The effects of global warming, climate change and landuse changes on catchment water balance and quality have become the main concerns in the watershed water resources management in recent years. One such area is the Taleghan watershed in the Northwest of Tehran, the Iran’s capital with an area of 930.62 km2. This watershed has undergone excessive landuse changes during the last two decades due to the dam construction. Both dam construction and its reservoir have highly increased the land prices in this area, causing drastic landuse changes. Digital Image Processing (DIP) technique was introduced to recognize landuse change detection for different periods. To evaluate landuse change, the whole upper part of the watershed was considered over two decades of 1987 to 2007. The results of image processing indicated that after the approval of dam building, the watershed rangeland areas declined from 82.7 to 35.4%. Land ownership caused drastic degradation in landuse during that period. As the consequence, dry farming activities lost their stability and severely declined. The good rangeland (G1) area which was initially 32287 ha in 1987, decreased to 5693 ha by late 2007 due to overgrazing, weak landuse management and climate change. This is a significant change during the last 20 years from 34.5 to 5.90%. On the other hand, concurrently, the poor rangeland increased from 19.0 to 23.4%. Immigration and rush for land purchase and suburb house construction increased the percentages of rural area to urban textures which translates to 3.1 km2 in 2007 compared with its original density of 1.74 km2 in 1987.
Key words: Taleghan, landuse, image processing.
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