Pub Date : 2023-07-14DOI: 10.5194/nhess-23-2523-2023
Vipasana Sharma, Sushil Kumar, R. Sushil
Abstract. Snow avalanches cause danger to human lives and property worldwide in high-altitude mountainous regions. Mathematical models based on past data records can predict the danger level. In this paper, we are proposing a neural network model for predicting avalanches. The model is trained with a quality-controlled sub-dataset of the Swiss Alps. Training accuracy of 79.75 % and validation accuracy of 76.54 % have been achieved. Comparative analysis of neural network and random forest models concerning metrics like precision, recall, and F1 has also been carried out.
{"title":"A neural network model for automated prediction of avalanche danger level","authors":"Vipasana Sharma, Sushil Kumar, R. Sushil","doi":"10.5194/nhess-23-2523-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2523-2023","url":null,"abstract":"Abstract. Snow avalanches cause danger to human lives and property\u0000worldwide in high-altitude mountainous regions. Mathematical models based on past data records can predict the danger level. In this paper, we are\u0000proposing a neural network model for predicting avalanches. The model is\u0000trained with a quality-controlled sub-dataset of the Swiss Alps. Training\u0000accuracy of 79.75 % and validation accuracy of 76.54 % have been\u0000achieved. Comparative analysis of neural network and random forest models\u0000concerning metrics like precision, recall, and F1 has also been carried out.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44605677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-13DOI: 10.5194/nhess-23-2475-2023
Melissa Wood, I. Haigh, Quan Le, H. Nguyen, Hoang Tran, S. Darby, R. Marsh, N. Skliris, J. Hirschi, R. Nicholls, N. Bloemendaal
Abstract. Coastal floods, driven by extreme sea levels, are one of the most dangerous natural hazards. The people at highest risk are those living in low-lying coastal areas exposed to tropical-cyclone-forced storm surges. Here we apply a novel modelling framework to estimate past and/or present and future storm-surge-level and extreme-sea-level probabilities along the coastlines of southern China, Vietnam, Cambodia, Thailand, and Malaysia. A regional hydrodynamic model is configured to simulate 10 000 years of synthetic tropical cyclone activity, representative of a past/present (1980–2017) and high-emission-scenario future (2015–2050) period. Results show that extreme storm surges, and therefore total water levels, will increase substantially in the coming decades, driven by an increase in the frequency of intense tropical cyclones. Storm surges along the southern Chinese and northern and southern Vietnamese coastlines increase by up to 1 m, significantly larger than expected changes in mean sea-level rise over the same period. The length of coastline that is presently exposed to storm surge levels of 2.5 m or greater will more than double by 2050. Sections of Cambodian, Thai, and Malaysian coastlines are projected to experience storm surges (at higher return periods) in the future, not previously seen, due to a southward shift in tropical cyclone tracks. Given these findings, coastal flood management and adaptation in these areas should be reviewed for their resilience against future extreme sea levels.
