Downscaling of global climate outputs is necessary to transfer projections of potential climate change scenarios to local levels. This is of special interest to dry mountainous areas, which are particularly vulnerable to climate change due to risks of reduced freshwater availability. These areas play a key role for hydrology since they usually receive the highest local precipitation rates stored in form of snow and glaciers. In the central-northern Chile (Norte Chico, 26-33oS), where agriculture still serves as a backbone of the economy as well as ensures the well being of people, the knowledge of water resources availability is essential. The region is characterised by a semiarid climate with a mean annual precipitation inferior to 100mm. Moreover, the local climate is also highly influenced by the ENSO phenomenon, which accounts for the strong inter-annual variability in precipitation patterns. Although historical and spatially extensive precipitation data in the headwaters of the basins in this region are not readily available, records at coastal stations show worrisome trends. For instance, the average precipitation in La Serena, the most important city located in the Coquimbo Region, has decreased dramatically in the past 100 years. The 30-year monthly average has decreased from 170 mm in the early 20th century to values less than 80 mm nowadays. Climate Change is expected to strengthen this pattern in the region, and therefore strongly influence local hydrological patterns.
Upper Diguillín and Renegado are two neighbouring Andean basins of south-central Chile, with different specific discharges that cannot be explained solely by their difference in size. To address this issue, this study considers three separate but complementary approaches: (a) long-term analysis of rainfall and flow trends; (b) determination of hydrogeological properties at the watershed scale; and (c) analysis of the temporal evolution of groundwater storage. First, a trend test detected a statistically significant discharge decrease for Renegado in summer, unrelated to a coincidental precipitation trend, which seems to be associated with an increased use of water in that season related to tourism activity in the area. Second, there were no important differences in hydraulic conductivity or drainable porosity between the two study areas. However, it was found that there is a long-term negative trend in groundwater storage for Renegado; that is, water that contributes to the lower Diguillín streamflow through numerous springs.
The ability of two‐dimensional hydrodynamic models to accurately and efficiently predict the propagation of floods over large urban areas is of paramount importance for flood risk assessment and management. Paradoxically, it is in these highly relevant urban domains where flood modeling faces some of the most challenging obstacles. This is because of the very high‐resolution topography that is typically required to capture key hydraulic features, which significantly increases the computational time of the model. One particularly interesting solution to this difficulty was recently proposed in the form of a numerical scheme for the solution of a simplified version of the shallow water equations, which yields a system of two explicit equations that captures the most relevant hydraulic processes at very high computational efficiency. However, some stability problems were reported, especially when this formulation is applied to low friction areas. This is of particular importance in urban areas, where smooth surfaces are usually abundant. This paper proposes and tests two modifications of this previous numerical scheme that considerably improves the numerical stability of the model. Model improvements were assessed against a structured set of idealized test cases and finally in the simulation of flood propagation over complex topography in a highly urbanized area in London, United Kingdom. The enhanced stability achieved by the new formulation comes at no significant additional computational cost and, in fact, the model performance can benefit from the longer time steps that are allowed by the new scheme.
Driven by rapid climate, socio-economic, environmental, and political change, flood risks in urban regions are on the rise. Given that cities and urban regions are highly complex and integrated systems comprising social, ecological and infrastructure domains, flood risks in urban regions are characterized by high levels of complexity, such as cascading effects, interconnected risks and interacting risk drivers. To ensure the effectiveness of risk management interventions, enhanced understanding and empirical evidence of the complex nature of urban flood risks is needed. Failing to understand how risks interact across systems, and not identifying interactions of underlying risk drivers and root causes can lead to maladaptation in planning. Addressing this, we use impact chains and impact webs, i.e. conceptual risk models that have been co-created and validated in a participatory manner, to break down and understand the complex nature of flood risks, using the highly flood-prone urban region of Hue in Central Vietnam as a case study. Results show that flood risks and impacts in Hue are deeply interconnected, with cascading effects across systems. Further, our analysis reveals that risks and impacts are induced by the same underlying risk drivers and root causes. The co-development of conceptual flood risk models in Hue provides a useful methodology to move from systemic flood risk analysis to systemic flood risk management.
