Retrospective and prospective evaluation of water budgets at Lange Bramke, Harz Mountains, Germany: effects of plant cover and climate change

摘要

Effects of forest structure, forest management and climate change on water budget components and indicators for drought stress have been evaluated for Lange Bramke, a small forested catchment in the Harz Mountains, Germany. Water budget components have been simulated with the hydrological model WaSiM-ETH. Climatic projections until 2050 are based on the IPCC-SRES scenario A1B and have been downscaled with the statistical model WETTREG. For the parameterization of interception and evapotranspiration, past and future characteristics of forest stands such as stand height and leaf area index (LAI) have been simulated using the statistical WaldPlaner model. To differentiate between effects of stand development and climatic change, water budget simulations were carried out for scenarios with constant stand characteristics and with stand development. Model simulations show that evapotranspiration has increased at Lange Bramke during the last 60 years due to a combined effect of stand development and climate change. The effect of forest growth is much more relevant than climate change. Stand development has affected interception mainly during the first 20 years, whereas transpiration has increased over the whole period. In the course of the next 40 years, drought stress for forest stands at Lange Bramke will increase due to a higher evaporative demand of the atmosphere. As a consequence, adaptation strategies for forest management are necessary to mitigate adverse effects of climate change.