Rainfall Disaster Research Articles

Natural or man-made disaster? Lessons from the extreme rain and flood disaster in Zhengzhou, China on "2021.7.20"

Driven by extreme weather events, precipitation-induced flood disasters are occurring more frequently, posing substantial threats to both economic development and public safety. Increased human production activities have further intensified the impact of flood disasters. However, understanding of the factors influencing flood disasters and their associated risk assessments remains limited. To better formulate flood prevention and disaster reduction strategies suited to local conditions, this paper takes the "7.20" extreme rainfall event in the main urban area of Zhengzhou, Henan Province, China, on July 20, 2021, as a case study and uses geographic detectors to incorporate human activities into the quantitative analysis of influencing factor contributions. Based on the three aspects of disaster incubation, disaster causation, and disaster bearing, this study proposes using the influence values obtained from geographic detectors as objective weight assignments for risk assessment, thereby conducting a locally adapted risk assessment of Zhengzhou's main urban area. Research results indicate that the "7.20" heavy rainstorm in Zhengzhou's main urban area involved a superposition of natural and human factors. Impervious surfaces had the highest explanatory power, followed by population density, confirming that this flood disaster arose from the interaction of multiple factors. The flood disaster risk assessment for Zhengzhou's main urban area shows higher risk levels in the central area and relatively lower levels in peripheral areas. The central area features flat terrain, with high population density and a large proportion of impervious surfaces. Among these, 22 subdistricts are located in extremely high-risk flood zones, while 6 subdistricts, classified as low-risk, account for over 60% of the low-risk area, making them relatively lower-risk communities. Comparison with flood waterlogging point data verifies the accuracy of the risk assessment through statistical analysis, allowing for further analysis of the spatial differentiation of flood risk. The findings of this study offer valuable insights for preventing and managing urban extreme rainfall disasters.

Systematization of a toxicity screening method based on a combination of chemical analysis and the delayed fluorescence algal growth inhibition test for use in emergency environmental surveys.

In recent years, heavy rainfall disasters linked to climate change have become more frequent, raising concerns about the release of chemicals stored in factories. Assessing chemical contamination during such emergencies therefore necessitates the development of a quick and easy method for evaluating hazardous contaminants in combination with toxicity testing. This study proposes a "toxicity screening" method that combines biological response testing and chemical analysis to systematically evaluate hazardous contaminants in emergency situations. The toxicity screening method evaluates the water quality in three steps, including water quality measurements and a delayed fluorescence (DF) assay, metal content measurements and a DF assay, and targeted screening analysis and a DF assay. The efficacy of this method was tested using industrial wastewater from 14 locations. Seven of the samples were non-toxic, while the other seven samples were toxic, displaying no observed effect concentration (NOEC) values ranging from 0.625 to 20%. Two toxic samples in the first phase possessed high total chlorine concentrations (0.4mg L-1) and conductivities (2200 mS m-1), indicating that the main sources of toxicity were residual chlorine and a high salt concentration. In the second phase, metal content analysis identified metals as the toxicity cause in four samples. In the third phase, the organic contaminants were analyzed, and tri-n-octyl phosphate (TNOP) was detected at a concentration of 0.00027mg L-1. The results of solid-phase extraction experiments and exposure tests with TNOP alone indicated that the contribution of TNOP to the toxicity was negligible and that chemicals not adsorbed on the solid-phase extraction cartridges were the cause of toxicity. The proposed method can therefore be considered effective for disaster-related water quality assessment, delivering results within 12days.

Institutional vulnerability to urban flood risk management: A case study of the 7·20 flooding disaster in Zhengzhou, China

AbstractThe ‘vulnerability’ approach highlights institutional factors as the primary drivers of flooding risk. However, the intricate connections between institutional vulnerability and urban flood disaster risk have not been extensively explored until now. This study aims to address this gap by examining the case of the 7·20 heavy rainfall disaster in Zhengzhou. Employing a hybrid analysis methodology that integrates text coding, fault tree analysis and analytic hierarchy process methods, the study seeks to identify and assess the distinct contributions of various institutional factors and their interplay, culminating in ineffective urban flood risk management. In contrast to previous research findings that emphasize the determinant role of policy‐making and organizational coordination, this study demonstrates that inadequate legislative compliance constitutes the root cause determining the ineffectiveness of urban flood risk management. It is further exacerbated by insufficient policy attention, resulting in inadequate allocation of resources that ensure the legislative quality, risk coping skills and knowledge and stakeholders' coordination and collaboration. By emphasizing the significance of legislative compliance and policy attention, the study offers a fresh conceptual perspective to understand the factors influencing the efficiency of urban flood risk management. It provides valuable insights to develop targeted countermeasures for mitigating similar urban flood risks in the future.

