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| Titel |
Biotic pump of atmospheric moisture as driver of the hydrological cycle on land |
| VerfasserIn |
A. M. Makarieva, V. G. Gorshkov |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 11, no. 2 ; Nr. 11, no. 2 (2007-03-27), S.1013-1033 |
| Datensatznummer |
250009230
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| Publikation (Nr.) |
 copernicus.org/hess-11-1013-2007.pdf |
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| Zusammenfassung |
| In this paper the basic geophysical and ecological principles are jointly
analyzed that allow the landmasses of Earth to remain moistened
sufficiently for terrestrial life to be possible. 1. Under gravity, land
inevitably loses water to the ocean. To keep land moistened, the
gravitational water runoff must be continuously compensated by the
atmospheric ocean-to-land moisture transport. Using data for five
terrestrial transects of the International Geosphere Biosphere Program we
show that the mean distance to which air fluxes
can transport moisture over non-forested areas, does not exceed several
hundred kilometers; precipitation decreases exponentially with distance
from the ocean. 2. In contrast, precipitation over extensive natural
forests does not depend on the distance from the ocean along several
thousand kilometers, as illustrated for the Amazon and Yenisey river
basins and Equatorial Africa. This points to the existence of an active
biotic pump transporting atmospheric moisture inland from the ocean. 3. Physical
principles of the biotic moisture pump are investigated based on
the previously unstudied properties of atmospheric water vapor, which can
be either in or out of aerostatic equilibrium depending on the lapse
rate of air temperature. A novel physical principle is formulated
according to which the low-level air moves from areas with weak
evaporation to areas with more intensive evaporation. Due to the high
leaf area index, natural forests maintain high evaporation fluxes,
which support the ascending air motion over the forest and "suck in"
moist air from the ocean, which is the essence of the biotic pump of
atmospheric moisture. In the result, the gravitational runoff water
losses from the optimally moistened forest soil can be fully compensated
by the biotically enhanced precipitation at any distance from the ocean.
4. It is discussed how a continent-scale biotic water pump mechanism
could be produced by natural selection acting on individual trees. 5. Replacement
of the natural forest cover by a low leaf index vegetation
leads to an up to tenfold reduction in the mean continental precipitation
and runoff, in contrast to the previously available estimates made
without accounting for the biotic moisture pump. The analyzed body of
evidence testifies that the long-term stability of an intense terrestrial
water cycle is unachievable without the recovery of natural,
self-sustaining forests on continent-wide areas. |
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