Abstract:
Maize is the second most important cereal crop in eastern Ethiopia. However, climate change and variability is affecting its productivity in the region. Thus, studies that included survey, climate data analysis, and field experiment were therefore conducted with five objectives: 1) to assess smallholder maize farmers’ perception of climate change, their current adaptation options, and factors affecting their use of adaptation options in eastern Ethiopia; 2)to analyze past and projected trends of rainfall and temperature parameters in Eastern and Western Hararghe Zones, Ethiopia; 3) to calibrate and evaluate CERES-Maize model for the study environment; 4) to assess the projected impact of climate change on maize productivity, and 5) to evaluate the selected adaptation strategies to minimize the impact of climate change. In the first chapter, data were collected from 364 household heads in three districts and six kebeles based on maize production potential to assess the perception and response of maize farmers to climate change. The multinomial logit model was used to evaluate determinants of climate change perception and adaptation. The results of the study showed that smallholder maize farmers perceived an increase in temperature (78%) and a reduction in rainfall (83%) amount. Farmers also perceived climate variability in terms of erratic rainfall, late-onset and early cessation were consistent with observed historical climate data analysis. Adaptation strategies that the farmers apply to counteract the negative impact of climate change were found to be influenced by socioeconomic and institutional factors. In the second chapter, a climate analysis was made using data from five stations selected from East and West Hararghe Zones, based on a relatively long period of past data records. Projected changes in rainfall and temperature under the future climate periods (2030s and 2050s) under (Representative Concentration Pathways) RCP4.5 and RCP8.5 from 17 CMIP5 (Coupled Model Inter-comparison Project Phase Five) GCMs (Global Circulation Models) were also analyzed. The result of the study revealed that for the past three decades rainfall showed variability. Maximum and minimum temperature showed an increasing trend with significant Belg season minimum temperature across the study districts. The ensemble model projection of rainfall and temperature in 2030s (2021–2050) and 2050s (2041–2070) under RCP4.5 and RCP8.5 indicated a significant change in the parameters compared to the baseline period (1988–2017). The mean annual minimum temperatures are projected to increase by up to 2.92 °C in 2030, and 4.15 °C in 2050 while the mean maximum temperature is expected to increase by 1.14 °C in 2030, and 1.87 °C in 2050. Annual rainfall amount is also projected to increase by up to 29% in 2030, and 32% in 2050 under both RCP. In the third chapter, a field experiment was conducted in 2019 and 2020 main crop growing seasons using four maize cultivars at Haramaya, eastern Ethiopia to calibrate and evaluate the CERES-maize model. In both experiments, treatments were arranged in a randomized complete block design (RCBD) and replicated three times per treatment. Growth, development, and yield data were collected for model calibration and evaluation. The result indicated that the CERES maize model well simulated the growth, development and yield of maize cultivars with observed and simulated values in good agreement indicating that the model can be used to simulate maize response to environmental factors in the study area. Hence, it can be used further for assessing the impact and adaptation strategies under the conditions of Haramaya, eastern Ethiopia’s xviii ecological conditions. In the fourth chapter, an impact analysis study was performed using 2030s and 2050s projected climate data under RCP4.5 and 8.5 with and without CO2 fertilization.The result of the study indicated that the projected changes in temperature and rainfall by 2030s and 2050s without CO2 fertilization are expected to reduce the grain yields of the maize cultivars by up to 12.3%, and 9.2%, respectively across GCMs under both RCP. However, increased CO2 concentration across the studied cultivars and climate models predicted an increase in grain yield by up to 1% in 2030s and 2% in 2050s compared to simulated yield without CO2 fertilization under both RCP. In the fifth chapter, potential adaptation practices (five planting dates, four nitrogen fertilizer rates, and two maize maturing groups) were evaluated. According to the predicted result, the interaction effect of cultivars, planting dates and nitrogen fertilizer rates significantly (p < 0.01) influenced maize grain yield in the baseline climate. Planting late maturing (BH661) in the early 01 and mid (31 May) with an application of 130.5 kg N ha–1 gave a higher yield than the rest of the treatments under the baseline climate. In 2030s and 2050s under RCP4.5 and 8.5 the interaction effect of cultivars, planting dates, and nitrogen fertilizer rates is predicted not to significantly influence maize grain yield. However, in 2030s the interaction effect of cultivar and planting date, cultivar and nitrogen fertilizer rate, and nitrogen fertilizer rates and planting date is projected to significantly (p < 0.01) influence maize grain yield under RCP4.5 and 8.5. The results of the study indicated that planting a late-maturing cultivar (BH661) on the 15th of May with an application of 130.5 kg N ha–1 predicted a higher yield than the rest of the treatments studied. In 2050s the interaction effect of cultivar and nitrogen fertilizer rate under both RCP as well as nitrogen fertilizer rates and planting dates under RCP8.5 significantly (p < 0.01) influence maize grain yield. Planting late maturing (Raare-1) cultivar with 87 kg ha–1 nitrogen fertilizer application under RCP4.5 and late maturing (BH661) cultivar with 130.5 kg ha–1 nitrogen fertilizer application under RCP8.5 is predicted to give higher maize grain yield. The study, in general, indicated an increase in temperature and variability of rainfall under the future climate affect the productivity of maize in Eastern Ethiopia. Using late-maturing maize cultivars by optimizing planting dates and fertilizer applications showed promise to offset the impact of climate change on maize productivity in Eastern Ethiopia and similar environments.