Influence of approach shape of debris flow on impact load to open Sabo dam in experiment

Recently, the magnitude of landslide caused by torrential rain and typhoons is increasing in Japan. This high intensity rainfall disaster induces some structural failure of steel pipe open Sabo dams. Thus, current static design loads and impact loads are being considered. To prevent some structural failure of the dam, a new design concept is necessary at the severe load that is exceeding the present design load. However, the influence of debris flow impact load on steel pipe open Sabo dam is not clear to make a design load. The study experimentally approaches a vertical load distribution shape and its time history based on a comparison with a wedge approach shape and a front boulder concentrated shape. The load and moment action of a front boulder concentrated shape debris flow is greater than that of a wedge approach shape. Mechanism making the difference is made clear by observation of vertical detail measurement of impact load.

Robust Emergency Preparedness Planning for Resilience Enhancement of Energy-Transportation Nexus Against Extreme Rainfalls

This paper proposes a robust emergency preparedness planning (EPP) scheme to optimally pre-position diverse mobile emergency resources (MERs) in staging locations and perform proactive network reconfiguration for resilience enhancement of energy-transportation nexus (ETN) against extreme rainfalls. Based on rainfall-runoff simulation with hydrodynamic partial differential equations, a risk identification approach for flood-prone transportation modeling is developed for vehicle travel time estimation and MER routing optimization. To handle uncertainties in line outages and flooded roads incurred by extreme rainfalls, a tri-level robust EPP model is proposed to determine the optimal emergency preparedness plan immunized against the worst-case realization of uncertainties. Furthermore, a tailored solution method combining nested column-and-constraint generation algorithm with multiple linearization techniques is devised to cope with the proposed nonlinear robust EPP model. Comparative studies have validated the effectiveness of the proposed scheme for resilience enhancement of the ETN confronted with extreme rainfall disasters.

Coherent amplification of the Okhotsk high, Korean trough, and northwestern Pacific subtropical high during heavy rainfall over Japan in August 2021

In August 2021, rain front stagnation in Japan resulted in prolonged and disastrous rainfall across the entire country. During the heavy rainfall period, the large-scale atmospheric field over the East Asian–western North Pacific region was characterized by meridional tripolar circulation anomalies: the Okhotsk high (OH), the trough over the Korean Peninsula (Korean trough), and the northwestern Pacific subtropical high (NWPSH). Simultaneously, tropical convective activity was enhanced over the eastern Indian Ocean and suppressed over the tropical western–central Pacific. This study investigates the dynamic mechanism of linkage of the extratropical tripolar anomalies and the effects of tropical convective modulation using a reanalysis dataset, a cutoff low detection scheme, the potential vorticity inversion method, and numerical experiments. Upper-tropospheric blocking over eastern Siberia connected to the surface OH is conducive to the stagnation of synoptic depressions, including cutoff lows and troughs, over the Korean Peninsula, contributing to the development and maintenance of the quasi-stationary Korean trough. Rossby waves emanating from the Korean trough excite an anticyclonic anomaly over the northwestern Pacific. This upper-level anomalous anticyclone acts to enhance the surface NWPSH through zonal heat transport, accompanied by a northward tilting structure with height. Simultaneously, the tropical intraseasonal oscillation is amplified over the Indo–western Pacific Ocean sector under the negative-phase Indian Ocean dipole and multi-year La Niña conditions. The combination of enhanced convection over the eastern Indian Ocean and suppressed convection across the tropical western–central Pacific reinforces the NWPSH. The anomalous circulation associated with the extratropical tripolar pattern and concurrent tropical heat forcing causes more moisture transport, convergence, and anomalous ascent, which contribute to heavy rainfall in Japan. These results suggest that the dynamically correlated amplification of tropical and extratropical circulation anomalies plays a crucial role in precipitation variability in East Asia.

