Origin and fate of atmospheric moisture over continents

Abstract

[1] There has been a long debate on the extent to which precipitation relies on terrestrial evaporation (moisture recycling). In the past, most research focused on moisture recycling within a certain region only. This study makes use of new definitions of moisture recycling to study the complete process of continental moisture feedback. Global maps are presented identifying regions that rely heavily on recycled moisture as well as those that are supplying the moisture. An accounting procedure based on ERA-Interim reanalysis data is used to calculate moisture recycling ratios. It is computed that, on average, 40% of the terrestrial precipitation originates from land evaporation and that 57% of all terrestrial evaporation returns as precipitation over land. Moisture evaporating from the Eurasian continent is responsible for 80% of China's water resources. In South America, the Río de la Plata basin depends on evaporation from the Amazon forest for 70% of its water resources. The main source of rainfall in the Congo basin is moisture evaporated over East Africa, particularly the Great Lakes region. The Congo basin in its turn is a major source of moisture for rainfall in the Sahel. Furthermore, it is demonstrated that due to the local orography, local moisture recycling is a key process near the Andes and the Tibetan Plateau. Overall, this paper demonstrates the important role of global wind patterns, topography and land cover in continental moisture recycling patterns and the distribution of global water resources.

Relating seasonal dynamics of enhanced vegetation index to the recycling of water in two endorheic river basins in north-west China

“…time series one) can consistently approximate the state in a second variable (time series two). The method is able to provide reliable description of causality even in the presence of system feedback and confoundedness (Sugihara et al, 2012). Moreover, convergent cross-mapping involves convergence, an important methodological attribute that differentiates causation from ordinary correlation (Maher and Hernandez, 2015).…”

“…Correlation is employed in this study primarily to establish the strength of association between paired combinations of state variables to help form an initial description of potentially relevant ecohydrometeorological relationships. Recent advances in dynamic-systems analysis have resulted in the development of innovative methods for identifying causality in time series data (Sugihara et al, 2012). One such method, convergent cross-mapping, is a model-free ap- proach that helps identify causality and direction of causality in dynamically evolving systems.…”

“…It is always possible to get bi-directional convergence when variables are strongly forced by an external third variable, resulting in synchrony between variables being assessed. Synchrony should be tested for convergent cross-mapping to determine bi-directional pairing (Sugihara et al, 2012;Clark et al, 2015). When synchrony exists, it can sometimes be minimised by processing the "first difference" of cross-correlated variables by subtracting previous observations (at time t − 1) from current observations (at t) in the original time series prior to performing the analysis (Granger and Newbold, 1974).…”

“…When curves for both variables are convergent (as is the case here), bi-directional causality and, thus, feedback is indicated. Analyses are based on embedded dimensions and time delays of 4 and 1, respectively (Sugihara et al, 2012). supporting plant biochemical processes (∼ 1-5 % of available water). As plants produce leaf biomass, increasing leafsurface area (and, thus, enhanced vegetation index), transpirational fluxes become stronger providing that solar irradiation, atmospheric conditions (e.g.…”

“…1). External contribution of moisture to the Hexi Corridor from Europe and western Asia (Warner, 2004;van der Ent et al, 2010) is anticipated to be low and of marginal importance to the localised recycling of water in west-central Gansu.…”