A global assessment of the impact of climate change on water scarcity (original) (raw)

Climate change and global water resources

Global Environmental Change, 1999

By 2025, it is estimated that around 5 billion people, out of a total population of around 8 billion, will be living in countries experiencing water stress (using more than 20% of their available resources). Climate change has the potential to impose additional pressures in some regions. This paper describes an assessment of the implications of climate change for global hydrological regimes and water resources. It uses climate change scenarios developed from Hadley Centre climate simulations (HadCM2 and HadCM3), and simulates global river #ows at a spatial resolution of 0.5;0.53 using a macro-scale hydrological model. Changes in national water resources are calculated, including both internally generated runo! and upstream imports, and compared with national water use estimates developed for the United Nations Comprehensive Assessment of the Freshwater Resources of the World. Although there is variation between scenarios, the results suggest that average annual runo! will increase in high latitudes, in equatorial Africa and Asia, and southeast Asia, and will decrease in mid-latitudes and most subtropical regions. The HadCM3 scenario produces changes in runo! which are often similar to those from the HadCM2 scenarios * but there are important regional di!erences. The rise in temperature associated with climate change leads to a general reduction in the proportion of precipitation falling as snow, and a consequent reduction in many areas in the duration of snow cover. This has implications for the timing of stream#ow in such regions, with a shift from spring snow melt to winter runo!. Under the HadCM2 ensemble mean scenario, the number of people living in countries with water stress would increase by 53 million by 2025 (relative to those who would be a!ected in the absence of climate change). Under the HadCM3 scenario, the number of people living in countries with water stress would rise by 113 million. However, by 2050 there would be a net reduction in populations in stressed countries under HadCM2 (of around 69 million), but an increase of 56 million under HadCM3. The study also showed that di!erent indications of the impact of climate change on water resource stresses could be obtained using di!erent projections of future water use. The paper emphasises the large range between estimates of`impacta, and also discusses the problems associated with the scale of analysis and the de"nition of indices of water resource impact.

Estimating future global per capita water availability based on changes in climate and population

2012

Human populations are profoundly affected by water stress, or the lack of sufficient per capita available freshwater. Water stress can result from overuse of available freshwater resources or from a reduction in the amount of available water due to decreases in rainfall and stored water supplies. Analyzing the interrelationship between human populations and water availability is complicated by the uncertainties associated with climate change projections and population projections.

Multimodel assessment of water scarcity under climate change

Proceedings of the National Academy of Sciences, 2014

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2°C above present (approximately 2.7°C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500 m 3 per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2°C, whereas indicators of very severe impacts increase unabated beyond 2°C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.

Compounding Impacts of Human-Induced Water Stress and Climate Change on Water Availability

Scientific Reports

The terrestrial phase of the water cycle can be seriously impacted by water management and human water use behavior (e.g., reservoir operation, and irrigation withdrawals). Here we outline a method for assessing water availability in a changing climate, while explicitly considering anthropogenic water demand scenarios and water supply infrastructure designed to cope with climatic extremes. The framework brings a top-down and bottom-up approach to provide localized water assessment based on local water supply infrastructure and projected water demands. When our framework is applied to southeastern Australia we find that, for some combinations of climatic change and water demand, the region could experience water stress similar or worse than the epic Millennium Drought. We show considering only the influence of future climate on water supply, and neglecting future changes in water demand and water storage augmentation might lead to opposing perspectives on future water availability. While human water use can significantly exacerbate climate change impacts on water availability, if managed well, it allows societies to react and adapt to a changing climate. The methodology we present offers a unique avenue for linking climatic and hydrologic processes to water resource supply and demand management and other human interactions. Water resources are sensitive to climate change and variability 1-5 , especially in arid and semi-arid regions 6-8. Regional and global hydrologic models forced with Global climate model simulations have been widely used to assess future changes in water resources 9-11. Water availability is also closely associated with operations of water supply infrastructure (surface water reservoirs and desalination plants, etc.), and human water use behavior (e.g., growth and seasonal cycles in water demands) 12. Some modeling frameworks used for climate/hydrology projections typically simulate the natural hydrologic cycle 13-17 (Fig. 1 (top right)) without considering anthropogenic water demand, human interactions 18, 19 and man-made infrastructure such as dams and reservoirs 20 (Fig. 1(top left)). Storage infrastructure can significantly alter water flow and distribution 21. Man-made surface reservoirs control 22 about 20% of the global annual river discharge (~8000 km 3 out of 40000 km 3 ; ref. 23) and provide resilience against droughts, in addition to their role in water resource management and energy production 24-27. Since early 2000s, several major modeling efforts have tackled integrating water demand, irrigation and other human dimensions in water stress and availability analysis 10, 28-41. Man-made local water supply infrastructure (in particular surface water reservoirs) affects future water availability because it is, generally speaking, built specifically to cope with climatic extremes. A system with distributed and different water storage, and therefore more local resilience, will be less vulnerable to climatic change and variability compared to a system with limited local capacity to cope with extremes. As a result, different regions will see different water availability changes depending on their local infrastructure and capacity to cope with variability or adapt to change. Omitting surface water reservoirs from large-scale water cycle models introduces a large source of uncertainty in current assessments of the global water cycle and hinders evaluation of climate change

