DSpace Angular :: Browsing by Author "Rojas, Octavio"

Browsing by Author "Rojas, Octavio"

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A temporal analysis of the consequences of the drought regime on the water footprint of agriculture in the Guadalupe Valley, Mexico
(2024) Novoa, Vanessa; Rojas Quezada, Carolina Alejandra; Rojas, Octavio; Ahumada-Rudolph, Ramón; Moreno-Santoyo, Rebeca
Changes in water availability have a substantial impact on the sustainability and maintenance of agriculture, with water footprint (WF) being a robust methodology to assess these transformations. The Guadalupe Valley is one of the places with the highest agricultural production in Mexico. Despite its semi-arid climatic conditions, it provides high-quality crops that are well-positioned in the world. The historical trend of rainfall and temperatures between 1987 and 2017 was analyzed to identify climatic patterns in the territory. Through the calculations of the water footprint of Grapevine and Olive crops, the sensitivity of the crops to recurrent water deficit and their adaptation in their yields to drought episodes was identified. The reduction in precipitation and occurrence of extreme temperatures have contributed significantly towards augmenting crop evapotranspiration and, consequently, intensifying crop irrigation demands. As a result, there has been an apparent increase in the consumption of WFagricultural since 2007. Thus, the period of highest WFagricultural consumption was 2014 (Extremely dry), as opposed to 2011 (Very wet). In particular, the lowest WFgreen consumptions were observed in extremely dry years, that is, > 20% of the WFagricultural intensifying drought events. Therefore, these periods were compensated with higher uses of WFblue and WFgray, which are inversely correlated with precipitation, where vine crops consume 73% more WFagricultural compared to olive plantations, showing greater interannual variability. These results contribute to analyzing the temporal evolution of water consumption for agriculture, providing a basis for rational water use strategies.
Assessment of the flood mitigation ecosystem service in a coastal wetland and potential impact of future urban development in Chile
(2022) Rojas, Octavio; Soto, Evelyn; Rojas Quezada, Carolina Alejandra; López, J. Javier; CEDEUS (Chile)
A worldwide increase in flooding due to climate change and population growth in exposed areas is expected, especially in coastal areas; therefore, nature-based solutions (NBS) for risk reduction are necessary to increase the resilience of cities, particularly in developing countries, which usually lack large budgets for structural measures but have natural areas such as wetlands that can be used as NBS. The flood mitigation ecosystem service of a coastal wetland in central Chile was analyzed. Using hydrological and topo-bathymetric data, two flood hazard scenarios were modeled: (i) S1 current and (ii) S2 projected, which was established based on land-use planning instruments and urban projects developed since 1954. Flood hazard maps for different return periods were obtained and indicators related to the mitigation potential of the wetland were calculated. It was proven that urban project development has intensified since 2000, mainly in the form of real estate development, with an increase in occupation of 50%, and the wetland area is projected to be further reduced by around one third, decreasing potential flood mitigation. Thus, for an extreme return period, in this case 500 years, the water volume stored by the wetland would decrease by more than 38% and the flooded area of the wetland by 30%, increasing flooding and vulnerability of the urban area, with various repercussions for surrounding neighborhoods and infrastructure. The number of people and homes affected would increase by around 6% and 8%, respectively, such that the affected land value would reach an additional US$55 million, which would be very detrimental in a city that has seen its natural spaces encroached upon by gray infrastructure. This research reaffirms the need to support the restoration and conservation of coastal wetlands under pressure from urban development in an area with a lack of green infrastructure planning.
Coastal Wetlands: Ecosystems Affected by Urbanization?
(2020) Rojas Quezada, Carolina Alejandra; Novoa, Vanessa; Rojas, Octavio; Ahumada-Rudolph, Ramón; Sáez, Katia; Fierro, Pablo; CEDEUS (Chile)
Coastal wetlands are ecosystems that provide multiple benefits to human settlements; nonetheless, they are seriously threatened due to both a lack of planning instruments and human activities associated mainly with urban growth. An understanding of their functioning and status is crucial for their protection and conservation. Two wetlands with different degrees of urbanization, Rocuant-Andalién (highly urbanized) and Tubul-Raqui (with little urbanization), were analyzed using temperature, salinity, dissolved oxygen, pH, turbidity, granulometry, fecal coliform, and macroinvertebrate assemblage variables in summer and winter. In both wetlands marked seasonality in salinity, temperature and sediment texture classification, regulated by oceanic influence and changes in the freshwater budget, was observed. In the Rocuant-Andalién wetland, the increases in pH, dissolved oxygen, gravel percentage, and coliform concentration were statistically significant. Urbanization generated negative impacts on macroinvertebrate assemblage structure that inhabit the wetlands; greater richness and abundance (8.5 times greater) were recorded in the Tubul-Raqui wetland than in the more urbanized wetland. The multivariate statistical analysis reflects the alteration of these complex systems.
