Simulation of drought for a Scots pine forest (Pinus sylvestris L.) in the southern upper Rhine plain

Abstract

For the period 1978 to 2001, the physically based model BROOK90 has been applied to simulate the water balance of the Scots pine forest (Pinus sylvestris L.) at the forest meteorological experimental site Hartheim with emphasis on drought. The forest is located in the southern upper Rhine plain, which shows climate conditions similar to those predicted by regional climate models for Central Europe. The transpiration index (ratio of actual transpiration and potential transpiration) has been chosen as an ecophysiologically based drought index on a daily basis. Simulations exhibit that the transpiration index depends not only on the weather conditions but also on forest characteristics like maximum leaf conductance and projected leaf area index. Taking into account different time scales for the transpiration index (daily, monthly and annual basis), a tendency of the occurrence of drought significant to the forest could not be determined for the investigation period. August turned out to be the month with the highest drought risk. Drought for the forest was most pronounced in the year 1991 (annual transpiration index: 0.53), whereas the year 2000 was the only one with an optimal water supply of the Scots pine forest (annual transpiration index: 1.0).