2.1.1. Analysis of the Impact of Urbanization on the Coastal Perimeter: UTD Index

The phenomena of fast urbanization are one of the elements most commonly associated with coastal vulnerability. On the one hand, this fast urbanization usually introduces an important process of physical transformation of the coast that generates important environmental impacts on the original status of the territory. These impacts may cause alterations in coastal dynamics whose effects may not become apparent for years or even decades. The situation became especially interesting in this complex territorial context where we have a coastal perimeter that is highly urbanized as a consequence of tourism in the last decades and two seas separated by an ancient dune cord now strongly urbanized since the middle of the 1960's (Figure 2).

**Figure 2.** (**a**) Current situation of the Mar Menor: Urbanized areas, protected salt marshes and wadis. (**b**) La Manga ancient dune cord in 1950 (**up**) and now (**down**, source: Paisajes Españoles S.A.).

On the other hand, fast and uncontrolled urbanization processes tend to notably increase the vulnerability risks associated with natural hazards such as floods. In this case, the coastal perimeter is strongly threatened as it is the mouth of numerous wadis in its Eastern and Southern perimeters. This context, coupled with the accelerated urban growth on the coast and the Mediterranean weather in which the rains are scarce but torrential, form a dangerous cocktail. In this sense, we can find several recent episodes in which these runoff waterways (through which water usually does not circulate), have become the natural floods channels, devastating important coastal settlements such as Los Alcazares (Figure 3).

**Figure 3.** Floods occurred in the coastal town of Los Alcazares in (**a**) 1953 and (**b**) 2016 (source: Town Council of Los Alcazares).

To evaluate the impact of the urbanization processes in the coastal perimeter in the last decades, a long-term analysis will be carried out using a GIS indicator of urban transformation density *UTD* (1). This indicator will make a comparison between the state of a territory during a period *t*<sup>1</sup> − *t*<sup>2</sup> and the intensity of urbanization detected during a similar previous period of time *t*<sup>0</sup> − *t*1. In this way, the indicator will take into account both the processes of transformation of natural areas into urbanized ones, as well as the transformation of areas already urbanized by new buildings. This will give us at the surface level not only an idea of the intensity of transformation of the coastal territory, but also a map of its building density. The indicator is formulated as follows:

$$ITTD\_{t\_1 - t\_0}^{t\_2 - t\_1} = \frac{\iiint F(x, y, z)\_{t\_1}^{t\_2}}{\iiint H(x, y, z)\_{t\_0}^{t\_1}} \tag{1}$$

with *F*(*x*, *y*, *z*) *t*2 *<sup>t</sup>*<sup>1</sup> being the distribution of building density increase between *t*<sup>1</sup> and *t*<sup>2</sup> and *H*(*x*, *y*, *z*) *t*1 *t*0 the building density increase between *t*<sup>0</sup> and *t*<sup>1</sup> for a coastal buffer of 2 km.

#### 2.1.2. Analysis of the Impact of the Construction of Marine Infrastructures (CIR)

The Mar Menor and the Mediterranean Sea have in these coastal perimeters a varied catalog of marinas (11) and seaside infrastructures such as dikes and breakwaters (>20, Figure 4). All these elements have been built mainly during the 1970's, 1980's, and 1990's with the arrival of tourism.

**Figure 4.** Marinas and coastal infrastructures built in the Mar Menor and the Mediterranean Sea since the 1950's (data source: SITmurcia [43]).

To evaluate the impact of these infrastructures, the evolution of the changes in the coastal perimeter over time associated with their construction will be analyzed spatially. The analysis will be carried out through the use of a GIS indicator. This indicator will measure the surface area of the seaside perimeter altered derived from the construction of each infrastructure during a period of time, in relation to the alteration observed during an analogous period on the same stretch of coastline before the construction of the infrastructure. As the area of influence of each of the infrastructures, a length of 200 m buffer will be taken upstream and downstream on the coastline perimeter from the location of the infrastructure. This length of analysis will be reduced if unchanged behavior is detected during 50 consecutive meters, since the coastal area of influence of the infrastructure is understood as minor. The GIS indicator will be called the Index of Coastal Infrastructure Repercussion (CIR) and it is obtained, as shown in Reference (2):