Flooding in Central Chile : Implications of Tides and Sea Level Increase in the 21st Century
(2018) Rojas, Octavio; Mardones, María; Martínez Reyes, Carolina del Pilar; Flores, Luis; Sáez, Katia
Mapping coastal wetlands using satellite imagery and machine learning in a highly urbanized landscape
(2022) Munizaga, Juan; García, Mariano; Ureta, Fernando; Novoa, Vanessa; Rojas, Octavio; Rojas Quezada, Carolina Alejandra; CEDEUS (Chile)
Coastal wetlands areas are heterogeneous, highly dynamic areas with complex interactions between terrestrial and marine ecosystems, making them essential for the biosphere and the development of human activities. Remote sensing offers a robust and cost-efficient mean to monitor coastal landscapes. In this paper, we evaluate the potential of using high resolution satellite imagery to classify land cover in a coastal area in Concepción, Chile, using a machine learning (ML) approach. Two machine learning algorithms, Support Vector Machine (SVM) and Random Forest (RF), were evaluated using four different scenarios: (I) using original spectral bands; (II) incorporating spectral indices; (III) adding texture metrics derived from the grey-level covariance co-occurrence matrix (GLCM); and (IV) including topographic variables derived from a digital terrain model. Both methods stand out for their excellent results, reaching an average overall accuracy of 88% for support vector machine and 90% for random forest. However, it is statistically shown that random forest performs better on this type of landscape. Furthermore, incorporating Digital Terrain Model (DTM)-derived metrics and texture measures was critical for the substantial improvement of SVM and RF. Although DTM did not increase the accuracy in SVM, this study makes a methodological contribution to the monitoring and mapping of water bodies’ landscapes in coastal cities with weak governance and data scarcity in coastal management.
Patrones de urbanización en la biodiversidad de humedales urbanos en Concepción metropolitano
(2015) Rojas Quezada, Carolina Alejandra; Sepúlveda Zúñiga, Einer; Barbosa, Olga; Rojas, Octavio; Martínez Reyes, Carolina del Pilar
Risk factors and perceived restoration in a town destroyed by the 2010 Chile tsunami
(2017) Martínez Reyes, Carolina del Pilar; Rojas, Octavio; Villagra, Paula; Aránguiz, Rafael; Sáez Carrillo, Katia
Spatial interactions between perceived biophilic values and neighborhood typologies in urban wetlands
(2024) Villagra, Paula; Rojas Quezada, Carolina Alejandra; Rojas, Octavio; Alves, Susana
Wetlands provide a wide range of ecosystem services; however, little is known about their perception value or use for improving urban planning and wetland management. This study explores the perception values towards the Los Batros Wetland in Chile, by inhabitants from different neighborhood typologies. A sample of 457 responses evaluated the wetland by applying the Kellert framework of 9 biophilic values using a Public Participation Geographic Information Systems (PPGIS) approach. A spatial autocorrelation analysis with hotspot revealed that the spatial distribution of biophilic values varies by neighborhood typology. Subsequent ANOVA and T-test suggest that such distribution is affected by perceived accessibility and visitation purposes, and is influenced by socio-demographic aspects that vary among neighborhood typology. Inhabitants of the garden city typology located next to the wetland area, whose residents have higher education and income levels and who have easy and moderate access to the wetland, agreed with a diverse type of biophilic values. In the garden city, the ecologistic-scientific value has the higher spatial concentration. In the condominium typology, with similar education and income levels and accessibility, but situated far from the wetland, there was less agreement with biophilic values, and these were more dispersed, i.e. biophilic values are less representative. In this case, the aesthetic value prevails over others. At the north area of the neighborhood unit, where residents had lower education and income levels along with moderate to difficult physical access to the wetland, but they developed horticultural activities alongside the wetland, inhabitants agree with various biophilic values, highlighting its symbolic value. Conversely, biophilic values of people in the favela were not in agreement nor disagreement, regardless they have similar physical access and distance to the wetland as residents in the condominium typology, but have the lowest income and education level. Findings suggest that effective wetlands management requires appreciation of the clusters of values assigned to wetland environments, which in this case relate to neighborhood typologies. These clusters should be considered when planning to restore, protect, and improve urban wetlands.
Spatiotemporal vegetation dynamics in a highly urbanized Chilean coastal wetland: Insights on long-term natural and anthropogenic influences
(2024) Munizaga, Juan; Rojas, Octavio; Lagos, Bernardo; Rojas Quezada, Carolina Alejandra; Yepez, Santiago; Hernández, Esteban; Ureta, Fernando; de la Barrera, Francisco; Jato-Espino, Daniel
This study analyzes the spatiotemporal dynamics of the vegetation of a highly urbanized coastal wetland in the 2000–2020 period, considering natural disturbances and anthropogenic stressors. The wetland system was stratified into four domains: Coastal, Intertidal, Freshwater, and Urban, differentiated by their geomorphological, topographical, and water salinity characteristics, which were validated by ground vegetation sampling. In these domains, spectral indicators of vegetation were used on 884 Landsat images in the Google Earth Engine to determine vegetation types, trends, and phenology. The start of the growing season coincides with the beginning of the Austral winter, exhibiting seasonal behavior, which was interrupted by abrupt natural disturbances such as floods and tsunamis. In addition, a progressive trend associated with the replacement of native species by exotic species was reported in areas with significant anthropogenic stressors (e.g., highways, city edges, and grazing areas), with 45 % presenting an increase in the normalized difference vegetation index. Areas far from anthropogenic stressors maintained their behavior, which is explained by natural factors such as precipitation, temperature, and evapotranspiration. The proposed method strengthens our understanding of the interrelationship between factors that modify the behavior of vegetation in coastal wetlands pressured by anthropogenic stressors and contributes to their management and protection.
