## 2 Background and Study Area  
The municipality of Tijuana is located in the northwest of the state and the national territory, right at the border with the neighboring country of the United States of America (USA) (Figure 1). It covers a land area of 123.8 thousand hectares, which represents 1.70% of the total area of the state and 0.06% of the country's total area [48]. Tijuana stands out from the rest of the country due to its rapid urban growth, albeit not in the expected manner [49; 50]. Coupled with the lack of infrastructure provision, this has led to a compact urban structure influenced by geography and vulnerable to natural events [48]. The urban area of Tijuana is composed of nine districts (Figure 2): San Antonio de los Buenos, Sanchez Taboada, La Presa, Cerro Colorado, Playas de Tijuana, La Mesa, Centro, Otay-Centenario, and Presa Este. It is worth mentioning that each district has its own administration, providing services related to urban control, civil registry, inspection and verification, public works, community development, and supervision of public lighting. This results in varying urban and demographic behaviors across the city, leading to imbalances in infrastructure development and overpopulation in some areas. Given its geographical location, this municipality exhibits a highly diverse topography, with various elevations across its territory (Figure 3). The altitude ranges from 100 m above sea level (masl) to 1200 masl [51]. The city is situated amidst hills, canyons, ravines, and streams. In the central part lies a valley through which flows the channelized course of the Tijuana River. To the north is La Mesa de Otay, an almost flat plateau at about 160 m altitude, while to the south, extensive hills and mountains are dominating the landscape. Among the most significant are Cerro Colorado at 550 masl, Cerro Gordo at 1100 masl, and the hills of Consuelo and Grande in the municipality center at 900 masl. Tijuana hosts a system of hydrological basins and sub-basins, primarily belonging to the Transboundary Tijuana River Basin, which includes four aquifer recharge areas: Arroyo Alamar, Arroyo Florido, Arroyo Matanuco, and Arroyo de las Palmas [52]. Figure 1: Location of the Municipality of Tijuana, BC, Mexico. Regarding the terrain conditions by delegation, Oday-Centenario, La Presa, La Mesa, and part of Presa Este have 80.00% of their surface area consisting of flat land. These are followed by Playas de Tijuana and Centro, which have two-thirds of their surface area characterized as flat. In contrast, Cerro Colorado, San Antonio de los Buenos, and Sanchez Taboada have the majority of their surface area classified as mountainous terrain [53]. It is worth mentioning that the municipality of Tijuana is the most populous in the nation, with slightly more than 1.9 million inhabitants, representing 51.00% of the total population of Baja California [6]. This significant population growth is largely due to continuous immigration from other states of the republic [54] and even from other countries [55], with individuals either seeking to cross the border into the USA or intending to remain in the nation. Figure 3: Topography of the Municipality of Tijuana, BC, Mexico. Figure 2: Delegations of the Municipality of Tijuana, BC, Mexico. the city to improve their quality of life. However, this has led to a substantial increase in the population over the past decades [56], which in turn has heightened the demand for housing, infrastructure, and services. On the other hand, this demographic increase has resulted in a phenomenon of overpopulation, which has been accompanied by the emergence of informal settlements. These settlements are characterized by illegally self-built homes on private lands, lacking available services and infrastructure [57]. Moreover, this phenomenon has environmental impacts that pose barriers to environmental sustainability, affecting both developing and developed countries [58].