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Scientific risk assessment of dammed lakes is vitally important for emergency response planning. In this study, based on the evolution process of the disaster chain, the logic topology structure of dammed lake risk was developed. Then, a quantitative risk assessment model of dammed lake using Bayesian network is developed, which includes three modules of dammed lake hazard evaluation, outburst flood routing simulation, and loss assessment. In the model, the network nodes of each module were quantified using statistical data, empirical model, logical inference, and Monte Carlo method. The failure probability of a dammed lake, and the losses of life and property were calculated. This can be multiplied to assess the risk a dammed lake imposes after the uniformization of each loss type. Based on the socio-economic development and longevity statistics of dammed lakes, a risk-level classification method for dammed lakes is proposed. The Baige dammed lake, which emerged in China in 2018, was chosen as a case study and a risk assessment was conducted. The obtained results showed that the comprehensive risk index of Baige dammed lake is 0.7339 under the condition without manual intervention, identifying it as the extra-high level according to the classification. These results are in accordance with the actual condition, which corroborates the reasonability of the proposed model. The model can quickly and quantitatively evaluate the overall risk of a dammed lake and provide a reference for decision-making in a rapid emergency response scenario. [ABSTRACT FROM AUTHOR]

The Uttarakhand Himalaya is highly prone to geo-hydrological disasters—landslides, flash floods, cloudbursts, debris flows, rock falls, extreme weather, and land submergence. Cloudbursts and glacier bursts generally trigger these disasters, which are very active and frequent in the Uttarakhand Himalaya and occur mainly during the monsoon season. This study examines the geo-hydrological disasters in the Uttarakhand Himalaya, which occurred from 2020 to 2023 mainly during the three months of Monsoon season. Further, the study assesses the magnitude of the disaster and maps the disaster hotspot areas. Both qualitative and quantitative approaches were used to conduct this study. Data on geo-hydrological hazards that occurred from 2020 to 2023 in Uttarakhand were gathered from multiple sources such as the records of the State Disaster Management Department, Dehradun, various media reports—print and electronic, and personal observation of some affected areas through field visits. Further, an empirical study of the Bandal and Song River valleys was conducted. These valleys were severely hit by a cloudburst-triggered flash flood and debris flow. Household-level survey of the damage caused by huge flash floods and debris flows in three villages of Bandal Valley was carried out. The data were analyzed and mapped and the Uttarakhand Himalaya was divided into disaster hotspots and frequency zones. ArcGIS was used to construct maps and the Google Earth imagery and Sentinel 1-SAR were the major sources of maps. This study recommends that the construction of settlements, infrastructural facilities, and economic avenues should be banned in the most disaster-affected areas, along river valleys, and on fragile slopes. Eco-disaster risk reduction, such as conserving forests and wetlands, and plantation drives in the most degraded areas such as the river banks and fragile slopes, can help communities to prepare for disasters. [ABSTRACT FROM AUTHOR]

Cascading hazards are becoming more prevalent in the central Himalayas. Primary hazards (e.g., earthquakes, avalanches, and landslides) often trigger secondary hazards (e.g., landslide dam, debris flow, and flooding), compounding the risks to human settlements, infrastructures, and ecosystems. Risk management strategies are commonly tailored to a single hazard, leaving human and natural systems vulnerable to cascading hazards. In this commentary, we characterize diverse natural hazards in the central Himalayas, including their cascading mechanisms and potential impacts. A scientifically sound understanding of the cascading hazards, underlying mechanisms, and appropriate tools to account for the compounding risks are crucial to informing the design of risk management strategies. We also discuss the need for an integrated modeling framework, reliable prediction and early warning system, and sustainable disaster mitigation and adaptation strategies. [ABSTRACT FROM AUTHOR]

Large-volume rock slope failures are one of the main hazards in high mountain glaciated valleys, inducing severe damage to population and infrastructure, representing a high risk for society, ecosystems and infrastructure. The Andes Mountain Range is shaped by glacial activity and therefore by megalandslides due to changes in shear strength and deformation during periods of glaciation and deglaciation, which modify the slope stress state and, along with other processes, induce progressive damage in the rock mass, eventually leading to failure. The study focuses on validating the hypothesis that glacier unloading contributes to these types of landslides. The research numerically modelled the effects of glacier unloading on stress distribution and its potential impact on landslides, particularly using two Chilean cases: The 1987 Estero Parraguirre and the 2018 Yerba Loca rock slides. These models used the Universal Distinct Element Code, along with geological and geotechnical data from previous studies and field observations. The numerical results showed that the combination of shear stress changes due to glacial unloading and structural control from main discontinuities could cause landslides, with the deglaciation of glaciers potentially preparing the slope for catastrophic failure that may occur due to external climatic or tectonic triggers. The results suggest that stress redistribution and damage to the rock mass caused by deglaciation can lead to progressive failure. Further work is needed to understand better the slope failure mechanics to assess the geohazards in the Andes and other mountain regions. [ABSTRACT FROM AUTHOR]

