Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen OPUS4-52410 Wissenschaftlicher Artikel Porada, Philipp; Van Stan, John T.; Kleidon, Axel Significant contribution of non-vascular vegetation to global rainfall interception Non-vascular vegetation has been shown to capture considerable quantities of rainfall, which may affect the hydrological cycle and climate at continental scales. However, direct measurements of rainfall interception by non-vascular vegetation are confined to the local scale, which makes extrapolation to the global effects difficult. Here we use a process-based numerical simulation model to show that non-vascular vegetation contributes substantially to global rainfall interception. Inferred average global water storage capacity including non-vascular vegetation was 2.7 mm, which is consistent with field observations and markedly exceeds the values used in land surface models, which average around 0.4 mm. Consequently, we find that the total evaporation of free water from the forest canopy and soil surface increases by 61% when non-vascular vegetation is included, resulting in a global rainfall interception flux that is 22% of the terrestrial evaporative flux (compared with only 12% for simulations where interception excludes non-vascular vegetation). We thus conclude that non-vascular vegetation is likely to significantly influence global rainfall interception and evaporation with consequences for regional-to continental-scale hydrologic cycling and climate. New York Nature Publ. Group 2018 7 Nature geoscience 11 8 563 + 10.1038/s41561-018-0176-7 Institut für Biochemie und Biologie OPUS4-43567 Wissenschaftlicher Artikel Porada, Philipp; Tamm, Alexandra; Raggio, Jose; Yafang, Cheng; Kleidon, Axel; Pöschl, Ulrich; Weber, Bettina Global NO and HONO emissions of biological soil crusts estimated by a process-based non-vascular vegetation model The reactive trace gases nitric oxide (NO) and nitrous acid (HONO) are crucial for chemical processes in the atmosphere, including the formation of ozone and OH radicals, oxidation of pollutants, and atmospheric self-cleaning. Recently, empirical studies have shown that biological soil crusts are able to emit large amounts of NO and HONO, and they may therefore play an important role in the global budget of these trace gases. However, the upscaling of local estimates to the global scale is subject to large uncertainties, due to unknown spatial distribution of crust types and their dynamic metabolic activity. Here, we perform an alternative estimate of global NO and HONO emissions by biological soil crusts, using a process-based modelling approach to these organisms, combined with global data sets of climate and land cover. We thereby consider that NO and HONO are emitted in strongly different proportions, depending on the type of crust and their dynamic activity, and we provide a first estimate of the global distribution of four different crust types. Based on this, we estimate global total values of 1.04 Tg yr⁻¹ NO-N and 0.69 Tg yr⁻¹ HONO-N released by biological soil crusts. This corresponds to around 20% of global emissions of these trace gases from natural ecosystems. Due to the low number of observations on NO and HONO emissions suitable to validate the model, our estimates are still relatively uncertain. However, they are consistent with the amount estimated by the empirical approach, which confirms that biological soil crusts are likely to have a strong impact on global atmospheric chemistry via emissions of NO and HONO. Göttingen Copernicus Publ. 2019 29 Biogeosciences 16 2003 2031 10.5194/bg-16-2003-2019 Institut für Biochemie und Biologie OPUS4-38198 Wissenschaftlicher Artikel Zehe, E.; Ehret, U.; Pfister, L.; Blume, Theresa; Schroeder, Boris; Westhoff, M.; Jackisch, C.; Schymanski, Stanislauv J.; Weiler, M.; Schulz, K.; Allroggen, Niklas; Tronicke, Jens; van Schaik, Loes; Dietrich, Peter; Scherer, U.; Eccard, Jana; Wulfmeyer, Volker; Kleidon, Axel HESS Opinions: From response units to functional units: a thermodynamic reinterpretation of the HRU concept to link spatial organization and functioning of intermediate scale catchments According to Dooge (1986) intermediate-scale catchments are systems of organized complexity, being too organized and yet too small to be characterized on a statistical/conceptual basis, but too large and too heterogeneous to be characterized in a deterministic manner. A key requirement for building structurally adequate models precisely for this intermediate scale is a better understanding of how different forms of spatial organization affect storage and release of water and energy. Here, we propose that a combination of the concept of hydrological response units (HRUs) and thermodynamics offers several helpful and partly novel perspectives for gaining this improved understanding. Our key idea is to define functional similarity based on similarity of the terrestrial controls of gradients and resistance terms controlling the land surface energy balance, rainfall runoff transformation, and groundwater storage and release. This might imply that functional similarity with respect to these specific forms of water release emerges at different scales, namely the small field scale, the hillslope, and the catchment scale. We thus propose three different types of "functional units" - specialized HRUs, so to speak - which behave similarly with respect to one specific form of water release and with a characteristic extent equal to one of those three scale levels. We furthermore discuss an experimental strategy based on exemplary learning and replicate experiments to identify and delineate these functional units, and as a promising strategy for characterizing the interplay and organization of water and energy fluxes across scales. We believe the thermodynamic perspective to be well suited to unmask equifinality as inherent in the equations governing water, momentum, and energy fluxes: this is because several combinations of gradients and resistance terms yield the same mass or energy flux and the terrestrial controls of gradients and resistance terms are largely independent. We propose that structurally adequate models at this scale should consequently disentangle driving gradients and resistance terms, because this optionally allow sequifinality to be partly reduced by including available observations, e. g., on driving gradients. Most importantly, the thermodynamic perspective yields an energy-centered perspective on rainfall-runoff transformation and evapotranspiration, including fundamental limits for energy fluxes associated with these processes. This might additionally reduce equifinality and opens up opportunities for testing thermodynamic optimality principles within independent predictions of rainfall-runoff or land surface energy exchange. This is pivotal to finding out whether or not spatial organization in catchments is in accordance with a fundamental organizing principle. Göttingen Copernicus 2014 21 Hydrology and earth system sciences : HESS 18 11 4635 4655 10.5194/hess-18-4635-2014 Institut für Geowissenschaften