ABSTRACT Flooded rice ecosystems are typically maintained with a 5–10 cm water layer, which strongly influences surface energy and water balance processes. As evapotranspiration (ET) is a crucial part of surface water and energy cycles, understanding its response to ponding depth is essential for water resource management. A two‐year experiment was conducted using lysimeters to investigate the seasonal dynamics of ET under different ponding depths: shallow flooding (SF, 0–2 cm), medium flooding (MF, 5–7 cm), and deep flooding (DF, 8–10 cm). Results showed that evaporation ( E ) gradually decreased with increasing water depth, whereas transpiration (Tr) first increased and then declined. Seasonal ET followed the order MF (511.65 mm) > DF (498.55 mm) > SF (484.25 mm), consistent with the pattern observed for grain yield, while no significant differences in water use efficiency were detected among treatments. Daytime ET rates varied across the growth stages, with the order SF > MF > DF in the early stages and MF > SF in the middle and late stages. This shift was related to the partitioning of E and Tr and their distinct responses to water depth. Structural equation modelling analysis indicated that radiation was the dominant meteorological driver of ET through direct effects. LAI exerted an important indirect influence. Water depth affected microclimate and crop physiological parameters, resulting in different responses of E and Tr. E was exponentially correlated with water temperature and declined with increasing ponding depth, whereas Tr exhibited a logarithmic relationship with canopy conductance, as determined by LAI and leaf stomatal conductance, in the order of MF > SF. This study provides insights into the effects of irrigation management on rice water use and the environmental and biophysical controls that influence rice ET.
Wang et al. (Thu,) studied this question.