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• Introducing climate (CS) and vegetation seasonality (VS) into the Budyko framework. • CS and VS jointly contribute more than the changes in P and ET 0 in water partitioning. • In average the contributions of VS and CS in water partitioning are equally important. Climate and vegetation changes are main factors influencing water partitioning. However, their impacts on water partitioning are still not well understood. To revisit the interactions among climate, vegetation and water partitioning, this study introduces the climate seasonality (CS) and vegetation seasonality (VS) into the Budyko framework, by using a statistical approach combining the three-parameter Log-logistic probability distribution and multiple linear regression, based on the monthly 〈 P - ET 0 〉 (precipitation (P) minus potential evapotranspiration ( ET 0)) and Normalized Difference Vegetation Index (NDVI). This method is then validated and applied in 86 global catchments to quantify the contribution of climate and vegetation changes to evapotranspiration (ET). Results show that this model can predict well (mean R 2 = 0.81 ± 0.05, P < 0.05) the parameter n , a parameter reflecting the interactions between land surface and atmosphere in the Budyko framework. More importantly, CS and VS jointly control the variation in parameter n , and in average jointly contribute more (mean relative contribution of 57.1 ± 2.3 %) than the changes in P and ET 0 (mean of 42.9 ± 2.3%) to ET. These indicate that CS and VS are at least as important as the changes in P and ET 0 in affecting water balance. Furthermore, the VS contributes slightly lower (mean of 24.9 ± 0.3%) than the CS does (mean of 32.2 ± 2.3%), implying that CS and VS play comparable roles in water partitioning. These findings would be valuable for water resources management and assessing the impacts of climate and land surface changes on water balance in a gradually changing environment. [ABSTRACT FROM AUTHOR]

Understanding evapotranspiration–vapor pressure deficit ( ET - VPD ) hysteresis for different ecosystems can improve our knowledge of vegetation adaptability to a changing environment. However, no previous studies have compared the controlling factors of ET - VPD hysteresis for different agroforestry ecosystems in karst landscapes. Therefore, this study explored ET - VPD hysteresis patterns and the controlling factors for three agroforestry ecosystems, using field observations in a subtropical humid karst catchment from March 12, 2015 to May 26, 2016. The results showed both similarities and differences in ET - VPD hysteresis among the three ecosystems. For example, all three agroforestry ecosystems exhibited noticeable ET - VPD hysteresis, and the hysteric magnitude showed noticeable seasonality with higher values during the growing season. For all three ecosystems, the ET - VPD hysteretic magnitude had no significant relationship with the daily mean environmental factors (e.g. meteorological factors and soil moisture ( θ )), but it was highly ( R 2 > 0.59) correlated to changing rates of meteorological factors (e.g. temperature ( Ta ), relative humidity ( RH ), and vapor pressure deficit ( VPD )) in the morning. The ET - VPD hysteretic magnitude of the forest–grass mixed ecosystem (142.48 ± 74.16 min) was significantly higher than that of the grass ecosystem (104.37 ± 82.93 min). Hysteresis reflected the extent of imbalance between water demand and water supply for ecosystems during a day. Therefore, this study may be helpful in modeling ET and further understanding ecosystem responses to environmental change. [ABSTRACT FROM AUTHOR]

Knowledge of vegetation water depletion and the underlying mechanisms are essential for understanding eco-hydrological processes and fragile ecological environment protection. Based on a 2-year field experiments, this study investigated the transpiration and its influencing factors for three karstic climax forest communities located in the depression (DeC), mid-slope (MsC) and summit (SuC) of a typical karst hill in southwestern China. The meteorological factors, sap-flow, eddy covariance and soil moisture were measured. Results showed that the annual transpiration for SuC, MsC and DeC, were 701.0 mm yr−1, 626.4 mm yr−1 and 663.1 mm yr−1, respectively. The daily transpiration was significantly correlated to the air temperature (r > 0.6, P < 0.05), solar radiation (r > 0.8, P < 0.05) and water vapor pressure deficit (r > 0.3, P < 0.05), but showed no strong relationship with the shallow layer water content (SLWC, 0–40 cm). Moreover, the transpiration of the three communities generally maintained high rate (e.g., > 4.0 mm d−1 in the growing seasons), even when the SLWC dropped to about 0.15 cm3 cm−3 in the SuC during dry spells. Overall, 77.6%, 78.3% and 90.8% of the transpired water in the SuC, MsC and DeC respectively, came from the shallow layer. These suggested that the plants in this region could uptake water from deep layers when the SLWC is limited, and implied that the climax forest communities were generally not limited by water, at least in normal years. • Transpiration of karstic climax forest (KCF) was mainly affected by meteorology. • Most of the water transpired by KCF came from the shallow layer (0–40 cm). • KCF also maintain high transpiration even during dry spells. • KCF should use deeper sources when water in shallow layer is limited. [ABSTRACT FROM AUTHOR]