In April, the usual trend that sees temperature almost consistently above average suffered a setback: the month was cooler than normal (anomaly -0.6°C compared to the average of the thirty years 1991-2020) and in practically all sectors of Italy the differences were negative, except in Sardinia which closed with an average figure . The largest anomalies in the North-East (-1.1°C) and in the South (-1°C); followed by the Center (-0.5°C), the North-West (-0.2°C) and Sicily (-0.1°C).
The thermal trend was most probably influenced by the consequences of the end of February heating of the Stratospheric Polar Vortex, reinforced by the natural seasonal transit towards an anticyclonic circulation in the polar stratosphere. In practice, at the tropospheric level, some important situations of anticyclonic blockade have taken shape in the European area, with consequent descents of polar or arctic air masses towards the Mediterranean. The two cold breaks the most important occurred in the first week and in the middle of the month, but the first event in particular contributed to the reporting full winter conditions with minimum temperatures below zero and with aftermath even in the Easter period.
Towards the end of the month, on the other hand, a torrid mass of air rising towards south-western Europe also managed to touch our regions, causing a rise in temperatures, particularly in Sardinia where on the 29th the peaks went slightly over 30°C. The warmer core of this subtropical air mass hits the Spain where they were observed new records for the month of April, among which i 38.8°C of Cordoba, in a context of severe drought that is affecting this country.
Returning to Italy, the average accumulation of rainfall at national level does not deviate much from the norm (-3% overall anomaly), but with marked differences between the different areas. In the North and in Sardinia, about a third of the normal rainfall was missing (-36% in the North-West, -35% in Sardinia and -34% in the North-East), but with some areas more heavily affected by the Drought compared to others, such as the lower Po valley, Emilia-Romagna and western Liguria; in these regions there were few rainfall events of a certain importance, the most significant of which occurred on the 13th and 20th.
In the South, on the other hand, the rainy phases were more frequent and distributed above all in the first two decades of the month with consequent accumulations much more abundant than the average in most of the sector (+73% anomaly). Also in Sicily the final figure (+74%) follows that found in the South, but mostly thanks to the abundant rainfall in the north-eastern sector of the island. Of note i significant monthly accumulations for the month of April in Brindisi (147 mm) and Messina (175 mm) which represent the highest values since at least 1979.
Drought: spring always precedes a water deficit. From January to April -44% of rain in the North-West
The spring season always proceeds with a water deficit (-10% nationally), but above all due to the lack of precipitation on the northern regions (-47% in the North-West, -25% in the North-East) and in Sardinia (-37%); slight prevalence of quantities below the norm also in the Center (-7%). In the South and in Sicily, on the other hand, the two-month period saw above-average accumulations (+45% and +10% respectively). Since the beginning of the year, a slight deficit has been confirmed at national level (-5%), but always with marked differences depending on the areas: the North-West continues to be the area most affected by Drought with a difference of -44% compared to the norm; a negative figure also in the North-East (-15%) and to a lesser extent also in Sicily (-7%). The South, on the other hand, is distinguished by the above-average rainfall (+32%), while in the Center and in Sardinia the accumulation since the beginning of the year is, for the moment, very close to the norm (+3% and +4% respectively).
As for the seasonal temperatures, the combination of two very different months has resulted in fairly contained and largely positive anomalies: +0.3°C throughout Italy, +0.6°C in Sardinia, +0.5°C in the North-West, +0.4 °C in the Center and in Sicily. Overall, the North-East closed on average, while spring is proceeding slightly below normal in the South (-0.1°C).
Naturally, the negative figure for April helped to smooth out the overall anomaly from the beginning of the year which, however, remains positive (+0.6°C), as in all sectors of our country, but with a predominance of the North ( +1°C in the North-West, +0.8°C in the North-East), followed by the Center (+0.6°C) and finally by the Islands and the South (+0.2°C and +0.1°C respectively).
