Articles | Volume 15, issue 8
Hydrol. Earth Syst. Sci., 15, 2495–2508, 2011

Special issue: Looking at catchments in colors: new ways of generating, combining...

Hydrol. Earth Syst. Sci., 15, 2495–2508, 2011

Research article 11 Aug 2011

Research article | 11 Aug 2011

Generating reference evapotranspiration surfaces from the Hargreaves equation at watershed scale

C. Aguilar and M. J. Polo C. Aguilar and M. J. Polo
  • Fluvial Dynamics and Hydrology Research Group, University of Córdoba, Córdoba, Spain

Abstract. In this study, Hargreaves' formulation is considered to be appropriate for the water and energy balance at a daily scale due to its simplicity of application once the distributed values of temperature are available at cell scale. However, the coefficient of the Hargreaves equation must be previously calibrated. The interplay of different factors at different temporal scales became evident in the calibration process at the local scale of weather stations. The best fits against daily estimates by ASCE-PM were achieved when differentiating between the wet and the dry season. For the spatial distribution of Hargreaves coefficient at watershed scale, a regionalization in the area around each weather station was proposed in terms of areas of influence. The best results at watershed scale were obtained after a spatial correction for alpine areas, when the average of the difference cell by cell between ASCE-PM and Hargreaves's distributed daily estimates were 0.02 and 0.15 mm day−1 for the wet and the dry seasons, respectively. In all the cases, the best interpolation results were obtained using C-I (calculate and interpolate) procedures.