The existential risk space of climate change.

Climate change is widely recognized as a major risk to societies and natural ecosystems but the high end of the risk, i.e., where risks become existential, is poorly framed, defined, and analyzed in the scientific literature. This gap is at odds with the fundamental relevance of existential risks for humanity, and it also limits the ability of scientific communities to engage with emerging debates and narratives about the existential dimension of climate change that have recently gained considerable traction. This paper intends to address this gap by scoping and defining existential risks related to climate change. We first review the context of existential risks and climate change, drawing on research in fields on global catastrophic risks, and on key risks and the so-called Reasons for Concern in the reports of the Intergovernmental Panel on Climate Change. We also consider how existential risks are framed in the civil society climate movement as well as what can be learned in this respect from the COVID-19 crisis. To better frame existential risks in the context of climate change, we propose to define them as those risks that threaten the existence of a subject, where this subject can be an individual person, a community, or nation state or humanity. The threat to their existence is defined by two levels of severity: conditions that threaten (1) survival and (2) basic human needs. A third level, well-being, is commonly not part of the space of existential risks. Our definition covers a range of different scales, which leads us into further defining six analytical dimensions: physical and social processes involved, systems affected, magnitude, spatial scale, timing, and probability of occurrence. In conclusion, we suggest that a clearer and more precise definition and framing of existential risks of climate change such as we offer here facilitates scientific analysis as well societal and political discourse and action.

Developing a science-based policy network over the Upper Indus Basin.

The Upper Indus Basin's (UIB) unique geographical positioning and its ecosystem contributions to the downstream basin in the form of water and energy are of critical importance. UIB is also among the most vulnerable water towers in the world vis-a-vis climate as well as a host of environmental and socio-economic changes. The paucity of ground observations and their associated unknowns make it imperative to study and highlight the grey areas for attention and action by policy planners and basin government and management at different levels in order to improve the management and the governance structures for better water resource management. As this river basin is shared between countries, enhanced co-creation of knowledge can provide greater understanding of the challenges to stakeholders so that they can make better decisions regarding the development of the region. With this in view, the UIB network, comprising four national chapters (Afghanistan, China, India and Pakistan) linked strategically at regional level, was conceived to provide better understanding of the critical issues associated with the UIB. The network strives for a resilient and empowered UIB region through science-based regional cooperation, which promotes coordination and collaboration among organizations working in the UIB to ensure improved understanding of present and future water availability, demand and hazards and to develop gender sensitive solutions for all stakeholders. The special issue is one of such efforts from the network in knowledge generation, exchange, and dissemination to contribute towards an enhanced understanding of climate change impacts in the Indus. The paper presents a time-wise evolution of the network to highlight the importance of cross boundary knowledge and the relevance of such networks. Such a science-based network can provide important information for science-backed policies for the basin countries. It also details the achievements of the network, lessons learnt from such knowledge networks, and the potential for future contributions to basin countries taking into consideration the transboundary nature of the UIB.

Towards integrated assessments of water risks in deglaciating mountain areas: water scarcity and GLOF risk in the Peruvian Andes.

Different water related risks such as lake outburst floods and water scarcity are typically assessed by separate methods and often by separate research communities. However, in a local context such as in mountain regions of the developing world different water risks are intertwined and shaped by multi-dimensional natural and socio-economic drivers. Progressing glacier melt and the associated growing number of lakes rises the threat of glacier lake outburst floods (GLOFs); at the same time declining melt water supply changes the hydrological regime, resulting in changing water availability, especially during dry seasons. Here, we address this challenge by integratively assessing water scarcity and GLOF risks and their interactions for two study sites in glacierized catchments in the Cordillera Blanca and Urubamba in the Peruvian Andes. We used hydrological modelling, GLOF flow path modelling, and interviews with local people and technical experts to assess the hazard and risks of water scarcity and GLOFs. We incorporate perspectives of people living in those areas in order to gain a more comprehensive view on risks. While metrics of flood and water scarcity hazards are difficult to compare, we found insightful results using a comparative analysis of elements at risk from different water related hazards with different probabilities of occurrence. Furthermore, our study shows that considering the diverse local perspectives on risks as well as the social, cultural, economic and political context is essential to more successful and sustainable disaster risk reduction, climate change adaptation and integrated water management.

