail: (i) an ev apotranspiration increase in the Rhine Valley between northerly statio ns (e.g., Karlsdorf, 510 mm) and southerly stations (e.g., Sasbach, 62 0 mm) was found, although there is only a small difference in altitude between both stations (27 m). The increase can be related to the incr ease in precipitation. Nearly a constant ratio of 0.8 between evapotra nspiration and precipitation is given. The higher precipitation can be related to orographic effects, because the southerly stations are sit uated in the luff of higher mountains (Hornisgrinde about 1100 m high) than the stations in the north (Kraichgau about 300 m high). Hence th e differences in evapotranspiration in the Rhine Valley can be explain ed by a remote effect of the orography. (ii) the increase in the sensi ble and the decrease of the latent heat fluxes with the altitude at th e slope of the Black Forest, although there is a strong increase in pr ecipitation from Sasbach (880 mm) at the bottom to Hornisgrinde (1340 mm) at the crest of the Black Forest. Explanations for this behaviour can be given by theoretical consideration about the height dependence of the Bowen ratio, which is mainly influenced by the air temperature and by the ratio of the temperature gradient to the moisture gradient.