title: Nonrainfall water origins and formation mechanisms.
abstract: 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 (2H,18O, and17O) 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 the17O-18O 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.
authors.affiliation: Department of Earth Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA.
authors.forename: Kudzai Farai
authors.identifier: 0000-0002-3856-0711
authors.initials: KF
authors.lastname: Kaseke
authors.affiliation: Department of Earth Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA.
authors.forename: Lixin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Desert Research Foundation of Namibia, 7 Rossini Street, Windhoek, Namibia.; Gobabeb Research and Training Centre, Walvis Bay, Namibia.
authors.forename: Mary K
authors.identifier: 0000-0002-0594-1294
authors.initials: MK
authors.lastname: Seely
keywords: 17O; 18O; deuterium; dew; ecohydrology; fog, desert; groundwater; stable isotopes