Abstract

The Ethiopian Constitution asserts state ownership of land. There are no private property rights in land – it is the common property of the people of Ethiopia; however, the state may allocate small plots of land to farmers. Since the 1990s, the government has formulated a long-term economic development strategy called Agriculture Development Led Industrialization (ADLI), which is its overarching policy response to Ethiopia’s food security and agricultural productivity challenge. The strategy focuses primarily on the expansion of large-scale commercial farms and improved productivity in smallholdings. The Ethiopian government identified Gambella region as one of the regions in Ethiopia suitable for agricultural investments, and classified most parts of the area as under-utilized, having a huge potential for agriculture production. However, the unintegrated plan on large-scale land acquisition has caused tremendous environmental devastation in the region, including deforestation, biodiversity depletion, and the draining of wetlands. There are several issues that need to be addressed in depth for a future, sustainable development. This thesis, however, will focus mainly on three aspects: (1) examining the rate, extent and distribution of various land-use land-cover changes (LULCC) in Gambella Regional State and looking at the expansion of farmland and different farming intensities in the region; (2) estimating the magnitude and extent of the intensification potential of the key Gambella cereal crops (maize and sorghum) and seeking to identify potential cropland expansion areas in the region; and (3) investigating the impacts of future climate change on potential crop yields, with maize as an exemplar, under climate change scenarios in Gambella, Ethiopia. 1) In the last three decades (1987–2017), the rate, extent and distribution of various LULCC in Gambella has depended on three main factors: resettlement, population growth and increasing agricultural land pressure. All three factors contribute to LULCC in the region. An LULCC analysis was conducted, based on Landsat 5 and Sentinel 2A satellite images and fieldwork. The results show that farmland decreased by 26km2 from 1987–2000; however, during the last two decades, agricultural land area increased by 599km2, mainly at the cost of tropical grasslands and forests. The results also show that tropical grasslands declined by 17.76% from 1987–2017. Gambella National Park, which is the nation’s largest national park and ecosystem, was also affected by cropland expansion. 2) Over the past few decades, population growth has aggravated rapid agricultural land expansion and intensification in the region. As a result, the Ethiopian government has used agricultural intensification and cropland expansion as the key policies to increase food production in Ethiopia. Although Gambella is one of the regions in Ethiopia that is highly suitable for agriculture, the local people still face food shortages. Thus, to understand the potential food production of the region, the biophysical process-based model PROMET (Process of Radiation Mass and Energy Transfer) was run for the Gambella region on both the actual and all potentially suitable cropland for six selected scenarios (different degrees of intensification, ranging from low-input rainfed to high-input irrigated agriculture and degrees of expansion, considering the best 30% or 50% of land to be utilized for expansion) for the period 1997–2017, with a spatial raster grid of 30 arc seconds (approx. 940 × 940m) resolution,to provide information on potential crop yields. Land-use scenarios of agricultural intensification and expansion results reveal that Gambella could serve as a bread basket for the entire country, which could improve national food production. The potential calorie production in the potential area of the region by far exceeds the current and possible future caloric requirements of Gambella’s population. For instance, for the top 50% expansion scenario, calorie production increased by +428% for the low input scenario and by +1,092% for the high-input scenario, compared to the reference calorie crop production of the region. By assuming a daily diet of 2,200 kcal/cap/day, Gambella region’s calorie production in high-input scenarios could nourish up to 21 million people, thus improving national food production. 3) Unintegrated large-scale agricultural investment, inappropriate cropland expansion, poor intensification and changing climate conditions have caused tremendous impacts on agricultural production. In the region, temperature increase, changing soil water availability and atmospheric CO2 concentration have different effects on the simulated yield potential, and the results demonstrate that the dominance of heat response under future climate conditions is contributing to 85% of changes in total yields. For the Gambella region, on today’s cropland and to the best (in terms of highest potential yields) 50% expansion area, under rainfed and irrigated conditions, climate change impacts on yields until 2100 for Representative Concentration Pathways (RCPs) 2.6, 4.5, and 8.5 from a climate model ensemble show that rainfed yields will decrease by 15% and 14% respectively for RCPs 2.6 and 4.5, and that yields will decrease by up to 32% under RCP 8.5. Irrigated maize yield decreases by 4.3%, 23.0% and 44.5% under RCPs 2.6, 4.5 and 8.5, respectively, for same period. While higher temperature determines the phenological progress of crops and decreases the growing period of maize by up to 23 days under rainfed agriculture, temperature stress also reduces the rate of photosynthesis. We show that temperature stress is mainly responsible for yield reduction under future climate conditions in the Gambella region. Therefore, new varieties with higher growing degree days are primarily required for the region in order to adapt to future climate conditions. To sum up, the thesis shows the intricacies between LULCC, potential yield production and future impact of climate change on the potential food production in the region. Gambella region is still far away from a terminal stage of human interference. This opens up the chances to develop and implement policies to ensure the sustainable future agriculture development of the region.