One of the most common and severe natural hazards, flood has been intensified by anthropogenic climate change in many mountain regions affecting socioeconomic conditions during the twenty-first century. The study synthesized the past 50 years (1971–2020) flood loss data; then generated district-wise flood loss spatial maps and explored flood loss mitigation gaps in diverse topography of Nepal Himalaya through literature reviews. Over the past 50 years, on an average, all disasters together caused two deaths per day while more than 300 families got affected daily in Nepal. The proportion of flood disaster alone found 11.43% flood occurrences, 9.33% fatalities, 38.42% missing, 0.75% injury, 61.60% family suffering, and 10.16% property damages. Compared to the 1970s, the number of flood occurrence has increased to more than six folds causing four times human fatalities in the post 2000s. While acknowledging the population growth, the flood loss still shows increasing trend, but the incremental rate is found reduced to almost half. District-wise flood loss spatial maps depict the highest number of flood occurrences in Jhapa while Sarlahi, Surkhet, Chitwan, Mahottari, Sunsari, and Bardiya districts experienced the highest number of peoples' fatalities, missing, injuries, family suffering, fully and partially damages of privately-owned houses, respectively. Although proactive legislations are promulgated, our study found no subsequent reduction in flood loss arguing no progression in holistic flood risk management in Nepal. Our synthesis and identified research gaps highlight the urgent need for adopting evidence-based basin-scale approach to develop effective and sustainable flood mitigation measures. [ABSTRACT FROM AUTHOR]

Deglaciation has intensified in alpine regions with climate warming, causing increasingly intense paraglacial debris flows (PDFs). Examining the hydromechanical mechanism and initiation of PDFs is essential to disaster relief in downstream areas. However, the establishment of source initiation of PDFs and early warning criteria are hampered by a lack of in situ observations of PDFs; therefore, providing a PDF early warning is still challenging. In this study, on the basis of long-time series field monitoring of rainfall, temperature, soil moisture, and surface displacement in the Tianmo gully, southeast of the Tibetan Plateau, the initiation mechanism of PDFs and the evolutions of the effective saturation, matrix suction, and suction stress were analyzed by combining the hydromechanical coupling analysis method of a slope for a long-term sequence. The measured evidence for the formation and evolution process of slope stability in PDF source area was provided under the conditions of precipitation and ablation. Furthermore, through the inversion of the key slope stability parameters, the thresholds of the hydraulic factors for the provenance slope failure were established, which could be used for early warning of PDFs. This study provides theoretical reference and long-time field data for monitoring and early warning of PDFs in paraglacial hazard-prone areas under global warming sequences. [ABSTRACT FROM AUTHOR]

The Indian Himalayan Region features climatically sensitive and extremely rugged topography. In recent years, risks to human settlements, infrastructure, and the mountain ecosystem have increased manifold because of frequent occurrences of natural hazards. In this context, the Chamoli flash flood event that occurred on February 7, 2021, in Uttarakhand was an extraordinary event causing unprecedented destruction in Rishiganga and Dhauliganga river valleys. This study attempts to simulate the event from the source up to 40.8 km downstream using a hydrodynamic modeling approach. HEC-RAS software was employed to model a hypothesized storage breach of 26.4 × 106 m3 at the source location, generating a peak inflow of 12,761.88 m3/s. The breach was simulated as an unsteady flow with a computational interval of 5 s and a mapping interval of 2 min for 6 h. The model-generated peak discharge values range between 7908.8 and 7975.26 m3s−1 near Rishiganga HEP and between 5779.53 and 5957.46 m3s−1 near Tapovan HEP. Also, flow depths at the above locations were 19.85 and 18.15 m, respectively. The flow velocities were 6.92 and 3.86 m/s, respectively. The model output shows good agreement with the extent and height of actual debris assessed using systematic pre- and post-event analysis of high-resolution satellite datasets. The presented modeling and damage assessment approach may be applied in dynamic mountain ecosystems where population and infrastructure growth require continuous evaluation of hazards. Furthermore, this study proposes implementable recommendations highlighting key issues of specific inadequacies and unpreparedness in the remote high mountain regions of Uttarakhand and elsewhere. [ABSTRACT FROM AUTHOR]

On the southeastern Tibetan Plateau, an area widely covered by alpine glaciers, two types of debris flow generally occur: glacier-related debris flows (GDFs) and rainfall-related debris flows (RDFs). It is widely accepted that topographic conditions influence debris flow activities; however, few studies have examined the differences between such influence on GDFs and RDFs. This study investigated the GDFs and RDFs in the periglacial area of the Parlung Tsangpo Basin, and calculated 12 geomorphic indexes to reveal the topographic features associated with these two types of debris flow. It was found that lower values in the drainage area, main channel length, and relative elevation occurred in RDFs compared to the GDFs. In contrast, higher values in the channel gradient, relief ratio, and effective basin area appeared in RDFs. The discrepancy is mainly related to the different topographic and geomorphic shaping of modern glaciers. According to its geomorphological characteristics, the Parlung Tsangpo Basin can be divided into the upper V-shaped canyon section, middle wide valley section, and lower steep canyon section. The scale and frequency of debris flow in the upstream canyon region are substantially lower than those in the downstream. Moreover, the frequency and scale of RDFs are considerably different from those of GDFs, primarily because of the different geomorphic evolutionary stages of debris flow gullies in different regions. [ABSTRACT FROM AUTHOR]

