It is now mid-April, and we can “close the books” on the availability of water contained in the snow: past the accumulation period, in fact, the water contained in the snow that has fallen so far today is what we will be able to count on for the warmer months of spring and summer. Unfortunately, it is very little: the mild temperatures and low rainfall this winter have resulted in a -64 percent deficit nationally compared to the past 12 years, which puts us basically in the conditions historically recorded only in late June
We have now reached the middle of April, leaving behind the days in which, historically, the greatest snowfall is marked, those around mid-March. In other words, today the accounts we can make regarding Italian snow are the final ones of the season, the ones on which we can and should base our strategies for water management in the months to come. Unfortunately, they only reiterate a trend observed throughout the winter months: little precipitation and mild temperatures have led to a significant snow deficit compared to the past decade. With this snow shortage we will have to deal with our water needs in spring and summer.
Our Hydrology and Hydraulics Department has been closely monitoring the situation over the months, recording precipitation and estimating the Snow Water Equivalent, the variable that defines the amount of water in snow on the ground. The data speak for themselves: in April, nationwide, the deficit compared to the previous 12 years is -64 percent; only in mid-January, heavy snowfall in the Apennines had partially improved the situation, but high temperatures caused the snow that had managed to settle to melt quickly.
Figure 1: National snow water equivalent trends. The orange line represents the snow water equivalent for the current season, total over the entire national territory. The blue line represents the total snow water equivalent for the past season, while the green line and gray band represent the average over the historical period and interannual variability, respectively.
Figure 2: Daily Snow Water Equivalent for each Italian administrative region, in 10⁹ m³.
The line at the bottom of the plot shows total, daily Snow Water Equivalent across Italy, again in 10⁹ m³.
“The most recent data indicate that the amount of snow available today is the same amount that, historically, we have in late June-especially on the Po: in other words, it is as if we are two months ahead of the classic seasonal snowmelt. So, we enter the months when the demand for water supply becomes more important with two months of melting that will likely be missed,” says Francesco Avanzi, researcher in the Hydrology and Hydraulics Department of CIMA Research Foundation. “And if the scarcity of snow was already felt last year during the summer drought, today we close with just half as much available snow as in 2022.”
The peak snowfall is recorded, in Italy, in March. This year was the lowest ever in the last 12 years: in fact, all Italian Regions reported a negative anomaly.
Figure 3: Annual peak Snow Water Equivalent for each Italian administrative region, in 10⁹ m³. Each circle represents one year of data. The size of the circle correlates with peak Snow Water Equivalent for a given year and a given region. The colorbar represents the difference between peak Snow Water Equivalent for a given year and a given region and the 2011-2021 average for the same region. For example, 2014 was the snowiest year on record for most of northern Italian region, thus large and blue circles for that year (because of high, above-average peak Snow Water Equivalent).
Looking at the data in more detail, the Alps (from Liguria to Friuli-Venezia Giulia) are the ones that mark the most significant deficits, with -67 percent compared to the historical period. As we have repeatedly mentioned, however, it is precisely these mountains that are the most important in terms of water availability in our peninsula: in fact, they supply water to the Po River basin, the largest in the country and of enormous economic importance. Basins such as the Po or Adige show even larger deficits than the Alps: -66 percent for the Po, and even -73 percent for the Adige.
Figure 4: Trend of the snow water equivalent of the Po River. The orange line represents the snow water equivalent for the current season. The blue line represents the total snow water equivalent for the past season, while the green line and gray band represent the average over the historical period and interannual variability, respectively.
Figure 5: Trend of the snow water equivalent of the Adige River. The orange line represents the snow water equivalent for the current season. The blue line represents the total snow water equivalent for the past season, while the green line and gray band represent the average over the historical period and interannual variability, respectively.
The conditions in the Apennines (which host, on average, 10 percent of the national snow water equivalent) are comparable, with the deficit standing at -58 percent. As mentioned earlier, snowfall in January had granted a brief snow recovery, but temperatures quickly rose, and remained mild between February and April. The result was an early melting of the snowpack, such that this valuable resource could not be “stockpiled.” “This dynamic only underscores the importance of the simile that we so often employ to refer to snow accumulation: it is not a 100-meter race, in which we can count on a quick sprint to close the gap, but rather a marathon that requires several months of suitable conditions (heavy rainfall and sufficiently cold temperatures),” Dr Avanzi says. “In fact, sporadic snowfalls, although also quite heavy, have not rebalanced the snow condition to the historical period.” The condition of the Tiber River is a good example of this: despite the abundant snowfall in the Apennines, in fact, rapid snowmelt resulted in conditions comparable to those in the Alps.
Figure 6: Trend of the snow water equivalent of the Tevere River. The orange line represents the snow water equivalent for the current season. The blue line represents the total snow water equivalent for the past season, while the green line and gray band represent the average over the historical period and interannual variability, respectively.
“In summary, the winter of 2022-23 was a tale of low precipitation, which prevented snow accumulation, and mild temperatures, which instead played anticipating the melting of what little snow was available. Then again, in a world of increasing temperatures, even the heaviest snowfall is put to the test,” Dr Avanzi concludes. “Although there are usually wetter months ahead, such as April and May, snow melt is slow and steady…. It is the perfect method for water to infiltrate the soils and thus recharge our aquifers. This mechanism is less significant with the heavy rains typical of the summer months, and this is another element that leads us to look carefully at summer – a period that, lately, is also characterized by very high temperatures that only increase the demand for water: the perfect storm, in short. As CIMA Research Foundation, we will continue to monitor the situation and the availability of water resources in the coming months, tracking the ongoing drought and its impacts on the territory.”