{"title":"Climate-induced storminess forces major increases in future storm surge hazard in the South China Sea region","authors":"Melissa Wood, I. Haigh, Quan Le, H. Nguyen, Hoang Tran, S. Darby, R. Marsh, N. Skliris, J. Hirschi, R. Nicholls, N. Bloemendaal","doi":"10.5194/nhess-23-2475-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2475-2023","url":null,"abstract":"Abstract. Coastal floods, driven by extreme sea levels, are one of the most dangerous\u0000natural hazards. The people at highest risk are those living in low-lying\u0000coastal areas exposed to tropical-cyclone-forced storm surges. Here we\u0000apply a novel modelling framework to estimate past and/or present and future storm-surge-level and extreme-sea-level probabilities along the coastlines of southern\u0000China, Vietnam, Cambodia, Thailand, and Malaysia. A regional hydrodynamic\u0000model is configured to simulate 10 000 years of synthetic tropical cyclone\u0000activity, representative of a past/present (1980–2017) and high-emission-scenario future (2015–2050) period. Results show that extreme storm surges, and therefore total water levels, will increase substantially in the coming decades, driven by an increase in the frequency of intense tropical\u0000cyclones. Storm surges along the southern Chinese and northern and southern Vietnamese\u0000coastlines increase by up to 1 m, significantly larger than expected changes in mean sea-level rise over the same period. The length of coastline that is presently exposed to storm surge levels of 2.5 m or greater will more than double by 2050. Sections of Cambodian, Thai, and Malaysian coastlines are projected to experience storm surges (at higher return periods) in the\u0000future, not previously seen, due to a southward shift in tropical cyclone\u0000tracks. Given these findings, coastal flood management and adaptation in\u0000these areas should be reviewed for their resilience against future extreme\u0000sea levels.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41490100","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-12DOI: 10.5194/nhess-23-2449-2023
Sang-Guk Yum, Moon-Soo Song, M. Adhikari
Abstract. The inner shelf and coastal region of the Yellow Sea along the Korean Peninsula are frequently impacted by typhoons. The Mokpo coastal region in South Korea was significantly affected by Typhoon Soulik in 2018, the deadliest typhoon strike to the southwestern coast since Typhoon Maemi in 2003. Typhoon Soulik overran the region, causing extensive damage to the coast, shoreline, vegetation, and coastal geomorphology. Therefore, it is important to investigate its impact on the coastal ecology, landform, erosion/accretion, suspended-sediment concentration (SSC), and associated coastal changes along the Mokpo region. In this study, the net shoreline movement (NSM), normalized difference vegetation index (NDVI), fractional vegetation coverage (FVC), coastal-landform change model, normalized difference suspended-sediment index (NDSSI), and SSC–reflectance relation have been used to analyze the coastal morphodynamics over the typhoon periods. We used pre- and post-typhoon Sentinel-2 MultiSpectral Instrument (MSI) images for mapping and monitoring the typhoon effect and recovery status of the Mokpo coast through short- and medium-term coastal-change analysis. The findings highlighted the significant impacts of typhoons on coastal dynamics, wetland vegetation, and sediment resuspension along the Mokpo coast. It has been observed that typhoon-induced SSC influences shoreline and coastal morphology. The outcome of this research may provide databases to manage coastal environments and a long-term plan to restore valuable coastal habitats. In addition, the findings may be useful for post-typhoon emergency response, coastal planners, and administrators involved in the long-term development of human life.
{"title":"Assessing Typhoon Soulik-induced morphodynamics over the Mokpo coastal region in South Korea based on a geospatial approach","authors":"Sang-Guk Yum, Moon-Soo Song, M. Adhikari","doi":"10.5194/nhess-23-2449-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2449-2023","url":null,"abstract":"Abstract. The inner shelf and coastal region of the Yellow Sea along the Korean\u0000Peninsula are frequently impacted by typhoons. The Mokpo coastal region in\u0000South Korea was significantly affected by Typhoon Soulik in 2018, the\u0000deadliest typhoon strike to the southwestern coast since Typhoon Maemi in 2003.\u0000Typhoon Soulik overran the region, causing extensive damage to the coast,\u0000shoreline, vegetation, and coastal geomorphology. Therefore, it is important to investigate its impact on the coastal ecology, landform,\u0000erosion/accretion, suspended-sediment concentration (SSC), and associated\u0000coastal changes along the Mokpo region. In this study, the net shoreline movement (NSM), normalized difference\u0000vegetation index (NDVI), fractional vegetation coverage (FVC), coastal-landform change model, normalized difference suspended-sediment index\u0000(NDSSI), and SSC–reflectance relation have been used to analyze the coastal\u0000morphodynamics over the typhoon periods. We used pre- and post-typhoon\u0000Sentinel-2 MultiSpectral Instrument (MSI) images for mapping and monitoring the typhoon effect and\u0000recovery status of the Mokpo coast through short- and medium-term coastal-change analysis. The findings highlighted the significant impacts of\u0000typhoons on coastal dynamics, wetland vegetation, and sediment resuspension\u0000along the Mokpo coast. It has been observed that typhoon-induced SSC\u0000influences shoreline and coastal morphology. The outcome of this research\u0000may provide databases to manage coastal environments and a long-term plan to restore valuable coastal habitats. In addition, the findings may be useful for post-typhoon emergency response, coastal planners, and administrators involved in the long-term development of human life.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46358022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-11DOI: 10.5194/nhess-23-2443-2023
R. Ingrosso, P. Lionello, M. Miglietta, G. Salvadori
Abstract. A methodological approach is proposed to provide an analytical (exponential-like) expression for the probability of occurrence of tornadoes as a function of the convective available potential energy and the wind shear (or, alternatively, the storm relative helicity). The resulting expression allows the probability of tornado occurrence to be calculated using variables that are computed by weather prediction and climate models, thus compensating for the lack of resolution needed to resolve these phenomena in numerical simulations.