Flash floods are natural hazards and often occur in small and mountainous river basins with low monitoring. The hydrological and hydrodynamic reconstruction of past rainfall events is useful for understanding the phenomena that led to a flood. This study aims to reconstruct a rainfall event that triggered landslides and floods in 2017 in the Rolante basin (771 km2), southern Brazil, a region with low monitoring. Due to the large magnitude of the flood event, a question was raised whether only the basin response to intense rainfall could have caused that flood. Therefore, different rainfall scenarios were tested with the use of official rain gauges and unofficial rainfall information from local farmers to determine the spatial and temporal distribution of rainfall. The reconstruction of the rainfall event was performed with the use of a hydrologic model (HEC-HMS) to define hydrographs and a hydrodynamic model (Nays2D Flood) to simulate flood propagation, with adjusted methods for the poorly monitored basin. The maximum flood depth and extent were analysed for three rainfall scenarios. The results showed that, with the information provided by the residents, it was possible to determine that extreme and concentrated rainfall occurred in the mountainous area and the basin ordinary response to that rainfall may have caused a flood of that great magnitude. The analysis of past extreme events can contribute to verifying if there are changes in the rainfall patterns and can assist in risk mitigation and disaster management, primarily in ungauged basins. [ABSTRACT FROM AUTHOR]

In Brazil, research related to the occurrence and prevention of debris flows is incipient when compared to the extent of the impacts caused by the phenomena. There is a need for further studies that consider susceptibility and hazard, especially in areas that are environmentally and socioeconomically vulnerable. This study aimed at assessing debris-flow hazard in the Rio das Pedras watershed, in Cubatão (State of São Paulo, Brazil), based on a set of different physiographic parameters (geomorphological, morphometric, geological) and in the application of empirical models. The hazard assessment was based on: (1) the evaluation of the history of events in the region; (2) the identification of the geomorphic controlling factors; (3) the estimation of the magnitude of a potential event; and (4) the identification of the elements at hazard. The results show that a debris-flow event in Rio das Pedras would more severely impact the Anchieta Highway (SP-150), the gas pipeline GASAN, the oil pipeline OSSP and the districts Pinhal do Miranda and Cota 95. These results highlight the relevance of geomorphological and geological parameters when estimating the extent of debris runoff, which is essential when defining the hazard in a debris-flow-prone watershed. [ABSTRACT FROM AUTHOR]

Channel bed erosion accompanying debris flows can significantly magnify the flowing mass and increase the associated risk. However, the mechanics of this geological phenomenon is extremely complex, which greatly increases the difficulty of predicting the dynamical behavior and bulking process of large-scale debris flows. This study employs the depth-averaged two-phase r.avaflow model to numerically analyze the flow propagation and sediment erosion processes. Two modified empirical erosion laws are further embedded in the r.avaflow framework to comparatively compute the channel erosion of a typical catastrophic debris flow occurring in Wenchuan earthquake-affected mountainous areas. The results show that both of the two erosion models can effectively reproduce the movement and channel erosion of the debris flows under investigation. In addition, the most serious sediment erosion has been found to occur along the two sides of the channels. Additionally, r.avaflow model with its simple CE-controlled erosion law relating the erosion coefficient to the slope topography is further applied to predict the dynamical behavior and bulking process of the Hongchun gully debris flow under 50- and 100-year recurrence intervals. The discharge and hazard intensity are shown to greatly increase under the effect of the typically ignored sediment erosion. This study provides more scientific basis for risk assessment and hazard mitigation for large-scale debris flows in mountainous areas. [ABSTRACT FROM AUTHOR]

