## 3 Results
### Class-Based LULC Classification
Mixed forest occupied about 18% of city and its metropolitan area for the analyzed period, reaching its minimum in 2019 when the precipitation reached its lowest value (Figure 6). As previously mentioned, at this point, one can confirm that vegetation established in the urban areas were mostly mixed forest, having more pixels where the city was initially developed than where the more recent residential areas in the west of the city have been developed. Shrublands, in general, showed an increment over time. They reached their maximum percentage area, equal to 5.31%, in 2020 with some fluctuations in 2017, a yearpreceded by annual precipitation below 1500 mm, which represents the driest year of the analyzed period. One of the most representative classes in this classification is wetland (i.e, swamps) because it represents multiple biological, economic and social values. Swamps provide services to ecological well-being, such as groundwater recharge, water purification, micro-climate regulation, food resources, biodiversity and carbon storage [76, 77, 78]. In the last decades, in Coatzacoolcos, urbanization has degraded swamps indiscriminately through industrial development or residential areas. These developments followed the erroneous idea that swamps were areas with dangerous species, such as snakes, alligators, mosquitoes, etc., which represented risks to the nearby areas [79]. This study evidences how wetland or swamp degradation continues. Visually, swamps located south and southeast of the city have mostly transitioned to some degree of vegetation density, either from water stress or landfill. In 2015, swamps represented about 2% of the study area, whereas, in 2021, this fraction reached 0.92%. This fact makes this study a good indicator to prevent and preserve swamps and wetlands within Coatzacoolcos and its metropolitan area due to the important ecological services that they represent. Dunes, in Figure 8, are located along the coastline of the study area. In addition, there are some banks utilized by the industry (sandblasting) in the east area across the  
Figure 8: Maps of the class-based classification for the study period (2015–2021). Units: meters. Projection: WGS84 / UTM Zone 15N. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Class** & **2015** & **2016** & **2017** & **2018** & **2019** & **2020** & **2021** \\ \hline Sea & 20.10 & 20.1 & 20.1 & 20.09 & 20.1 & 20.1 & 20.1 \\ Water courses & 6.10 & 6.31 & 6.31 & 6.31 & 6.32 & 6.33 & 6.34 \\ Water bodies & 1.91 & 1.96 & 2.00 & 1.98 & 1.93 & 2.01 & 2.00 \\ Industry & 2.74 & 2.76 & 2.76 & 2.76 & 2.76 & 2.76 & 2.76 \\ Residential & 11.85 & 11.86 & 12.16 & 12.07 & 12.24 & 12.24 & 12.20 \\ Commercial & 0.52 & 0.51 & 0.46 & 0.55 & 0.45 & 0.44 & 0.50 \\ Roads & 4.77 & 4.78 & 4.84 & 4.84 & 4.81 & 4.83 & 4.87 \\ Mixed forest & 18.56 & 18.60 & 19.02 & 18.68 & 18.14 & 18.67 & 18.60 \\ Shrubland & 5.15 & 5.21 & 4.82 & 5.18 & 5.16 & 5.31 & 5.28 \\ Weldand & 1.86 & 1.40 & 1.10 & 1.13 & 1.13 & 0.93 & 0.92 \\ Dume & 2.83 & 2.79 & 2.28 & 2.30 & 2.15 & 1.96 & 1.96 \\ Bare surfaces & 19.31 & 20.71 & 22.12 & 22.02 & 22.61 & 23.19 & 23.20 \\ Sparse vegetation & 2.79 & 2.19 & 1.31 & 1.36 & 1.72 & 0.79 & 0.84 \\ Grassland & 1.51 & 0.81 & 0.64 & 0.66 & 0.41 & 0.41 & 0.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Percentage area estimated for the class-based classification. Coatzacoalcos river. One can see that dunes were replaced mainly by residential areas in the northwest part of the city. In 2015, dunes occupied almost 3% of the area in question. However, this area declined to 1.96% in 2021. The most significant evolution of urbanization occurred from 2017 to 2019. Additionally, the western coastline presented a transition from dunes to bare surfaces because that area is naturally preserved and the absence of tourism has improved the growth of native vegetation. Lastly, bare surfaces are the dominant land use along with mixed forest and residential areas (Figure 8).