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2017 ; 3
(3
): e1603131
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Nonrainfall water origins and formation mechanisms
#MMPMID28345058
Kaseke KF
; Wang L
; Seely MK
Sci Adv
2017[Mar]; 3
(3
): e1603131
PMID28345058
show ga
Dryland ecosystems cover 40% of the total land surface on Earth and are defined
broadly as zones where precipitation is considerably less than the potential
evapotranspiration. Nonrainfall waters (for example, fog and dew) are the
least-studied and least-characterized components of the hydrological cycle,
although they supply critical amounts of water for dryland ecosystems. The
sources of nonrainfall waters are largely unknown for most systems. In addition,
most field and modeling studies tend to consider all nonrainfall inputs as a
single category because of technical constraints, which hinders prediction of
dryland responses to future warming conditions. This study uses multiple stable
isotopes ((2)H, (18)O, and (17)O) to show that fog and dew have multiple origins
and that groundwater in drylands can be recycled via evapotranspiration and
redistributed to the upper soil profile as nonrainfall water. Surprisingly, the
non-ocean-derived (locally generated) fog accounts for more than half of the
total fog events, suggesting a potential shift from advection-dominated fog to
radiation-dominated fog in the fog zone of the Namib Desert. This shift will have
implications on the flora and fauna distribution in this fog-dependent system. We
also demonstrate that fog and dew can be differentiated on the basis of the
dominant fractionation (equilibrium and kinetic) processes during their formation
using the (17)O-(18)O relationship. Our results are of great significance in an
era of global climate change where the importance of nonrainfall water increases
because rainfall is predicted to decline in many dryland ecosystems.