{"title":"Brief communication: Towards a universal formula for the probability of tornadoes","authors":"R. Ingrosso, P. Lionello, M. Miglietta, G. Salvadori","doi":"10.5194/nhess-23-2443-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2443-2023","url":null,"abstract":"Abstract. A methodological approach is proposed to provide an analytical (exponential-like) expression for the probability of occurrence of tornadoes as a function of the convective available potential energy and the wind shear (or, alternatively, the storm relative helicity). The resulting expression allows the probability of tornado occurrence to be calculated using variables that are computed by weather prediction and climate models, thus compensating for the lack of resolution needed to resolve these phenomena in numerical simulations.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48048047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-06DOI: 10.5194/nhess-23-2419-2023
Maliko Tanguy, Michael Eastman, E. Magee, L. Barker, Thomas Chitson, C. Ekkawatpanit, D. Goodwin, J. Hannaford, I. Holman, Liwa Pardthaisong, S. Parry, Dolores Rey Vicario, S. Visessri
Abstract. Droughts in Thailand are becoming more severe due to climate change. Developing a reliable drought monitoring and early warning system (DMEWS) is essential to strengthen a country's resilience to droughts. However, for a DMEWS to be valuable, the drought indicators provided to stakeholders must have relevance to tangible impacts on the ground. Here, we analyse drought indicator-to-impact relationships in Thailand, using a combination of correlation analysis and machine learning techniques (random forest). In the correlation analysis, we study the link between meteorological drought indicators and high-resolution remote sensing vegetation indices used as proxies for crop yield and forest growth impacts. Our analysis shows that this link varies depending on land use, season and region. The random forest models built to estimate regional crop productivity allow a more in-depth analysis of the crop- and region-specific importance of different drought indicators. The results highlight seasonal patterns of drought vulnerability for individual crops, usually linked to their growing season, although the effects are somewhat attenuated in irrigated regions. Integration of the approaches provides new, detailed knowledge of crop- and region-specific indicator-to-impact links, which can form the basis of targeted mitigation actions in an improved DMEWS in Thailand and could be applied to other parts of Southeast Asia and beyond.
