Monthly calibration of Hargreaves–Samani equation using remote sensing and topoclimatology in central-southern Chile

ABSTRACT

Reference evapotranspiration (ET_o) has a key role in irrigation scheduling. In this sense, the Hargreaves–Samani equation (HS) is a reliable and widely used method to estimate ET_o. The HS equation just requires temperature and solar radiation data, making it a suitable method for places that lack of wind speed and relative humidity information. However, literature shows that a local calibration of its empiric parameter is needed for its complete application. This work shows a calibration for the Maule region in central-southern Chile. For this purpose, the Penman–Monteith equation from FAO-56 (PM) was considered as a reference, using a network of 400 meteorological stations between the 32^° and 39^° of south latitude for the 1973–2011 period. The calibration was based on the computation of the ratio of ET_o calculated by HS and PM and the spatial behaviour of input variables and parameters. The spatial distribution was done by geographical weighted regression and ordinary Kriging with a linear variogram, assisted by a digital elevation model from the Shuttle Radar Topography Mission and surface reflectances from Moderate Resolution Imaging Spectroradiometer. The process of calibration was validated with daily data through all months, with comparative errors of 5% against PM.

Acknowledgements

This research was partially supported by the Research Program on Adaptation of Agriculture to Climate Change (PIEI A2C2) of the University of Talca and FONDECYT (1130139, 1020202, and 1161809).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Universidad de Talca, Research Program on Adaptation of Agriculture to Climate Change (A2C2) and FONDECYT [1130139, 1020202, 1161809];