Adequacy Analysis Using UAV of Heavy Rainfall Disaster Reduction Facilities According to Urban Development in Republic of Korea

Urban development is a project that enhances human life, but its hydrological impact increases runoff by expanding impervious areas. Furthermore, localized and intense rainfall resulting from the effects of climate change is exacerbating damage to urban areas. The Republic of Korea has established detention ponds as reduction facilities for heavy rainfall disasters, and the law stipulates that the impact of disasters that increase due to the development projects will remain unchanged from before. However, ensuring precision in millimeter or centimeter units during the design of reduction facilities is challenging. In this study, our aim is to assess the suitability of using unmanned aerial vehicles (UAVs) for the detention pond, a facility that reduces runoff resulting from urban development. The target area is a detention pond located in Innovation City, Ulsan Metropolitan City, Republic of Korea. We compared and analyzed design drawings and topographical data. The increased runoff due to the development project was 0.59 m3/s, and the effectiveness of disaster reduction was evaluated by the installation of a detention pond. The detention pond’s reduction effect was analyzed to be 1.16 m3/s for the design drawing and 1.57 m3/s for the topographical analysis. The detention pond currently in place in the target area was found to provide additional disaster reduction benefits compared to the original design plan. The findings of this study can be utilized in relevant laws and guidelines as a method to evaluate the suitability of future reduction facilities.

Response of vegetation normalized different vegetation index to different meteorological disaster indexes in karst region of Guangxi, China

Fragile karst areas of Guangxi are the key areas of vegetation protection and restoration work of the government. It is of great significance to study the effects of meteorological disasters on vegetation change for disaster prevention and reduction and ecological protection in the karst areas. The Normalized Differential Vegetation Index (NDVI), as a tool for monitoring vegetation growth, has a strong responsiveness to vegetation and can qualitatively and quantitatively evaluate the vegetation cover and its growth vitality. Therefore, in this study, we analyzed the trend of vegetation change and the impacts of multiple meteorological hazards, such as drought, torrential rainfall, high temperature, and low temperature, on the vegetation of the karst region in Guangxi by using the linear trend method, GIS spatial analysis, and correlation analysis, using the MODIS NDVI and temperature and precipitation information from 2000 to 2020 in the karst region of Guangxi. The results show that: (1) NDVI increased significantly in the karst areas, and 32.2% of the areas had significant improvement in vegetation. The improvement was the most obvious mainly in the central part of the study area, while the vegetation degradation trend was obvious in partial scattered areas in northeast and southwest. (2) On the interannual scale, NDVI was negatively correlated with some meteorological disaster indexes, such as relative humidity index, the number of drought days, the amount of extremely heavy rainstorm, the amount of heavy rainstorm, the number of days with high temperature of ≥35 °C, the number of days with high temperature of 35–37 °C, the number of days with high temperature of ≥37 °C, the minimum temperature, and the effective accumulated temperature of ≤0 °C. The obvious negative effect area of drought on vegetation was mainly concentrated in the middle of the study area, and that of rainfall was mainly distributed in the southwest, northeast and northwest; that of high temperature was mainly distributed in the northwest and northeast, and that of low temperature was mainly concentrated in the southwest and north. (3) On the multi-year monthly scale, the responses of NDVI to drought, high temperature and low temperature disaster indexes had a lag effect, but had no lag effect on rainfall disaster indexes. The lag time of vegetation to drought was 1 month, and the lag time to high temperature and low temperature was 3 months.

Subgrid Model of Fluid Force Acting on Buildings for Three-Dimensional Flood Inundation Simulations

In recent years, large-scale heavy rainfall disasters have occurred frequently in several parts of the world. Therefore, a quantitative approach to understanding how buildings are damaged during floods is necessary to develop appropriate flood-resistant technologies. In flood inundation simulations for the quantitative evaluation of a building’s resistance to flooding, a subgrid model is necessary to appropriately evaluate the resistance of buildings smaller than the grid size at a medium grid resolution. In this study, a new subgrid (SG) 3D inundation model is constructed to evaluate the fluid force acting on buildings and assess the damage to individual buildings during flood inundation. The proposed method does not increase the computational load. The model is incorporated into a 2D and 3D hybrid model with high computational efficiency to construct a 3D river and inundation flow model. Its validity and effectiveness are evaluated through comparisons with field observations and the conventional equivalent roughness model. Considering horizontal and vertical velocity distributions, the proposed model showed statistically significant improvements in performance in terms of building loss indices such as velocity and fluid force. These results suggest that the SG model can effectively evaluate the fluid force acting on buildings, including the vertical distribution of flow velocities.