{"title":"Indicator-to-impact links to help improve agricultural drought preparedness in Thailand","authors":"Maliko Tanguy, Michael Eastman, E. Magee, L. Barker, Thomas Chitson, C. Ekkawatpanit, D. Goodwin, J. Hannaford, I. Holman, Liwa Pardthaisong, S. Parry, Dolores Rey Vicario, S. Visessri","doi":"10.5194/nhess-23-2419-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2419-2023","url":null,"abstract":"Abstract. Droughts in Thailand are becoming more severe due to\u0000climate change. Developing a reliable drought monitoring and early warning\u0000system (DMEWS) is essential to strengthen a country's resilience to\u0000droughts. However, for a DMEWS to be valuable, the drought indicators\u0000provided to stakeholders must have relevance to tangible impacts on the\u0000ground. Here, we analyse drought indicator-to-impact relationships in\u0000Thailand, using a combination of correlation analysis and machine learning\u0000techniques (random forest). In the correlation analysis, we study the link\u0000between meteorological drought indicators and high-resolution remote sensing vegetation indices used as proxies for crop yield and forest growth impacts. Our analysis shows that this link varies depending on land use, season and region. The random forest models built to estimate regional crop productivity allow a more in-depth analysis of the crop- and region-specific importance of different drought indicators. The results highlight seasonal patterns of drought vulnerability for individual crops, usually linked to their growing season, although the effects are somewhat attenuated in irrigated regions. Integration of the approaches provides new, detailed knowledge of crop- and region-specific indicator-to-impact links, which can form\u0000the basis of targeted mitigation actions in an improved DMEWS in Thailand\u0000and could be applied to other parts of Southeast Asia and beyond.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41458019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-05DOI: 10.5194/nhess-23-2387-2023
L. Bodenmann, J. Baker, B. Stojadinović
Abstract. Ground-motion correlation models play a crucial role in regional seismic risk modeling of spatially distributed built infrastructure. Such models predict the correlation between ground-motion amplitudes at pairs of sites, typically as a function of their spatial proximity. Data from physics-based simulators and event-to-event variability in empirically derived model parameters suggest that spatial correlation is additionally affected by path and site effects. Yet, identifying these effects has been difficult due to scarce data and a lack of modeling and assessment approaches to consider more complex correlation predictions. To address this gap, we propose a novel correlation model that accounts for path and site effects via a modified functional form. To quantify the estimation uncertainty, we perform Bayesian inference for model parameter estimation. The derived model outperforms traditional isotropic models in terms of the predictive accuracy for training and testing data sets. We show that the previously found event-to-event variability in model parameters may be explained by the lack of accounting for path and site effects. Finally, we examine implications of the newly proposed model for regional seismic risk simulations.
{"title":"Accounting for path and site effects in spatial ground-motion correlation models using Bayesian inference","authors":"L. Bodenmann, J. Baker, B. Stojadinović","doi":"10.5194/nhess-23-2387-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2387-2023","url":null,"abstract":"Abstract. Ground-motion correlation models play a crucial role in regional seismic risk modeling of spatially distributed built infrastructure. Such models predict the correlation between ground-motion amplitudes at pairs of sites, typically as a function of their spatial proximity. Data from physics-based simulators and event-to-event variability in empirically derived model parameters suggest that spatial correlation is additionally affected by path and site effects. Yet, identifying these effects has been difficult due to scarce data and a lack of modeling and assessment approaches to consider more complex correlation predictions. To address this gap, we propose a novel correlation model that accounts for path and site effects via a modified functional form. To quantify the estimation uncertainty, we perform Bayesian inference for model parameter estimation. The derived model outperforms traditional isotropic models in terms of the predictive accuracy for training and testing data sets. We show that the previously found event-to-event variability in model parameters may be explained by the lack of accounting for path and site effects. Finally, we examine implications of the newly proposed model for regional seismic risk simulations.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48297024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-28DOI: 10.5194/nhess-23-2349-2023
C. Lanfranconi, P. Frattini, G. Sala, G. Dattola, D. Bertolo, Juanjuan Sun, G. Crosta
Abstract. The presence of trees along the slope and block fragmentation at impact strongly affect rockfall dynamics and hazard as a consequence. However, these phenomena are rarely simulated explicitly in rockfall studies. We performed rockfall simulations by using the 3D rockfall simulator Hy-Stone, modeling both the presence of trees and fragmentation through specific algorithms implemented in the code. By comparing these simulations with a more classical approach that attempts to account implicitly for such phenomena in the model parameters and by using a new probabilistic rockfall hazard analysis (PRHA) method, we were able to quantify the impact of these phenomena on the design of countermeasures and on hazard. We demonstrated that hazard changes significantly when accounting explicitly for these phenomena and that a classical implicit approach usually overestimates both the hazard level and the 95th percentile of kinetic energy, leading to an oversizing of mitigation measures.
