# Climate Change Impact on Corrosion of Reinforced Concrete Bridges and Their Seismic Performance
## 2 Climate Change's Impact on the Corrosion Rate  
As highlighted in [39; 40; 41], the durability and reliability of RC bridges are significantly affected by climate change, which involves variations in three fundamental environmental parameters: (i) temperature, (ii) relative humidity, and (iii) CO2 (carbon dioxide) concentration levels. In this research work, the attention is focused on the variation in temperature due to climate change and its influence on the evolution of the mean corrosion current density \(i_{corr}\)[42]. The evaluation of future climate evolution is based on several assumptions regarding future trends in socio-economic dynamics, future concentrations of greenhouse gasses, and variations in land use and land cover, which determine an increase in radiative forcing, as the variation in the energy flux in the year 2100 will be equal to 2.6, 4.5, 6.0, and 8.5 W/m\({}^{2}\), in comparison with the values of the pre-industrial era. From this, we can define the representative concentration pathways (RCP), as reported in [43]. Two main scenarios are considered in climate risk studies [44; 45; 46; 47]: (i) RCP4.5 and (ii) RCP8.5. According to the last IPCC (Intergovernmental Panel on Climate Change) report [48], an average increase in global mean surface air temperature of 2.7 \({}^{\circ}\)C and 4.4 \({}^{\circ}\)C is expected at the end of the century (in the period of 2081-2100) for RCP4.5 and RCP8.5 scenarios, respectively. In fact, for these two scenarios, several climate projections can be found in current literature and, for this reason, have been adopted in this research work, considering that they correspond to medium and maximum pathways. The expected variation in the climate parameters is evaluated through the analysis of obtained climate projections, considering high-resolution regional climate models run according to RCP4.5 and RCP8.5, provided by the EURO-CORDEX project [47]. It is important to notice that only a limited number of climate projections are available, and, for this reason, it is useful to evaluate the increase in temperature over time using a probabilistic approach based on weather generation techniques, such as suggested in [49]. As mentioned in Section 1, the temperature variation over the years due to climate change is strictly linked to the increase in the corrosion rate of steel reinforcements, following the model developed by [43]:  
\[ \begin{split} i_{corr}(t)&=i_{corr,20}[1+0.025(T(t )-20)]\ for\ T(t)<20^{\circ}C\\ i_{corr}(t)&=i_{corr,20}[1+0.073(T(t)-20)]\ for\ T(t)>20^{ \circ}C\end{split}  \tag{1}\]  
where \(i_{corr,20}\) represents the value of the mean corrosion current density at 20 \({}^{\circ}\)C, which is strictly related to environmental exposure. Focusing attention on the location of the investigated RC bridge, i.e., Massa-Carrara (longitude: 10.141; latitude: 44.025), an ensemble of climate projections of daily temperatures is extracted from the Copernicus Data Store and combined with the available observations at the closest weather station. In fact, climate models provide gridded data, which are always characterized by a different resolution from point observations, and there is a need to bridge this scale gap to use these data in engineering applications [50]. Among the different calibration strategies [51], the delta change approach is adopted, and the time series of future temperatures are evaluated by adding, to the observed time series at the weather station, the climate change signal derived from the analysis of climate projections [52]. Figure 1a shows the resulting trend of yearly average temperatures at the investigated location, while in Figure 1b the related percentage increase in corrosion rate is reported. The  
variation in corrosion rate up to 14% is expected at the end of the century, when taking into account only yearly variation, but even higher changes are expected when daily variations are considered in the analysis [42].