The status quo effect in the sociohydrology of floods
(2024) Leal, Catalina Mendoza; Coloma, Rocio; Ponce, Diego; Alarcon, Benjamin; Guerra, Maricarmen; Stehr, Alejandra; Carrasco, Juan Antonio; Alcayaga, Hernan; Rojas, Octavio; Link, Felipe; Link, Oscar
Two behavioural types in sociohydrology of floods have been described in more detail than others: the levee effect and the learning effect. However, additional types of behaviour operate and need further research. Taking the case of frequent flash floods occurring in an ephemeral stream, a tributary of the Vilama River, located in San Pedro de Atacama, Chile, at the interphase between the Atacama desert and the Andean Altiplano, we explore the existence of further behavioural types in the sociohydrology of floods at four neighbourhoods along the tributary. Fieldwork to reconstruct a recent flood event, hydrological analysis and semistructured interviews with key informants to characterize people's responses to floods were conducted. Results show evidence that the so-called status quo effect is present at the riparian community scale, i.e. when communities do not learn and adapt to prevent damage even when exposed to frequent floods. Possible causes of the status quo effect are discussed.
The generation of new tsunami risk areas due to an intentionally biased reconstruction process: Case study of llico after the 2010 Chile tsunami
(2020) Aranguiz, Rafael; Martinez, Carolina; Rojas, Octavio; Hoffmann, Constanza; Lopez, Pablo
Tsunamis are among the most significant hazards in coastal settlements. Mitigation measures have been focused mainly on physical aspects, and few studies have addressed vulnerability and resilience in a multidimensional approach. The main objective of the present work is to assess changes in vulnerability and, consequently, risk, considering a time-space dimension. Three deterministic tsunami scenarios based on historical events were analyzed, and vulnerability analysis with an emphasis on social cohesion and community organization in pre reconstruction (2012) and post-reconstruction (2017) conditions was carried out using physical, socioeconomic and social organization variables. The extreme scenario was found to be a 2010-like tsunami, and high levels of social trust and community cooperation were found in pre-reconstruction conditions, which decreased in post-reconstruction conditions due to the relocation of the affected population to other parts of the region. Therefore, it can be concluded that even though physical aspects are important for improving the livability of an affected place and the quality of life of its inhabitants, intentionally biased reconstruction processes (focused mainly on physical aspects) do not effectively reduce risk. Finally, it is crucial to include social capital and social resilience in public policies to implement more comprehensive and successful reconstruction processes.
Urban development versus wetland loss in a coastal Latin American city : lessons for sustainable land use planning
(2019) Rojas, Carolina; Munizaga, Juan; Rojas, Octavio; Martínez; Reyes, Carolina del Pilar; Pino, Joan; CEDEUS (Chile)
Urban Growth and Flood Disasters in the Coastal River Basin of South-Central Chile (1943–2011)
(2017) Rojas, Octavio; Mardones, María; Rojas, Carolina; Martínez Reyes, Carolina del Pilar; Flores, Luis
Water footprint and virtual water flows from the Global South: Foundations for sustainable agriculture in periods of drought
(2023) Rojas Quezada, Carolina Alejandra; Novoa, Vanessa; Rojas, Octavio; Ahumada-Rudolph, Ramón; Arumí, José Luis; Munizaga, Juan; Cabrera-Pardo, Jaime R.; CEDEUS (Chile)
Freshwater availability has decreased alarmingly worldwide, with agriculture playing a vital role in this trend. The assessment of the agricultural water footprint (WFagricultural) and virtual water flows (VWF) is fundamental not only in local water resources management and protection, but also in our understanding of the synergies between local water consumption and global markets. Thus, the WFagricultural – broken down into its components (blue, green, and gray) – of the leading 21 crops (grouped in fruit, legumes, cereals, and vegetables), grown in four basins with the most significant agricultural activity in central Chile was determined, estimated in two consecutive years 2017–2018. In addition, due to their great importance in exports, VWFs were assessed, establishing connections according to their origins and destinations. The results show that the green and gray water footprints increased significantly in the south-central basins, while blue water consumption increased in the basins of the central zone, reflecting an evident WFagricultural transition in accord with latitude and climate conditions. Furthermore, VWF showed an annual increase of 44 %, in about 116 destinations, with Asia, Europe, and North America being the preferred destinations, with annual variations of VWFblue- gray associated with increases in exports of apples, cherries, grapes, blueberries, and walnuts, market preferences and growing areas. The present study is an initial step toward sustainable agriculture in a commodity exporting country, one that is relevant in the exploitation of virtual water yet faces severe water deficit problems, distribution, and local water policies. Therefore, contributing to encouraging the efficiency and value of water in the process of a new institutional framework.

Browsing by Author "Rojas, Octavio"

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