Quantifying recycled moisture fraction in precipitation of an arid region using deuterium excess

Abstract

Terrestrial moisture recycling by evapotranspiration has recently been recognised as an important source of precipitation that can be characterised by its isotopic composition. Up to now, this isotope technique has mainly been applied to moisture recycling in some humid regions, including Brazil, Great Lakes in North America and the European Alps. In arid and semi-arid regions, the contribution of transpiration by plants to local moisture recycling can be small, so that evaporation by bare soil and surface water bodies dominates. Recognising that the deuterium excess (d-excess) of evaporated moisture is significantly different from that of the original water, we made an attempt to use this isotopic parameter for estimating moisture recycling in the semi-arid region of Eastern Tianshan, China. We measured the d-excess of samples taken from individual precipitation events during a hydrological year from 2003 to 2004 at two Tianshan mountain stations, and we used long-term monthly average values of the d-excess for the station Urumqi, which are available from the International Atomic Energy Agency–World Meteorological Organization (IAEA–WMO) Global Network of Isotopes in Precipitation (GNIP). Since apart from recycling of moisture from the ground, sub-cloud evaporation of falling raindrops also affects the d-excess of precipitation, the measured values had to be corrected for this evaporation effect. For the selected stations, the sub-cloud evaporation was found to change between 0.1 and 3.8%, and the d-excess decreased linearly with increasing sub-cloud evaporation at about 1.1‰ per 1% change of sub-cloud evaporation. Assuming simple mixing between advected and recycled moisture, the recycled fraction in precipitation has been estimated to be less than 2.0±0.6% for the Tianshan mountain stations and reach values up to 15.0±0.7% in the Urumqi region. The article includes a discussion of these findings in the context of water cycling in the studied region

Controls on Deuterium Excess across Asia

“…Accordingly, d-excess is used to constrain both the source of precipitation and the conditions during vapor transport [3][4][5][6].…”

Factors controlling stable isotope composition of precipitation in arid conditions: an observation network in the Tianshan Mountains, central Asia

“…Hou et al, 1999;Yao et al, 1999;Zhang et al, 2003;Pang et al, 2011;Feng et al, 2013;Kong et al, 2013). This region provides an important platform to investigate hydrological processes occurring in an endorheic drainage basin in an arid climate; a good understanding of the isotopes in rainfall of the region is helpful for paleoclimate reconstruction using ice cores and speleothems as well as local water resource management during water shortages.…”

Comparison of GCM-simulated isotopic compositions of precipitation in arid central Asia

“…In arid central Asia, the existing isotopic studies showed that the hydrogen and oxygen isotopes in precipitation were mainly controlled by air temperature (also known as temperature effect), instead of precipitation amount (Yao et al, 1999;Feng et al, 2013;Liu et al, 2014). The extremely arid condition may influence below-cloud secondary evaporation and local moisture recycling (Pang et al, 2011;Kong et al, 2013).…”