Annual variations of T/ET in a semi-arid region: Implications of plant water use strategies

•An intra-annual bimodal dynamic of monthly T/ET (0.14–0.84) was revealed.•Switches of physiologic status relating to dormancy produced dramatic changes in T/ET.•SIF is linearly related with T/ET and WUE_T at a monthly scale.•Monthly WUE_T increases from 1.84 to 2.76 gC/kgH2O to survive non-growing seasons.•Monthly WUE_T remains 2.1 gC/kgH2O during growing seasons for production.