{"title":"Accounting for the effect of forest and fragmentation in probabilistic rockfall hazard","authors":"C. Lanfranconi, P. Frattini, G. Sala, G. Dattola, D. Bertolo, Juanjuan Sun, G. Crosta","doi":"10.5194/nhess-23-2349-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2349-2023","url":null,"abstract":"Abstract. The presence of trees along the slope and block fragmentation at impact\u0000strongly affect rockfall dynamics and hazard as a consequence. However,\u0000these phenomena are rarely simulated explicitly in rockfall studies. We\u0000performed rockfall simulations by using the 3D rockfall simulator Hy-Stone,\u0000modeling both the presence of trees and fragmentation through specific\u0000algorithms implemented in the code. By comparing these simulations with a\u0000more classical approach that attempts to account implicitly for such\u0000phenomena in the model parameters and by using a new probabilistic rockfall\u0000hazard analysis (PRHA) method, we were able to quantify the impact of these\u0000phenomena on the design of countermeasures and on hazard. We demonstrated that hazard changes significantly when accounting explicitly\u0000for these phenomena and that a classical implicit approach usually\u0000overestimates both the hazard level and the 95th percentile of kinetic\u0000energy, leading to an oversizing of mitigation measures.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42252483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-28DOI: 10.5194/nhess-23-2365-2023
Rhoda A. Odongo, H. de Moel, A. V. van Loon
Abstract. There have been numerous drought propagation studies in data-rich countries, but not much has been done for data-poor regions (such as the Horn of Africa, HOA). In this study, we characterize meteorological, soil moisture and hydrological drought and the propagation from one to the other for 318 catchments in the HOA to improve understanding of the spatial variability in the drought hazard. We calculate the standardized precipitation index (SPI), standardized soil moisture index (SSMI) and standardized streamflow index (SSI). In addition, we use the variable threshold method to calculate the duration of drought below a predefined percentile threshold for precipitation, soil moisture and discharge. The relationship between meteorological and soil moisture drought is investigated by finding the SPI accumulation period that has the highest correlation between SPI and SSMI, and the relationship between meteorological and hydrological drought is analysed by the SPI accumulation period that has the highest correlation between SPI and SSI time series. Additionally, we calculated these relationships with the ratio between the threshold-based meteorological-drought duration and soil moisture drought duration and the relation between threshold-based meteorological-drought duration and streamflow drought duration. Finally, we investigate the influence of climate and catchment characteristics on these propagation metrics. The results show that (1) the propagation from SPI to SSMI and the mean drought duration ratio of meteorological to soil moisture drought (P / SM) are mainly influenced by soil properties and vegetation, with the short accumulation periods (1 to 4 months) of SPI in catchments with arable land, high mean annual precipitation, and low sand and silt content, while longer accumulations (5 to 7 months) are in catchments with low mean annual upstream precipitation and shrub vegetation; (2) the propagation from SPI to SSI and precipitation-to-streamflow duration ratio are highly influenced by the climate and catchment control, i.e. geology, elevation and land cover, with the short accumulation times in catchments with high annual precipitation, volcanic permeable geology and cropland and the longer accumulations in catchments with low annual precipitation, sedimentary rocks and shrubland; and (3) the influence of mean annual upstream precipitation is more important for the propagation from SPI to SSI than from SPI to SSMI. Additionally, precipitation accumulation periods of approximately 1 to 4 months in wet western areas of the HOA and of approximately 5 to 7 months in the dryland regions are found. This can guide forecasting and management efforts as different drought metrics are thus of importance in different regions.