Physical Modeling and Intelligent Prediction for Instability of High Backfill Slope Moisturized under the Influence of Rainfall Disasters

The stability of high backfill slopes emerges in practice due to the expansion of transportation infrastructures. The seepage and infiltration of rainfall into the backfills brings challenges to engineers in predicting the stability of the slope, weakening the shear strength and modulus of the soil. This study carried out a series of model tests under a plane strain condition to investigate the stability of a high backfill slope moisturized by rainfalls, considering the influences of rainfall duration and intensity. The slope displacements were monitored by a laser displacement sensor and the moisture content in the backfill mass were obtained by a soil moisture sensor. The test results show that increasing the rainfall intensity and duration caused the slope near the surface to be saturated, resulting in significant influences on the lateral displacement of the slope and the reduction of stability as well as the sizes of the sliding mass. Based on the model tests, the numerical analysis was adopted to extend the analysis cases, and the backpropagation (BP) neural network model was further adopted to build a model for predicting the stability of a high backfill slope under rainfall. The trained BP model shows the average relative error of 1.02% and the goodness of fitness of 0.999, indicating a good prediction effect.

The Process and Challenges of Resident-Led Reconstruction in a Mountain Community Damaged by the Northern Kyushu Torrential Rain Disaster: A Case Study of the Hiraenoki Community, Asakura City, Fukuoka Prefecture, Japan

Frequent torrential rainfall disasters have occurred worldwide in recent years. In Japan, the Northern Kyushu Torrential Rainfall disaster in July 2017 caused extensive damage to Fukuoka and Oita prefectures and significantly impacted local landscapes, from which residents derive pride and identity and, hence, are of the utmost importance. Local communities in Japan are also at risk of extinction due to progressive depopulation. This study discusses community revitalization through landscape creation and related challenges based on the case of the Hiraenoki Community affected by the Northern Kyushu Torrential Rainfall disaster. We conducted long-term participant observations over two years and semi-structured interviews with all households in the community. We found that the landscape project revitalized local pride and involved numerous people outside the community, including the prefectural extension center, university, and Non-Profit Organization (NPO), and provided them with an opportunity to connect. On the other hand, our investigation also revealed the danger of obscuring the original purpose of reconstruction activities because of collaboration with outsiders. This case study elucidates the possibilities and challenges of resident-led reconstruction activities in communities that are facing depopulation and aging problems and are working with organizations within and outside the community.

Experimental study on disaster mechanism of completely weathered granite landslide induced by extreme rainfall

BackgroundWith the increased frequency of extreme weather, landslides induced by extremely heavy rainfall pose a major threat to human lives and property safety. In July 2020, a landslide occurred in the strongly weathered Laoshan Scenic Spot in Qingdao, China, and a short period of heavy rainfall was the main factor inducing the landslide.MethodBased on the similarity criterion, three groups of laboratory model tests under different extreme rainfall conditions were conducted using a large landslide model test box. The rainfall infiltration responses under different rainfall intensities, deformation processes, and failure modes of the slope were analyzed. The inducing mechanism and rainfall disaster process of granite landslides induced by extreme rainfall in strongly weathered areas were summarized.ResultThe results showed that (1) a completely weathered granite landslide induced by rainfall had four stages, i.e., infiltration erosion, surface deformation, damage deepening, and overall instability, and the landslide was characterized by "sheet slip". (2) With greater rainfall intensities, the rainfall infiltration rate was higher, the changes in soil pressure, pore water pressure, water content, and matrix suction were faster, and the hysteresis effect was weaker. (3) A certain spatial distribution pattern was observed between slope deformation/damage and rainfall infiltration, and the research results could provide references for landslide warning and treatment in strongly weathered granite areas.

