Assessment of Socio-Environmental Vulnerability Due to Tropical Cyclones in La Paz, Baja California Sur, Mexico

: Climate change will increase the likelihood of adverse events such as droughts, forest ﬁres, and intensiﬁcation of tropical cyclones, which are known to cause ﬂooding (IPCC, 2014). The e ﬀ ects of these events are a cause of concern for both authorities and citizens, so they prioritize actions that reduce adverse impacts, especially in cities with higher risk. Therefore, the objective of this work was to measure the degree of socio-environmental vulnerability of households to identify the risk areas in the city of La Paz, Baja California Sur, one of the regions with a high degree of incidence of hurricanes in the northwest of Mexico. For this, surveys were carried out with heads of households in 251 homes, and information was aggregated to calculate the vulnerability index through principal components analysis (PCA), which were stratiﬁed by the Dalenius–Hodges method, the degree of vulnerability was classiﬁed into three categories by the Opiyo method, considering three strata of the Likert scale, 1 = highly vulnerable, 2 = moderately vulnerable, 3 = less vulnerable. The results showed that households that are in the highly vulnerable category are 33% within a range of the index − 3.77243 to − 0.939141. Moderately vulnerable households constitute 36% with values from − 0.929141 to 0.956385. While the least vulnerable represent 31% of households with an index range of 0.966385 to 5.6952. The results have revealed the levels of high and moderate socio-environmental vulnerability by tropical cyclones of 69% homes in La Paz. The above allowed to generate risk maps that will be taken into account in planning and civil protection over adverse events.


Introduction
The effects of climate change have become one of the main concerns of citizens and authorities globally. According to the report of the Intergovernmental Panel on Climate Change (IPCC), global climate change will increase the likelihood of adverse events, including heat waves, droughts, forest fires, intensification, and increased tropical cyclone frequency, as well as heavy rainfall that could cause flooding and landslides [1].
These events can affect the population in multiple dimensions, vulnerability to natural disasters caused by adverse weather events has spatial, environmental, social, economic, and cultural dimensions. The IPCC defines vulnerability as "the degree to which a system is susceptible and unable to cope with the adverse effects of climate change, including climate variability and adverse events". It also In Baja California Sur, TC impact at least once a year during the months of May to November and the most frequent effects in the cities are: Flooding, landslides, strong winds, storm surge, and lack of communication due to flooding of streams.
Conclusive to the above, the objective of this study was to measure the degree of socioenvironmental vulnerability of households to identify risk areas in the city of La Paz, Baja California Sur, one of the cities in Northwestern Mexico with the highest degree of incidence of adverse climatic events.

Study Area
The municipality of La Paz is located in the State of Baja California Sur (24°08′32″ N 110°8′39″ W) and has an area of 20,275 km 2 . According to the National Institute of Geography and Statistics (INEGI by its Spanish acronym) [18], the city has a population of 272,711 inhabitants. According to the State Plan of Action against Climate Change (IPCC), La Paz is one of the main municipalities with the greatest vulnerability to TC, because their homes have a greater probability of impact each year (48%) at a greater risk, according to NOAA data that recorded 125 TC in the Northeast Pacific with direct impact in Mexico. It has even been detected that this municipality is the one that most frequently receives the impact of category 1 hurricanes (according to the scale Saffir-Simpson) with a return period of 5.6 years [17].

Methods
Assessing climate change vulnerability is a widely complex challenge and has become a multidisciplinary task since it affects several areas of activities and resources [19][20][21]. There have been several recent studies that aimed to assess the effects of climate change on coastal cities by using different approaches [22][23][24][25][26]. Moreover, there have been many studies to assess the perception and vulnerability due to hurricane impacts and effects [27][28][29][30]. Since there are several methods and approaches to evaluate vulnerability, the Dalenius-Hodges and Opiyo methods [31] were adopted for this research, due to their easy application, estimation, and interpretation. Moreover, it is an integrated assessment approach that combines socio-economic and biophysical factors, commonly used in the analysis of regionally-based vulnerability [9,32].
With the objective of obtaining information to estimate the vulnerability index, a survey was applied where the sampling unit was the dwelling, and in this one, household heads of households in the municipality of La Paz were interviewed. Data were obtained from 251 private homes, which exceeds the representative sample for population size, the date of application was September 2017. The survey included four sections: (1) Demographic and economic characteristics of the household, (2) physical conditions and services which provides for housing, (3) level of severity of damage caused by Hurricane Odile and (4) level of social capital of households related to education and culture for disaster prevention by TCs. The Likert scale from 1 to 5 was used in ascending order. The first part of

Study Area
The municipality of La Paz is located in the State of Baja California Sur (24 • 08 32" N 110 • 8 39" W) and has an area of 20,275 km 2 . According to the National Institute of Geography and Statistics (INEGI by its Spanish acronym) [18], the city has a population of 272,711 inhabitants. According to the State Plan of Action against Climate Change (IPCC), La Paz is one of the main municipalities with the greatest vulnerability to TC, because their homes have a greater probability of impact each year (48%) at a greater risk, according to NOAA data that recorded 125 TC in the Northeast Pacific with direct impact in Mexico. It has even been detected that this municipality is the one that most frequently receives the impact of category 1 hurricanes (according to the scale Saffir-Simpson) with a return period of 5.6 years [17].

