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Scientific evidence shows that most glaciers in South Asia's Hindu Kush Himalayan region are retreating, but the consequences for the region's water supply are unclear, this report finds. The Hindu Kush Himalayan region is the location of several of Asia's great river systems, which provide water for drinking, irrigation, and other uses for about 1.5 billion people. Recent studies show that at lower elevations, glacial retreat is unlikely to cause significant changes in water availability over the next several decades, but other factors, including groundwater depletion and increasing human water use, could have a greater impact. Higher elevation areas could experience altered water flow in some river basins if current rates of glacial retreat continue, but shifts in the location, intensity, and variability of rain and snow due to climate change will likely have a greater impact on regional water supplies. Himalayan Glaciers: Climate Change, Water Resources, and Water Security makes recommendations and sets guidelines for the future of climate change and water security in the Himalayan Region. This report emphasizes that social changes, such as changing patterns of water use and water management decisions, are likely to have at least as much of an impact on water demand as environmental factors do on water supply. Water scarcity will likely affect the rural and urban poor most severely, as these groups have the least capacity to move to new locations as needed. It is predicted that the region will become increasingly urbanized as cities expand to absorb migrants in search of economic opportunities. As living standards and populations rise, water use will likely increase-for example, as more people have diets rich in meat, more water will be needed for agricultural use. The effects of future climate change could further exacerbate water stress. Himalayan Glaciers: Climate Change, Water Resources, and Water Security explains that changes in the availability of water resources could play an increasing role in political tensions, especially if existing water management institutions do not better account for the social, economic, and ecological complexities of the region. To effectively respond to the effects of climate change, water management systems will need to take into account the social, economic, and ecological complexities of the region. This means it will be important to expand research and monitoring programs to gather more detailed, consistent, and accurate data on demographics, water supply, demand, and scarcity.

Mountains are the water towers of the world, supplying a substantial part of both natural and anthropogenic water demands 1 , 2 . They are highly sensitive and prone to climate change 3 , 4 , yet their importance and vulnerability have not been quantified at the global scale. Here we present a global water tower index (WTI), which ranks all water towers in terms of their water-supplying role and the downstream dependence of ecosystems and society. For each water tower, we assess its vulnerability related to water stress, governance, hydropolitical tension and future climatic and socio-economic changes. We conclude that the most important (highest WTI) water towers are also among the most vulnerable, and that climatic and socio-economic changes will affect them profoundly. This could negatively impact 1.9 billion people living in (0.3 billion) or directly downstream of (1.6 billion) mountainous areas. Immediate action is required to safeguard the future of the world’s most important and vulnerable water towers. The worldwide distribution and water supply of water towers (snowy or glacierized mountain ranges) is indexed, showing that the most important water towers are also the most vulnerable to socio-economic and climate-change stresses, with huge potential negative impacts on populations downstream.

\"International Water Scarcity and Variability considers international water management challenges created by water scarcity and environmental change. Although media coverage and some scholarship tend to cast natural resource shortages as leading inexorably toward war, Shlomi Dinar and Ariel Dinar prove that there are many examples of and mechanisms for more peaceful dispute resolution regarding natural resources, even in the face of water paucity and climate change. The authors base these arguments on both global empirical analyses and case studies. Using numerous examples that focus on North America, Europe, Central Asia, and the Middle East, this book asks scholars and policy makers to consider strategies and incentives to help lessen conflict and motivate cooperation under scarcity and increased variability of water resources\"--Provided by publisher.

The Earth's human population is expected to pass eight billion by the year 2025, while rapid growth in the global economy will spur ever increasing demands for natural resources. The world will consequently face growing scarcities of such vital renewable resources as cropland, fresh water, and forests. Thomas Homer-Dixon argues in this sobering book that these environmental scarcities will have profound social consequences--contributing to insurrections, ethnic clashes, urban unrest, and other forms of civil violence, especially in the developing world. Homer-Dixon synthesizes work from a wide range of international research projects to develop a detailed model of the sources of environmental scarcity. He refers to water shortages in China, population growth in sub-Saharan Africa, and land distribution in Mexico, for example, to show that scarcities stem from the degradation and depletion of renewable resources, the increased demand for these resources, and/or their unequal distribution. He shows that these scarcities can lead to deepened poverty, large-scale migrations, sharpened social cleavages, and weakened institutions. And he describes the kinds of violence that can result from these social effects, arguing that conflicts in Chiapas, Mexico and ongoing turmoil in many African and Asian countries, for instance, are already partly a consequence of scarcity. Homer-Dixon is careful to point out that the effects of environmental scarcity are indirect and act in combination with other social, political, and economic stresses. He also acknowledges that human ingenuity can reduce the likelihood of conflict, particularly in countries with efficient markets, capable states, and an educated populace. But he argues that the violent consequences of scarcity should not be underestimated--especially when about half the world's population depends directly on local renewables for their day-to-day well-being. In the next decades, he writes, growing scarcities will affect billions of people with unprecedented severity and at an unparalleled scale and pace. Clearly written and forcefully argued, this book will become the standard work on the complex relationship between environmental scarcities and human violence.

