Wavelet transform analysis of reference crop evapotranspiration during the growing season in three typical regions of Inner Mongolia, China

Management and scheduling of irrigation water requires consideration of evapotranspiration, one of the most important hydrological variables. This study investigates the variations in the daily potential evapotranspiration (ET₀), and its aerodynamic (ET_a) and radiometric (ET_r) components in three areas (western, central and eastern) of the Inner Mongolia Autonomous Region (IMAR) during the growing season (April–September, 2007). In this study, a data-driven approach was followed, and the wavelet transformation analysis method was used to investigate the evapotranspiration characteristics of a relatively large geographic region. The results show that there are close correlations in the variations of ET₀ with those of ET_a and ET_r. For the western area of the IMAR, the timing of the largest ET_a is 1 month earlier and its wave period is 10 days shorter than those of ET₀ and ET_r. For the central area, the wave period of ET_a is 20 days shorter, and the timing of the largest ET_a is approximately 1 month earlier than those of ET₀ and ET_r. For the eastern area, there are two large fluctuations in ET_a, and they occur 1 month earlier than those of ET₀.