{"title":"Propagation from meteorological to hydrological drought in the Horn of Africa using both standardized and threshold-based indices","authors":"Rhoda A. Odongo, H. de Moel, A. V. van Loon","doi":"10.5194/nhess-23-2365-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2365-2023","url":null,"abstract":"Abstract. There have been numerous drought propagation studies in data-rich countries, but not much has been done for data-poor regions (such as the Horn of Africa, HOA). In this study, we characterize meteorological, soil moisture and\u0000hydrological drought and the propagation from one to the other for 318\u0000catchments in the HOA to improve understanding of the spatial variability in the drought hazard. We calculate the standardized precipitation index (SPI),\u0000standardized soil moisture index (SSMI) and standardized streamflow index\u0000(SSI). In addition, we use the variable threshold method to calculate the\u0000duration of drought below a predefined percentile threshold for\u0000precipitation, soil moisture and discharge. The relationship between\u0000meteorological and soil moisture drought is investigated by finding the SPI\u0000accumulation period that has the highest correlation between SPI and SSMI,\u0000and the relationship between meteorological and hydrological drought is\u0000analysed by the SPI accumulation period that has the highest correlation\u0000between SPI and SSI time series. Additionally, we calculated these\u0000relationships with the ratio between the threshold-based meteorological-drought duration and soil moisture drought duration and the relation\u0000between threshold-based meteorological-drought duration and streamflow\u0000drought duration. Finally, we investigate the influence of climate and\u0000catchment characteristics on these propagation metrics. The results show\u0000that (1) the propagation from SPI to SSMI and the mean drought duration\u0000ratio of meteorological to soil moisture drought (P / SM) are mainly influenced by soil properties and vegetation, with the short accumulation periods (1 to 4 months) of SPI in catchments with arable land, high mean annual precipitation, and low sand and silt content, while longer accumulations (5 to 7 months) are in catchments with low mean annual upstream precipitation\u0000and shrub vegetation; (2) the propagation from SPI to SSI and precipitation-to-streamflow duration ratio are highly influenced by the climate and\u0000catchment control, i.e. geology, elevation and land cover, with the short\u0000accumulation times in catchments with high annual precipitation, volcanic\u0000permeable geology and cropland and the longer accumulations in catchments\u0000with low annual precipitation, sedimentary rocks and shrubland; and (3) the\u0000influence of mean annual upstream precipitation is more important for the\u0000propagation from SPI to SSI than from SPI to SSMI. Additionally,\u0000precipitation accumulation periods of approximately 1 to 4 months in wet\u0000western areas of the HOA and of approximately 5 to 7 months in the dryland regions are found. This can guide forecasting and management efforts as different drought metrics are thus of importance in different regions.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41412630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-26DOI: 10.5194/nhess-23-2333-2023
Leon Scheiber, Christoph Gabriel David, Mazen Hoballah Jalloul, J. Visscher, H. Nguyen, Roxana Leitold, J. Revilla Diez, T. Schlurmann
Abstract. Urban flooding is a major challenge for many megacities in low-elevation coastal zones (LECZs), especially in Southeast Asia. In these regions, the effects of environmental stressors overlap with rapid urbanization, which significantly aggravates the hazard potential. Ho Chi Minh City (HCMC) in southern Vietnam is a prime example of this set of problems and therefore a suitable case study to apply the concept of low-regret disaster risk adaptation as defined by the Intergovernmental Panel on Climate Change (IPCC). In order to explore and evaluate potential options of hazard mitigation, a hydro-numerical model was employed to scrutinize the effectiveness of two adaptation strategies: (1) a classic flood protection scheme including a large-scale ring dike as currently constructed in HCMC and (2) the widespread installation of small-scale rainwater detention as envisioned in the framework of the Chinese Sponge City Program (SCP). A third adaptation scenario (3) assesses the combination of both approaches (1) and (2). From a hydrological point of view, the reduction in various flood intensity proxies that were computed within this study suggests that large-scale flood protection is comparable but slightly more effective than small-scale rainwater storage: for instance, the two adaptation options could reduce the normalized flood severity index (INFS), which is a measure combining flood depth and duration, by 17.9 % and 17.7 %, respectively. The number of flood-prone manufacturing firms that would be protected after adaptation, in turn, is nearly 2 times higher for the ring dike than for the Sponge City approach. However, the numerical results also reveal that both response options can be implemented in parallel, not only without reducing their individual effectiveness but also complementarily with considerable added value. Additionally, from a governance perspective, decentralized rainwater storage conforms ideally to the low-regret paradigm: while the existing large-scale ring dike depends on a binary commitment (to build or not to build), decentralized small- and micro-scale solutions can be implemented gradually (for example through targeted subsidies) and add technical redundancy to the overall system. In the end, both strategies are highly complementary in their spatial and temporal reduction in flood intensity. Local decision-makers may hence specifically seek combined strategies, adding to singular approaches, and design multi-faceted adaptation pathways in order to successfully prepare for a deeply uncertain future.