Methods
Assessing climate change vulnerability is a widely complex challenge and has become a multidisciplinary task since it affects several areas of activities and resources [19][20][21]. There have been several recent studies that aimed to assess the effects of climate change on coastal cities by using different approaches [22][23][24][25][26]. Moreover, there have been many studies to assess the perception and vulnerability due to hurricane impacts and effects [27][28][29][30]. Since there are several methods and approaches to evaluate vulnerability, the Dalenius-Hodges and Opiyo methods [31] were adopted for this research, due to their easy application, estimation, and interpretation. Moreover, it is an integrated assessment approach that combines socio-economic and biophysical factors, commonly used in the analysis of regionally-based vulnerability [9,32].
With the objective of obtaining information to estimate the vulnerability index, a survey was applied where the sampling unit was the dwelling, and in this one, household heads of households in the municipality of La Paz were interviewed. Data were obtained from 251 private homes, which exceeds the representative sample for population size, the date of application was September 2017. The survey included four sections: (1) Demographic and economic characteristics of the household, (2) physical conditions and services which provides for housing, (3) level of severity of damage caused by Hurricane Odile and (4) level of social capital of households related to education and culture for disaster prevention by TCs. The Likert scale from 1 to 5 was used in ascending order. The first part of the survey refers to the physical conditions of the home. The questions considered in the questionnaire, which make up the items of the socio-environmental dimensions are shown in Appendix A.
To generate the socio-environmental vulnerability index due to the impact of TCs, the regression method was used in order to obtain the matrix of standardized coefficients, the standardized values of each variable and the sample in the corresponding equation of each factor were substituted. The scores obtained correspond to the vulnerability indices of each dimension: (1) Exposure, (2) adaptive capacity, (3) sensitivity. To obtain the general vulnerability index, the formula developed by the IPCC was applied, which is the following: (1) If the adaptive capacity exceeds sensitivity and exposure, the home will be less vulnerable to impacts from tropical cyclones, and if the capacity is lower it means that the home is more vulnerable.
The degree of vulnerability was classified into three categories by the method of Opiyo et al. [31], the least vulnerable households are those in a situation where they can cope with impacts of a tropical category 1 cyclone on the Saffir-Simpson scale, moderately vulnerable households are those that require temporary assistance in case of stress or shock, while the highly vulnerable are those which, even with immediate assistance, are not able to resume the level of well-being prior to a tropical cyclone impact.
Once the socio-environmental vulnerability index for TC in La Paz was obtained, the degree of vulnerability was classified by means of the Dalenius-Hodges stratification technique [33], which consists in the formation of strata privileging that the previous variance of each stratum is minimum and maximum between each of them, forming homogeneous strata.
For the construction of a vulnerability index the model is as follows: where V 1 is the vulnerability index, the Ys and Xs are the sensitivity and exposure values, the As correspond to the coefficient matrix values obtained by the principal component analysis (PCA). The use of the PCA technique has allowed the construction of composite indicators that measure different levels of social vulnerability of the population against threats due to adverse hydro-meteorological events and have been validated in international and local studies [34,35]. It is important to mention that this work is based on an implementation of vulnerability methods that used PCA to derive this phenomenon according to the IPCC recommendations. Three layers of the Likert scale were considered, 1 = highly vulnerable, 2 = moderately vulnerable, 3 = less vulnerable. Adaptive capacity is the effects of facing climate change or some situations, which helps to reduce impacts or to anticipate them. Adaptive capacity is the ability of a system to adjust to climate change, including variability and adverse climate effects, to moderate potential damage, seize opportunities and deal with the consequences [36].
Exposure is identified by changes in climatic conditions, either by an increase or decrease in adverse events. The exhibition is the presence of people, livelihoods, species or ecosystems, environmental functions, services and resources, infrastructure, or economic, social or cultural assets in places and environments that could be negatively affected [1]. This indicator was considered taking into account the following factors: Frequency of adverse events, modeled changes in the climate, and environmental problems.
The ten components or variables that were analyzed to calculate the index were the following: (1) Type of roofing and housing construction material, (2) type of housing floor construction material, (3) perception of the degree of damage caused by flood, (4) perception of the degree of damage caused by flooding, (5) perception of the degree of damage caused by high winds, (6) perception of the degree of damage caused by storm surge, (7) perception of the degree of damage caused by floods of streams, (8) degree of information on risks and housing, (9) type of risk reported, (10) means of information for monitoring civil protection bulletins.