The quantitative assessment of glacier changes and freshwater availability under future climate change is inevitable for sustainable water resources management and preventing natural disasters. Limiting the uncertainties in glacio-hydrological modeling and exploring spatiotemporal distributions of runoff and its components along the vertical profile are critical for such investigations. The present study quantifies glacio-hydrological changes using the Spatial Processes in HYdrology (SPHY) model forced by CMIP6 climate data (shared socioeconomic pathways: SSP126, SSP245, and SSP585) in the Upper Indus Basin (UIB) over twenty-first century. The model was calibrated based on in situ glacier changes, snow cover changes, and streamflow records to avoid the risk of equifinality. Variations in vertical distribution of runoff components and their impact on glacio-hydrology were investigated using the critical zone approach. The projected remaining glacier area is 55 ± 10%, 32 ± 17%, and 15 ± 5%, and freshwater availability is reduced by − 12 ± 5%, − 30 ± 7%, and − 36 ± 6% in 2100, compared with 2005–2014, under SSP126, SSP245, and SSP585, respectively. The average changes in snowmelt, glacier melt, baseflow, and rain-runoff contributions to total runoff under SSP245 are projected as 25 ± 15%, − 30 ± 11%, − 20 ± 16%, and 242 ± 71%, respectively. The critical zone (3500 – 5500 masl) contributes 63% of total runoff during the reference period, with a significant reduction (51–81%) in the projected period, indicating a diminishing influence of glacier runoff (with 50% reduction) in future hydrology compared with historical period. In turn, low flows (October–March) are projected to increase (9 − 58%), and high flows (April–September) will likely decrease (− 2 to − 13%). Warming temperature was identified as the dominant driver for the glacier area changes (r = − 0.85*) and total runoff (r = − 0.75*) at 0.05 level of significance. Our findings indicate a rainfall-runoff-dominant hydrological regime in future, highlighting critical freshwater availability conditions and associated socioeconomic risks in terms of agricultural applications and natural disasters. We recommend building infrastructure for water storage and conveyance in the Indus basin to prevent the adverse impacts of future climate change. [ABSTRACT FROM AUTHOR]

This study analyses a previous debris flow hazard as a consequence of emerging risks related to climate and regional physical changes. In addition to the increasing flood frequencies, there is an increasing risk of mud or debris flow due to increasing temperature and heavy precipitation resulting in glacier melting. One of the most recent dramatic examples of the debris flow incident took place in Barsem, Tajikistan, in 2015. As a result of heavy precipitation and excess temperature, the melting of glaciers caused debris flow which ended up with a catastrophic damage at Barsem Town. In this study, a methodology for modelling debris flow and related hazard is developed by examining the 2015 incident in detail with a commercially available software, Hydrological Engineering Centre-River Analysis System (HEC-RAS). Simulations and hazard assessment of the incident suggest that assessment of debris flow hazard can be implemented similar to flood hazard. Moreover, it is seen that debris flow inundation area can be predicted accurately by low-resolution free-source digital elevation models (DEMs), while in the present work they could not predict the debris flow hazard assessment accurately. Sensitivity results also reveal that free-source DEMs with higher resolutions do not necessarily give better predictions than free-source DEMs with lower resolutions. [ABSTRACT FROM AUTHOR]

Soil infiltration and geomorphic change affect all flood parameters of dam-break floods. These flood parameters are important for flood risk analysis and management. However, the huge submerged area of dam-break floods and complicated soil parameters of the inundated region lead to the neglect of soil infiltration and geomorphic change in calculating flood parameters, so the influence of soil infiltration and geomorphic change on flood parameters is unclear. We simulated the dam-break flood of Luhun Reservoir to quantify the impact of soil infiltration and geomorphic change on main flood parameters. It was concluded that (1) the average changes of the inundation area, and maximum flood depth, velocity, and duration of the entire inundated region caused by soil infiltration were − 4.02 km2, − 0.1 m, 0 m/s, and − 2.89 d, respectively, that caused by geomorphic change were 6.36 km2, 0.08 m, 0.01 m/s, and − 1.21 d, respectively; (2) the changes of the maximum flood depth, velocity, and duration in local inundated areas caused by soil infiltration were − 4.14 ~ 0.01 m, − 4.32 ~ 3.13 m/s, and − 13.72 ~ 12.73 d, respectively, that caused by geomorphic change were − 1.30 ~ 3.16 m, − 9.8 ~ 6.30 m/s, and − 13.77 ~ 14.00 d, respectively. In order to evaluate flood consequences or draw flood risk map accurately, we suggested that soil infiltration and geomorphic change should be considered in calculating main parameters of dam-break floods. [ABSTRACT FROM AUTHOR]

The Leh Valley which lies within the Trans Himalayan state of Ladakh, India, is known to be affected almost annually by debris flows ranging from minor to catastrophic scale events. The effect has been getting magnified due to increased urbanization and rapid growth in tourism industry. Though these flows are triggered by intense and abnormal rainfall events the conditioning factor has always been the topography and sediment availability. A lucid acknowledgement of the terrain condition and the degree of vulnerability of such events is required. For this a detail investigation of sediment availability, topographic conditions and their relation with known events becomes crucial. This study utilizes index of connectivity (IC) model to understand the sediment source-sink relationship and farther applied Flow-R model to simulate the probable scenario of events through predefined algorithms. We then use the Weights of evidence (WOE) method to compute the statistical probability of debris flow occurrence. This paper demonstrates the application of these three independent techniques and their implementation in a highly rugged terrain of Ladakh which is a region of frequent debris flows onslaught. The IC and Flow-R models are found to be counter supportive and effective in delineating areas which could be affected by flows that will solely originate in upstream areas where high angle channels directly connected to sediment sources are present. WOE-based model determines the probability of the rare and extensive flows that results from downward integration of other drainage networks in an open fan area. [ABSTRACT FROM AUTHOR]

