Abstract
The evapotranspiration demand of the Awati irrigation district has changed with irrigation development since 1980. During the first period of traditional irrigation expansion from 1980 to 1997, reference crop evapotranspiration (ET0) decreased as irrigation intensity increased. Since the second period of water-saving irrigation extension began in 1998, the gross irrigation quota has decreased as the water use efficiency improved, whereas ET0 has been increasing accordingly. The increasing evapotranspiration demand has enlarged the irrigation water requirement per unit area, which partly weakens the effects of water-saving irrigation. Findings show that irrigation-induced changes in evapotranspiration demand should be considered when evaluating the performance of water-saving technologies in irrigation districts in arid areas.
Highlights
As the most important component of water use, irrigation accounts for approximately 80% of global freshwater consumption [1]
Irrigation water use is classified as either consumptive or non-consumptive, considering that only a fraction of irrigation water withdrawal is lost through evaporation [2]
As the purpose of this study is to evaluate the changes in water requirement corresponding to irrigation expansion, a single growing cycle for each crop was assumed during the study period
Summary
As the most important component of water use, irrigation accounts for approximately 80% of global freshwater consumption [1]. Evapotranspiration is the most important part of consumptive use [3], which includes crop evapotranspiration, excess soil water and phreatophyte evapotranspiration, and canal and reservoir evaporation. Where P is precipitation; I is irrigation water withdrawal from outside; ETcrop is crop evapotranspiration; ETn is non-crop evapotranspiration, i.e., evapotranspiration from water surface, natural vegetation, and bare soil; D is discharge to drainage; ∆Sw is change in regional water storage; and R is local river runoff. Beneficial use is defined as that which supports crop production; ETcrop is regarded as the main component of beneficial use, whereas the majority of ETn is considered to be of non-beneficial use [2]. Soil evaporation in excess of basal is considered to be non-beneficial in the arid southwest part of the United States [9]
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