Descriptive Statistics: Analysis of Demographic Aspects and Damage Perception
The results of the survey on demographic characteristics and physical conditions of the household, showed the following aspects in their descriptive statistics: 69.7% of the heads of households were born in the entity. Regarding the type of material with which the house was built, we found that 79.3% had a roof of concrete material, 15.5% had sheets of cardboard, metal, asbestos, or fiber cement, 3.6% had a wooden roof, and 0.4% had tiles. While 1.2% of private homes had a roof of waste materials. With regard to the material with which the walls of the houses were built, we found that 13.9% had Sustainability 2020, 12, 1575 5 of 11 reed, palm, cardboard, asbestos, or metal walls. These indicators are part of the variables related to exposure.
The previous data show us that one in every five homes was built with weak materials, and therefore, they were in a degree of exposure that potentiates the probability of occurrence of a natural disaster due to the possible impact of winds or floods.
The analysis of the perception of the degree of damage caused by flooding was carried out through the question: How would you rate the degree of damage caused to your home due to flooding in your street, block, or neighborhood? It was found that 3.2% of the surveyed homes were highly vulnerable to floods, 14.4% were moderately vulnerable, and 82.4% were little vulnerable to flooding in their homes. Households that are highly vulnerable to flooding could cause the loss of material assets, increase the risk of disease, require a financial burden for the replacement of lost material assets and repairs to their homes.
In the case of landslides, the perception is that 94.2% of households are little or not vulnerable to this type of affectations. However, in the case of damage caused by high winds, the percentage of homes with very serious and serious damage reaches up to 47.4%. High winds affect homes due to their strength, and can cause the total loss of home and material goods, by lifting, by tilting or tipping over. In the street or block, the effects are falling poles and trees. Figure 2 shows the georeferenced surveys applied in the municipality of La Paz in inhabited private homes, and the risks map with areas susceptible to flooding by risk level: Low, medium, high, and very high.

Descriptive Statistics: Analysis of Demographic Aspects and Damage Perception
The results of the survey on demographic characteristics and physical conditions of the household, showed the following aspects in their descriptive statistics: 69.7% of the heads of households were born in the entity. Regarding the type of material with which the house was built, we found that 79.3% had a roof of concrete material, 15.5% had sheets of cardboard, metal, asbestos, or fiber cement, 3.6% had a wooden roof, and 0.4% had tiles. While 1.2% of private homes had a roof of waste materials. With regard to the material with which the walls of the houses were built, we found that 13.9% had reed, palm, cardboard, asbestos, or metal walls. These indicators are part of the variables related to exposure.
The previous data show us that one in every five homes was built with weak materials, and therefore, they were in a degree of exposure that potentiates the probability of occurrence of a natural disaster due to the possible impact of winds or floods.
The analysis of the perception of the degree of damage caused by flooding was carried out through the question: How would you rate the degree of damage caused to your home due to flooding in your street, block, or neighborhood? It was found that 3.2% of the surveyed homes were highly vulnerable to floods, 14.4% were moderately vulnerable, and 82.4% were little vulnerable to flooding in their homes. Households that are highly vulnerable to flooding could cause the loss of material assets, increase the risk of disease, require a financial burden for the replacement of lost material assets and repairs to their homes.
In the case of landslides, the perception is that 94.2% of households are little or not vulnerable to this type of affectations. However, in the case of damage caused by high winds, the percentage of homes with very serious and serious damage reaches up to 47.4%. High winds affect homes due to their strength, and can cause the total loss of home and material goods, by lifting, by tilting or tipping over. In the street or block, the effects are falling poles and trees. Figure 2 shows the georeferenced surveys applied in the municipality of La Paz in inhabited private homes, and the risks map with areas susceptible to flooding by risk level: Low, medium, high, and very high.