Urban waterlogging mitigation based on the concept of sponge city

In recent years, many cities around the world have experienced severe urban waterlogging disasters due to decreasing rainfall infiltration caused by land cover changes with rapid urbanization, and increased frequency of heavy rainfall events, including localized torrential rain. Traditional drainage systems and internal control concepts have failed to meet the requirements of urban safety. To address the challenging problem of urban waterlogging, China proposed the Sponge City in 2014. From the perspective of natural climate and urban construction planning, this paper makes an analysis of the causes of urban waterlogging, points out the limitations of traditional drainage facilities, and discusses the many hazards associated with urban waterlogging. This paper explains the meaning of Sponge City and the basic ideas of Sponge City construction. Based on the discussion of Sponge City development, this paper analyzes the Sponge City construction in Xixian New Area, and explains the significance of Sponge City to solve the problem of urban waterlogging. Through this idea, I would like to explore the common issues in countries suffering from heavy rainfall disasters such as Japan and Malaysia. The study hopes to provide a deeper thinking on ways to use nature to solve the waterlogging.

Influence of approach shape of debris flow on impact load subjected to open Sabo dam under an overturning experiment of open Sabo dam

Recently high intensity rainfall disaster induces some structural failure of steel pipe open Sabo dam. To prevent such failure of the dam, a new design concept is necessary at the severe load exceeding the present design load. However, influence of debris flow impact load on steel pipe open Sabo dam is not clear to make a design load. The study experimentally approaches a vertical load distribution shape and its time history based on comparison with a wedge approach shape or a front boulder concentrated shape. The load and moment action of a front boulder concentrated shape debris flow is greater than that of a wedge approach shape. Mechanism making the difference is made clear by observation of vertical detail measurement of impact load.

Predicting the Potential of Rainfall Disaster Risk using Cellular Automata in Small Urban Declining Areas

Purpose: In declining cities, it is vulnerable to disaster risks due to the complex reasons such as aging of the buildings, decreases in population and slowly development of infrastructure. When making regeneration plans for declining areas, it is necessary to analyze and predict disaster risks. Therefore, this paper aims to predict the potentials of disaster risks in small-scale declining areas in cities that show risks in the future. Method: This study predicts potential of disaster risk by using cellular automata. By simulating the heavy rainfall disaster using RCP scenarios, 10-year unit change simulation results for heavy rainfall disaster risk are acquired. After simulating disasters that affect to the heavy rainfall disaster, we applied cellular automata to obtain a 10-year unit disaster risk potential. Result: By considering the yearly change values of disaster risk elements in small-scale urban regeneration regions, this study suggests a prediction method of disaster risk potential simulation for heavy rainfall. Our research contributes to the analysis and forecasting of disaster risks in aging small declining areas settings. We expect that the suggested model would be helpful to identify disaster risks and prioritize urgent areas in small decline cities in the future.

Rainfall disasters under the changing climate: a case study for the Rio de Janeiro mountainous region

Rainfall disasters under the changing climate: a case study for the Rio de Janeiro mountainous region

From Sponge Cities to Sponge Watersheds: Enhancing Flood Resilience in the Sishui River Basin in Zhengzhou, China

Increasing extreme rainfall and increasingly severe flood disasters worldwide make it essential to enhance flood resilience research and practice. The Sponge City Approach (SCA) has been proposed as a nature-based solution for solving pressing water problems in cities, but there is an urgent need to apply the approach at the broader catchment scale to address the rising challenges driven by climate change. This study established a Sponge Watershed Approach (SWA) using the “Source-Flow-Sink” framework and applied it in the Sishui River Basin in Zhengzhou, China, to reconstruct a town after a heavy rainfall disaster and enhance its resilience to future floods. An integrated modeling approach utilizing hydrologic, hydraulic, and flood-loss curve models was used to analyze and evaluate the flood-reduction effects of different strategies under multiple scenarios. The results show that: (1) a strategy focusing solely on interventions at the source of runoff cannot adequately cope with extreme rainfall, and a whole-system approach to managing floods is necessary instead; (2) the effectiveness of the flow strategy depends on the intervention magnitude and the location where interventions are made; (3) the sink strategy offers the most effective way (approximately 30% decrease in flood loss) to adapt to extreme rainfall; (4) the risk and impact of flood disaster in the town was significantly reduced with the SWA (approximately 35–50% decrease in flood loss) compared to those without any interventions; (5) the effects of these strategies are interactive, and the optimal strategy depends on the rainfall condition. These results demonstrate the practicability of SWA by integrating the source, flow, and sink strategy at the whole-catchment scale, which will help promote natural flood management and enhance the climate resilience of catchments worldwide.

