Nikolaos A. Skondras

Integrated water resources management uses decision-making and planning techniques in developing long-term strategies to ensure the sustainability of water resources and the resulting water security of future generations. Policy formulation through such integrated planning interlinks with indicators serving as an information channel to decision-makers. The present effort aims to develop a specific methodology using technical, environmental, and social indicators, formulating composite indices to identify vulnerability to changing water conditions. Thus, a set of indices developed through a multiyear research effort in Latin America, namely Drought Vulnerability Index (DVI), Water Stress Vulnerability Index (WSTVI), Water Scarcity Vulnerability Index (WSCVI), and Water Changing Conditions Vulnerability Index (WCCVI). Time series analysis covered the years 1991–2020, whereas the reference period was 1961–2020. Climate and water resources information is mainly obtained from ERA5-Land reanalysis; social, economic, infrastructure, and institutional data derived from harmonized sources (COROADO Project-EU, FAO, The World Bank, WHO/UNICEF JMP). Statistical tests and Principal Component Analysis (PCA) identified the indicators included in the equations for each index. Expert knowledge played an important role in the development as data were collected according to known local specificities and global trends, as well as scientific criteria and methodological rigor regarding the proposed new indices. Finally, application of such a framework for spatially explicit analysis indicated higher levels of vulnerability to changing water conditions in the northern part of Mexico, the Andes, Bolivia, Paraguay, and Central America, and lower levels in Chile, Brazil, Uruguay, and Argentina. This application demonstrates that the produced composite indices may be implemented with matching success all over Latin America and, therefore, in diversified natural, technical, environmental, social and economic conditions.

Estimating evapotranspiration is crucial for irrigation and agricultural applications. Although the FAO-56 Penman–Monteith method is highly accurate under conditions of abundant data, its extensive requirements limit its practical application. In the Mediterranean region, most empirical formulas used to estimate evapotranspiration are temperature-based and require calibration to be effective. The current study aims to introduce a novel formula to determine reference evapotranspiration using temperature, relative humidity, and extraterrestrial radiation daily in the Mediterranean region and evaluate its performance. Multi-linear regression was applied to agrometeorological data from the California Irrigation Management Information System (CIMIS) to develop the ETo formula. The formula was then validated using data from 252 stations in four countries (Greece, Spain, Portugal, and Cyprus) over the growing period of six years (2018–2023). The GAIA formula consistently outperformed formulas with the same or fewer variables, including Berti and Ahooghalaandari, across all metrics. The largest differences were observed in RMSE and the index of agreement. There is a strong correlation between GAIA and the FAO-56 Penman–Monteith formula (coefficient of determination = 0.88). While the GAIA formula shows a high coefficient of determination, its performance is somewhat lower than that of Copais and Valiatzas, particularly in terms of Pearson correlation and the coefficient of determination. A key difference is that Copais and Valiatzas rely on incoming solar radiation, whereas GAIA uses extraterrestrial radiation. Relative humidity was found to be the most influential variable, accounting for over 71% of the variance in ETo. Effective evapotranspiration (ETo) calculation methodologies, especially in areas with limited agrometeorological data, can significantly enhance irrigation system efficiency and promote sustainable water management. The GAIA formula offers a cost-effective method for estimating reference evapotranspiration (ETo) during the growing season with enhanced accuracy, eliminating the need for expensive equipment. However, its primary limitation is that it is validated in the Mediterranean region and within a specific geographical latitude range.