Biotic pump of atmospheric moisture as driver of the hydrological cycle on land

Abstract

Abstract. 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 Correspondence to: A. M. Makarieva (elba@infopro.spb.su) 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.

Where do winds come from? A new theory on how water vapor condensation influences atmospheric pressure and dynamics

“…Some have been discussed in previous papers, for example with regard to the development of hurricanes (Makarieva and Gorshkov, 2009a,b) and the significance of vegetation and terrestrial evaporation fluxes in determining large scale continental weather patterns (Makarieva et al, 2006Makarieva and Gorshkov, 2007;Sheil and Murdiyarso, 2009). Recently accumulated evidence directly documents air flows induced by the phase transitions of water vapor (Chikoore and Jury, 2010).…”

“…Equation (37) shows that the difference between the scale heights h v and h (Eq. 25) of the vertical pressure distributions for water vapor and moist air leads to the appearance of a horizontal pressure gradient of moist air as a whole (Makarieva and Gorshkov, 2007;Gorshkov et al, 2012). This equation contains the ratio of vertical to horizontal velocity.…”

“…In the case of water vapor k v > 0 is caused by a steep vertical temperature gradient that causes vapor to condense (Makarieva and Gorshkov, 2007;Gorshkov et al, 2012, Sect. 3).…”

HESS Opinions "Biological catalysis of the hydrological cycle: life's thermodynamic function"

“…Energy is conserved while the entropy of the universe is augmented, as required by the first and second laws of thermodynamics respectively. Makarieva and Gorshkov (2007) have described a biotic pump that operates as a result of a non-equilibrium vertical distribution of water vapor occurring over heavily transpiring woodland areas. Condensation of water vapor above the forest canopy reduces its partial pressure, leading to a region of low pressure above the forest which then sucks in moistureladen air from neighboring water bodies.…”

How the Biotic Pump links the hydrological cycle and the rainforest to climate: Is it for real? How can we prove it?

“…The im-plications of the Russian theory are important for a wide range of scientific fields as it involves the global regulation and distribution of water, and not least an association with the physiology of different types of vegetation. In effect, Makarieva and Gorshkov propose that forest cover can, by means of moisture evaporation and condensation, generate the large-scale pressure gradients, that create the ocean-to-land moisture convergence that supplies rainfall across continents, contingent on there being sufficient cover of closed canopy forest (Makarieva & Gorshkov, 2007;. Other than emphasizing the fragile equilibrium of tropical rainforests with regards to human-induced deforestation, the theory could potentially provide answers to questions of angiosperm evolution and the relationship between life on Earth and the interior watering of continents.…”