Hi Marcel, as you know. transpiration depends a lot upon tree species, phenology and soil moisture, and hence obtaining this from climate data has questionable accuracy. However, as a first approximation, meteorological data ( net solar radiation, air temp, RH and windspeed)  can be used to estimate ET using a variety of models (like Penman Monteith for alfalfa, or crops with added crop coefficients, or Shuttleworth version of PM that has veg height and LAI). Just temperatue alone can be used wih Hemon's eqn for instance. for ET. Note again that these models estimate ET and not just T. If you have diurnal water level profiles, can use White method (1932) to estimate plamt water uptake, with some assumptions. 

It is difficult to estimate sweating this way. But it is possible to calculate the Evapotranspiration (transpiration and evaporation of a local and a culture). ETo and ETc of the culture .... view attachments work and references.

Transpiration can be calculated using the calibrated thermocouples inserted into stems or trunks of trees. Using micrometerological data you are measuring or evaluating using any of the different techniques both soil evaporation and transpiration.