Computing Evaporanspiraton from Weather Data Obtained from Distant, Non-Reference Weather Stations in a Hyper-Arid Region

Problem statement: Reference agro-climatic Weather Stations (WS) are rarely found in newly reclaimed areas. The usage of weather data from non-reference WS may lead to inaccurate estimations of Evapo Transpiration (ET), especially if the non-reference stations are distant from the reclaimed location. Approach: Weather data from four WS located at Riyadh were used to calculate ET by using Penman Monteith (PM) and Hargreaves equations. PM equation was applied with both alfalfa and grass reference crops. Calculations were done with and without temperature correction for non-reference weather stations. All calculations were compared with measured lysimeter data and corrections in Hargreaves formula were suggested. Results: (1): Weather data from non-reference WS can be used safely to calculate ET only when temperature corrections are applied. (2) Hargreaves formula underestimates ET at all locations in the study area. By applying the simple linear correction to the data, highly acceptable results are obtainned. (3) The ET ratio between alfalfa and grass in Riyadh is 1.25. Conclusion: The study concluded that temperature correction for non-reference WS is essential to ensure acceptable ET calculations. Usage of Hargreaves formula is recommended with the corrections suggested in the study due to its simplicity.