Abstract
Abstract. 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 (T) and run-off (q), to maximise inter-belt differences and minimise intra-belt variability. 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 T and q 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. Hydroregions (median size 4.7 M km2) are highly contrasted, with the average q ranging between 6 and 1393 mm yr−1 and the average T between −9.7 and +26.3 °C, and a population density ranging from 0.7 to 0.8 p km−2 for the North American boreal region and some Australian hydroregions to 280 p km−2 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. 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 geotypes.net.
Highlights
Mapping global water resources was first done for precipitation and run-off; the maps were at a very coarse resolution due to sparsely available data, a lack of global models and a lack of satellite imagery
The re-aggregation of the world’s river basins results in we present the hydrophysical characteristics a definition for 246 hydrological entities; these entities are of the hydrobelts, the limitations of their delineation limited by the natural drainage area limits
Many differences are noted as (i) the overestimation of population living in cold areas, when Eastern Europe is mixed with Siberia, and the population living with run-off less than 20 mm yr−1; (ii) a biased message provided for highly heterogeneous regions/countries in Australia, Northern America or South America
Summary
Mapping global water resources was first done for precipitation and run-off; the maps were at a very coarse resolution due to sparsely available data, a lack of global models and a lack of satellite imagery. Natural hydrological boundaries, which delineate rivers basins, are often stated to be more appropriate to analyse a society’s water consumption behaviour and manage its water-related issues (Millennium Ecosystem Assessment, 2005; World Water Assessment Programme, 2009) We postulate that both the analysis and tabulation of multiple water-related issues is better performed when using defined permanent spatial entities, when done on a global scale, rather than traditional reporting scales.
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