Qualifier Seminar by Mr Nugroho Christanto Dept. of Earth Systems Analysis, ITC Analyzing the driving factors of land degradation of a watershed in Java: integrating land use changes and weather variability

Java, the most populated island in Indonesia, experiences much environmental stress from its increasingly intensive agricultural use. Massive conversion from forest into cultivated land is a consequence of rising population. The need of food has forced the land conversion and expansion of agricultural land. Two driving factors have a direct effect on the land degradation in Java: land use changes and the occurrence and variability of extreme rainfall events. Land degradation manifests itself in the Serayu watershed as severe soil erosion, leading to a loss of fertile soil, damage to crops and gullying, and the occurrence of landslides that threaten lives and property. Apart from these onsite effects there are also off site effects: the occurrence of mudfloods and siltation of a dam downstream. Over the years agricultural expansion has lead to deforestation on the steeper slopes, and systems of terraces are built for agricultural crops. The efficiency of these terraces is not clear: they may prevent runoff because of the decreased slope, but may become prone to sliding when saturated. An analysis of land use change, relief and soil characteristics leads to identification of hazardous areas. However, to quantify the on-site and off-site effects and predict where and when soil erosion and landslides occur, two more things are needed: knowledge on the spatial variability of rainfall during extreme events, and dynamic hydrological modeling as a tool to bring all factors together. Information on spatial rainfall is available through meteosat satellite images and derivative products. Although they have a low spatial resolution, their temporal resolution is high and they can be used to analyze likely locations of rainfall which will be integrated with the hydrological modeling. This analysis should lead to a reduced risk for the people and design better soil and water conservation strategies. To improve land degradation analysis, the influence of land use will be analyzed. Coupling land-use landscape processes will be applied. In combination with rainfall distribution analysis (from remote sensing data), identifying of area prone to landslides and soil erosion will be improved by means of where exactly something happens and simulation of on and off site effects. In order to achieve that, coupled land degradation and land-use change modeling, CLUE-s, will be applied. Keywords: Java, land degradation, landuse change, weather variability

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