Special Issue on NIED Frontier Research on Science and Technology for Disaster Risk Reduction and Resilience 2022

We are very pleased to publish this special issue, dedicated to NIED Frontier Research on Science and Technology for Disaster Risk Reduction and Resilience 2022. There are four papers, two reviews, and one note in this issue. In the last year of the NIED’s fourth mid/long term plan period, which began in 2016, natural disasters have occurred every year, including earthquake disasters such as the 2016 Kumamoto earthquake (M7.3) and the 2018 Iburi, Hokkaido earthquake (M7.1). Rainfall disasters include the heavy rainfall in northern Kyushu in July 2017, southwestern Japan in July 2018, northern Kyushu in August 2019, Kanto and Tohoku in October 2019, and Kyushu in July 2020. In the summer of 2022, the heavy rainfall and extreme weather continued over Japan. The first three papers and one note contain hazard and risk information. Dohi et al. present the development of Japan Tsunami Hazard Information Station (J-THIS), Cui et al. present a study of the estimation of damage based on analysis of SNS Information, Nakamura provides avalanche risk information, and Ise et al. note information linkage by the Shared Information Platform for Disaster Management (SIP4D). Horiuchi et al. review the contribution of the E-Defence shaking table. This special issue also includes two social science works. Nagata et al. present tsunami disaster risk reduction education programs, and Yamazaki-Honda reviews promoting coherence among disaster risk reduction, climate change adaptation, and sustainable development for disaster resilience. In the first half of the 21st century, a mega disaster such as the Nankai Trough earthquake is expected to occur. Extreme climatic events are also becoming more frequent: typhoons, floods, heavy rains and snows, landslides, and heat waves. We hope this issue provides information useful to all readers who study natural disasters.

Can satellite precipitation estimates capture the magnitude of extreme rainfall Events?

ABSTRACT With the increasing frequency of extreme rainfall events, the likelihood of rainfall disasters is also increasing, presenting serious risks of casualties and economic losses. Therefore, exploring the capability of Satellite-based Precipitation Products (SPPs) to capture the magnitudes of extreme rainfall events is significant for preventing precipitation-related disasters. Selecting ten heavy rainfall events in wet seasons over China, this study evaluated the performance of mainstream SPPs from the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) and Global Satellite Mapping of Precipitation (GSMaP) in determining the extreme values of heavy rainfall events. The main findings are as follows: (1) SPPs significantly underestimated the magnitudes of extreme rainfalls events, with the most underestimated and closest values for certain events reaching only one-tenth and 50% of ground station values, respectively; (2) the evaluation of the top 1% hourly precipitation presented similar evident errors, with mean relative bias (BIAS) and root mean square error (RMSE) of approximately −80% and 40 mm hour−1; (3) the spatiotemporal patterns of IMERG-Final were closer to those of the ground station and GSMaP-Now captured more maximum values of the ten events. Nevertheless, the accuracy of these SPPs is still not sufficient for the analysis of extreme rain disasters.

Natural disaster in the mountainous region of Rio de Janeiro state, Brazil: Assessment of the daily rainfall erosivity as an early warning index

Rainfall erosivity is defined as the potential of rain to cause erosion. It has great potential for application in studies related to natural disasters, in addition to water erosion. The objectives of this study were: i) to model the Rday using a seasonal model for the Mountainous Region of the State of Rio de Janeiro (MRRJ); ii) to adjust thresholds of the Rday index based on catastrophic events which occurred in the last two decades; and iii) to map the maximum daily rainfall erosivity (Rmaxday) to assess the region's susceptibility to rainfall hazards according to the established Rday limits. The fitted Rday model presented a satisfactory result, thereby enabling its application as a Rday estimate in MRRJ. Events that resulted in Rday > 1500 MJ ha−1.mm.h−1. day−1 were those with the highest number of fatalities. The spatial distribution of Rmaxday showed that the entire MRRJ has presented values that can cause major rainfall. The Rday index proved to be a promising indicator of rainfall disasters, which is more effective than those normally used that are only based on quantity (mm) and/or intensity (mm.h−1) of the rain.