Improvement of Hargreaves–Samani Reference Evapotranspiration Estimates with Local Calibration

Abstract

Improving irrigation water management is an important asset when facing increased water shortages. The Hargreaves–Samani (HS) method is a simple method that can be used as an alternative to the Penman–Monteith (PM) method, which requires only temperature measurements for estimating reference evapotranspiration (ETo). However, the applicability of this method relies on its calibration to local meteorological specificities. The objective of this study was to investigate the effects of local calibration on the performance of the HS equation. The study was carried out for the middle portion of the São Francisco River Basin (MSFB), Brazil, and considered four calibration approaches: A1—single calibration for the entire MSFB; A2—separate calibration by clusters of months; A3—by clusters of stations; and A4—for all contexts resulting by combining A2 and A3. Months from the wet season showed larger improvements by the calibration of the HS model, since mean air temperature and its daily range showed stronger correlations to ETo. On the other hand, the months from the dry season and stations from the eastern region of MSFB performed poorly regardless of the calibration approach adopted. This occurred because, in those cases, ETo presented larger correlation to variables that are missing in the HS equation, and the use of the full PM equation seems unavoidable.

Evapotranspiration in the Brazilian municipalities surrounding the Itaipu Binacional reservoir: characterization process and estimation methods

“…07) for estimating solar radiation may be a good alternative for the region. In relation to the HG-S method, it shows great potential to be applied in the region, since it is easy to apply, requires only maximum and minimum air temperature data and presents the possibility of local calibration of its coefficients, which can reduce the estimation errors [5,34].…”

ETo‐Brazil: A Daily Gridded Reference Evapotranspiration Data Set for Brazil (2000–2018)

“…When lacking meteorological data or a complete meteorological station, many researchers and decision makers have used methods, which are limited in input or neighbor stations (Althoff et al, 2019; Feng et al, 2017; Ferreira et al, 2019; Hargreaves & Allen, 2003; Landeras et al, 2018; Zhu et al, 2019). Yet the performance of those methods is, in many cases, and even after calibration, lower than the performance of the gridded ETo developed here.…”

Improvement of reference crop evapotranspiration estimates using limited data for the Brazilian Cerrado

“…The small or insignificant improvements for the methods on a seasonal basis are, despite the better-adjusted parameters, the result of their lack of information on variables such as wind speed and relative humidity. For instance, other studies also concluded that only minor improvements could be achieved for the HS equation in the dry season for a border region between the Cerrado, Caatinga, and Atlantic rainforest with climate classified as tropical, semi-arid, and humid subtropical for the weather stations studied (Althoff et al, 2019). As wind speed correlation to ETo increases in the dry season, and relative humidity also has a relatively high correlation to ETo, it is difficult for the models to capture the ETo dynamics in this period without them.…”