$$CIR\_{t\_1 - t\_0}^{t\_2 - t\_1} = \frac{\iint\_{t\_1}^{t\_2} F(\mathbf{x}, y)}{\iint\_{t\_0}^{t\_1} H(\mathbf{x}, y)}\tag{2}$$

with *F*(*x*, *y*) being the function that spatially quantifies the neighboring coastal surface area modified from the construction of an infrastructure from the time of its construction (*t*1) to the present (*t*2) and *H*(*x*, *y*) the function that spatially quantifies the evolution of this coastal surface into a period

*t*<sup>0</sup> − *t*<sup>1</sup> analogous in time and prior to the construction of the infrastructure (see null-hypothesis in Section 2.1.4).

#### 2.1.3. Analysis of Direct Land Transformations (DLT) in the Coastal Edge

There are other factors with major impacts that may generate an artificial alteration of the coastal configuration by direct anthropization not linked to building constructions or marine infrastructures. This is the case, for example, of channel dredging, agricultural land use modifications, coastal landfills, or simply alterations of the coastal space that cannot be attributed to a single cause or whose origin is unknown. In the case analyzed, we have a varied catalog of anthropic activities in this field (Figure 5), to which the territorial complexity of the existence of the ancient dune cord that separates the Mar Menor from the Mediterranean Sea must also be added. These two water masses are connected through 5 channels called "golas", whose configuration is quite heterogeneous. On the one hand we find three such channels in the Northern area, which, being located in an environmentally protected area, remain theoretically unaltered. On the other hand, the other two channels are further South and there is also an interior dredged area in the shape of a clover in the North, whose natural configurations were altered, with its bottom having been widened and dredged to facilitate maritime navigation of large boats. This last phenomenon has given rise to controversies about a possible "mediterraneanisation" process of the Mar Menor, which will be discussed later.

**Figure 5.** Marinas and coastal infrastructures of the Mar Menor and the Mediterranean Sea (data source: SITmurcia [43]).

Another important issue in this section is the alteration of the coastal territory through land fillings or land use change. In the first case, we find important alterations of the original profile of the beaches with sand landfills or land gained from the sea, especially in La Manga area. In the second case, the transformation of land for agricultural activities stands out especially in the innermost perimeter of the Mar Menor. This transformation affects the urbanized and non-urbanized areas of the coast by modifying the natural relief of the soil, influencing the arrival of water and sludge as a result of flooding.

All these concepts represent different forms of anthropization of the coastal perimeter through different processes of direct transformation of land that will be grouped in the index of direct land transformation (*DLT*):

$$DLT\_{t\_2 - t\_0}^{t\_2 - t\_1} = \iiint \frac{G\_1(\mathbf{x}, \mathbf{y}, z)\_{t\_1}^{t\_2}}{f\_1(\mathbf{x}, \mathbf{y}, z)\_{t\_3}^{t\_0}} + \iiint \frac{G\_2(\mathbf{x}, \mathbf{y}, z)\_{t\_1}^{t\_2}}{f\_2(\mathbf{x}, \mathbf{y}, z)\_{t\_3}^{t\_0}} + \iiint \frac{G\_3(\mathbf{x}, \mathbf{y}, z)\_{t\_1}^{t\_2}}{f\_3(\mathbf{x}, \mathbf{y}, z)\_{t\_3}^{t\_0}} \tag{3}$$

with *Gi* being the function that quantifies direct land transformations by the dredging actions (1), coastal landfills (2), and non-urban land use changes (3) for a coastal strip 2 km wide between *t*<sup>1</sup> and *t*2, and *Ji* the function that spatially quantifies the same coastal area transformed because of these three phenomena during a period *t*<sup>0</sup> − *t*<sup>1</sup> analogous in time and prior to *t*<sup>1</sup> − *t*<sup>2</sup> (see null-hypothesis in Section 2.1.4).
