Contrasting roles of interception and transpiration in the hydrological cycle – Part 2: Moisture recycling

Abstract

Abstract. The contribution of land evaporation to local and remote precipitation (i.e. moisture recycling) is of significant importance to sustain water resources and ecosystems. But how important are different evaporation components in sustaining precipitation? This is the first paper to present moisture recycling metrics for partitioned evaporation. In the companion paper Wang-Erlandsson et al. (2014) (hereafter Part 1), evaporation was partitioned into vegetation interception, floor interception, soil moisture evaporation and open-water evaporation (constituting the direct, purely physical fluxes, largely dominated by interception), and transpiration (delayed, biophysical flux). Here, we track these components forward as well as backward in time. We also include age tracers to study the atmospheric residence times of these evaporation components. We present a new image of the global hydrological cycle that includes quantification of partitioned evaporation and moisture recycling as well as the atmospheric residence times of all fluxes. We demonstrate that evaporated interception is more likely to return as precipitation on land than transpired water. On average, direct evaporation (essentially interception) is found to have an atmospheric residence time of 8 days, while transpiration typically resides for 9 days in the atmosphere. The process scale over which evaporation recycles is more local for interception compared to transpiration; thus interception generally precipitates closer to its evaporative source than transpiration, which is particularly pronounced outside the tropics. We conclude that interception mainly works as an intensifier of the local hydrological cycle during wet spells and wet seasons. On the other hand, transpiration remains active during dry spells and dry seasons and is transported over much larger distances downwind, where it can act as a significant source of moisture. Thus, as various land-use types can differ considerably in their partitioning between interception and transpiration, our results stress that land-use changes (e.g. forest-to-cropland conversion) do not only affect the magnitude of moisture recycling, but could also influence the moisture recycling patterns and lead to a redistribution of water resources. As such, this research highlights that land-use changes can have complex effects on the atmospheric branch of the hydrological cycle.

A revised picture of the atmospheric moisture residence time

“…A first hint to the controversy provide van der Ent and Savenije [2011] by referencing Bosilovich et al [2002] with the statement that "actual residence times should be calculated by taking a Lagrangian approach." Using moisture age tracers in a simple two-layer water accounting model, van der Ent et al [2014] recently obtained that moisture lifetimes over the continents substantially differ from depletion time constants from van der Ent and Savenije [2011] in some regions of the world, e.g., Newfoundland and Australia. In a water vapor tracer study, Winschall et al [2012] argue that moisture from North Atlantic evaporation hot spots (areas of latent heat fluxes 250 W m −2 ) is "typically transported toward Europe within one to four days" before it precipitates.…”

Aerial and surface rivers: downwind impacts on water availability from land use changes in Amazonia

“…Since the 1960s, there has been substantial clearing of the Amazon forest for agricultural purposes; about 15 % of the Brazilian Amazon rainforest has been cleared (INPE, 2017). Deforested areas are most often (80 %; Veiga et al, 2002) used as pastureland. Rice, cassava, maize, and soybean cropping have also driven deforestation Barona et al, 2010).…”

Atmospheric residence times from transpiration and evaporation to precipitation: An age‐weighted regional evaporation tagging approach

“…The response of the hydrological cycle to the climate regime can be studied by investigating, for example, the relationship between evaporation (E) and precipitation (P), particularly the atmospheric water residence time, here defined as time between the original evaporation and the returning of its respective water masses to the land surface as precipitation. This concept is used in various studies [Trenberth, 1998;Numaguti, 1999;James, 2003;van der Ent and Savenije, 2011;Tuinenburg et al, 2012;Wang-Erlandsson et al, 2014;van der Ent et al, 2014;Läderach and Sodemann, 2016]. It provides additional information on the timescales of evaporation and precipitation and reflects the complexity of the atmospheric water pathways and the phase changes including the formation of precipitation.…”

“…These and similar other modeling studies either have been conducted on large scales with a coarse resolution or have used relatively simple schemes for atmospheric dynamical and physical processes. This may limit the accuracy of estimates of atmospheric residence times, e.g., due to an inadequate representation of the complex atmospheric features, especially, when directional wind shear is present or strong moist convection happens [Goessling and Reick, 2013;van der Ent et al, 2013].…”

“…To overcome these difficulties, sophisticated three-dimensional regional climate models (RCMs) with a built-in evaporation tagging (E-Tagging) algorithm are suitable for local-scale moisture tracking studies over a monsoon-controlled region van der Ent et al [2013]. An E-Tagging algorithm was firstly implemented in a RCM by Sodemann et al [2009].…”