Comment on "Biotic pump of atmospheric moisture as driver of the hydrological cycle on land" by A. M. Makarieva and V. G. Gorshkov, Hydrol. Earth Syst. Sci., 11, 1013–1033, 2007

In their paper "Biotic pump of atmospheric moisture as driver of the hydrological cycle on land", Makarieva and Gorshkov (Hydrol. Earth Syst. Sci., 11, 1013–1033, 2007) derive from "previously unstudied" properties of atmospheric water vapor, the existence of a hitherto unknown "evaporative force". From this, a novel physical principle is deduced, according to which low-level air flows from regions with weak, to regions with strong evaporation. As such, natural forests are claimed to "suck in" moist air from the ocean, a process labeled the "biotic pump of atmospheric moisture". This commentary focuses on the physical foundations of the Biotic Pump Theory (BPT). It is shown that the "evaporative force" on which the theory is built, is not supported by basic physical principles. The problem of moisture transport and its dependence on vegetation cover considered by Makarieva and Gorshkov is certainly important, but cannot be solved along the lines proposed by them