Prof. Dr. Andreas Christen

Biography

From 1995 to 2000, Andreas Christen studied Geography with minors in Chemistry, Earth Sciences and Meteorology at the University of Basel, Switzerland. In 2005 he received his PhD in Meteorology from the University of Basel with a dissertation on "atmospheric turbulence and surface energy exchange in urban environments" (under the supervision of Prof. Eberhard Parlow and Prof. Mathias Rotach). In 2005/06 he was post-doctoral researcher and lecturer at the Institute for Ecology of the Technical University of Berlin in the group of Prof. Dieter Scherer. Between 2006 and 2013 he was appointed assistant professor and from 2013 to 2017 associate professor in Geography and the Atmospheric Science Program at the University of British Columbia, Vancouver, Canada, where he also led the “Laboratory for Atmospheric Research on Greenhouse Gas Exchange”. In 2012/13 he was visiting professor in the lab of Prof. Marc B. Parlange at the École Polytechnique Fédérale de Lausanne (EPFL), Switzerland. Since 2017 he is Full Professor in Environmental Meteorology at the University of Freiburg and heads the chair of Environmental Meteorology in the Faculty of Environment and Natural Resources.

Research

Working the field of environmental meteorology, Christen and his team measure and model the effect of environmental changes on weather and climate. They investigate and describe the coupling between land surfaces and the atmosphere in the climate system, with emphasis on the near-surface wind field and turbulence, the exchange of trace gases and of  urban climate effects. The outcomes of this research will allow improved assessments and scenarios on how cities, forests, and other land surfaces behave in a changing climate and how changes in land surface dynamics affect the climate system in reverse. A core interest of Andreas Christen is the development of new micrometeorological measurement methods, analysis and prediction techniques.

Current Research Projects

• CATRINE - Carbon Atmospheric Tracer Research to Improve Numerical schemes and Evaluation (EU HORIZON) 
• ECOSENSE (DFG SFB)
• Hartheim Research Forest ICOS Site
• PAUL "Pilot Application in Urban Landscapes – towards integrated city observatories for greenhouse gases" / ICOS Cities (EU H2020)
• Urban Air (EU HORIZON)
• urbisphere (ERC Synergy Grant)

Selected Past Research Projects

• Clim’Ability Design (EFRE INTERREG)
• I4C - Intelligence for Cities (KI-Leuchttürme, BMU)
• Namib Turbulence EXperiment (NamTEX

Current and Past Offices

• Associate Dean of the Faculty of Environment and Natural Resources, University of Freiburg (2024-).
• Co-Speaker of the Institute of Earth and Environmental Sciences, University of Freiburg (2020-2021).
• Director of the M.Sc. Program in Environmental Sciences, University of Freiburg.
• Secretary of the International Association for Urban Climate (IAUC), 2018-2022.

Editorial board memberships

• Editorial Board Member "Boundary-Layer Meteorology" (2013-2023)
• Editorial Board Member "Theoretical and Applied Climatology" 

Awards

• Graham K. Walker Award, Canadian Society of Agricultural and Forest Meteorology, 2017
• Amerbach-Preis, Preis der Universität, University of Basel, 2005

Recent Publications

Textbooks

• Oke TR, Mills G, Christen A, Voogt JA 2017: Urban Climates, Cambridge University Press, ISBN 978-11-074-2953-6

