5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Land use-land cover and

Land use-land cover and normalized difference vegetation index changes in Wello The field survey revealed that the study area has been severely affected by both in-situ and offsite land degradation impacts. As indicated on the DEM, 40% of the study area is steep to very steep (>30%). Steep-slope landscapes are non-resilient to LULC change. As a result, any inappropriate change immediately and permanently impacts the environment negatively. People explained the severity of the problem by comparing the current river flow with that of some years ago. Elderly people witnessed that some decades ago rivers were not as wide as today (Figure 4.9a) and most now flow throughout the year and have ample water. In peak rainy seasons, rivers did not use to carry stones and boulders. In recent decades, during the main rainy seasons (July to September), rivers become full just after peak rains, while in the dry seasons rivers discharge reduces critically and in some cases completely dry. The field survey also indicated that gently sloping lands and valley plains are severely affected by expanding river courses, by land dissection by gullies, and by landslides and all forms of soil erosion (Figure 4.9a). Rivers are expanding on agriculturally potential lands located in valley plains. Land degradation due to river course erosion is not only encroaching on agricultural land but is also creating problems for the traditional irrigation system and threatening accessibility. Traditionally, farmers use earthen irrigation diversions. However, the degradation hampers the practices as the rivers are becoming wide and deep. Moreover, rivers and streams occasionally change direction, consequently damaging farmlands. It is also observed that due to the river and stream route changes, agricultural lands have been destroyed by gravel, stone and boulder deposition. The SWC measures implemented have led to tangible changes in the environment. A clear difference can be observed between areas with and without conservation measures (Figure 4.9). People living around the protected area clearly perceive the advantages. Vegetation cover, bio-diversity and soil fertility restoration and improved forage production are some of in-situ advantages of the conservation. The various offsite advantages of SWC such as exclosure include improvement of downstream hydrology, and decrease in flood risk and riverbank erosion. However, to fully halt the impact of degradation, long-term efforts and large investments are necessary. 54

Land use-land cover and normalized difference vegetation index changes in Wello Figure 4.9 Contrast between (a) degraded and (b) rehabilitated environment 4.3.4 Possible drivers of LULC change in Wello Population growth and LULC changes Agricultural land demand and the need to increase production through shifting cultivation in order to meet the growing population food demand was a major push factor of the LULC change in the Ethiopian highlands (Amsalu et al. 2007). Elderly people mentioned that shifting cultivation, locally termed as Mofer Zemet Ersha, was practiced for a long period in order to maintain soil fertility and crop production. Shifting cultivation and expansion of cultivation and grazing took place at the expense of forest lands (Badege 2001; Amsalu et al. 2007). Conversion of forest lands to cultivation and grazing in the Ethiopian highlands took place on favorable land. The practice still continues on steep landscapes as land becomes limited. The same applies to expansion of cultivation and grazing onto marginal land, which has aggressively continued until recent (Tekle 1999; Amsalu et al. 2007). Population growth has been cited as the major push factor of the LULC change, which in turn results in severe degradation in most northern highlands. A highland reclamation study (FAO 1986) identified the population-pressure-driven LULC as the major cause of land degradation. The studies indicated that expansion of agricultural land already passed the maximum limit for agricultural use, i.e., cultivation and grazing has exhausted marginal lands (Tekle 1999; Badege 2001; Tefera et al. 2002). After the 1984/85 drought, the government took measures such as enclosure and tree plantations to alter the direction of the LULC change (Tekle 1999; Nyssen et al. 55

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