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The Galapagos Islands are a global hotspot of environmental change. However, despite their potentially major repercussions, little is known about current and expected changes in regional terrestrial climate variables and sea surface temperatures (SST). Here, by analysing existing meteorological observations and secondary datasets, we find that the Islands have warmed by about 0.6 °C since the early 1980s, while at the same time becoming drier. In fact, the onset of the wet season is currently delayed 20 days. This drying trend may reverse, however, given that future climate projections for the region suggest mean annual precipitation may increase between 20 and 70%. This would also be accompanied by more extreme wet and hot conditions. Further, we find that regional SST has increased by 1.2 °C over the last two decades. These changes will, in turn, translate into deterioration of marine ecosystems and coral, proliferation of invasive species, and damages to human water, food, and infrastructure systems. Future projections, however, may be overestimated due to the poor capacity of climatic models to capture Eastern-Pacific ENSO dynamics. Our findings emphasize the need to design resilient climate adaptation policies that will remain robust in the face of a wide range of uncertain and changing climatic futures.

At present, there is a global deficit in infrastructure and the World Bank Group (WBG) is one of the major sources of financing to reduce this gap worldwide. The WBG has policies and protocols for approving investments taking into consideration financial and economic indicators while ensuring social and environmental safeguards. In recent years, these safeguards have been updated to include the effects of climate change and robustness and resilience to support climate-informed project investment decision-making. A series of tools for screening projects for climate vulnerabilities and identification of risk management options have been developed to help project teams comply with these requirements. One of these tools is the hierarchical four-phased Decision Tree Framework (DTF) that, beyond screening, helps to analyze plans and project vulnerabilities, climate-related or otherwise, using a decision scaling approach, and explore risk management options, if necessary. The four phases of the DTF are (i) project screening, (ii) initial analysis, (iii) stress test, and (iv) climate risk management. This paper reviews applications of the DTF from the climate change screening phase to non-climate uncertainty screening and decision-making for project investments and prioritization. A peek into work in progress for incorporating resilience in the decision-making process, both for projects and through projects, is also provided, as well as next steps, looking forward.

Megacities are increasingly confronted with water supply challenges, requiring innovative and diversified management strategies to ensure sustainability. This study examines Mexico City’s Cosecha de Lluvia program, a government initiative promoting residential rainwater harvesting (RWH). This case study offers valuable lessons for other megacities facing similar water security issues. The study particularly explores result-based financing (RBF) as a promising strategy to strengthen Mexico City’s RWH sector. Despite its potential, research on RBF for water supply diversification remains limited, especially from the perspective of practitioners. To address this gap, the study employs a systems thinking approach supported by qualitative methods, including a literature review and interviews. Thematic networks analysis revealed that RBF could enhance Cosecha de Lluvia by improving monitoring and results measurement, facilitating information exchange, and increasing transparency—key factors for successful water supply diversification. While these identified benefits do not address all of Cosecha de Lluvia’s challenges and RBF could have implementation challenges, there is a clear opportunity for this financial mechanism to enhance programs like the one studied and have a positive impact on several of its elements. As part of the RBF suitability assessment, three different funding sources were evaluated—public, private, and philanthropic—to determine their effectiveness in overcoming Cosecha de Lluvia’s challenges. The findings suggest that no single source of finance markedly influences the program’s effectiveness alone. Instead, a blended financing approach that integrates all three sources is recommended as a strategy to explore further for implementing RBF in water supply diversification efforts. Overall, the study highlights the necessity of diversifying water supply to build climate resilience in megacities. While programs like Cosecha de Lluvia are crucial, significant room for improvement exists. RBF offers a promising mechanism to enhance such initiatives, and its potential merits further exploration.

