CLIMATE CHANGE IMPACT ON WATER REQUIREMENTS OF MAIZE AND WHEAT IN UPPER GUDER CATCHMENT, UPPER ABAY BASIN, ETHIOPIA

Abstract

With respect to the relations between the hydrological cycle and the climate system, every change on the climate could affect all meteorological parameters and this leads to change in the crop water requirement. Considering this, a study was carried out to investigate the likely impact of climate change on water requirement of maize and wheat in Upper Guder catchment, Upper Blue Nile Basin. Downscaling canESM2 (Canadian Earth System Model of second generation) global climate model using Statistical Downscaling Model (SDSM) used in this study. Future scenario analysis was performed for the 2020s and 2050s. CanESM2 model consists of Representative Concentration Pathway (RCP) RCP4.5 (medium low emission) and RCP8.4 (medium to high emission) scenarios. CROPWAT8.0 model (FAO, 1992) was used to simulate the daily and seasonal total crop water requirement (CWR) as well as irrigation requirements for the present and the future decades. After quality control, the rainfall data were subjected to computation of rainfall variability indicator indices such as rainfall totals, rainfall start and end dates, length of growing period (LGP), number of rainy and dry days using INSTAT v3.37 software. The analyses of observed data revealed that annual, seasonal Kiremt and Belg rainfall totals were characterized by low amount, short duration and early cessation for both Kiremt and Belg seasons in most of the stations in the study area. The projected increasing change in rainfall totals and decreasing change in rainy days indicated that the future Kiremt season will probably experience water logging/flood over the majority stations and this will affect crop production. The General Circulation Model (GCMs) used in the study agreed on reduction of rainfall amount in the Belg season and shortening of the LGS in both the Belg and Kiremt seasons by 2020s and 2050s in most of stations for both scenarios. The result of downscaled precipitation and temperature reveals a systematic increase in all future time periods for both RCP4.5 and RCP8.5 scenarios. These increases in climate variables are expected to create likely change in total amount of crop water requirement for maize by 4.14% and 6.87% (2020s) and 10.03% and 12.47% (2050s) for RCP4.5 and RCP8.5 scenarios respectively. In line with this, the total amount of crop water requirement for wheat would be expected to increase by 2.45% and 6.01% (2020s) and 7.79% and 11.69% (2050s) for RCP4.5 and RCP8.5 scenarios respectively. In conclusion, results of climate change in this study shows there is likely increase in temperature and rainfall in all time periods. To meet the increasing water demand and to increase yield, over all water resources should be increased by doing water conservation practices (ex situ and in situ) effectively and also farmers’ should be motivated to use supplemental irrigation system.