Impacts of climate change and rising atmospheric CO2 on future projected reference evapotranspiration in Emilia-Romagna (Italy)

The continuous increase of atmospheric CO2 content mainly due to anthropogenic CO2 emissions is causing a rise in temperature on earth, altering the hydrological and meteorological processes and affecting crop physiology. Evapotranspiration is an important component of the hydrological cycle. Thus, understanding the change in evapotranspiration due to global warming is essential for better water resources planning and management and agricultural production. In this study, the effect of climate change with a focus on the combined effect of temperature and elevated CO2 concentrations on reference evapotranspiration (ETo) was evaluated using the Penman–Monteith equation. A EURO-CORDEX regional climate model (RCM) ensemble was used to estimate ETo in five locations in the Emilia-Romagna region (Northern Italy) during the period 2021–2050. Then, its projected changes in response to different CO2 concentrations (i.e., 372 ppm and 550 ppm) under two Representative Concentration Pathways (RCP) scenarios (i.e., RCP4.5 and RCP8.5) were analyzed. Simulation results with both scenarios, without increasing CO2 levels (372 ppm), showed that the annual and summertime ETo for all locations increased by an average of 4 to 5.4% with regard to the reference period 1981–2005, for an increase of air temperature by 1 to 1.5 °C. When the effect of elevated CO2 levels (550 ppm) was also considered in combination with projected changes in temperature, changes in both annual and summer ETo demand for all locations varied from − 1.1 to 2.2% during the 2021–2050 period with regard to the reference period 1981–2005. This shows that higher CO2 levels moderated the increase in ETo that accompanies an increase in air temperature

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

Evaluation of some evapotranspiration estimation models under CO2 increasing concentrations: A review

The total volume of CO2 emissions is building up dramatically, and because of the effect of this gas on the growth, physiology, and biochemistry of plants, it is becoming increasingly necessary to look into the impact of the relentless rise of carbon dioxide. Although there are several developed approaches that tried to model the canopy resistance, many of these methodologies ignored the effect of CO2 or were not incorporated with the existing evapotranspiration calculation methodologies, mainly due to the complexity of the modeling procedure and the short time framework of the conducted studies. This review explores the few models estimating crop water requirements that account for this effect and examines their assumptions and theories. The inclusion of canopy resistance models in evapotranspiration calculation may be of questionable utility without improvements in some modeling aspects, such as the relationship between the stomatal conductance and CO2 and the climatic variables taken in consideration in the modeling process

COMPARISON AND VALIDATION OF DAILY METEOROLOGICAL DATA FROM ERA5 RIANALYSIS WITH OBSERVATIONAL SURFACE DATA, FOR THE EMILIA-ROMAGNA REGION

The European Center for Weather Forecasts ECMWF operates within the European Copernicus project for the dissemination of meteorological, environmental and satellite data. In the present work are compared the hourly data of the ERA5 reanalysis, recently produced by ECMWF and made available through the Copernicus Climate Service, with surface observational meteorological data from ARPAE and DISTAL databases. The comparison was made for the 2008-2018 period, using data from the stations of Cadriano (DISTAL), Martorano, San Pancrazio, San Pietro Capofiume and Rimini Urbana (ARPAE). The hourly data, extracted from ERA5 database, refer to: 2m air temperature, 10m horizontal and vertical wind components, 2m dew point temperature, surface net solar radiation and global solar radiation. From these data the 2m daily wind speed, Dew point temperature, 2m daily minimum and maximum temperature were deducted. The data extracted from ARPAE database are: 2m minimum and maximum daily temperature, 2m dew point temperature, daily net radiation, hourly global radiation and daily mean wind speed at 10m. From these data, daily global radiation and 2m wind speed at 2m were calculated. Grid values are compared with local observation using the nearest grid point method. The final aim of this work is the elaboration of climate indices for the Emilia-Romagna region for agro-meteorological purposes, starting from the ERA5 data