Veniaminof Volcano on the Alaska Peninsula of southwest Alaska is one of a small group of ice-clad volcanoes globally that erupts lava flows in the presence of glacier ice. Here, we describe the nature of lava-ice-snow interactions that have occurred during historical eruptions of the volcano since 1944. Lava flows with total volumes on the order of 0.006 km3 have been erupted in 1983–1984, 1993–1994, 2013, and 2018. Smaller amounts of lava (1 × 10−4 km3 or less) were generated during eruptions in 1944 and 2021. All known historical eruptions have occurred at a 300-m-high cinder cone (informally named cone A) within the 8 × 10-km-diameter ice-filled caldera that characterizes Veniaminof Volcano. Supraglacial lava flows erupted at cone A, resulted in minor amounts of melting and did not lead to any significant outflows of water in nearby drainages. Subglacial effusion of lava in 1983–1984, 2021 and possibly in 1944 and 1993–1994 resulted in more significant melting including a partially water-filled melt pit, about 0.8 km2 in area, that developed during the 1983–1984 eruption. The 1983–1984 event created an impression that meltwater floods from Mount Veniaminof's ice-filled caldera could be significant and hazardous given the large amount of glacier ice resident within the caldera (ice volume about 8 km3). To date, no evidence supporting catastrophic outflow of meltwater from lava-ice interactions at cone A has been found. Analysis of imagery from the 1983–1984 eruption shows that the initial phase erupted englacial lavas that melted ice/snow/firn from below, producing surface subsidence outward from the cone with no discernable surface connection to the summit vent on cone A. This also happened during the 2021 eruption, and possibly during the 1993–1994 eruption although meltwater lakes did not form during these events. Thus, historical eruptions at Veniaminof Volcano appear to have two different modes of effusive eruptive behavior, where lava reaches the ice subglacially from flank vents, or where lava flows are erupted subaerially from vents near the summit of cone A and flow down the cone on to the ice surface. When placed in the context of global lava-ice eruptions, in cases where lava flows melt the ice from the surface downward, the main hazards are from localized phreatic explosions as opposed to potential flood/lahar hazards. However, when lava effusion/emplacement occurs beneath the ice surface, melting is more rapid and can produce lakes whose drainage could plausibly produce localized floods and lahars. [ABSTRACT FROM AUTHOR]

A catastrophic debris flow in the Rishiganga and Dhauliganga rivers in Uttarakhand, India, on 7 February 2021 left a trail of disaster. Around 100–150 people lost their lives according to Uttarakhand Chief Secretary statement given to ANI news portal, two hydropower projects were badly damaged and a bridge across the Rishiganga River was washed off in the event. Study shows that the debris flow is caused due to detachment of 0.59 km2 right lobe of a hanging glacier and resultant ice-rock avalanche. This right lobe of the glacier was located over a mountain slope having an average slope of 35° at 4700–5555 m a.s.l. and travelled 12.4 km before hitting the infrastructure projects. Role of precipitation, snow cover, land surface temperature, and permafrost processes were investigated for identifying causes of the event. Since 2012, monsoon precipitation and mean annual land surface temperature (LST) showed significant increasing trend. Snow cover during monsoon months showed increasing trend and September, October and November experienced decreasing trend at glacier elevations. Mean annual LST increased from − 0.3 °C in 2012 to a peak of 0.4 °C in 2016. Central lobe of the glacier advanced during this period and eventually fell off in 2016 suggesting that the LST warming forced reduction of frictional drag at the interface facilitating it advancement and eventual dislodgement. Permafrost modelling suggests warm permafrost below 50 m and conditions favourable for intense frost cracking up to 10–15 m. At ~ 40 m depth, the delayed response of 2012–2016 warming produced peak positive temperature conditions by December and probably facilitated the formation of thin film of water at the deeper layers acting as a lubricant for glacier sliding. It is also suggested that the increase in summer precipitation might have forced thickening of the accumulation area and thereby increasing the shear stress for sliding of the glacier. It is proposed that the recent change in the weather conditions in the region is primarily responsible for this event through geological, glaciological, and permafrost processes. Flood modelling study suggests a flood volume of ~ 10 MCM generating 24.5 m flow depth at the bridge site with 12.7 m/s flow velocity. The event highlighted the need for improved monitoring of the cryosphere areas of the Himalaya to capture the early warning signs for better preparedness. [ABSTRACT FROM AUTHOR]

