Detection and Analysis of Land Use and Land Cover Changes in Tigray, North-Ethiopia

SummaryMany parts of the world are suffering from environmental problems such as deforestation. Many papers described the causes and consequences of deforestation but very little information is available on mechanisms and effective policy measures that slow down deforestation rates. The motivation behind this PhD-research research was the hope that a better understanding of the mechanisms would help policy makers take the appropriate actions to stimulate forest transitions. The northern Ethiopian highlands were selected as a case study because evidence was available that at least in some local, possibly isolated cases, regreening was observed during the last decades. This research addressed 3 main questions: (1) what are the regional trends of land use and land cover change that took place in the northern Ethiopian highlands? (2) Can the observed land use and land cover change be linked with socio-economic, demographic, political or environmental factors? (3) Is it possible to outline optimal land use patterns that minimize future land degradation and maximize production and profitability?Detection of differential greening is, therefore, premeditated under chapter 2. This chapter presents a methodology to evaluate land cover changes on the basis of NDVI time-series derived from NOAA_AVHRR and SPOT vegetation sensors. The results show that the aggregated greenness in Tigray has declined between 1982 and 2010. On the basis of interpolated rainfall data, it was tried to disentangle the effect of fluctuations in preceding rainfall and human impact on the landscape greening. From 2000 onwards the degreening trend was slowed down and in some cases even reversed, which could partially be attributed to land abandonment on completely degraded land and the relative success of soil conservation measures.To evaluate the link between observed land use and land cover change and the socio-economic, demographic, political or environmental factors, a detailed study was carried out in 5 rural villages (chapter 3) and the Dessa a forest (chapter 4) for 3 different time-frames: 1965, 1994 and 2007. The maps were based on the interpretation of aerial photographs and high-resolution satellite imagery in combination with field validation. The results from rural villages showed a strong decrease of the forest and bush land in favor of arable land and rangeland from 1965 till 1994. This trend was, however, slowed down and even reversed from 1994 onwards whereby some of the arable land and rangeland is abandoned allowing shrubs and bushes to regenerate. However, household interviews and census data showed that the rural population number was still increasing while the productivity of the farming activities did not show a significant increase. The observed abandonment of marginal farm and rangeland was, therefore, only made possible through food aid and the import of food from other regions. The results from the Dessa a forest also showed that the forest cover of the area has decreased. While the area ofarable land and built-up surfaces have increased during these years. Population pressure was the most influential factor for the decline in forest cover in the study villages. Distance to built-up surfaces, distance to main roads and rivers, variation in slope, elevation and aspect were significant variables on forest degradation on major part of the study area. Changes in forest policies, have also contributed to the decline in forest cover. The extent to which land use patterns can be optimized to minimize further land degradation and to maximize the incomes generated from farming was examined (chapter 5) in the catchment of the Geba River. An ordinal classification of soil erosion rates and profitability assessments were put in a spatial decision support system in order to generate optimal land use patterns. The profit maximisation scenario showed that in order to generate higher profits, the landscape must be organised in a sort of Von Thünen landscape with concentric rings surrounding the market places. The erosion minimization scenario showed that a concentration of all the arable land in the less erodible places would reduce the average soil erosion rate. The mixed scenario s in which reduction of erosion and increase of profitability were both taken into account showed that the definition of the weights of the performance indicators is of crucial importance. If the generation of total profits is emphasized, the corresponding land use pattern would consist of even more arable land than the present day situation. If soil conservation received more weight the optimal landscape would consist of less arable land but with a higher area-specific profitability.nrpages: 217status: publishe