Abstract: 【Objective】The Changwu Tableland was taken as a study area in consideration of its typical representative of the Loess Plateau. The purposes of the study were to estimate water consumption rate of 19 a apple trees at different time scales by environmental factors, and provide a theoretical basis for the scientific distribution, sustainable management and production capacity of apple trees. 【Method】Thermal dissipation probe (TDP) was used to measure sap flow velocity of 8 standard 19 a apple trees on the Changwu Tableland located on the Loess Plateau from May to September, 2014, the data collector CR1000 (Campbell Scientific, UN) was used to collect and analyze the data, and the meteorological data were monitored continuously by automatic weather station 50 m away from the plot. The characteristics of sap flow were analyzed, and the relationship model between the rate of sap flow rate and environmental factors at different time scales was established.【Result】 The most close correlations between the sap flow velocity of the 19 a apple tree and various environmental factors at the hour scale was vapor pressure difference (VPD). Radiation (Rs), wind velocity (Ws) and soil temperature (Ts) also showed significant correlations with the sap flow. The sap flow curve had a single peak. The empirical model for the hour scale was: v=-11.683+2.3VPD+0.009Rs+0.55Ts+0.880Ws. At the day scale, Ts and VPD were significantly correlated with the sap flow velocity. The empirical model for the day scale was: v=1.637+0.404Ts- 3.097VPD. The sap flow velocity showed an order of August＞July＞June＞September＞May. Only Ts showed a correlation with the sap flow velocity. The empirical model for the month scale was: v=-3.524+0.509Ts. With the increasing time scales, the number of environmental factors associated with the sap flow velocity was gradually reduced, but Ts was the dominant factor at every scale and the correlation coefficients were gradually increased. Wind velocity (Ws) showed a significant correlation at the hour scale. VPD had a significantly positive correlation with the sap flow velocity at the hour scale and a significant and negative correlation at the day scale. The correlation between the Rs and sap flow velocity at the three time scales was not found. For the three stepwise regression equations, the correlation coefficient for the month scale was the largest. 【Conclusion】 At the larger time scale, the consumption of water can be estimated by monitoring a small number of environmental factors, but at the smaller time scales, most of the environmental factors will influence the sap flow. Therefore, estimates of the consumption by the environmental factors cannot be achieved with a great accuracy, and the method of TDP needs to be used to monitor the consumption.

Key words: apple, TDP, sap flow velocity, time scale, environment factor