**4. Discussion**

### *4.1. Dynamics of the Urban-Rural Gradient Zones of the Port-au-Prince Agglomeration*

Since 1986, the various sociopolitical crises that have occurred in Haiti have led to a massive influx of rural populations into the Port-au-Prince agglomeration. In addition, the rapid population growth of the Port-au-Prince agglomeration is largely dependent on unplanned and informal urbanization to meet its housing needs [16]. As a result, the Port-au-Prince agglomeration has experienced rapid spatial urban expansion, particularly towards the north-east, and densification of preexisting built-up areas. The significant spatial expansion of the urban zone in the Port-au-Prince agglomeration seems to indicate a spatial densification of the built-up area in the urban core. These findings should be viewed within the context of an increase in built-up density closer in proximity to the

otherwise more densely populated urban core [16]. This exacerbates the vulnerability of this disadvantaged population due to the mixing of highly densified marginal and risky urban and peri-urban spaces [22,28].

Furthermore, to meet the additional need for housing, the Port-au-Prince agglomeration tends to connect with peripheral municipalities [16], thus justifying the regressive dynamics of the rural zone to the benefit of the peri-urban zone. The rapid spatial urban expansion of Port-au-Prince city towards peripheral areas leads to the discontinuity of urban patches, further suggesting that the geographical space represents a limited resource [6].

The current pattern of urban expansion seems to be influenced by a more favorable topography (the Cul-de-Sac Plain). It has been recognized that topography could influence the expansion of urban areas [31,49]. However, in recent years, urbanization continues to progress, particularly in the south of the study area, in the foothills of the Massif de la Selle, especially on Morne l'Hôpital, despite its status as a reserved area [28]. Indeed, within a context of buildable land becoming scarce and relatively expensive and where the cost of living does not allow for the rental of flats in the urban zone, poor populations settle in risky areas, which lack urban planning infrastructure, and construct houses with salvaged materials [18]. These observations are similar to those of [50] in Cap-Haitian (the second largest city in Haiti), which shows the settlement of the poor population in risky areas such as mangrove forests and mountainsides. Moreover, urban growth is linked to the occurrence of natural disasters in the country (hurricanes and earthquakes), which have led the population to relocate to spaces reserved for agricultural use, mostly unsuitable for building, etc. [51]. Thus, it was revealed that the decade of 2010–2021 was characterized by a stronger urban expansion than other periods studied. Indeed, the urban dynamic during this period seems to have been determined by the 2010 earthquake, which pushed residents without housing and those coming from rural zones to occupy vacant spaces without basic infrastructure [18]. Indeed, new townships, including Canaan with nearly 250,000 inhabitants, emerged after the 2010 earthquake in the municipality of Croix des Bouquets, which bears a rural morphological status [16,18].

### *4.2. Landscape Dynamics of the Urban Core towards the Rural Areas Adjacent to the Port-au-Prince Agglomeration*

The rapid evolution of the peri-urbanization process in the Port-au-Prince agglomeration between 1986 and 2021 is manifested by the anarchic expansion of built-up land to the detriment of the fields. Indeed, in recent decades, agricultural areas have been increasingly transformed into housing and roads [51]. This trend is similar to the findings of [50] on the city of Cap-Haitian (Haiti) and [52] in the French Antilles (Guadeloupe and Martinique), according to which agricultural land in peri-urban areas is constantly being invaded by anarchic buildings. However, agricultural activity is essential to boost the economy of the city and the peri-urban area, to regreen it, and to protect against food insecurity [53].

Moreover, the process of peri-urbanization contributes to the regression of woody vegetation, which is becoming scarcer in both lowland and mountain areas due to their accessibility [28]. This situation risks creating an imbalance between rainwater infiltration and groundwater exploitation in the Cul de Sac Plain, given that the quantity of water drawn from the aquifer is estimated between 63 and 86% of the annual recharge for a growing population [54]. It should be noted that, with an increasingly low poverty line, the population of the Port-au-Prince agglomeration is exploiting and destroying vegetation in favor of subsistent farming activities.

The landscape dynamics of the municipalities located in the rural zone of the Portau-Prince agglomeration are marked by a decrease in woody vegetation in favor of fields. Indeed, the socioeconomic situation of the rural population, characterized by increasing poverty, has pushed a large proportion of the population into agriculture, particularly slash-and-burn agriculture. Despite the low average productivity of the agricultural sector and the low economic surplus generated, it remains the refuge sector *par excellence* for the population in the rural zone [55]. In addition, due to the increasing demand for charcoal by

the urban and peri-urban population [56], pressure on vegetation in the rural zone is intensifying, especially since charcoal accounts for more than 70% of the country's energy needs. The degradation of vegetation in the Port-au-Prince agglomeration leads to a reduction in its resilience and could thus lead to an increase in flooding in the (peri-)urban zone and an increase in the risk of landslides and rockfalls [28]. In addition, this anthropization of the Port-au-Prince landscape could also lead to runoff and silting of the drainage networks during each rainfall event in the urban sectors located downstream of the mountain, thus obstructing the city's drainage infrastructure, which causes recurrent damage in the lowest areas [20,28].