Targets agreed to in Paris in 2015 aim to limit global warming to 'well below 2 °C and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels'. Despite the far-reaching consequences of this multi-lateral climate change mitigation strategy, the implications for global river flows remain unclear. Here we estimate the impacts of 1.5 °C versus 2.0 °C mitigation scenarios on peak flows by using daily river flow data from a multi-model ensemble which follows the HAPPI Protocol (that is specifically designed to simulate these temperature targets). We find agreement between models with regard to changing risk of river flow extremes. Moreover, we find that the response at 2.0 °C is not a uniform extension of the response at 1.5°, suggesting a non-linear global response of peak flows to the two mitigation levels. Yet committing to the 2.0 °C warming target, rather than 1.5 °C, is projected to lead to an increase in the frequency of occurrence of extreme flows in several large catchments. In the most affected areas, predominantly in South Asia, while region-specific features such as aerosol loads may determine precipitation patterns, we estimate that under our 1.5 °C scenario the historical 1-in-100 year flow occurs with a frequency of 1-in-25 years. At 2.0 °C, similar increases are observed in several global regions. These shifts are also accompanied by changes in the duration of rainy seasons which influence the occurrence of high flows.

The Ili-Balkhash basin (IBB) is considered a key region for agricultural development and international transport as part of China’s Belt and Road Initiative (BRI). The IBB is exemplary for the combined challenge of climate change and shifts in water supply and demand in transboundary Central Asian closed basins. To quantify future vulnerability of the IBB to these changes, we employ a scenario-neutral bottom-up approach with a coupled hydrological-water resource modelling set-up on the RiverWare modelling platform. This study focuses on reliability of environmental flows under historical hydro-climatic variability, future hydro-climatic change and upstream water demand development. The results suggest that the IBB is historically vulnerable to environmental shortages, and any increase in water consumption will increase frequency and intensity of shortages. Increases in precipitation and temperature improve reliability of flows downstream, along with water demand reductions upstream and downstream. Of the demand scenarios assessed, extensive water saving is most robust to climate change. However, the results emphasize the competition for water resources among up- and downstream users and between sectors in the lower Ili, underlining the importance of transboundary water management to mitigate cross-border impacts. The modelling tool and outcomes may aid decision-making under the uncertain future in the basin.

In June 2013, Uttarakhand experienced a hydro-meteorological disaster due to a 4 d extreme precipitation event of return period more than 100 years, claiming thousands of lives and causing enormous damage to infrastructure. Using the weather@home climate modelling system and its Half a degree Additional warming, Prognosis and Projected Impacts simulations, this study investigates the change in the return period of similar events in a 1.5 °C and 2 °C warmer world, compared to current and pre-industrial levels. We find that the likelihood of such extreme precipitation events will significantly increase under both future scenarios. We also estimate the change in extreme river flow at the Ganges; finding a considerable increase in the risk of flood events. Our results also suggest that until now, anthropogenic aerosols may have effectively counterbalanced the otherwise increased meteorological flood risk due to greenhouse gas (GHG) induced warming. Disentangling the response due to GHGs and aerosols is required to analyses the changes in future rainfall in the South Asia monsoon region. More research with other climate models is also necessary to make sure these results are robust.

Water utilities' supply systems are vulnerable to several climate‐related hazards, including droughts, floods and cyclones. Here we propose a generally applicable framework for conducting multi‐hazard risk assessments of water supply systems and use it to quantify the impact of present and future climate extremes on the national water supply network in Jamaica. The proposed framework involves stress‐testing a model of the system with a large set of spatially coherent drought, cyclone and pluvial and fluvial flood events to calculate the number of water users whose supplies would be disrupted during an event, that is, the Customer disruption days (CDD). We estimate the total multi‐hazard annual expected disruption to be approximately 5 days per year per utility customer under present conditions. This is increased by a factor of between 2 and 2.5 when end‐of‐century climate scenarios are propagated through the model. Our analysis shows that more high probability drought events lead to greater CDD compared with asset damage events. However, extreme asset damage events, despite manifesting over shorter timescales (days) compared to drought events (months), can lead to more widespread CDD. This quantified risk framework would allow utility managers to compare the risk of both asset damage‐ and water shortage‐induced disruptions via a common, decision‐relevant metric. However, applications to other utilities would require tailored hazard modeling approaches. The proposed risk assessment is intended to inform prioritization of infrastructure investments, ranging from asset protection to drought mitigation projects, with the goal of enhancing water supply resilience in the face of a changing climate. Key Points We propose a spatial multi‐hazard risk framework for analyzing present‐day and future climate risks to water users We propose the use of customer disruption days as a common metric for comparing different hazards impacts The framework can be used by decision makers to prioritize investments across asset protection against flooding and cyclones, and drought mitigation options