On 7th February 2021, a catastrophic flash flood occurred in Raunthi Gad, Rishi Ganga catchment of Dhualiganga Basin. It caused the death of around 200 people and devastated the hydropower projects and other associated infrastructure in the downstream areas of the basin. While the extent of damage and devastation in the downstream region around Rini and Tapovan has been extensively reported, the reconstruction of the event has still not been definitively established. Based on an analysis of the data reported in previous papers and our field and remote-sensing data, we present a detailed reconstruction of the events that occurred in Raunthi Gad that morning. Our analysis supports previous reports that the basic cause was that a portion of the hanging glacier located at Raunthi peak (5600 m asl) along with a large amount of rock fell and hit the Raunthi valley at about 1.5 km downstream of the current snout of Raunthi glacier at an elevation of around 3800 m asl. We present evidence, supported by previous data of transient ponding in the region between the impact zone and the confluence of Raunthi Gad and Rishi Ganga. We estimate the flood volume at Rini to be around 10 MCM and the volume of water available in the valley in the form of ice and snow to be around 6 MCM. We argue that this deficit can be accounted for by the debris volume. The material gained around 8 × 1014 J of energy during the initial slide whereas around 1.5 × 1014 J is required to melt the ice and snow. [ABSTRACT FROM AUTHOR]

On October 17 and 29, 2018, two rock and ice avalanches occurred on the western slope of the Sedongpu Basin upstream of the Yarlung Zangbo River in the Tibetan Plateau. Both avalanches formed the disaster chains and damaged many bridges and roads. Both avalanches on high mountain slope at an elevation of 6000 m asl above sea level triggered long-runout disaster chains, including debris flow, river blocking and flood. In this study, the disaster characteristics and dynamic process were analyzed by multitemporal satellite imagery. The results show that both of the initial sliding bodies were composed of rock and ice. Due to the large elevation difference, the initial sliding bodies rapidly descended into valley floor and immediately transformed into a debris flow after impact and fragmentation. And then, this study divided the disaster chain into four zones by satellite images and field observation, including source zone, dynamic erosion zone, deposition and damming zone, and flash flood zone. This study also carried out the numerical simulation of the disaster by RAMMS. The numerical results reproduced the dynamical process of the debris flow. Furthermore, the potential causes of disaster, evolution process, and the geohazard tendency are discussed. [ABSTRACT FROM AUTHOR]

This study evaluated the efficiency of different Digital Elevation Models (DEMs), including ALOS-12.5 m, SRTM-30 m, SRTM-90 m, and ASTER-30 m v3 when being applied for the hydraulic simulation of flood inundation areas. HEC-RAS-2D model was employed to simulate inundation extent of a 400-year flood (Mar 17, 2019, with peak discharge ~ 547.92 m3/s) along 70 km reach of low-gradient Gorganrood River, northeastern Iran. Fit percentage indicator (FI) and BIAS percentage indicator (BI) were used to evaluate the results in comparison with the remotely sensed inundated area data. The results revealed that the accuracy and capability of the ALOS and SRTM-30 m were higher in simulation of flood extend area (FI ~ 52, BI ~ − 22) and in deriving peak discharge in downstream of the study reach (RMSE ~ 20%). The ASTER showed the worst performance in both floods extend area and peak discharge, despite dramatic improvements in the new version. The results of this study can be considered as a baseline for the selection of DEM sources for deriving flood inundation mapping. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to mitigate the flood impact which may be caused by uncertain future extreme high rainfall-runoff events. To accomplish the objective, an integrated hydrologic–hydrodynamic flood modeling has been performed in the Periyar river basin by utilizing the HEC-RTS framework including reservoir simulation, optimization and calibration of modeling parameters. For the reconstruction of historical floods, seven historical extreme high rainfall-runoff events have been identified (2002 to 2018) and the event-based flood modeling and continuous flood modeling were performed. Simulated floods showed a good agreement with reference to observed floods (at Neeleswaram gauge) (where R2 is recorded as 0.80 and 0.67 for flood event 2018 and continuous simulation, respectively). The historical flood event (i.e., July–August 2018) was reconstructed using HEC-RESSIM and the operating rules were modified for Mullaperiyar and Idukki reservoirs. The regulated flood flows were generated for all seven historical extreme events utilizing the daily meteorological time series datasets. The flood frequency analysis (FFA) has been performed to generate the return period floods and probabilistic flood maps. For hydrodynamic flood simulation, one-dimensional (1D) flood routing was performed in the downstream sections. For the accuracy assessment, the computed flood inundation area and depths were compared with the existing reference datasets like (i) Central Water Commission (CWC) flood data, (ii) real-time flood inundation captured in Sentinel satellite data and (iii) flood maps prepared by DARTMOUTH Flood Agency USA, which showed a reliable agreement. [ABSTRACT FROM AUTHOR]

