Evapotranspiration: Present and Future Challenges

The thesis first explored and evaluated some of the most used models that were developed to account for the effect of CO2 on evapotranspiration. This review depicts the complexity of the modeling procedure and underlines the advantages and shortcomings of each model. Then, the projected climate change in the near future (2021-2050) in different locations in Emilia-Romagna (Italy) was studied, with an emphasis on the opposite effect of an increase in both air temperature and CO2 levels on ETo. The case study used reanalysis data as a surrogate to historical weather stations measurements and an ensemble of regional climate models (RCMs) for the future projections. Results show that higher CO2 levels moderated the increase in ETo that accompanies an increase in air temperature, taking in consideration the change in other weather variables i.e. solar radiation, wind speed and dew point temperature. The outcomes of this study show that considering the CO2 fertilization effect when calculating reference evapotranspiration might give a more realistic estimation of water use efficiency and irrigation requirements in Emilia-Romagna and a better analysis of the future availability and distribution of water resources in the region. Finally, data from a model forecasting reference evapotranspiration (FRET) and the different variables involved in its calculation for the state of California (USA) were compared with similar data from the regional weather station network (CIMIS) to evaluate their accuracy and reliability. The evaluation was done in locations with different microclimates and included also sample irrigation schedules developed using FRET ETo. The obtained results demonstrate that FRET ETo forecasts are a viable alternative to traditional ETo measurements with some differences depending on the climatic condition of the location considered in this study. This implies that FRET could be replicated in other areas with similar climate settings.