Dynamic Risks for Cascading Himalayan Hazards

影响喜马拉雅山脉内部和边缘社区的自然灾害种类繁多，主要是地震、山体滑坡和洪水。为了减少山体滑坡和洪水的风险，社区开发了下游村庄和城镇的早期预警系统，使预先计划的反应成为可能。预警系统要求地方当局意识到潜在的危险。例如，对已知不稳定的陡峭山坡，特别是在大雨期间，应监测过去曾发生山泥倾泻的证据。然而，为了让当地地区灾害管理当局(DDMA)知道在哪里监测，需要了解不同灾害可能造成的风险的中期预测。例如，某些地区更容易发生地震，其他地区则更容易发生山体滑坡和山洪暴发。如果这些来自不同危害的风险随着时间的推移保持不变，那么对每个社区的预测和监测也保持稳定。然而，危险并不是孤立的，而是形成级联，每个事件都会触发另一个事件。因此，来自多重危险的风险不是稳定的，而是动态的，并随着上游触发因素的变化而变化。例如，滑坡导致大坝决口形成泥石流，然后由于沙子和砾石堵塞河道而增加随后发生洪水的风险。该项目旨在利用一系列新的建模技术提供对多种危险级联的全面定量预测，这些预测受到北阿肯德邦加尔鲸尔喜马拉雅山脉实地观测历史的限制。该地区最近遭到山体滑坡和山洪暴发的破坏，如2013年的基达纳特灾难和2021年的Chomli山体滑坡。在这些陡峭的山谷中厚厚堆积的沉积物被称为“沉积物炸弹”，因为它们对下游社区构成了危险；这种沉积物炸弹可能会在冰川退缩或山体滑坡堵塞山谷的地方形成。在这个项目中，印度和英国的团队将联合起来，整合数字地形、遥感、计算机模型和现场监测的新方法，以了解冰川和山体滑坡产生的沉积物如何引发沉积物炸弹，以及这些堆积如何被动员起来形成泥石流、山洪暴发和下游洪水。通过了解这些过程中涉及的分布和比率，我们将产生中期预测，并将其提供给阿拉克南达山谷社区开发的早期预警系统。如上所述的方法表明，物理科学模型将是考虑动态风险的唯一输入；但它不可能那么简单。与这一风险共存的社区以及管理早期预警系统的防灾减灾中心必须参与科学方法的产生和迭代。因此，我们正在与英国和印度的社会科学家合作，他们有通过研讨会和采访与喜马拉雅社区合作的经验，尊重不同的文化、种族和性别视角。到项目结束时，我们将为地区当局制定一个决策工作流程，将动态风险纳入其中期预测，以应对连锁灾害。在加尔鲸尔喜马拉雅地区展示了这一进程后，我们打算与印度和尼泊尔的国家灾害管理当局合作，促进国家动态风险评估战略。

There are a wide range of natural hazards that impact communities living within, and at the edge of the Himalayan mountains; these are dominated by earthquakes, landslides and floods. In order to reduce the risk from landslides and floods, communities have developed early warning systems to downstream villages and towns, enabling pre-planned responses. Early warning systems require local authorities to be aware of potential dangers. For example, a steep hillslope that is known to be unstable with evidence of past landslides should be monitored, particularly during periods of heavy rainfall. However, in order for the local District Disaster Management Authorities (DDMAs) to know where to monitor, medium-term forecasts of the likely risk from different hazards need to be known. For example, certain areas are more prone to earthquakes, and others to landslides and flashfloods. If these risks from different hazards remain constant through time, then the forecasts and monitoring for each community remains steady. However, hazards do not act in isolation, but form cascades, each event triggering another. As a result, the risk from multiple hazards is not stable, but dynamic, and changes in response to upstream triggers. For example a landslide, that leads to a dam that breaks out to form a debris flow that then increases subsequent risk to floods due to choking of river channels with sand and gravel.This project aims to provide the first fully quantitative forecasts of multihazard cascades using a range of new modelling techniques constrained by a history of field observations from the Garwhal Himalaya, Uttarakhand. This area has been devastated by recent landslides and flashfloods such as the Kedarnath disaster in 2013 and the Chomli landslide in 2021. Thick accumulations of sediment in these steep mountain valleys are known as 'sediment bombs' as they pose a danger to downstream communities; such sediment bombs may form where glaciers retreat or where landslides block valleys. In this project, the Indian and UK teams will combine to integrate new methodologies from digital topography, remote sensing, computer models and field monitoring to understand how sediment yield from glaciers and landslides initiate sediment bombs, and how these accumulations are then mobilised to form debris flows, flash floods and downstream flooding. Through understanding the distribution and rates involved in these processes, we will generate medium term forecasts that feed into early warning systems developed in the communities of the Alaknanda Valley.The approach as outlined above suggests that the physical science models will be the sole input into consideration of dynamic risk; but it can't be as simple as that. The communities that live with this risk, and the DDMAs that manage the early warning systems have to be involved in the generation and iteration of the scientific methodology. Consequently, we are working with social scientists in the UK and India who have experience working with communities in the Himalaya through workshops and interviews that respect the diverse cultural, ethnic and gender-based perspectives. By the end of the project, we will have generated a decisional workflow for district authorities that integrates dynamic risk into their medium term forecasts in response to cascading hazards. Having demonstrated this process in the Garwhal Himalaya, we intend to work with the National Disaster Management Authorities in India and Nepal to promote national strategies for dynamic risk assessment.