Large-scale landslides often cause severe damage due to their long run-out distances and having disaster chain effects. Scenario simulation has been adopted in the current work in order to analyze the Xiaomojiu landslide dynamic processes. The landslide characteristics and topography data are obtained via field investigations, whereas high-resolution topographic data (0.17 m) are obtained using an Unmanned Aerial Vehicle. The landslide sliding velocity, deposition characteristics, and flood outburst after a landslide dam failure were obtained using Particle Flow Code (PFC-3D) which introduced the changeable friction coefficient and the HEC-RAS software. The results showed that: 1. The landslide presents a scallop shape with a length of 1110 m, an average width of 950 m, and an area of 1.05 × 106 m2. The average thickness and volume of the sliding body are approximately 50 m and 5.45 × 107 m3. The InSAR (Interferometric Synthetic Aperture Radar) deformation analysis showed that the Xiaomojiu landslide has a maximum annual displacement rate of 60 mm/y and a maximum accumulation deformation of 180 mm since November 25, 2017. 2. The failure process of the Xiaomojiu landslide lasted for 65 s with a maximum velocity of 78.2 m/s. According to the landslide simulation results, the deposited area is approximately 2023 m long, 900 m wide, and has a maximum height of approximately 149 m. 3. A landslide-dammed lake with an elevation of 2940 m and a storage capacity of 4.13 × 109 m3 is formed after the landslide blocks the Jinsha River, and the maximum peak flow rate of the breach is 12051.7 m3/s, 43,451.4 m3/s, 148,635.6 m3/s, and 304,544.7 m3/s for the landslide-dammed failure degrees of 15%, 25%, 50%, and 75%, respectively. These results provide a reference for the risk analysis and mitigation of the landslide. [ABSTRACT FROM AUTHOR]

Landslide-dammed lake outburst floods (LLOFs) may pose serious safety threats to nearby residents and their livelihoods, as well as cause major damages to the downstream areas in mountainous regions. This study presents the Diexi ancient landslide-dammed lake (DALL), located along the Upper Minjiang River, in the eastern margins of the Tibetan Plateau. The DALL is known to have an estimated previous maximal lake area of 1.1 × 107 m2 and an impounded volume of 2.9 × 109 m3. At approximately 27 ka BP, the ancient landslide dam failed, and catastrophic LLOFs occurred. It was determined that the peak discharge of the Diexi ancient LLOFs could be reconstructed using regression, parametric, and boulder competence approaches. The reconstructed average maximum peak discharge was approximately 79,500 m3/s, with an estimated uncertainty bound of 70,000 to 90,000 m3/s. This indicated that the Diexi ancient LLOFs were the largest outburst floods to have occurred in the Upper Minjiang River Valley since the Late Pleistocene Period. The differences in the widths and slopes within the former and latter reaches of the dam indicated that the geomorphic influences on the river channel resulting from the DALL and its LLOFs have been present for tens of thousands of years. These findings were of major significance in deepening the understanding of the existence and disappearances of important river knickpoints on a time scale of tens of thousands of years. [ABSTRACT FROM AUTHOR]

On July 25, 2020, a debris flow occurred in the Wujia Gully, Sichuan Province, China. The last debris flow in this gully occurred 70 years ago and severely impacted the area downstream. The primary goal of this study was to analyze the impact of the topography on the movement process of the debris flow. To gain a precise understanding, a dataset was compiled, including metrological data, field data, accounts from locals, field sampling to obtain specific information using Unmanned Aerial Vehicle (UAV) photography, and the rheological properties of the debris flow slurry obtained through soil mechanics and rheological experiments. The movement process of the debris flow was simulated using the depth-integrated continuum approach. Based on numerical simulation analysis, the influence of the Wujia gully's topography on the debris flow's dynamic process was examined. It was found that the debris flow in the Wujia Gully was a typical viscous debris flow, and the debris flow slurry had the properties of a Bingham fluid. The dynamic process of the debris flow was divided into four stages: an acceleration stage, a deceleration stage in the channel, a smooth movement stage, and a slow accumulation stage. The topography was the main factor controlling the formation of the four stages of the dynamic process. Furthermore, Manning's resistance coefficient did not change the debris flow's dynamic process, but it significantly affected the velocity and duration of each stage. The results of this study provide a reference for future research on debris flow kinematics and flow channels of typical slope debris flows and their movement processes. [ABSTRACT FROM AUTHOR]

An effective risk assessment and response to flood disasters will help ensure the sustainable development of a region. A perfect flood disaster assessment index system should consider the interactions between indexes. The Choquet integral method can effectively solve the problems of index interactions and information overlap and can be used to aggregate relevant decision criteria and express the preferences of decision makers, making it a useful supplement to traditional indicator integration methods. A flood disaster risk assessment model based on the Choquet integral was constructed by considering the meteorological factors, geographical conditions, economic development, population status, medical conditions, education level, and crop sowing in the Yangtze River Delta region (including Shanghai, Jiangsu, Zhejiang, and Anhui) from 2006 to 2017. The model quantified the interaction between the evaluation indexes, taking the minimum information redundancy as the goal; subsequently, a flood disaster risk assessment was performed. The results showed that the meteorological conditions, geographical factors, exposure, and vulnerability have negative interactions with emergency and recovery capabilities. Because of the influence of the first three criteria, the information contained in the criteria for emergency and recovery capabilities is weakened or underestimated. Anhui Province was the largest flood disaster risk area in the Yangtze River Delta region from 2006 to 2017. Zhejiang Province ranked second, and Jiangsu Province and Shanghai City ranked third and fourth, respectively. The assessment results can provide a useful reference for flood disaster risk management in the Yangtze River Delta region. [ABSTRACT FROM AUTHOR]

