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.
Highlights
The severity of water shortage due to increasing demands for inputs is an important issue of socioeconomic and global sustainability [1]
We investigate the effects of local calibration of the Hargreaves–Samani equation
The meteorological data from the MSFB were shown to be more effectively segregated by their seasonal similarities, as opposed to regional similarities
Summary
The severity of water shortage due to increasing demands for inputs is an important issue of socioeconomic and global sustainability [1]. In this context, Brazil is one of the few countries that is able to increase its productivity in a sustainable way [2]; despite the water abundance, most of this resource is available in less populated areas. Its heterogeneous distribution results in conflicts over its use being more common than expected. These disputes arise mainly due to the insufficient amount of water to supply for humans and animals [3]. In the Brazilian Northeast, this problem is commonly related to lower rainfall rates and the large amount of water withdrawn by irrigation activities [4].
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