Climatic and hydrological projections to changing climate under CORDEX-South Asia experiments over the Karakoram-Hindukush-Himalayan water towers.

The complex snow and glacier (cryosphere) dynamics over the "third pole" mountainous regions of the Karakoram-Hindukush-Himalayas (HKH) makes this region challenging for accurate hydrological predictions. The objective of this study is to investigate the impacts of climate change on major hydrological components (precipitation-runoff, snow- and glacier-runoff, evapotranspiration and inter-annual change in streamflows) over the Hunza-, Gilgit- and Astore-River basins, located in HKH. For this purpose, three different hydrological models (snowmelt runoff (SRM), HEC-HMS and HBV are tested over snow- and glacier-covered river basins. These are subsequently integrated with the climate projections simulated from regional climate models (RCMs) developed under CORDEX-SA experiments. The basin-wide RCM-simulations for future scenarios exhibited an increase in precipitation but decline in intensity of rise over high-altitude zones. The temperature rise showed a maximum increase during monsoon by 4.18 °C, 4.37 °C and 4.34 °C over Hunza-, Gilgit- and Astore-River basins, respectively, for the period 2071-2099 (2090s) and a high emission scenario (RCP8.5). Further, in response to rise in precipitation and temperature, the SRM simulations showed a significant increase in snow- glacier-melt runoff (49%, 42% and 46% for SRM) and precipitation runoff (23.8%, 15.7% and 27% for HEC-HMS) in the Hunza-, Gilgit- and Astore-River basins, respectively, for the 2090s under RCP8.5. The streamflow projections for SRM showed a shift in hydrological regime with an increase by 369 (168.4%), 216.5 (74.8%) and 131.8 m3/s (82%) during pre-monsoon in the Hunza-, Gilgit- and Astore-River basins, respectively and then decline by -73.2 m3/s (-13.9%) and -45.4 m3/s (23.4%) during monsoon of the 2090s, in the Hunza- and Astore-River basins, respectively, under RCP8.5. Overall, the projections show that the pre-monsoon and monsoon seasons are expected to be strongly influenced by climate change, through alterations in snow- and glacier-accumulation, and melt regimes with substantial consequences for river runoff in the region.

Managing risks and future options from new lakes in the deglaciating Andes of Peru: The example of the Vilcanota-Urubamba basin.

Rapidly growing lakes in deglaciating mountain regions represent both: emerging risks and options for human livelihoods. In the Andes of Peru, seasonal water scarcity and Glacial Lake Outburst Floods (GLOF) pose a serious threat for highly exposed and vulnerable people. In addition, water demand is growing due to increasing irrigated agriculture, population and hydropower production. In this context, we assess current and future water risks and management options for the Vilcanota-Urubamba basin, Southern Peru. Therefore, the GLOF susceptibility of glacier lakes and the potential maximum reach of damaging flow were analysed. Eighteen out of 134 current and another six out of 20 future glacier lakes were identified as potentially highly susceptible to GLOF. A total of eight existing and one possible future lakes indicate very high risk potentials. Furthermore, a comprehensive surface water balance scheme for five selected subcatchments reveals that future river discharge could be reduced by some 2-11% (7-14%) until 2050 (2100). Particularly in headwaters and during dry seasons, glacier contribution representing roughly 15-25% to total streamflow is crucial and would substantially decrease to below 4-22% (1-3%) until 2050 (2100) with strong glacier shrinkage under intense warming (scenario RCP8.5). In the middle and lower basin, long-term water availability could be jeopardized by growing irrigated agriculture and hydropower capacity. Combining a GLOF and water shortage risk assessment, three key hotspots of current and future water risks were identified. In the context of the identified risks and complex intertwining of water users involving conflict potentials, robust adaptation planning is necessary within an integrative water and risk management framework. Therefore, it is crucial to incorporate ancestral and local knowledge for long-term management planning and implementation. This process should take place beyond temporarily limited governmental and project agency and strengthen broad acceptance of corresponding measures for adapting to hydroclimatic and socioeconomic changes.