The prediction of time to slope failure (TOF) is one of the most pivotal concerns for both geological risk researchers and practitioners. Conventional inverse velocity method (IVM), based on the analysis of displacement monitoring data, has become an effective method to solve this problem because it is easy to perform and the prediction results are generally acceptable. Practically, some limitations like random instrumental noise, environmental noise, and measurement error are ubiquitous factors hampered the reliability of the prediction. In this work, traditional IVM method and modified IVM with three different filters are respectively detected on velocity time series from an landslide event in an open-pit coal mine with the propose of improving, in retrospect, the accuracy of failure predictions. Simultaneously, the effects of noise on the appraisal of IVM graphics are also assessed and explanation. The results demonstrate that the sliding process of landslides can be divided into three signature stages based on the IVM. Noteworthily, the slope failure critical point occurs at the end of the progressive stage and generally coincides with a major acceleration event in which almost integrity of the slope is lost, transitioning to a linear trend ever since. Additionally, the short-term smoothing filter (SSF) and long-term smoothing filter (LSF) models can provide more accuracy and useful information about the probable failure time. Finally, with the intention of enhancing the feasible use of the method and supporting pre-determined response plans, two-level alert procedures combing SSF and LSF are proposed. [ABSTRACT FROM AUTHOR]

A large number of paleo-landslide deposits exist in the Southeastern margin of the Qinghai–Tibet Plateau. Once these deposits are destroyed, the disaster chain will cause huge damage to life and property and have an impact on local geomorphic evolution. Diverse models are applied to analyze different geological problems of paleo-landslide deposits, which can produce the advantages of different models fully, thereby making up for the shortcomings of poor applicability of a single model in a certain type of problem. In this study, the Baimu paleo-landslide deposit located at the North side of Dongjiuqu Bridge of Sichuan-Tibet Railway is taken as the research object to completely analyze the potential damage by combining various technical means and numerical model, aiming to provide certain reference for the design and construction of the project. Firstly, site investigation and terrain interpretation confirm the existence of local deformation and damage. Secondly, the finite element model based on the strength reduction method is used to analyze the stability of the deposit and determine the potential damage area. For the potential damage area, debris avalanche and debris flow as two disaster transformation modes are considered. The discrete element model and shallow flow model are used to simulate the dynamic process of debris avalanche and debris flow under complex terrain, respectively. The results show that potential debris avalanche or debris flow will accumulate at the mouth of the Baimu gully, and there will be no direct threat to the bridge. Finally, the formation and evolution sequence of the deposit is proposed, which plays an important role in analyzing the evolution of local river geomorphology. [ABSTRACT FROM AUTHOR]

Pakistan, being an agro-based economy, is considered most vulnerable to the impacts of climate change. The country is susceptible to many natural catastrophes and climate-induced events due to intra-geographical and intra-topographical disparities. This paper is an attempt to measure the relative vulnerability of diverse topographies in rural areas of Pakistan using vulnerability and capacity index tool. The results are based on the findings of primary survey data (350 households from 17 rural communities). Accordingly, and as expected, the key relative differences are attributed to topographical conditions besides the basic quandary of rural areas of Pakistan. The topographical attributes are largely linked to the nature of hazards and relative impacts. While the other aspects of vulnerability in all topographies stem out of inappropriate infrastructure, low education, and institutional factors. The absence of multi-sectoral and productive economic opportunities also poses an adverse impact on the resilience of households in rural areas. The women and households headed by females are found relatively more vulnerable than male-headed households. [ABSTRACT FROM AUTHOR]

Check dam systems are extensively utilized on the Loess Plateau. However, the development of the check dam system is restrained due to the failure hazard. To investigate the failure process of the check dam system and the corresponding effect, a hydrodynamic simulation was conducted in this study based on the failure of a typical check dam system, which occurred on 15 July 2012. The simulation was regarded as satisfactory based on verification with observed data of the peak discharge at the outlet of the catchment (NSE = 0.61, R2 = 0.83), breaches of damaged check dams (relative error < 20%) and maximum water depths in the front of 2 check dams (relative error of − 13.4% and + 4%). The simulation results indicated that the series failure in the tributary ditch did not cause the stack of peak discharges, and the peak flood discharge at the outlet of the catchment in this failure increased 20% compared to the status without dam-break and decreased 87% compared to the status without check dam. [ABSTRACT FROM AUTHOR]