Articles in peer-reviewed journals

• Exler J, Skeeter J, Christen A, Moore RD, 2025: Interannual climatic sensitivity of surface energy flux densities and evapotranspiration in a disturbed and rewetted ombrotrophic bog. Agricultural and Forest Meteorology, 367, 110501.
• Feigel G, Plein M, Zeeman M, Metzger S, Matzarakis A, Schindler D, Christen A, 2025: High spatio-temporal and continuous monitoring of outdoor thermal comfort in urban areas: a generic and modular sensor network and outreach platform. Sustainable Cities and Society, 119, 105991.
• Haberstroh S, Scarpa F, Seeger S, Christen A, Werner C, 2025: Continuous stem water potential measurements of a diffuse-porous tree species offer new insights into tree water relations. Ecohydrology, 18: e2761. 
• Shevchenko O, Sulzer M, Christen A, Matzarakis A, 2025: Coupling Indoor and Outdoor Heat Stress During the Hot Summer of 2022: A Case Study of Freiburg, Germany. Atmosphere 16 (2)
• Briegel F, Wehrle J, Schindler D, Christen A, 2024: High-resolution multi-scaling of outdoor human thermal comfort and its intra-urban variability based on machine learning. Geoscientific Model Development, 17, 1667-1688.
• Dogan Ciftci N, Şahin AD, Yousefpour R, Christen A, 2024: Effects of climate trends and variability on tree health responses in the Black Sea and Mediterranean forests of Türkiye. Theor Appl Climatol. 155, 3969–3991.
• Fenner D, Christen A, Grimmond CSB, Meier F, Morrison W, Zeeman M, Barlow J, Birkmann J, Blunn L, Chrysoulakis N, Clements M, Glazer R, Hertwig D, Kotthaus S, König K, Looschelders D, Mitraka Z, Poursanidis D, Tsirantonakis D, Bechtel B, Benjamin K, Beyrich F, Briegel F, Feigel G, Gertsen C, Iqbal N, Kittner J, Lean H, Liu Y, Luo Z, McGrory M, Metzger S, Paskin M, Ravan M, Ruhtz T, Saunders B, Scherer D, Smith ST, Stretton M, Trachte K, Van Hove M, 2024: urbisphere -Berlin campaign: Investigating multi-scale urban impacts on the atmospheric boundary layer, Bulletin of the American Meteorological Society, 105 (10), E1929–E1961.
• Hilland R,  Christen A, 2024: A Systematic Investigation of the Applicability of Taylor’s Hypothesis in an Idealized Surface Layer. Boundary-Layer Meteorology, 190, 22. 
• Sulzer M, Christen A 2024: Climate projections of human thermal comfort for indoor workplaces. Climatic Change 177, 28. 
• Wu S, Lin X, Bian Z, Lipson M, Lafortezza R, Liu Q, Grimmond S, Velasco E, Christen A, Masson V, Crawford B, Ward HC, Chrysoulakis N, Fortuniak K, Parlow E, Pawlak W, Tapper N,  Hong J, Hong JW, Roth M, An J, Lin C, Chen B, 2024: Satellite observations reveal a decreasing albedo trend of global cities over the past 35 years. Remote Sensing of Environment, 303, 114003
• Zeeman M, Christen A, Grimmond CSB, Fenner D, Morrison W, Feigel G, Sulzer M,  Chrysoulakis N, 2024: Modular approach to near-time data management for multi-city atmospheric environmental observation campaigns. Geoscientific Instrumentation, Methods and Data Systems, 13, 393–424. 
• Briegel F, Makansi O, Brox T, Matzarakis A, Christen A, 2023: Modelling long-term thermal comfort conditions in urban environments using a deep convolutional encoder-decoder as a computational shortcut. Urban Climate, 47, 101359.
• Satriawan TW, Nyberg M, Lee S-C, Christen A, Black TA, Johnson MS, Nesic Z, Merkens M, Knox SH, 2023: Interannual variability of carbon dioxide (CO2) and methane (CH4) fluxes in a rewetted temperate bog. Agricultural and Forest Meteorology, 342 (2023) 109696
• Skeeter J, Christen A, Henry GHR, 2023: Modelling growing season carbon fluxes at a low-center polygon ecosystem in the Mackenzie River Delta. Arctic Science, 9: 689–709.
• Sulzer M, Christen A, Matzarakis A, 2023: Predicting indoor air temperature and thermal comfort in occupational settings using weather forecasts, indoor sensors, and artificial neural networks. Building and Environment, 234, 110077.
• Jongen HJ, Steeneveld GJ, Beringer J, Christen A, Chrysoulakis N, Fortuniak K, Hong J, Hong JW, Jacobs CMJ, Järvi L, Meier F, Pawlak W, Roth M, Theeuwes NE, Velasco E, Vogt R, Teuling AJ, 2022: Urban Water Storage Capacity Inferred From Observed Evapotranspiration Recession. Geophysical Research Letters, 49 (3): e2021GL096069.
• Haberstroh S, Werner C, Grün M, Kreuzwieser J, Seifert T, Schindler D, Christen A, 2022: Central European 2018 hot drought shifts Scots Pine forest to its tipping point. Plant Biology, 24, 1186-1197.
• Hilland RVJ, Bernhofer C, Bohmann M, Christen A, Katurji M, Maggs-Kölling G, Krauß M, Larsen JA, Marais E, Pitacco A, Schumacher B, Spirig R, Vendrame N, Vogt R, 2022: The Namib Turbulence Experiment: Investigating Surface–Atmosphere Heat Transfer in Three Dimensions. Bulletin of the American Meteorological Society, 103 (3) E741–E760.
• Lipson M, Grimmond CSB, Best M, Chow WTL, Christen A, Chrysoulakis N, Coutts A, Crawford B, Earl S, Evans J, Fortuniak K, Heusinkveld BG, Hong J-W, Hong J, Järvi L, Jo S, Kim Y-H, Kotthaus S, Lee K, Masson V, McFadden JP, Michels O, Pawlak W, Roth M, Sugawara H, Tapper N, Velasco E, Ward, HC, 2022: Harmonized gap-filled datasets from 20 urban flux tower sites, Earth Syst. Sci. Data, 14, 5157–5178. 
• Nicolini G, Antoniella G, Carotenuto F, Christen A, Ciais P, Feigenwinter C, Gioli B, Stagakis S, Velasco E, Vogt R, Ward HC, Barlow J, Chrysoulakis N, Duce P, Graus M, Helfter C, Heusinkveld B, Järvi L, Karl T, Marras S, Masson V, Matthews B, Meier F, Nemitz E, Sabbatini S, Scherer D, Schume H, Sirca C, Steeneveld GJ, Vagnoli C, Wang Y, Zaldei A, Zheng B, Papale D, 2022: Direct observations of CO2 emission reductions due to COVID-19 lockdown across European urban districts. Science of The Total Environment, 830, 154662.
• Skeeter J, Christen A, Henry GHR, 2022: Controls on carbon dioxide and methane fluxes from a low-center polygonal peatland in the Mackenzie River Delta, Northwest Territories. Arctic Science, 8 (2): 471–497.
• Sulzer M, Christen A, Matzarakis M, 2022: A Low-Cost Sensor Network for Real-Time Thermal Stress Monitoring and Communication in Occupational Contexts. Sensors, 22 (5): 1828.
• Everard KA, Katul GG, Lawrence GA, Christen A, Parlange MB, 2021: Sweeping effects modify Taylor’s frozen turbulence hypothesis for scalars in the roughness sublayer. Geophysical Research Letters. 48: e2021GL093746.
• Gangwisch M, Fröhlich D, Christen A, Matzarakis A, 2021: Geometrical Assessment of Sunlit and Shaded Area of Urban Trees Based on Aligned Orthographic Views. Atmosphere. 12 (8), 968.
• Gubler M, Christen A, Remund J, Brönnimann S. 2021: Evaluation and application of a low-cost measurement network to study intra-urban temperature differences during summer 2018 in Bern, Switzerland. Urban Climate, 37, 100817.
• Lee S-C, Christen A, Black TA, Jassal RS, Briegel F, Nesic Z, 2021: Combining flux variance similarity partitioning with artificial neural networks to gap-fill measurements of net ecosystem production of a Pacific Northwest Douglas-fir stand. Agricultural and Forest Meteorology, 303, 108382