{"title":"Low-regret climate change adaptation in coastal megacities – evaluating large-scale flood protection and small-scale rainwater detention measures for Ho Chi Minh City, Vietnam","authors":"Leon Scheiber, Christoph Gabriel David, Mazen Hoballah Jalloul, J. Visscher, H. Nguyen, Roxana Leitold, J. Revilla Diez, T. Schlurmann","doi":"10.5194/nhess-23-2333-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2333-2023","url":null,"abstract":"Abstract. Urban flooding is a major challenge for many megacities\u0000in low-elevation coastal zones (LECZs), especially in Southeast Asia. In\u0000these regions, the effects of environmental stressors overlap with rapid\u0000urbanization, which significantly aggravates the hazard potential. Ho Chi\u0000Minh City (HCMC) in southern Vietnam is a prime example of this set of\u0000problems and therefore a suitable case study to apply the concept of\u0000low-regret disaster risk adaptation as defined by the Intergovernmental\u0000Panel on Climate Change (IPCC). In order to explore and evaluate potential\u0000options of hazard mitigation, a hydro-numerical model was employed to\u0000scrutinize the effectiveness of two adaptation strategies: (1) a classic\u0000flood protection scheme including a large-scale ring dike as currently\u0000constructed in HCMC and (2) the widespread installation of small-scale\u0000rainwater detention as envisioned in the framework of the Chinese Sponge\u0000City Program (SCP). A third adaptation scenario (3) assesses the combination of both approaches (1) and (2). From a hydrological point of view, the reduction in various flood intensity\u0000proxies that were computed within this study suggests that large-scale flood protection is comparable but slightly more effective than small-scale\u0000rainwater storage: for instance, the two adaptation options could reduce the normalized flood severity index (INFS), which is a measure combining flood depth and duration, by 17.9 % and 17.7 %, respectively. The\u0000number of flood-prone manufacturing firms that would be protected after\u0000adaptation, in turn, is nearly 2 times higher for the ring dike than for\u0000the Sponge City approach. However, the numerical results also reveal that\u0000both response options can be implemented in parallel, not only without\u0000reducing their individual effectiveness but also complementarily with\u0000considerable added value. Additionally, from a governance perspective,\u0000decentralized rainwater storage conforms ideally to the low-regret paradigm:\u0000while the existing large-scale ring dike depends on a binary commitment (to\u0000build or not to build), decentralized small- and micro-scale solutions can\u0000be implemented gradually (for example through targeted subsidies) and add\u0000technical redundancy to the overall system. In the end, both strategies are\u0000highly complementary in their spatial and temporal reduction in flood\u0000intensity. Local decision-makers may hence specifically seek combined\u0000strategies, adding to singular approaches, and design multi-faceted\u0000adaptation pathways in order to successfully prepare for a deeply uncertain\u0000future.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41919493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-26DOI: 10.5194/nhess-23-2313-2023
Leon Scheiber, Mazen Hoballah Jalloul, Christian Jordan, J. Visscher, H. Nguyen, T. Schlurmann
Abstract. Hydro-numerical models are increasingly important to determine the adequacy and evaluate the effectiveness of potential flood protection measures. However, a significant obstacle in setting up hydro-numerical and associated flood damage models is the tedious and oftentimes prohibitively costly process of acquiring reliable input data, which particularly applies to coastal megacities in developing countries and emerging economies. To help alleviate this problem, this paper explores the usability and reliability of flood models built on open-access data in regions where highly resolved (geo)data are either unavailable or difficult to access yet where knowledge