How well can we simulate complex hydro-geomorphic process chains? The 2012 multi-lake outburst flood in the Santa Cruz Valley (Cordillera Blanca, Perú).

Changing high-mountain environments are characterized by destabilizing ice, rock or debris slopes connected to evolving glacial lakes. Such configurations may lead to potentially devastating sequences of mass movements (process chains or cascades). Computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses. The present study explores the potential of the novel computational tool r.avaflow for simulating complex process chains. r.avaflow employs an enhanced version of the Pudasaini (2012) general two-phase mass flow model, allowing consideration of the interactions between solid and fluid components of the flow. We back-calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi-lake outburst flood in the Artizón and Santa Cruz valleys, Cordillera Blanca, Peru, involving four lakes and a substantial amount of entrained debris along the path. The documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy. However, small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks. Forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies, but particularly on the development of appropriate strategies for decision-making based on uncertain simulation results. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Future climate and cryosphere impacts on the hydrology of a scarcely gauged catchment on the Jhelum river basin, Northern Pakistan.

Streamflow projections are fundamental sources for future water resources strategic planning and management, particularly in high-altitude scarcely-gauged basins located in high mountain Asia. Therefore, quantification of the climate change impacts on major hydrological components (evapotranspiration, soil water storage, snowmelt-runoff, rainfall-runoff and streamflow) is of high importance and remains a challenge. For this purpose, we analysed general circulation models (GCMs) using a multiple bias correction approach and two different hydrological models i.e. the Hydrological Modelling System (HEC-HMS) and the Snowmelt Runoff Model (SRM), to examine the impact of climate change on the hydrological behaviour of the Jhelum River basin. Based on scrutiny, climate projections using four best fit CMIP5 GCMs (i.e. BCC-CSM1.1, INMCM4, IPSL-CM5A-LR and CMCC-CMS) were chosen by evaluating linear scaling, local intensity scaling (LOCI) and distribution mapping (DM) approaches at twenty climate stations. Subsequently, after calibration and validation of HEC-HMS and SRM at five streamflow gauging stations, the bias corrected projected climate data was integrated with HEC-HMS and SRM to simulate projected streamflow. Results demonstrate that the DM approach fitted the projections best. The climate projections exhibited maximum intra-annual rises in precipitation by 183.2 mm (12.74%) during the monsoon for RCP4.5 and a rise in Tmin (Tmax) by 4.77 °C (4.42 °C) during pre-monsoon, for RCP8.5 during 2090s. The precipitation and temperature rise is expected to expedite and increase snowmelt-runoff up to 48% and evapotranspiration and soil water storage up to 45%. The projections exhibited significant increases in streamflows by 330 m3/s (22.6%) for HEC-HMS and 449 m3/s (30.7%) for SRM during the pre-monfaf0000soon season by the 2090s under RCP8.5. Overall, our results reveal that the pre-monsoon season is potentially utmost affected under scenario-periods, and consequently, which has the potential to alter the precipitation and flow regime of the Jhelum River basin due to significant early snow- and glacier-melt.

Glacial lakes in the Indian Himalayas--from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes.

Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the world, but comparably little attention has been given to these topics in the Indian Himalayas. In this study we present a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial lakes >0.01 km(2). Lakes were detected in the five states spanning the Indian Himalayas, and lake distribution pattern and lake characteristics were found to differ significantly between regions. Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were then selected for a detailed risk assessment. Lake outburst probability, potential outburst magnitudes and associated damage were evaluated on the basis of high-resolution satellite imagery, field assessments and through the use of a dynamic model. The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to present moderate risks to downstream villages, whereas the lake in Sikkim severely threatens downstream locations. At the study site in Sikkim, a dam breach could trigger drainage of ca. 16×10(6)m(3) water and generate maximum lake discharge of nearly 7000 m(3) s(-). The identification of critical glacial lakes in the Indian Himalayas and the detailed risk assessments at three specific sites allow prioritizing further investigations and help in the definition of risk reduction actions.