Socio-Environmental Vulnerability Index due to the Impact of Tropical Cyclones
The analysis of the main components based on the standardization of variables mentioned above, resulted in a Kaiser-Meyer-Olkin value of 7.1 (0.713) which is considered acceptable for a reduction of data. The analysis showed three factors: Factor number 1 explains 27.92% of the total variance, in which it explains the exposure of households, through the perception of damage caused during Hurricane Odile.
Factor number 2 explains 23.09% of the total variance, in which it explains adaptive capacity, this information is through social capital, education, and culture for the prevention of natural disasters caused by climate change.
Factor number 3 explains 14.51% of the total variance, in which it explains the sensitivity of households to quality conditions in household construction materials.
The total variance explained by the three factors is 65.53%, as shown in the following Table 1. For the interpretation of the results through the correlation of the variables with respect to the factors by which they are grouped, the Varimax rotation was applied [37]. It was found that the level of severity of damage perceived by flood it is related (0.75) to the tropical cyclone exposure component. The results show that the majority of households are in the highly vulnerable category, with 33% within a range of the index −3.77243 to −0.939141. The moderately vulnerable constitute 36% with values from −0.929141 to 0.956385. While the least vulnerable represent 31% of households with an index range of 0.966385 to 5.6952. The results reveal levels of high and moderate socio-environmental vulnerability by TC of 69% in homes in La Paz.
The following Table 2 shows the main findings on socio-environmental vulnerability due to the impact of TC as a category I hurricane on the Saffir-Simpson scale.

Discussion
It is evident that the analysis and determination of vulnerability levels in cities are a priority activity, to lessen the negative impact of adverse events associated with climate change [9,15]. In the case of Mexico, some of the priority lines of research for adaptation to climate change are the characterization of vulnerability by type of threat and social sector, and the use of risk mapping and coastal-marine vulnerability [39], which has contributed to the knowledge on this important subject.
The results of this study have generated a useful tool for risk prevention through vulnerability maps. They have been used in cities that actively work on planning under a climate change adaptation approach such as Madrid, in a study where they generated maps for different types of impacts [8].
One of the advantages of this type of space-time vulnerability tool is that it allows the design of territorial and sectoral intervention strategies in strategic risk reduction [35].
Regarding the percentages of vulnerable populations, in general terms, international and national studies have shown a lower vulnerability in their cities. The population of Madrid resulted in lower percentages of the highly vulnerable population, 22.3% against the 33% found for La Paz, however, they estimated four levels of vulnerability, due to methodological differences [8]. In the case of national studies, the coastal city of Manzanillo did not show a polarization, because half of its population presented a low vulnerability and 23.5% a high vulnerability [35]. In the case of Baja California Sur, the city of Loreto showed that 70% of households were highly vulnerable to hurricane impacts [40].
It is important to note that in the presence of large-scale natural events, public action or civil protection authorities may be in different stages of intervention, either before, during, or after the occurrence, and the approaches to action may be of at least of two types. The first is civil protection or reactive action to safeguard the integrity of the inhabitants, and the second is impact of prevention or proactive action to safeguard the socio-economic functioning of the affected places [41]. The above is relevant because floods and tropical cyclones have contributed little more than 32% and 30%, respectively, to significant damage to the population, including deaths and people affected, so they occupy the first and second place in causes [42].
The study showed that within the prevention actions and strategies that increase adaptive capacity, it is important to provide timely information to the population about the Saffir-Simpson scale and the potential damages associated with each category, as well as information on the phases of the "Early Warning System" of Civil Protection [40]. The vulnerability of geo-referencing areas is a valuable tool for the prevention of risks associated with hurricanes and tropical cyclones, which are predictable. An important aspect to promote the resilience that must be considered in civil protection systems is the energy sustainability of buildings. This topic will be a new line of research to consider in future studies [13,14].

Conclusions
Vulnerability levels of La Paz, Baja California Sur, México households were determined using a univariate stratification technique to measure the magnitude of the degree of vulnerability to the impact of category 1 tropical cyclones on the Saffir-Simpson scale. According to the results, it is recommended to include within the urban planning and development system of the city of La Paz the infrastructure and urban equipment necessary to reduce the impacts of TC, as well as to avoid human settlements in flooding or moving areas identified in the risks map.
It seems paramount to strengthen the participation and action of the population at risk, and promote the dissemination of the information generated, risks maps for the impact of TC and, therefore, strengthen early warning systems, as well as prevention actions in case of emergencies due to hydrometeorological phenomena. In order to improve resilience in La Paz, in addition to increasing household knowledge, it is known that improving the conditions of the materials with which housing is built, specifically floors, walls, and ceilings, prevents the impact of the TC that represent a risk to the population. We obtained the vulnerability perception of the population and added it to the official flooding risk map, information that will be helpful in validating and providing more accurate information for civil protection in activities of prevention.
For resilience in the cities, it is important to develop more research about the effects of climate change in communities, and because the new plans and developments promote sustainability of buildings and better use of the land use, these studies should take into consideration the TC impacts on energy and water supply, both strategic elements for modern life standards.