naa a22 4500 530098512 20181026074614.0 cr unu---uuuuu 181026s2014 xx s 000 0 eng 10.3929/ethz-b-000084481 doi 10.5194/acp-14-4029-2014 doi (ETHRESEARCH)oai:www.research-collection.ethz.ch:20.500.11850/84481 Deuterium excess as a proxy for continental moisture recycling and plant transpiration [Elektronische Daten] [Franziska Aemisegger, Stephan; id_orcid 0000-0002-9872-6090 Pfahl, Harald Sodemann, Irene Lehner, Sonia I.; id_orcid 0000-0001-9528-2917 Seneviratne, Heini; id_orcid 0000-0001-9674-4837 Wernli] Atmos. chem. phys. Open access ethresearch Studying the evaporation process and its link to the atmospheric circulation is central for a better understanding of the feedbacks between the surface water components and the atmosphere. In this study, we use 5 months of deuterium excess (d) measurements at the hourly to daily timescale from a cavity ring-down laser spectrometer to characterise the evaporation source of low-level continental water vapour at the long-term hydrometeorological monitoring site Rietholzbach in northeastern Switzerland. To reconstruct the phase change history of the air masses in which we measure the d signature and to diagnose its area of surface evaporation we apply a Lagrangian moisture source diagnostic. With the help of a correlation analysis we investigate the strength of the relation between d measurements and the moisture source conditions. Temporal episodes with a duration of a few days of strong anticorrelation between d and relative humidity as well as temperature are identified. The role of plant transpiration, the large-scale advection of remotely evaporated moisture, the local boundary layer dynamics at the measurement site and recent precipitation at the site of evaporation are discussed as reasons for the existence of these modes of strong anticorrelation between d and moisture source conditions. We show that the importance of continental moisture recycling and the contribution of plant transpiration to the continental evaporation flux may be deduced from the d-relative humidity relation at the seasonal timescale as well as for individual events. The methodology and uncertainties associated with these estimates of the transpiration fraction of evapotranspiration are presented and the proposed novel framework is applied to individual events from our data set. Over the whole analysis period (August to December 2011) a transpiration fraction of the evapotranspiration flux over the continental part of the moisture source region of 62% is found albeit with a large event-to-event variability (0% to 89%) for continental Europe. During days of strong local moisture recycling a higher overall transpiration fraction of 76% (varying between 65% and 86%) is found. These estimates are affected by uncertainties in the assumptions involved in our method as well as by parameter uncertainties. An average uncertainty of 11% results from the strong dependency of the transpiration estimates on the choice of the non-equilibrium fractionation factor. Other uncertainty sources like the influence of boundary layer dynamics are probably large but more difficult to quantify. Nevertheless, such Lagrangian estimates of the transpiration part of continental evaporation could potentially be useful for the verification of model estimates of this important land-atmosphere coupling parameter. Creative Commons Attribution 3.0 Unported http://creativecommons.org/licenses/by/3.0 ethresearch Aemisegger Franziska joint author Pfahl Stephan; id_orcid 0000-0002-9872-6090 joint author Sodemann Harald joint author Lehner Irene joint author Seneviratne Sonia I.; id_orcid 0000-0001-9528-2917 joint author Wernli Heini; id_orcid 0000-0001-9674-4837 joint author Atmospheric Chemistry and Physics Göttingen : Copernicus 14 (8), pp. 4029-4054 1680-7375 http://hdl.handle.net/20.500.11850/84481 text/html WWW-Backlink auf das Repository (Open access) 1 Journal Article ethresearch ETHRESEARCH 856 40 http://hdl.handle.net/20.500.11850/84481 text/html WWW-Backlink auf das Repository (Open access) ETHRESEARCH 700 1- Aemisegger Franziska joint author ETHRESEARCH 700 1- Pfahl Stephan; id_orcid 0000-0002-9872-6090 joint author ETHRESEARCH 700 1- Sodemann Harald joint author ETHRESEARCH 700 1- Lehner Irene joint author ETHRESEARCH 700 1- Seneviratne Sonia I.; id_orcid 0000-0001-9528-2917 joint author ETHRESEARCH 700 1- Wernli Heini; id_orcid 0000-0001-9674-4837 joint author ETHRESEARCH 773 0- Atmospheric Chemistry and Physics Göttingen : Copernicus 14 (8), pp. 4029-4054 1680-7375 BK010053 XK010053 XK010000 ETHRESEARCH ETHRESEARCH ETHRESEARCH Journal Article Open access