Impact of climate change on maize productivity and potential adaptation options for the Central Rift Valley of Ethiopia: A case of Adama district

The study involves an assessment of the potential effects of greenhouse gas climate change, as well as the direct fertilization effect of CO2 on maize crop yield for Adama district. Adama district is located in eastern Showa Zone of the Oromia Regional State of Ethiopia, about 100 Kms east of the capital city, Addis Ababa, geographically with latitude of 8.33ºN and longitude of 39.17ºE. Adama is part of the central Rift Valley and dominated by flatlands stretching between the escarpments bordering the eastern and western sides of the Rift Valley. The altitude ranges from 1380 to 1740m. To estimate the level of impact of climate change on grain yield of Maize, climate change scenarios of precipitation and temperature were developed for future time period which spans from 2001 until 2099. The outputs of HadCM3 coupled atmosphere- ocean GCM model for the A2 and B2 SRES emission scenarios were used to produce the future scenarios. These outputs were downscaled to the production site scale through the application of the SDSM model. Generally, both maximum and minimum temperatures show an increasing trend from the 1971-2000 (base period) level which is estimated to be about 2.1ºC- 3.2ºC, which scales up the diurnal range of temperature to which maize is very sensitive. Further it is estimated that the average monthly and annual precipitation in the production site is likely to show a decreasing trend for the main growing season (June - September); which is estimated about 34% reduction from the base level, adding up critical strain to the already water stressed areas with high evaporative demand of the semiarid areas. The methodology involves coupling the transient diagnostics of atmosphere- ocean general circulation model, namely the Hadley Center's Had CM3, to the CropSyst crop model to simulate current and future (2011-2099) maize crop yield for the district. Hence, the downscaled climate scenarios were applied to CropSyst crop simulation model to simulate future grain yield of maize under the assumption of current production practices. The simulation result revealed that the total average grain yield might decline significantly for both A2a- and B2a-scenarios with yield reduction in the range of 21%-51%. This shows a worsening trend of maize yield reduction which further strains the food security over the area. This, combined with the unbalanced supply- demand equation of the water balance in the production site, is expected to have significant impact on grain production over the district in the future. The simulation results, thus, entails that maize production is likely to decrease in the future and be insufficient to meet future demands for alternative supply of food for the ever increasing population. The results also showed that the effect of temperature patterns on climate changes is much more important than that of precipitation. Findings call for further monitoring of climate change/ variability and dissemination of information to farmers, to encourage adaptation to climate changes as well as assessment of potential adaptation options for the changing future climate conditions. Some potential adaptation options are suggested to cope up with the possible reduction in maize productivity.