Global water resources affected by human interventions and climate change

Proceedings of the National Academy of Sciences, 2014

Humans directly change the dynamics of the water cycle through dams constructed for water storage, and through water withdrawals for industrial, agricultural, or domestic purposes. Climate change is expected to additionally affect water supply and demand. Here, analyses of climate change and direct human impacts on the terrestrial water cycle are presented and compared using a multimodel approach. Seven global hydrological models have been forced with multiple climate projections, and with and without taking into account impacts of human interventions such as dams and water withdrawals on the hydrological cycle. Model results are analyzed for different levels of global warming, allowing for analyses in line with temperature targets for climate change mitigation. The results indicate that direct human impacts on the water cycle in some regions, e.g., parts of Asia and in the western United States, are of the same order of magnitude, or even exceed impacts to be expected for moderate levels of global warming (+2 K). Despite some spread in model projections, irrigation water consumption is generally projected to increase with higher global mean temperatures. Irrigation water scarcity is particularly large in parts of southern and eastern Asia, and is expected to become even larger in the future.

A global water scarcity assessment under Shared Socio-economic Pathways – Part 1: Water use

Hydrology and Earth System Sciences, 2013

A novel global water scarcity assessment for the 21st century is presented in a two-part paper. In this first paper, water use scenarios are presented for the latest global hydrological models. The scenarios are compatible with the socioeconomic scenarios of the Shared Socioeconomic Pathways (SSPs), which are a part of the latest set of scenarios on global change developed by the integrated assessment, the IAV (climate change impact, adaptation, and vulnerability assessment), and the climate modeling community. The SSPs depict five global situations based on substantially different socioeconomic conditions during the 21st century. Water use scenarios were developed to reflect not only quantitative socioeconomic factors, such as population and electricity production, but also key qualitative concepts such as the degree of technological change and overall environmental consciousness. Each scenario consists of five factors: irrigated area, crop intensity, irrigation efficiency, and withdrawal-based potential industrial and municipal water demands. The first three factors are used to estimate the potential irrigation water demand. All factors were developed using simple models based on a literature review and analysis of historical records. The factors are grid-based at a spatial resolution of 0.5 • × 0.5 • and cover the whole 21st century in five-year intervals. Each factor shows wide variation among the different global situations depicted: the irrigated area in 2085 varies between 2.7 × 10 6 and 4.5 × 10 6 km 2 , withdrawal-based potential industrial water demand between 246 and 1714 km 3 yr −1 , and municipal water between 573 and 1280 km 3 yr −1. The water use scenarios can be used for global water scarcity assessments that identify the regions vulnerable to water scarcity and analyze the timing and magnitude of scarcity conditions.

Impact of socio-economic development and climate change on water resources and water stress

The global water model WaterGAP was applied to analyze the combined effects of climate change and socio-economic driving forces on the future distribution of the world's freshwater resources, the human water demand and the occurrence of water stress. A total number of four scenarios was applied, the IPCC A2 and B2 scenarios from the 'Dialogue on Water and Climate' project and the Order from Strength and Techno Garden scenarios from the 'Millennium Ecosystem Assessment'. The results clearly demonstrate that the effects of population growth, economic development, increase in water use efficiency and other driving forces on water stress can not be neglected in comparison with the impacts of climate change. Between current conditions and the 2050s, a strong increase in water stress is projected for major parts of the globe. The four scenarios show similar trends, however differences occur between the future spatial extent of water stress (as a consequence of different scenario assumptions). The principal cause of increasing water stress is growing water withdrawals while decreasing water stress (where it occurs) is mainly related to increasing water availability due to climate change.

Water Availability and Global Land Use Change

2012

The dual stressors of surging water demand and climate-induced variable water supply signal that global economy is entering an era of water scarcity. Under the scenario of average economic growth with no efficiency gains, global water requirements by 2030 would grow from 4,500 billion m3 today to 6,900 billion m3, which is a full 40 percent above current accessible, reliable supply (Addams, et al. 2009).