Drought and water resource assessment at the national level in Italy from 1951 to today

The aim of the work is to present the analysis of droughts, water resource availability and water stress conditions in Italy obtained based on estimates from ISPRA's BIGBANG national hydrological water budget model. Trends and variations on the availability of water resources and on the occurrence, persistence and magnitude of the drought events that have affected Italy from 1951 to today will also be presented in relation to the current and future impacts of the climate change, with an indication of the impacts on the exposed assets, such as people and cultural assets.

Italy, located in the center of the Mediterranean, one of the hotspots of the climate crisis, can only expect an amplified impact of droughts, which, associated with the increase in temperatures, will lead to an ever-decreasing availability of water resources. In recent decades, Italy has been subject to increasingly frequent drought events affecting not only the southern and insular areas, but also the central-northern and continental areas, which have a generally more humid climate. The ISPRA national analyses show, starting from the 1950s, a statistically increasing trend in the percentages of territory subject to extreme drought on an annual scale. The periods in which the extreme drought conditions affected more than 20% of the national territory were 5, namely 1989-1990, 2002, 2012, 2017 and 2022. The first of these periods is part of the "great drought" that hit Italy in the three-year period 1988-1990, the other 4 are all after that period, while no episode of this magnitude was recorded in the preceding period. This increase in extreme drought events is likely due to climate change.

The increase in water crises is therefore attributable to a lower availability of water resources over the years due to a changing climate, with persistent periods of precipitation deficit and high temperatures, with a negative trend, statically significant observed at the national level by means of BIGBANG estimates from 1951 to today. 

The annual national availability of natural water resources in 2022 is estimated at 221.7 mm, equivalent to approximately 67 billion cubic meters, which represents the historical minimum from 1951 to today. This value outlines a reduction of approximately 50% compared to the average annual availability of water resources estimated at 441.9 mm (133.5 billion cubic meters) for the last thirty-year climatological period 1991-2020.

In 2023, the annual value of the renewable water resource is estimated at 372.2 mm, corresponding to 112.4 billion cubic meters, approximately 18% compared to the average annual availability of the long period 1951-2023, resulting from the combined effect of a precipitation deficit and an increase in water volumes of evapotranspiration. The decrease in natural availability of water resources in 2023 was made less severe compared to 2022 by the high volume of precipitation that fell in May, estimated at approximately 49 billion cubic meters, which was, at a national level, more than double the average volume for the same month.

Future projections highlight possible further reductions in water resources.