GERHARD GEROLD, CONSTANZE LEEMHUIS
Georg-August-Universität Göttingen, Department of Landscape Ecology, Germany
The hydrological functions of tropical rainforests are a substantial argument for forest conservation. Global climatic variability (p.e. impact of El Nino Southern Oscillation) and regional deforestation often leads to an increased variability in discharge patterns, causing large fluctuations in water supply and water quality. On the other hand the demand for water rise due to population increase and economic development. In the tropical developping countries forest conversion continues, specially with accelerating rates in Indonesia (2 million .ha since 1996 every year). Studies that attempt to quantify the impact of El Nino and deforestation on the water yield and the seasonal water availability are still scarce. Concerning changes in the dry season flows, measurement results of various studies are ambiguous. Considerable increase or decrease of flow during dry season were observed. These changes can have a severe impact on rural water supply systems in regions of the humid tropics where the amounts of streamflow in the dry season are already critical and further reductions will limit the water supply. Further on ENSO years in South East-Asia (research area Central Sulawesi) are characterised by reduced rainfall during the dry season which led to a shortage of water availability. Concepts that analyse domestic traditional water use in the rural area, perceptions of the village people on water availability and water quality and hydrological modelling to assess the water resource situation and to study ENSO scenarios and rainforest conversion scenarios for the humid tropics are still scarce. Results of ongoing interdisciplinary research projects in Central Sulawesi (Indonesia) for two catchments will be presented (DEKLIM-C: www.gwdg.de/ impenso and SFB-552: www.storma.de). The physically based water balance model WASIM-ETH was adapted for the humid tropics and ENSO scenarios as well as forest conversion scenarios demonstrates the response of the hydrological system to rainfall anomalies and land cover changes. Combining this with increasing domestic water use (rapid growth of settlements at the rainforest border) and to keep sufficient wet rice production for the future the rural water management (community based) must combine traditional low cost water use systems with the prediction of water supply by water balance models.
Keywords: Central Sulawesi, hydrological modelling, Indonesia, land cover change, rainforest conversion, rural water management