## 4 Discussion  
The explosive activity of a volcano is driven by the fluids dissolved in the magma which determine its energy and characterize its degree of explosiveness. CO\({}_{2}\) is the predominant component of the dry composition of volcanic fluids and is normally monitored to assess the level of volcanic activity [2; 5; 11; 24; 25; 28; 29; 30; 31]. Furthermore, considering its lower solubility coefficient in magmas compared to other volcanic gases such as SO\({}_{2}\), CO\({}_{2}\) begins to be released at greater depths and can follow the degassing of magmas from the depth to the surface. For this reason, the monitoring of an extensive parameter such as the CO\({}_{2}\) soil flux represents one of the most useful tools to evaluate the volcanic activity level. Coupling this information with other geochemical intensive parameters, like fluid isotopes, ratios of chemicals in the plume, and geophysical parameters, can help to improve the comprehensive model of the plumbing system and make forecasting more constrained. In the case of the Stromboli volcano, the monitoring of soil CO\({}_{2}\) degassing began in 1999, and presently, we have a dataset unique in the world, with over 20 years of data on an hourly basis. This impressive database [2; 9; 11] allowed us to verify the CO\({}_{2}\) degassing models with the effusive activities and with paroxysmal activities that took place in the last two decades. Near-real-time measurements of soil CO\({}_{2}\) flux carried out in a fumarole field (STR02 station) located at the summit of Stromboli showed strong fluctuations likely described by an average increasing trend in the period 2005-2018 [9; 11], interrupted by several abrupt changes of CO\({}_{2}\), which is a signature of the input of magmatic volatiles [9; 11]. This average increasing trend determine a long lasting modification, with a positive increasing of 4.1 g m\({}^{2}\) d\({}^{-2}\)[11] of CO\({}_{2}\) flux, which was explained by the slow but continuous increase of the total volatile pressure in the shallow plumbing system of Stromboli [9; 11] due to a continuous refill from the depth. The flux of gases released from the new magma was higher than that from superficial degassing. The average degassing rate was determined from the difference between the daily degassing rates at the beginning and at the end of the period divided by the number of days in that period [11]. In the period 2016-2018, a new abrupt and strongly increasing rate of CO\({}_{2}\) degassing (24 g m\({}^{2}\) d\({}^{-2}\)) was also recorded, indicating the degassing of volatiles related to a new magmatic recharge that caused transient modifications of the summit volatiles fluxes reaching the value of 23,000 g m\({}^{2}\) d\({}^{-1}\) (Figure 2A). After a period of no data acquisition for technical problem (May-September 2018), the CO\({}_{2}\) flux suddenly incremented from October 2018 (3000 g m\({}^{2}\) d\({}^{-1}\)) to April 2019 overcoming the value of 10,000 g m\({}^{2}\) d\({}^{-1}\), with an average rate of 32 g m\({}^{2}\) d\({}^{-2}\) (Figure 2B). Figure 2: **(A)** Daily average of CO\({}_{2}\) fluxes at STR02 station expressed in g m\({}^{2}\) d\({}^{-1}\) of the 2016–2019 period. Two abrupt increasing of CO\({}_{2}\) flux has been recorded. The green-yellow and red dashed circle indicating the first abrupt increasing of CO\({}_{2}\) fluxes (24 g m\({}^{2}\) d\({}^{-2}\)) occurred in the 2016–2018 period; The dashed blue circle indicates the second abrupt increasing of CO\({}_{2}\) fluxes (32 g m\({}^{2}\) d\({}^{-2}\)) occurred from October 2018 to July 2019.The threshold value of 10,000 g m\({}^{2}\) d\({}^{-1}\) of CO\({}_{2}\) fluxes (orange line) have been reported; (**B**) Inset of daily average of CO\({}_{2}\) fluxes from October 2018 to July 2019; the threshold value of 10,000 g m\({}^{2}\) d\({}^{-1}\) of CO\({}_{2}\) fluxes (orange line) have been reported. Colored vertical lines represent main paroxysms (red), major explosions (grey), and overflows (green).