ASTRONOMICAL TIDE HEIGHT ALONG THE ITALIAN COASTS

Panel 1

Update date

2025-12-31

Authors

Andrea Bianco, Saverio Devoti, Sara Morucci, Luca Parlagreco

Abstract

The tide is a periodic phenomenon of rising and falling of the sea surface due to the gravitational attraction exerted by the Moon, the Sun and other celestial bodies on the masses of water present on Earth and secondarily also due to meteorological disturbances. Data from the National Mareographic Network (ISPRA) were used to characterize the amplitude of the astronomical component of the tide signal along the Italian coasts. As is well known, the astronomical tide presents profound differences in the different Italian seas, reaching its maximum excursion in the Northern Adriatic and in the Venice Lagoon, being also strongly influenced by the configuration of the basin.

Description

The tidal phenomenon is characterized by the rise and fall of sea level due to the gravitational attraction exerted mainly by the Moon and the Sun on the Earth's surface and, secondarily, by meteorological phenomena. Two components can therefore be distinguished, an astronomical, periodic and predictable one and a stochastic, meteorological component. The rising phase reaches its peak at the moment of maximum elevation of the sea level and is called high tide (or peak), while the minimum lowering phase is called low tide (or trough). The difference between high and low tide is called tidal range or amplitude. Tidal excursions vary in time depending on the relative position of the Earth-Sun-Moon system and in space, depending on morphological characteristics such as the depth of the seabed, the shape of the coasts and the surface of the water mass. Sea level is recorded along the Italian coasts by tide gauge stations, mainly located inside ports and managed by ISPRA. The astronomical tide was calculated using 69 harmonic constants, which take into account both the periodicities strictly linked to astronomical phenomena and the periodicities induced by meteorological phenomena. As known from the literature, for modeling application reasons only the 7 main harmonic constants can be used, especially in the Northern Adriatic and in the Venice Lagoon, where the phenomenon is more intense. Conversely, for strictly cognitive and scientific research reasons, the use of 69 harmonic constants throughout the Mediterranean is indicated.

Purpose

Monitoring and characterizing the astronomical tide component along the Italian coasts can be particularly useful for the purpose of identifying any anomalies and extreme tidal phenomena compared to the natural condition of the sea, which is different at each measurement point.

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 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

It responds to the knowledge needs set out in Directive 2000/60/EC regarding coastal waters and transition waters, and to the requests of Directive 2007/60/EC regarding floods and coastal inundations. There are no objectives set by law.

Panel 2

DPSIR

State

Indicator type

Descriptive (A)

References

https://www. mareografico. it/

Data quality assessment

Data source

ISPRA

Data collection frequency

Yearly

Continuos

Data availabilty

http://dati. isprambiente. it/dataset/rmn-la-rete-mareografica-nazionale/

Spatial coverage

Italian seas

Time coverage

1971 - 2024

Indicator assessment

Core SET

EEA - Set of Indicators

Processing methodology

The tides in the Mediterranean Sea have a frequency of approximately 12 hours, linked to the passage of the Moon above an observation point on Earth. The tide is therefore influenced differently over the course of the month depending on the phases of the moon. This component, called astronomical, is the one that is reconstructed and presented. The measured signal, subtracted from its harmonic component, provides the residuals, which contain information on the meteorological, stochastic, phenomena that occurred.

Update frequency

Year

Data quality

The astronomical tide represents an excellent indicator for promptly characterizing the normal oscillations of sea level, allowing a geographical comparison on a national scale and the monitoring over time of any variations induced by short or long-term physical phenomena. The data are acquired from the tide gauge stations of the National Tide Gauge Network (RMN), which guarantees spatial coverage across the entire national territory, hourly sampling and multi-year historical series. The sea level data were subjected to a validation procedure performed manually through expert judgment, L2 according to the WMO classification, and were analyzed using the most accredited and advanced statistical methods. In particular, 69 harmonic constants were used for the reconstruction of the astronomical tide signal. This indicator therefore allows for an excellent comparison on a national scale.

Status

Undefinable

Trend

Undefinable

State assessment/description

This indicator is defined on the basis of universal constants that describe a phenomenon without characterizing any state.

Trend assessment/description

This indicator is defined on the basis of universal constants, which are not expected to vary over time and therefore highlight any trend. The possible fluctuations and differences over the years can be attributed to purely stochastic phenomena and therefore the evaluation of a trend is not expected.

Comments

The indicator refers to 2024 and is presented with the aim of uniformly characterizing, along the Italian coasts, the locally expected astronomical tide, updating and updating its values compared to the observed data. As can be highlighted from the analyzes of the stations of Trieste and Venice, and as is well known, the level of the astronomical tide presents decidedly higher values in the Northern Adriatic (Venice and Trieste), with tidal maximums and minimums almost three times those recorded in other measuring stations (Tyrrhenian Sea) (Table 1). This can be seen in Figures 15, 16, 17, 18, both for the Venice and Trieste stations; Figures 15 and 17 represent the trend of the astronomical tide on the same scale as the other Italian stations, in order to highlight the greater intensity of the phenomenon (and their out-of-scale nature), and Figures 16 and 18 instead represent, on the appropriate scale, the astronomical tide in its entirety. The intense effect of the tide in the Venice Lagoon is well known, which is also reflected in the data presented in this indicator. The time series of approximately 50 years (1971-2024) allow us to study in detail any oscillations of the astronomical components of the tide, mainly due to stochastic phenomena, and to monitor their substantial stability over time, as expected from the physical phenomenon that governs them. Furthermore, the availability of data distributed along all the Italian coasts allows a precise evaluation of the astronomical phenomenon, of extraordinary interest and usefulness also in the operational forecasting field.

Data