Don't rely too much on trees: Evidence from flood mitigation in China

Pathways of ecosystem-based disaster risk reduction: A global review of empirical evidence

Ecosystems provide valuable services in reducing the risks of disasters through various pathways, which are increasingly recognized as sustainable strategies for disaster management. However, there remains limited information on the underlying ecological processes of risk reduction. This paper addresses this gap by synthesizing ecological mechanisms and evaluating the 'level of evidence' and 'scale of use' through a review of 64 peer-reviewed research articles published between 2015 to 2022. These research articles covered nine types of disasters, predominantly floods (42.19 %), followed by urban heat waves (18.75 %), storm runoff (10.94 %), coastal erosion (9.38 %), tsunamis (4.69 %), and avalanches and landslides (6.25 % each). The level of evidence supporting ecological processes for disaster risk reduction is moderate, as is the 'scale of use'. Results show that there are a few studies describing the mechanism of ecosystem-mediated risk reduction and are mostly limited to the causal relationship. Empirical evidence demonstrates that forest and freshwater ecosystems buffer the risk of urban heat through processes such as transpiration, solar radiation interception, and evaporative cooling, while flood risks are mitigated by enhancing evapotranspiration, reducing water runoff time, and facilitating infiltration rates. Coastal erosion is reduced by dissipating wave energy and through beach nourishment, which facilitates ecological succession. The review underscores that hazard attenuation depends on factors such as forest type (e.g., species composition, age structure, and area), and landscape characteristics (e.g., matrix, composition and configuration). Moreover, the geographic scope of published research is largely confined to developed countries and the global north. Multidisciplinary research involving ecologists and disaster experts is imperative to address existing knowledge gaps and enhance the integration of ecosystem-based adaptation into disaster risk reduction strategies.

Foundations of indigenous knowledge on disasters due to natural hazards: lessons from the outlook on floods among the Bayira of the Rwenzori region

The role of indigenous knowledge in increasing context specificity and exposing blind spots in scientific understanding is widely evidenced in disaster studies. This paper aims to structure the processes that shape indigenous knowledge production and its optimisation using the case of floods. An inductive analytical approach is applied among riparian indigenous communities (focus on the Bayira) of the Rwenzori region of Uganda where plenty of indigenous flood practices have been recorded. Indigenous knowledge of floods is found to be based on intimate comprehension of local hydrometeorological regularities. Insofar as these regularities follow natural dynamics, indigenous socio-epistemic processes are noted to be consistent with the laws of nature. Coupled with regular open sociocultural deliberations, the conceptualisation of hydrometeorological regularities induces an indigenous ontology and empiricist epistemology. This, together with the techniques used, is the driver of crucial epistemic virtues which enable indigenous knowledge to provide disaster solutions that are adapted, pragmatic, and holistic.

Woodland's role in natural flood management: Evidence from catchment studies in Britain and Ireland

Despite the attention currently given to the potential environmental benefits of large-scale forest planting, there is a shortage of clear observational evidence regarding the effects on river flows, and what there is has often been contradictory or inconclusive. This paper presents three independently conducted paired-catchment forestry studies covering 66 station-years of flow measurements in the UK and Ireland. In each case coniferous evergreen trees were removed from one catchment with minimal soil disturbance while the adjoining control catchment was left unchanged. Trees were removed from 20% - 90% of the three experimental basins. Following woodland removal there was an increase in dry weather baseflow at all sites. Baseflows increased by about 8% after tree removal from a quarter of the Hore basin and by 41% for the near-total cut at Howan. But the changes were more complex for peak flows. Tree harvesting increased the smallest and most frequent peak storm flows, indicating that afforestation would lead to the suppression of such events. This was however restricted to events well below the mean annual flood, indicating that the impact of forests upon the largest and most damaging floods is likely to be limited. Whilst a forest cover can be effective in mitigating small and frequent stormflows it should never be assumed to provide protection against major flood events.

