# Long-Term Analysis of Wave Climate and Shoreline Change along the Gulf of California
## 5 Discussion
Table 5 shows the monthly average number of cold fronts that passed through Mexico from 1981 to 2019. In this period, 50 cold fronts per year, on average, occurred in Mexico. Cold fronts usually enter Mexico from the central, southern and southeastern parts of the United States of America, and occasionally from the north west of Mexico, the latter situation being more intense [52] and the most recurrent one for the GC. Figure 7: Tracks of tropical storms that passed along the GC region from 1980 to 2019. Source: National Oceanic and Atmospheric Administration (2020). Storm waves and storm surges, associated with tropical cyclones and cold fronts, can induce a number of potential hazards such as beach and dune erosion, overwash processes, inundation and coastal facility damage [53; 54]. Figure 8 shows the episodic impact of tropical cyclones and cumulative impact of cold fronts on the GC coast. Although the impact of such extreme events on the GC coast is real and has been highlighted, its study has received little attention. These weather systems have been studied more from the meteorological and climatological point of view than through a coastal geomorphology approach. Human activities such as the construction of dams, the high population density, and the main economic activities including tourism, agriculture and aquaculture on coastal areas have caused or accelerated the process of erosion or accretion of the GC coastline [55; 56; 57]. This anthropogenic pressure on the coast is modifying the sedimentary dynamics, which ultimately affects the shoreline and can still be felt after several years [58; 59; 60; 61]. Recent investigations on CC in the region suggest an ostensible rise in the sea level and storm surge elevations [56]. The sea level rise in the Gulf appears to be lower compared to the global mean sea level rise; however, studies suggest that even moderate rates of sea level rise can cause significant shoreline retreat [62]. This shoreline retreat is due to permanent passive submersion (which may affect flat and low-lying areas) or coastal erosion (caused by coastal sediment redistribution due to waves and currents and their interactions with human intervention) [62]. In addition to the sea level, the wave energy has increased (as found in the present work), which may be the cause of the long-term shoreline change presented here, mainly on the east coast, where the relatively lower relief and higher human activity, in comparison to the west coast, suggest that it is more vulnerable to the effects of CC. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Landfall Location**} & \multicolumn{8}{c}{**Type of Tropical Cyclone**} \\ \cline{2-7}  & **td** & **ts** & **h1** & **h2** & **h3** & **h4** & **h5** & **Total** \\ \hline B.C. & 2 & 1 & — & — & — & — & — & 3 \\ B.C.S. & 4 & 7 & 5 & 3 & 2 & — & — & 21 \\ Sonora & 3 & 2 & 2 & — & — & — & — & 7 \\ Sinaloa & 5 & 6 & 5 & 5 & 3 & — & — & 24 \\ total & 14 & 16 & 12 & 8 & 5 & — & — & 55 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Number of tropical depressions (td), tropical storms (ts) and hurricanes (h) category 1 to 5 making landfall in the GC during the period 1980–2019. Source: National Oceanic and Atmospheric Administration (2020). \begin{table}
\begin{tabular}{c c c} \hline \hline \(\mathbf{N}^{\circ}\) & **Month** & **Cold Fronts** \\ \hline
1 & September & 3 \\
2 & October & 5 \\
3 & November & 6 \\
4 & December & 6 \\
5 & January & 7 \\
6 & February & 8 \\
7 & March & 6 \\
8 & April & 5 \\
9 & May & 4 \\  & Total & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Monthly average of cold front occurrence in Mexico between 1981 and 2019. Source: National Meteorological Service of Mexico (2020). Discerning between changes induced by natural processes, human activities and climate change in the Gulf coast, like in other parts of the world, is a very complicated task, because these factors are interrelated in time and space [63].