Abstract Vietnam is exposed to different types of floods that cause severe economic losses, damage to infrastructure, and loss of life. Reliable information on the drivers, patterns and dynamics of flood risk is crucial for the identification, prioritization and planning of risk reduction and adaptation measures. Here, we present a systematic review of existing flood risk assessments in Vietnam. We evaluate the current status, persisting gaps, and challenges regarding the understanding and assessment of flood risk in the country. The literature review revealed that: (i) 65 % of the reviewed papers did not provide a clear definition of flood risk, (ii) assessments had a tendency to prioritize physical and environmental drivers of risk over social, economic or governance‐related drivers, (iii) future‐oriented assessments tended to focus on hazard and exposure trends, while vulnerability scenarios were often lacking, (iv) large and middle‐sized cities were assessed more frequently than others, (v) only few studies engaged with relevant local stakeholders for the assessment of risk and the development of potential solutions, and (vi) ecosystem‐based adaptation and flood risk insurance solutions were rarely considered. Based on these findings, we point out several directions for future research on flood risk in Vietnam.
Based on a future temperature increase of 0.5°C and precipitation decrease of 25%, the climate elasticity of streamflow to precipitation and temperature changes in 12 Andean watersheds of the Coquimbo Region, north-central Chile, was assessed. Also, the possible relationships between this elasticity and specific physiographic characteristics of the watersheds (area, average elevation, slope distribution, terrain roughness, slope orientation, vegetation cover) were studied. Climate elasticity of streamflow ranged between 0 and 2.8. Watersheds presenting higher elevations, with a fairly well-balanced distribution of slope exposure tend to exhibit lower elasticity, which could be explained by the contribution of snowfall to the hydrological regime, more significant in those watersheds. Results should be considered when downscaling climate model projections at the basin scale in mountain settings. Finally, uncertainties in the approach, given by factors such as streamflow seasonality, data availability and representativeness and watershed characteristics, and therefore the scope of the results, are discussed.
In many West African river basins, households regularly experience floods and the associated impacts. In the absence of widely accessible formal risk transfer mechanisms (e.g., insurance), households often have to cope with financial impacts. Only a few studies have explored the financial effects of floods on agriculture-dependent households in the region and the role formal and informal risk transfer plays in their mitigation. This study addresses this gap, explores flood impacts with financial implications for households, and researches the existing strategies to mitigate them. Moreover, it aims to better understand how different measures influence the recovery process. The study draws on primary data from a household survey (n = 744) in the Lower Mono River basin, combined with stakeholder workshops and semi-structured interviews, and applies a generalized linear model to the survey data. The results reveal four flood impact types with financial implications: agricultural, material, health, and trade. Moreover, a shortened recovery time is significantly associated with assistance from savings groups and cooperatives—groups originally not formed to help during floods. In light of the severe and frequent flood impacts, effective and publicly accepted adaptation measures are needed to enable favorable conditions for creating sustainable and accessible risk transfer mechanisms.
Nival regimes, typical for arid mountainous areas, are highly dependent on precipitation and are strongly impacted by temperatures. Therefore, change detection in hydro-meteorological records is ot considerable importance for water resources management and planning in these regions. This study focuses on the analysis of recent (1964—2006) non-parametric trends of seasonal precipitation, temperature and discharge records in Norte Chico (29°S to 32°S), Chile. A strong warming signal and an increase in precipitation associated with a shift of the rainy season have been observed over recent decades. However, precipitation trends over longer periods are not consistent with recent observations. Consequently, the regional discharge mainly dependent on snowmelt was found to be strongly impacted by changes in precipitation and temperature patterns. These changes underline the importance of flexible and adaptive measures. Hence, beyond offering one of the few contributions about climate trends with a focus on this part of the Andes, this work is also of practical use for local and national stakeholders.
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