Transpiration theory and the Prospero component of GEOframe

Evapotranspiration plays a key role in the land-atmosphere interaction and has for long been recognized as the most important process in the determination of the exchanges of energy and mass among them, representing approximately the 40% of total precipitation and of the net radiation absorbed. Our ability to quantify evapotranspiration is limited by several factors such as the scarce availability of its measurements and the high uncertainty they present; and the lack of appropriate modeling methods, as highlighted by some recent papers and its response to climate change ('drought paradox'). In the first part of this thesis we present an extensive literature review of the transpiration theory starting from the milestones until the newest works. In particular we focused on the physics of the process and faced some omissions rising from recent studies. We also addressed some physiological feature of transpiration process and the rising issues from the upscaling techniques.Later on we introduced a newly developed model called "Prospero", used to estimate the evapotranspiration, that can be used as a component in the GEOframe hydrological modelling system. The physical description of the process provided by Prospero is in agreement with what emerged from the previous literature review and in particular corrects the omissions given by the feedback of the leaf temperature and the wrong representation of the transpiring area, further improved with the inclusion of a model of canopy layers. In addition, it also includes several environmental stress functions based on the physiology of the leaves. These improvements allow the closure of the energy balance and the conservation of the water mass.Finally the Prospero model is applied on two case studies: the first one is pointwise case study represented by two Alpine grasslands (Viote del Monte Bondone, Trentino and Torgnon, Valle d'Aosta) where the estimation of Prospero evapotranspiration is compared with eddy covariance station measurements, and the second one is represented by a small experimental basin in Ressi (Posina, Veneto). Even if not calibrated, Prospero provides good results in the prediction of evapotranspiration, capturing the daily trend and obtaining an error that can be compared with what was found in literature for similar cases. The estimation provided, even if it presents a greater dispersion, gives better results when compared to the other components of GEOframe. In both case studies the performance of Prospero is compared with the other GEOframe components for evapotranspiration. To this result, Prospero represents an improvement since it gives better performances if compared with the other GEOframe components and allow us to compute other environmental variable like sensible heat and canopy temperature. Thanks to its components-based structure Prospero can be easily improved and represents the core for a future ecohydrological or a lysimiter model.