Abstract
Reference evapotranspiration is very important parameter in the hydrological, agricultural and environmental studies and is accurately estimated by the FAO Penman-Monteith equation (FAO-PM) under different climatic conditions. However, due to data requirement of the FAO-PM equation, there is a need to investigate the applicability of alternative ETo equations under limited data. The objectives of this study were to evaluate twelve mass transfer based reference evapotranspiration equations and determine the impact of ETo equation on long term water management sustainability in Tanzania and Kenya. The results showed that the Albrecht, Brockamp-Wenner, Dalto, Meyer, Rohwer and Oudin ETo equations systematically overestimated the daily ETo at all weather stations with relative errors that varied from 34% to 94% relative to the FAO-PM ETo estimates. The Penman, Mahringer, Trabert, and the Romanenko equations performed best across Tanzania and the South Western Kenya with root mean squared errors ranging from 0.98 to 1.48 mm/day, which are relatively high and mean bias error (MBE) varying from -0.33 to 0.02 mm/day and the absolute mean error (AME) from 0.79 to 1.16 mm/day. For sustainable water management, the Trabert equation could be adopted at Songea, the Mahringer equation at Tabora, the Dalton and/or the Rohwer equations at Eldoret, the Romanenko equation at Dodoma, Songea and Eldoret. However, regional calibration of the most performing equation could improve water management at regional level.
Highlights
Evapotranspiration is an important parameter for climatological and hydrological studies as well as for agricultural water resources management [1] [2]
The Trabert equation could be adopted at Songea, the Mahringer equation at Tabora, the Dalton and/or the Rohwer equations at Eldoret, the Romanenko equation at Dodoma, Songea and Eldoret
The Albrecht, Brockamp-Wenner, Dalto, Meyer, Rohwer and Oudin ETo equations systematically overestimated the daily ETo at all nine weather stations with relative errors that varied from 34% to 94% relative to the FAO Penman-Monteith equation (FAO-PM) ETo estimates
Summary
Evapotranspiration is an important parameter for climatological and hydrological studies as well as for agricultural water resources management [1] [2]. The accuracy of reference evapotranspiration (ETo) estimates directly feeds into the decision making process for regional water resources planning and, especially under semi-arid and arid conditions. FAO-PM model requires maximum and minimum temperature, minimum and maximum relative humidity, solar radiation, and wind speed data to be run and these weather datasets are usually incomplete and/or not available in most developing countries. This data demand is the main constraint of use of the FAO-PM in locations where climate data is limited [14]-[17]. The evaluation of the suitability for each of the alternative ETo equations to determine the most suitable for particular locations using FAO-PM model as reference is required for the East Africa Region prior to their application
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