• Briegel F, Lee S-C, Black TA, Jassal RS, Christen A, 2020: Factors controlling long-term carbon dioxide exchange between a Douglas- fir stand and the atmosphere identified using an artificial neural network approach. Ecological Modelling, 435, 109266.
• Everard KA, Oldroyd HJ, Christen A, 2020: Turbulent Heat and Momentum Exchange in Nocturnal Drainage Flow Through a Sloped Vineyard. Boundary-Layer Meteorology, 175, 1–23.
• Krayenhoff ES, Jiang T, Christen A, Martilli A, Oke TR, Bailey BN, Nazarian N, Voogt JA, Giometto MG, Stastny A, Crawford BR, 2020: A multi-layer urban canopy meteorological model with trees (BEP-Tree): Street tree impacts on pedestrian-level climate. Urban Climate, 2020; 32: 100590.
• Lee S-C, Black TA, Jassal RS, Christen A, Meyer G, Nesic Z, 2020: Long-term impact of nitrogen fertilization on carbon and water fluxes in a Douglas-fir stand in the Pacific Northwest. Forest Ecology and Management, 455: 117645.
• Lee S-C, Christen A, Black TA, Jassal RS, Ketler R, Nesic Z, 2020: Partitioning of net ecosystem exchange into photosynthesis and respiration using continuous stable isotope measurements in a Pacific Northwest Douglas-fir forest ecosystem. Agr Forest Meteorol, 2020; 292-293: 108109.
• Skeeter J, Christen A, Laforce AA, Humphreys E, Henry GHR, 2020: Vegetation influence and environmental controls on greenhouse gas fluxes from a drained thermokarst lake in the western Canadian Arctic. Biogeosciences, 17, 4421-4441.

