Climate and precipitation in Italy. Anomalous data over the past decades

An average year less warm than the previous ones, with precipitation over the entire national territory overall lower than the climatological average (-7 percent), except for the months of January, July and November. The year in question is 2021 and the information about it is contained in the Ispra report "State and trends of climate in Italy," which illustrates climate trends over the past year and updates the estimate of climate variations in recent decades in our country. The report, presented in recent days, is based on data and climate indicators derived largely from the National System for the Collection, Processing and Dissemination of Climatological Data of Environmental Interest and is produced in collaboration and with data from the National System for the Protection of the Environment and other observation networks in Italy.

While we are facing a very hot summer characterized by severe drought, thanks to the report we can look back a few months and get an overall picture of what the climate in Italy was like in 2021: anomalous heat in February and several heat waves that hit the peninsula and its islands during the summer months. The most intense occurred in the second week of August, when 48.8°C was recorded in Syracuse, a European record awaiting confirmation from the World Meteorological Organization. There was no shortage of extreme precipitation events, such as those that occurred in the early days of October with strong and persistent thunderstorms recorded in Liguria, between the provinces of Genoa and Savona, with exceptionally intense rainfall and very high amounts; or those at the end of the same month of October, with the tropical cyclone localized over the Mediterranean that dumped extremely intense rainfall over southern Italy, so much so that on eastern Sicily the hourly intensity was the highest ever recorded in the region, causing flooding and overflowing of rivers and canals.

Bringing the collected and processed data into sharper focus, we see that 2021 had a positive mean temperature anomaly of +0.23°C compared to the 1991-2020 climatological average, making it a less warm year than previous ones. It is no coincidence that the climatological baseline is restricted to the most recent 30-year period, which better describes the current climate, which is warmer than the past climate. Since 2000, anomalies with respect to the climatological average of the past 30 years have always been positive, except for 2004, 2005, 2010 and 2013: 2021 was the eighth consecutive year to mark them. Over the entire country, the largest negative anomalies were recorded in April (-1.40°C), followed by May and October. While all other months of 2021 were warmer than average, with positive anomalies in February (+1.82°C), June (+1.64°C) and September (+1.50°C).

The warmest months, regardless of region, were June (with positive anomalies of +1.84°C in the North, +1.99°C in the Center and +1.71°C in the South and Islands). The coldest than average months were May and April in the North (-1.74°C and -1.73°C, respectively), April in the Center (-1.71°C), and October and April in the South and Islands (-1.0°C).

The surface temperature of the Italian seas has also changed: in 2021 it was higher than the 1991-2020 climatological average, ranking fifth in the entire series since 1961, with an average anomaly of +0.46°C.

In terms of precipitation, on the other hand, again compared to the 30-year period 1991-2020, Italy in 2021 ranked 24th least rainy in the entire series since 1961. Over the entire country, rainfall was low from February through October, and all months recorded below normal rainfall except for January, July, and November. The relatively driest months were March (-47 percent) and September (-44 percent), followed by June and August. The relatively wettest month was January, with a positive anomaly of +91%, followed by November with +39%.

The report shows negative precipitation anomalies in the North (-14%) and Center (-4%), close to normal in the South and Islands. In the North, the relatively driest month was March with -87%, September in the Center with -64% and May in the South and Islands with -56%. The rainiest month in the North and Center is confirmed to have been January with +103%, followed by July in the North (+33%) and December in the Center (+37%); in the South and Islands the rainiest month was November with +76%.

Coming to a climatic index as topical and heartfelt today as drought conditions, the highest values of the number of dry days in 2021 were recorded in eastern Liguria and Emilia Romagna, with +320 days. The maximum of 326 dry days was recorded in Mele, in the province of Savona.

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