Seasonal precipitation patterns along pathways of South

American low-level jets and aerial rivers

Germán Poveda, Liliana Jaramillo, Luisa F. Vallejo

1.4. The Biotic Pump Theory

The biotic pump of atmospheric moisture (BiPAM) theory was introduced by Makarieva and Gorshkov [2007, 2010] and Makarieva et al. [2009]. It states that the atmospheric circulation is driven by atmospheric pressure gradients, which in turn are set forth by condensation of the water vapor evapotranspired from forests. As such, the theory assigns a central role to forests in maintaining the ocean-to-land atmospheric circulation. A central argument in support of the BiPAM concept is that in forest-covered regions, annual precipitation does not decline with increasing distance from the ocean and may even grow as one proceeds several thousand kilometers inland, whereas, in contrast, where forests are lacking, precipitation decreases with an exponential length scale of a few hundred kilometers [Makarieva and Gorshkov, 2007; Sheil and Murdiyarso, 2009; Makarieva et al., 2009, 2013b]. A recent study by the same team of authors [Makarieva et al., 2013a] investigated the spatial distribution of long-term mean annual precipitation over the Amazon along a diagonal transect from the Atlantic Ocean to the Andes (0°S 50°W, 7.5°S 81.5°W). Those authors state that in year-round active tropical forests, the biotic pump should control annual precipitation, and conclude that annual precipitation in the Amazon forest remains approximately constant from coast to interior.

If finally proven correct, the BiPAM theory would constitute a major breakthrough to understand fundamental processes in atmospheric sciences, hydrology, meteorology, ecology, climatology, and plant and soil sciences, among others. As such, it has been submitted to thorough scrutiny by the scientific community, evidenced in the online discussions of the original paper by Makarieva and Gorshkov [2007], and their reply by the authors (http://www.hydrol-earth-syst-sci-discuss.net/3/2621/2006/ hessd-3–2621-2006-discussion.html). Another paper led by the same team of authors has been recently published containing an unusual comment by the Editor about the controversial status of this new theoretical framework [Makarieva et al., 2013b]. Therefore, here we aim at testing whether the spatial distribution of observed seasonal rainfall intensities along main pathways of South American ARs east of the Andes conforms to BiPAM’s theory and predictions. In particular, we are interested in testing whether seasonal rainfall decreases, increases, or remains constant over forested areas of tropical and subtropical South America.

(https://agupubs.onlinelibrary.wiley.com/doi/full/10.

1002/2013WR014087. Adaptado)