Exploring Options for Flood Risk Management with Special Focus on Retention Reservoirs

Floods are among the most frequent and deadliest natural disasters, and the magnitude and frequency of floods is expected to increase. Therefore, the effects of different flood risk management options need to be evaluated. In this study, afforestation, permeable concrete implementation, and the use of dry and wet retention reservoirs were tested as possible options for urban flood risk reduction in a case study involving the Glinščica river catchment (Slovenia). Additionally, the effect of dry and wet reservoirs was investigated at a larger (catchment) scale. Results showed that in the case of afforestation and permeable concrete, large areas are required to achieve notable peak discharge reduction (from a catchment scale point of view). The costs related to the implementation of such measures could be relatively high, and may become even higher than the potential benefits related to the multifunctionality and multi-purpose opportunities of such measures. On the other hand, dry and wet retention reservoirs could provide more significant peak discharge reductions; if appropriate locations are available, such reservoirs could be implemented at acceptable costs for decision makers. However, the results of this study show that reservoir effects quickly reduce with scale. This means that while these measures can have significant local effects, they may have only a minor impact at larger scales. We found that this was also the case for the afforestation and permeable concrete.

Does high risk mean high loss: Evidence from flood disaster in southern China

Southern China has suffered from flood disasters for over sixty years, which results in tremendous socio-economic loss. With the development of economy and the improvement of disaster reduction, both the exposure and potential loss of flood disaster are increasing. However, previous studies only focus on risk assessment, few has examined the comparison of potential risk and the actual losses caused by it. To this end, a method combing entropy weight and TOPSIS based on flood data (2008 to 2018) in China's national and provincial disaster database is applied to analysis flood risk and resulting loss in southern China. By using disaster system dimensions of hazard, exposure and vulnerability, the effect of natural, economic and social factors on flood risk are also examined. Results indicate that: (1) flood risk in southern China is relatively low from 2008 to 2014 and becomes severe since 2016; (2) the resulting losses of flood disasters in southern China are optimistic during most of the selected years in the study period; (3) flood risk is not always in line with the resulting loss; and (4) flood disasters in southern China are categorized into high-risk and low-loss situation, low-risk and high-loss situation, and the situation with the same level of risk and loss. To the best of our knowledge, this is the first study to assess southern China on a regional scale from both temporal and spatial perspectives, and has compensated for the lack of comparative research on flood risk and the resulting loss. In practice, our findings can protrude the priorities of flood prevention both in flood-prone areas and specific measures, which is conducive to improve the efficiency of resource allocation.

Land use management recommendations for reducing the risk of downstream flooding based on a land use change analysis and the concept of ecosystem-based disaster risk reduction

Sustainable management of ecosystems can provide various socio-ecological benefits, including disaster risk reduction. Through their regulating services and by providing natural protection, ecosystems can reduce physical exposure to common natural hazards. Ecosystems can also minimize disaster risk by reducing social and economic vulnerability and enhancing livelihood resilience. To showcase the importance and usefulness of ecosystem-based disaster risk reduction (Eco-DRR), this study (1) analyzed the land use change in a watershed in central Japan, (2) applied the concept of Eco-DRR, and made land use management recommendations regarding the watershed scale for reducing the risk of downstream flooding. The recommendations that emerged from the application, based on the land use change analysis, are: the use of hard infrastructure and vegetation to store and retain/detain stormwater and promote evapotranspiration is recommended for downstream, urban areas; the sustainable management of upland forest ecosystems and secondary forest-paddy land-human systems, and proactive land use planning in the lowland delta, where built land is concentrated, are key to the watershed-scale landscape planning and management to reduce downstream flooding risks.

Key coastal landscape patterns for reducing flood vulnerability

The purpose of the present study was to examine key coastal landscape patterns related to flood vulnerability to support resilience strategies for coastal green infrastructure. To this end, we assessed the flood vulnerability of coastal landscapes based on three indicators: exposure, including precipitation; sensitivity, including elevation, slope, soil, drainage, and density; and adaptability, including urban land-use. Subsequently, we investigated whether landscape patterns, including the shape index and subdivision index, would affect flood vulnerability through a multivariate regression analysis, which allowed us to determine key coastal landscape patterns. At the regional scale, including the overall study site, we suggested strategies for green infrastructure planning, focusing on patch shapes of forest, grassland, and water. At each local scale, a variety of landscape patterns were selected: the contiguity index of used area for the central subregion: the division index of forests, the contiguity of water, and the fractal dimension index of used area for the northeast subregion; the circumscribing circle index of barren and wetlands for the northwest subregion; the division and fractal index of forests for the southwest subregion; and the division index of forests and the fractal index of water for the southeast subregion. Based on the derived landscape patterns of each subregion, we propose coastal green infrastructure planning with resilience strategies.