Application of Budyko framework to irrigation districts in China under various climatic conditions.

Budyko's framework has been widely used to study basin‐scale water balance. In this study, we focus on the extended application of Fu's equation (one formulation of the Budyko‐type curves) to 371 large irrigation districts in China over a period of 2010–2017. Water balance method was used to estimate actual evapotranspiration ET in the irrigated areas. Considering the contribution of shallow groundwater to ET, the water availability in the Budyko framework defined as equivalent precipitation Pe for irrigation areas is the sum of irrigation water I, precipitation P and groundwater evaporation ETgw. Results showed that the relationships between evapotranspiration ET, water availability Pe and energy supply ET0 can be accurately described by the Budyko's curves. The optimal values of Budyko parameter ω for each irrigation district was obtained with multi‐annual data using least square method. The Fu's equation performed better in humid and semi‐humid regions than arid and semi‐arid regions. The comparison between ∂ET/∂Pe and ∂ET/∂ET0 confirmed the relative effect of water availability and energy supply on ET according to the variation of climatic conditions. Normalized difference vegetation index (NDVI) and soil properties (denoted by the proportion of clay and sand) were selected to develop empirical equation for parameter ω using multiple linear regression analysis method. This study shows that the Budyko framework can be extended to irrigation areas and provides useful information on evapotranspiration to assist in water management in irrigation areas. [ABSTRACT FROM AUTHOR]