FROST DAYS

Panel 1
Update date
Authors

Piero Fraschetti, Francesca Lena, Walter Perconti, Emanuela Piervitali, Giulio Settanta

Abstract

This indicator describes trends in cold extremes across Italy, specifically quantifying the number of frost days, defined as days with daily minimum air temperature less than or equal to 0°C. In 2023, a reduction of approximately 10 frost days was observed compared to the 1991–2020 climatological baseline.

Description

The presence of extreme temperature events and related long-term trends is assessed through the analysis of daily absolute minimum and maximum air temperatures. The indicator, based on definitions provided by the "CCL/CLIVAR Working Group on Climate Change Detection" refers to the number of days when the daily minimum air temperature is less than or equal to 0°C.

Purpose

The annual time series of the average number of frost days, expressed as an anomaly relative to a climatological baseline, enables the estimation of the frequency of cold extremes and the identification of significant trends over time.

Policy relevance and utility for users
It is of national scope or applicable to environmental issues at the regional level but of national significance.
It is able to describe the trend without necessarily providing an evaluation of it.
It is simple and easy to interpret.
It provides a representative overview of environmental conditions, environmental pressures, and societal responses.
It provides a basis for international comparisons
Analytical soundness
Be based on international standards and international consensus about its validity;
Be theoretically well founded in technical and scientific terms
Presents reliability and validity of measurement and data collection methods
Temporal comparability
Spatial comparability
Measurability (data)
Adequately documented and of known quality
Updated at regular intervals in accordance with reliable procedures
Readily available or made available at a reasonable cost/benefit ratio
An “adequate” spatial coverage
An “appropriate” temporal coverage
Main regulatory references and objectives

The indicator is not directly linked to any regulatory or legislative framework.

DPSIR
Driving force
Indicator type
Descriptive (A)
References

https://scia.isprambiente.it; 

APAT-OMS, 2007, Cambiamenti climatici ed eventi estremi: rischi per la salute in Italia;

ISPRA, 2022, I normali climatici 1991-2020 di temperatura e precipitazione in Italia; 

ISPRA, 2018, Variazioni della temperatura in Italia: estensione della base dati e aggiornamento della metodologia di calcolo – Stato dell’ambiente 81/2018;

ISPRA, 2016, Controlli di qualità delle serie di temperatura e precipitazione; 

ISPRA, 2015, Valori climatici normali di temperatura e precipitazione in Italia; 

ISPRA, 2014, Focus on "Le città e la sfida ai cambiamenti climatici"; 

ISPRA, 2013, Variazioni e tendenze degli estremi di temperatura e precipitazione in Italia; 

ISPRA, 2012, Elaborazione delle serie temporali per la stima delle tendenze climatiche; 

Peterson T.C ., Folland C , Gruza G, Hogg W, Mokssit A e Plummer N., 2001, Report on the activities of the Working Group on Climate Change Detection and Related Rapporteurs 1998-2001. World Meteorological Organization, Rep. WC DMP-47, WMO -TD 1071, Geneva, Switzerland, 143 pp.;

SNPA, 2024, Il clima in Italia nel 2023; 

Toreti A. e Desiato F., 2007, Changes in temperature extremes over Italy in the last 44 years, Int. J. Climatology, DO I 10.1002/joc.1576.

 

Further actions

Improvements in the estimation of frost days in Italy could result from the extension of the indicator calculation system to include additional sources of raw temperature data, with the aim of increasing the availability of long-term temperature time series that meet requirements of duration, continuity, and completeness.

Data source

ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale) 

Data collection frequency
Yearly
Data availabilty

SCIA – Sistema nazionale per l’elaborazione e diffusione di dati climatici (https://scia.isprambiente.it)

Spatial coverage

Italy
Time coverage

1961-2023
Core SET
7° Programma di azione per l’Ambiente Europeo (7° EAP) - Dati sull’ambiente
Processing methodology

To determine if a specific day of the year can be defined as a day with frost, a comparison is made between the minimum temperature of that particular day and the threshold temperature of 0°C. Therefore, daily minimum temperature data is required. The program used by the SCIA system (National System for the Processing and Dissemination of Climatic Data) processes the raw data and returns a daily minimum temperature value, which is accepted as valid data only if it has passed certain checks. If the daily minimum temperature data is correct, the difference between this value and the 0°C threshold is calculated to determine if the day can be considered a day with frost. The annual value of the indicator is calculated by summing the number of days with frost in a given year. This value is accepted as valid data only if at least 75% of the valid daily data for the year in question is available. The climatological base for the calculation of anomalies has been updated to the most recent 30-year period, 1991-2020. This choice is based on recent recommendations from the World Meteorological Organization to update the climatological base every ten years for operational climatology purposes.

Update frequency
Year
Data quality

The indicator adequately describes the trend of intense cold events in Italy. The calculation of the indicator is conducted using a standardized methodology and following the general criteria outlined by the World Meteorological Organization. The methodology is consistent over time and space. Both the input data and the indicator itself undergo validity checks conducted by the organizations responsible for the raw data (CRA-CMA (Research Unit for Climatology and Meteorology Applied to Agriculture), Synoptic Network (AM and ENAV), Regional Networks) and by the SCIA system (National System for the Processing and Dissemination of Climatic Data) of ISPRA. The use of average anomaly values across the entire national territory adequately meets the information requirements related to this indicator. The measurement stations whose data are used to calculate the anomaly and estimate the ongoing trend meet the requirements for duration, continuity, completeness, and homogeneity of the time series.

Status
Poor
Trend
Negative
State assessment/description

In 2023, a decrease of approximately 10 days with frost (average number of days with a minimum temperature less than or equal to 0°C) was observed compared to the average value calculated for the reference period 1991-2020. For the average number of frost days, 2023 ranks 3rd among the lowest of the entire historical series (Figure 1).
Trend assessment/description

In the last 10 years, frost days have consistently been below the norm, except for 2017. Since the main international political strategies and programs concerning climate change aim to counteract the ongoing warming in the climate system, the assessment of an unfavorable trend and the assignment of the corresponding icon can be considered in terms of deviation from this objective.
Comments

Based on the assessment of the time series of annual mean anomalies in the number of frost days in Italy, 2023 recorded a decrease of approximately 10 days compared to the baseline climatological average (1991–2020), ranking as the third lowest value in the entire historical dataset (Figure 1).

Data
Headline

Figure 1: Time series of annual mean anomalies in the number of frost days in Italy relative to the 1991–2020 baseline.

Data source

ISPRA

English