about elements at risk is crucial for mitigation planning. The example of Ho Chi Minh City, Vietnam, is taken to describe a comprehensive but generic methodology for obtaining, processing and applying the required open-access data. The overarching goal of this study is to produce preliminary flood hazard maps that provide first insights into potential flooding hotspots demanding closer attention in subsequent, more detailed risk analyses. As a key novelty, a normalized flood severity index (INFS), which combines flood depth and duration, is proposed to deliver key information in a preliminary flood hazard assessment. This index serves as an indicator that further narrows down the focus to areas where flood hazard is significant. Our approach is validated by a comparison with more than 300 flood samples locally observed during three heavy-rain events in 2010 and 2012 which correspond to INFS-based inundation hotspots in over 73 % of all cases. These findings corroborate the high potential of open-access data in hydro-numerical modeling and the robustness of the newly introduced flood severity index, which may significantly enhance the interpretation and trustworthiness of risk assessments in the future. The proposed approach and developed indicators are generic and may be replicated and adopted in other coastal megacities around the globe.
{"title":"The potential of open-access data for flood estimations: uncovering inundation hotspots in Ho Chi Minh City, Vietnam, through a normalized flood severity index","authors":"Leon Scheiber, Mazen Hoballah Jalloul, Christian Jordan, J. Visscher, H. Nguyen, T. Schlurmann","doi":"10.5194/nhess-23-2313-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2313-2023","url":null,"abstract":"Abstract. Hydro-numerical models are increasingly important to\u0000determine the adequacy and evaluate the effectiveness of potential flood\u0000protection measures. However, a significant obstacle in setting up\u0000hydro-numerical and associated flood damage models is the tedious and\u0000oftentimes prohibitively costly process of acquiring reliable input data,\u0000which particularly applies to coastal megacities in developing countries and\u0000emerging economies. To help alleviate this problem, this paper explores the\u0000usability and reliability of flood models built on open-access data in\u0000regions where highly resolved (geo)data are either unavailable or difficult\u0000to access yet where knowledge about elements at risk is crucial for\u0000mitigation planning. The example of Ho Chi Minh City, Vietnam, is taken to\u0000describe a comprehensive but generic methodology for obtaining, processing\u0000and applying the required open-access data. The overarching goal of this\u0000study is to produce preliminary flood hazard maps that provide first insights\u0000into potential flooding hotspots demanding closer attention in subsequent,\u0000more detailed risk analyses. As a key novelty, a normalized flood severity\u0000index (INFS), which combines flood depth and duration, is proposed to\u0000deliver key information in a preliminary flood hazard assessment. This index\u0000serves as an indicator that further narrows down the focus to areas where\u0000flood hazard is significant. Our approach is validated by a comparison with\u0000more than 300 flood samples locally observed during three heavy-rain events\u0000in 2010 and 2012 which correspond to INFS-based inundation hotspots in\u0000over 73 % of all cases. These findings corroborate the high potential of\u0000open-access data in hydro-numerical modeling and the robustness of the newly\u0000introduced flood severity index, which may significantly enhance the\u0000interpretation and trustworthiness of risk assessments in the future. The\u0000proposed approach and developed indicators are generic and may be replicated\u0000and adopted in other coastal megacities around the globe.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44042829","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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