[A-AS05] From Weather Predictability to Controllability

[AAS05-P02] An Analysis of Climate Variability and Agroclimatic Zone Shifts in the Tana River Basin

*Daniel Mwendwa Wambua^1,2, Hiroaki Somura¹, Toshitsugu Moroizumi¹ (1.Graduate School of Environmental and Life Science, Okayama University, Japan, 2.Department of Soil, Water, and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, Kenya )

Keywords:adaptation and mitigation, aridification , climpact indices, pastoralism , tea and coffee farming

This study aimed to assess climate variability and agroclimatic zone shifts in the Tana basin, considering historical and future climate scenarios from CMIP6. Six indices from the expert team on climate change detection and indices (ETCCDI), including standardized precipitation evapotranspiration index (SPEI), warm spell duration index (WSDI), cold spell duration index (CSDI), total precipitation (PRCPTOT), growing degree days (GDD), and consecutive dry days (CDD), were utilized. Statistical computations were performed using the CLIMPACT package in R, and spatial maps were generated in ArcGIS. The Tana basin's moisture index (MI) was calculated using CHIRPS precipitation and Global reference evapotranspiration data in ArcMap, delineating the watershed into agroclimatic zones via kriging interpolation based on Thornthwaite moisture index ranges. Results indicated a slight increase in WSDI alongside a decrease in CSDI during the historical period, impacting water resources availability, as reflected in more frequent drought events, SPEI<0. Under SSP scenarios, the catchment is projected to receive increased total precipitation, more warm spells, and reduced cold day spells. GDD decreased inland from the coast, while PRCPTOT increased inland for different scenarios and the historical period. CDD were highest downstream compared to upstream. Minimal shifts in agroclimatic zones were observed in 1981-2020, but an increase in the arid and sub-humid zones by 6.7% and 1.3%, respectively, occurred. The increase in arid zones will affect pasture and water resources which are important among the pastoral communities in these areas. Moreover, a reduction of moisture index in the sub-humid region dominated by tea and coffee by 2% will cause water stress among these crops and lead to reduced yields. In conclusion, significant spatial variations in rainfall, temperature, and water resources are expected in the Tana basin. Upstream areas may experience higher rainfall and favorable temperatures, while the rest of the basin may face reduced rainfall and elevated temperatures. Effective adaptation and mitigation strategies are crucial to prevent crop losses and optimize water resource utilization.