Impacts of Agricultural Expansion on Irrigation Water Requirements in Taita Hills, Kenya

Maeda, E.E. (2009). Impacts of Agricultural Expansion on Irrigation Water Requirements in Taita Hills, Kenya. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-09-056

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Abstract

The presented work aims to evaluate the impacts of agricultural expansion on irrigation water requirements in Taita Hills, SE-Kenya. The first procedure of this research consists in implementing and calibrating an Evapotraspiration (ET) model for the study area. The ET is an important component of the hydrological cycle and an accurate quantification of such component is crucial for the design, operation and managment of irrigation systems. Three temperature based ET models are evaluated, namely the Hargreaves, the Thornthwaite and the Blaney-Criddle, given that these are the most recommended approaches when only air temperature data are available at weather stations. To overcome the insufficient data retrieved from ground stations, remote sensing land surface temperature data are used as input for the models. One weather station with complete climate datasets is used to calibrate the selected model using as reference the FAO-56 Penman -Monteith method. Simultaneously, future land use scenarios are simulated using a Land Use and Land Cover Change (LUCC) model. Synthetic weather datasets (temperature and precipitation) are generated using a Monte Carlo simulation. Finally, the ET model and the LUCC model are integrated into a modeling framework in order to delineate Irrigation Water Requirement (IW) scenarios. The simulations indicate that throughout the next 20 years the low availability of space in highlands will drive agricultural expansion to areas with higher IWR in the foothills. However, climate changes predicted by GCMs will likely decrease IWR when compared with scenarios using the same temperature and precipitation averages as in the historical dataset.

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