Biotic pump of atmospheric moisture: A conceptual model

The Biotic Pump Theory, as described by Drs. Makarieva and Gorshkov (M&G), defines the mechanism by which water vapour is transported from areas of low evaporation to areas of high evaporation, conveniently termed “donor” and “acceptor” regions, respectively, and where only the latter exhibits condensation. The implications of such a theory are critical, especially to moisture regulation of tropical rainforests, yet highly controversial. Unfortunately, most of the theory’s physics cannot be evaluated due to the lack of atmospheric observations over such areas. This study aims at building a conceptual model of the theory over the Amazon basin as to quantitatively assess the existence and determine the properties of donor and acceptor regions statistically through their respective condensation rates. The model uses the predictive capabilities of Time-Delayed Neural Networks to downscale available atmospheric observations to calculate condensation rates at a scale suited for this analysis. Validation of the downscaling model reveals monthly Mean Absolute Errors to range between 0.022 m s-1 and 2.76 m s-1 in the predictions of vertical velocity and zonal wind speed, respectively. Findings quantitatively support the existence of a biotic mechanism regulating the transport of water vapour as these clearly show the presence of donor and acceptor regions. These regions have average spatial distributions of 42% - 58%, respectively, over the whole study area and correlations are found between wind speeds and condensation rates. Mean annual condensation rate for the Amazon basin is calculated to be of 0.23E-06 mol m-3 s-1. Results also show an increase in average condensation rate (0.06E-06 mol m-3 s-1) for the last 9 years, which does not strictly adhere to M&G’s views on the impacts of deforestation on precipitation. Outcomes hence also suggest a more complex relationship between evaporation and condensation, and therefore highlight the necessity to further refine this novel theory