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      Global hydrobelts and hydroregions: improved reporting scale for water-related issues?

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      Hydrology and Earth System Sciences

      Copernicus GmbH

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          Abstract

          <p><strong>Abstract.</strong> Global-scale water issues such as its availability, water needs or stress, or management, are mapped at various resolutions and reported at many scales, mostly along political or continental boundaries. As such, they ignore the fundamental heterogeneity of hydroclimates and natural boundaries of river basins. Here we describe the continental landmasses at two levels: eight hydrobelts strictly limited by river basins, defined at a 30' (0.5°) resolution, which are decomposed on continents as 26 hydroregions. The belts were defined and delineated, based primarily on the annual average temperature (<i>T</i>) and run-off (<i>q</i>), to maximise inter-belt differences and minimise intra-belt variability. <br><br> This new global puzzle defines homogeneous and near-contiguous entities with similar hydrological and thermal regimes, glacial and postglacial basin histories, endorheism distribution and sensitivity to climate variations. The mid-latitude, dry and subtropical belts have northern and southern analogues and a general symmetry can be observed for <i>T</i> and <i>q</i> between them. The boreal and equatorial belts are unique. Population density between belts and between the continents varies greatly, resulting in pronounced differences between the belts with analogues in both hemispheres. <br><br> Hydroregions (median size 4.7 M km<sup>2</sup>) are highly contrasted, with the average <i>q</i> ranging between 6 and 1393 mm yr<sup>−1</sup> and the average <i>T</i> between −9.7 and +26.3 °C, and a population density ranging from 0.7 to 0.8 p km<sup>−2</sup> for the North American boreal region and some Australian hydroregions to 280 p km<sup>−2</sup> for some Asian hydroregions. The population/run-off ratio, normalised to a reference pristine region, is used to map and quantify the global population at risk of severe water quality degradation. Our initial tests suggest that hydrobelt and hydroregion divisions are often more appropriate than conventional continental or political divisions for the global analysis of river basins within the Earth system and of water resources. <br><br> The GIS files of the hydrobelts and hydroregions are available at the supplement of this article and at doi:10.1594/PANGAEA.806957 as well as <a href="geotypes.net"target="_blank">geotypes.net</a>.</p>

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          Most cited references 39

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          Very high resolution interpolated climate surfaces for global land areas

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            Global threats to human water security and river biodiversity.

            Protecting the world's freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the world's population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.
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              Global hydrological cycles and world water resources.

              Water is a naturally circulating resource that is constantly recharged. Therefore, even though the stocks of water in natural and artificial reservoirs are helpful to increase the available water resources for human society, the flow of water should be the main focus in water resources assessments. The climate system puts an upper limit on the circulation rate of available renewable freshwater resources (RFWR). Although current global withdrawals are well below the upper limit, more than two billion people live in highly water-stressed areas because of the uneven distribution of RFWR in time and space. Climate change is expected to accelerate water cycles and thereby increase the available RFWR. This would slow down the increase of people living under water stress; however, changes in seasonal patterns and increasing probability of extreme events may offset this effect. Reducing current vulnerability will be the first step to prepare for such anticipated changes.
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                Author and article information

                Journal
                Hydrology and Earth System Sciences
                Hydrol. Earth Syst. Sci.
                Copernicus GmbH
                1607-7938
                2013
                March 13 2013
                : 17
                : 3
                : 1093-1111
                10.5194/hess-17-1093-2013
                © 2013

                https://creativecommons.org/licenses/by/3.0/

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