Groundwater is the world’s largest freshwater resource and is critically important for irrigation, and hence for global food security 1 – 3 . Already, unsustainable groundwater pumping exceeds recharge from precipitation and rivers 4 , leading to substantial drops in the levels of groundwater and losses of groundwater from its storage, especially in intensively irrigated regions 5 – 7 . When groundwater levels drop, discharges from groundwater to streams decline, reverse in direction or even stop completely, thereby decreasing streamflow, with potentially devastating effects on aquatic ecosystems. Here we link declines in the levels of groundwater that result from groundwater pumping to decreases in streamflow globally, and estimate where and when environmentally critical streamflows—which are required to maintain healthy ecosystems—will no longer be sustained. We estimate that, by 2050, environmental flow limits will be reached for approximately 42 to 79 per cent of the watersheds in which there is groundwater pumping worldwide, and that this will generally occur before substantial losses in groundwater storage are experienced. Only a small decline in groundwater level is needed to affect streamflow, making our estimates uncertain for streams near a transition to reversed groundwater discharge. However, for many areas, groundwater pumping rates are high and environmental flow limits are known to be severely exceeded. Compared to surface-water use, the effects of groundwater pumping are markedly delayed. Our results thus reveal the current and future environmental legacy of groundwater use. Estimates for when critical environmental streamflow limits will be reached—with potentially devastating economic and environmental effects—are obtained using a global model that links groundwater pumping with the groundwater flow to rivers.

Global food consumption drives irrigation for crops, which depletes aquifers in some regions; here we quantify the volumes of groundwater depletion associated with global food production and international trade. International food trade causes water depletion (Dalin 21403, Phys Letter) International trade is increasingly transporting 'hidden' resources and environmental factors from one country to another. For example, the water used to produce a spear of asparagus eaten in London might come from irrigation in South America. Similarly, pollution generated in China might be traceable to consumer demand in the United States. Carole Dalin et al . now extend this idea to the non-renewable groundwater that is consumed for agricultural trade. They find that 11 per cent of groundwater extraction is linked to agricultural trade, with Pakistan, the United States and India accounting for two-thirds of the global totals. The research reveals the degree to which food consumption in one country can lead to groundwater depletion in others, highlighting the need to better consider issues of sustainability and equity in the international food trade. Recent hydrological modelling 1 and Earth observations 2 , 3 have located and quantified alarming rates of groundwater depletion worldwide. This depletion is primarily due to water withdrawals for irrigation 1 , 2 , 4 , but its connection with the main driver of irrigation, global food consumption, has not yet been explored. Here we show that approximately eleven per cent of non-renewable groundwater use for irrigation is embedded in international food trade, of which two-thirds are exported by Pakistan, the USA and India alone. Our quantification of groundwater depletion embedded in the world’s food trade is based on a combination of global, crop-specific estimates of non-renewable groundwater abstraction and international food trade data. A vast majority of the world’s population lives in countries sourcing nearly all their staple crop imports from partners who deplete groundwater to produce these crops, highlighting risks for global food and water security. Some countries, such as the USA, Mexico, Iran and China, are particularly exposed to these risks because they both produce and import food irrigated from rapidly depleting aquifers. Our results could help to improve the sustainability of global food production and groundwater resource management by identifying priority regions and agricultural products at risk as well as the end consumers of these products.

The sustainability of aquaculture has been debated intensely since 2000, when a review on the net contribution of aquaculture to world fish supplies was published in Nature . This paper reviews the developments in global aquaculture from 1997 to 2017, incorporating all industry sub-sectors and highlighting the integration of aquaculture in the global food system. Inland aquaculture—especially in Asia—has contributed the most to global production volumes and food security. Major gains have also occurred in aquaculture feed efficiency and fish nutrition, lowering the fish-in–fish-out ratio for all fed species, although the dependence on marine ingredients persists and reliance on terrestrial ingredients has increased. The culture of both molluscs and seaweed is increasingly recognized for its ecosystem services; however, the quantification, valuation, and market development of these services remain rare. The potential for molluscs and seaweed to support global nutritional security is underexploited. Management of pathogens, parasites, and pests remains a sustainability challenge industry-wide, and the effects of climate change on aquaculture remain uncertain and difficult to validate. Pressure on the aquaculture industry to embrace comprehensive sustainability measures during this 20-year period have improved the governance, technology, siting, and management in many cases. The volume of global aquaculture production has tripled since 2000 with positive trends in environmental performance, but the sector faces mounting challenges including pathogen management, pollution, climate change, and increasing dependence on land-based resource systems.

This paper examines the relation between air pollution and individual investors’ trading behavior and performance. Using unique data on stock trades by 87,504 individuals from 34 cities in China, we find a negative relation between air pollution and trade performance. This result is obtained after controlling for investor-year fixed effects and date fixed effects, as well as local weather conditions. More strikingly, abnormal trade performance decreases monotonically with the levels indicating the severity of air pollution. Furthermore, we find evidence suggesting that air pollution makes investors more susceptible to the disposition effect and attention-driven buying behavior. Overall, the results highlight a hitherto-unexplored cost that ambient air pollution imposes on stock market investors. This paper was accepted by Tylor Shumway, finance .