Air Temperature and Actual Evapotranspiration Correlation Using Landsat 5 TM Satellite Imagery

Abstract

Actual evapotranspiration is a significant component of the water cycle and it is a function of weather data. Moreover, it is difficult to measure. Air temperature is normally measured in a number of weather stations. Since temperature relates to many other weather variables, temperature can be used to infer the characteristics of other weather data. For example, high temperature is associated with low humidity but high evaporation can occur under conditions of high temperature. Thus, the purpose of this study was to determine the relationship between air temperature and actual evapotranspiration. To achieve this objective, spatial temperature and spatial actual evapotranspiration were calculated using the concept of surface energy balance in conjunction with Landsat 5 TM satellite imagery. Thereafter, actual evapotranspiration for each temperature was averaged. Finally, the relationship between air temperature and actual evapotranspiration was determined using a polynomial equation. The results showed that the mean air temperature and the daily mean actual evapotranspiration were 296.4 °K (23.4 °C) and 4.1 mm, respectively. The temperature in Kelvin, could be explained by the equation y = -0.028x² + 17.069x - 2593.2, where y is the actual evapotranspiration (mm.) and x is the temperature. The equation can be applied to estimate the actual evapotranspiration when the temperature is known. Thereafter, daily actual evapotranspiration is defined when the reference evapotranspiration calculated from weather data in the same area is also known.