Global water security is known to depend on, among other things, the ability of societies to cope with hydrological risks. While there are several drivers that determine the severity of these risks, climatological mechanisms play an important role in describing their spatial and temporal characteristics. These mechanisms are often described as intra-annual and inter-annual sources of climate variability. Furthermore, anthropogenic climate change is understood to importantly perturb these mechanisms and in turn magnify hydrological risks. As such, understanding the way in which these mechanisms of climate variability influence hydrological processes has become a present and pressing scientific challenge. In particular, while existing methods look to explain the role of climate variability in hydrometeorological variables, namely precipitation and temperature, more research is required to explain how these mechanisms manifest in large-scale land surface hydrological processes and extremes. The objective of this thesis is to increase our understanding of the way that climate sources of variability influence the spatial and temporal heterogeneity of hydrological flows. This objective is addressed in a systematic way, by first exploring how hydrological flow characteristics are influenced by land surface hydrological processes in areas, with traditional rudimentary runoff representations. Building on this, this thesis secondly analyses the direct link between natural sources of climate variability and land surface hydrological processes and risks at the global scale. Lastly, the repercussions of anthropogenic climate change, in the context of current global climate agreements, in influencing hydrological extremes are explored. By examining the impacts of such extremes on global hydropower availability, a part of the ultimate consequences of hydrological risks on human systems are subsequently explored. In order to address these aims this thesis proposes a systemic framework that connects climate sources of variability and heterogeneity of flows, by combining various physical sub-models of a Land Surface Model (LSM) and other complementary tools. As such, this framework looks to link climate sources of variability, atmospheric responses, surface hydrological variables, hydrodynamics, hydrological extremes, and societal repercussions. To demonstrate the value of the framework, this thesis presents four case studies in which specific components and sub-models of this framework are utilized to address the mentioned objectives. The framework proposed here has helped to unveil and quantify new drivers that control river flows and hydrological risks. This includes explaining the snowpack characteristics that determine timing and magnitude of river flow peaks in snow-dominated regions. Also, by quantifying the inter-annual variability driven by Atmospheric Rivers, this thesis found that this form of moisture transport contributes to 22% of total global annual runoff and their variability importantly drives hydrological extremes in various global locations. Furthermore, by applying this framework, this thesis found that committing to a 1.5oC level of warming, instead of 2.0°C, as agreed in Paris in 2015, may importantly decrease high flow occurrences in regions such central Asia or western Europe. Similarly, this thesis found that the intensification of future low flow events, resulted from future climate targets, may lead to important global water losses which in turn would make almost a quarter of current global GHP vulnerable, importantly affecting the energy share in various Asian and Sub-Saharan countries.

The range of variability present in the Earth's climate presents a series of challenges to water managers and policy‐makers. Much recent work has shed light on the detailed natural patterns of Earth's climatic variability. including mechanisms such as El Niño and tropical monsoon systems, although there remains much to learn about their predictability. The importance of climate change as a critical factor in long‐term water resources policy and planning has introduced additional significant uncertainty in the magnitude of available water resources and the risks of extremes such as floods and droughts. This chapter reviews progress in these important fields and highlights some important results that have emerged from climate science and hydrology. The chapter also considers how water policy and management can take account of these new sources of information to inform long‐lived decision‐making.