• D'Acunha B, Morillas L, Black TA, Christen A, Johnson MS, 2019: Net ecosystem carbon balance of a peat bog undergoing restoration: integrating CO₂ and CH₄ fluxes from eddy covariance and aquatic evasion with DOC drainage fluxes. Journal of Geophysical Research - Biogeosciences, 124 (4): 884-901.
• Lenz S, Schönherr M, Geier M, Krafczyk M, Pasquali A, Christen A, Giometto M, 2019: Towards real-time simulation of turbulent air flow over a resolved urban canopy using the cumulant lattice Boltzmann method on a GPGPU. Journal of Wind Engineering and Industrial Aerodynamics; 189: 151-162.
• McKendry IG, Christen A, Lee S-C, Ferrara M, Strawbridge KB, O'Neill N, Black A, 2019: Impacts of an intense wildfire smoke episode on surface radiation, energy and carbon fluxes in southwestern British Columbia, Canada Atmospheric Chemistry and Physics. 19: 835-846
• Theeuwes NE, Ronda RJ, Harman IN, Christen A, Grimmond CSB, 2019: Parametrizing Horizontally-Averaged Wind and Temperature Profiles in the Urban Roughness Sublayer. Boundary-Layer Meteorology, 17, 321–348.
• Kokkonen TV, Grimmond CSB, Christen A, Oke TR, Järvi L, 2018: Changes to the Water Balance Over a Century of Urban Development in Two Neighborhoods: Vancouver, Canada. Water Resources Research, 54, 6625 - 6642.
• Stephens JJ, Black TA, Jassal RS, Nesic Z, Grant NJ, Barr AG, Helgason WD, Richardson AD, Johnson MS, Christen A, 2018: Effects of forest tent caterpillar defoliation on carbon and water fluxes in a boreal aspen stand. Agricultural and Forest Meteorology, 253-254: 176-189.
• Allen MA, Voogt JA, Christen A, 2018: Time-continuous hemispherical urban surface temperatures. Remote Sensing, 10 (1).
• Kokkonen TV, Grimmond CSB, Räty O, Ward HC, Christen A, Oke TR, Kotthaus S, Järvi L, 2018: Sensitivity of Surface Urban Energy and Water Balance Scheme (SUEWS) to downscaling of reanalysis forcing data. Urban Climate, 23: 36-52.
• Meyer G, Black TA, Jassal RS, Nesic Z, Coops NC, Christen A, Fredeen AL, Spittlehouse DL, Grant NJ, Foord VN, Bowler R, 2018: Simulation of net ecosystem productivity of a lodgepole pine forest after mountain pine beetle attack using a modified version of 3-PG. Forest Ecology and Management; 412: 41-52. :
• Tortini R, Coops NC, Nesic Z, Christen A, Lee S-C, Hilker T, 2017: Remote sensing of seasonal light use efficiency in temperate bog ecosystems. Scientific Reports, 7: 8563.
• Barlow J, Martin Best M, Bohnenstengel SI, Clark P, Grimmond CSB, Lean H, Christen A, Emeis S, Haeffelin M, Harman IN, Lemonsu A, Martilli A, Pardyjak E, Rotach MW, Ballard S, Boutle I, Brown A, Cai X, Carpentieri M, Coceal O, Crawford B, Di Sabatino S, Dou J, Drew DR, Edwards JM, Fallmann J, Fortuniak K, Gornall J, Gronemeier T, Halios CH, Hertwig D, Hirano K, Holtslag AAM, Luo Z, Mills G, Nakayoshi M, Pain K, Schlünzen KH, Smith S, Soulhac L, Steeneveld G-J, Sun T, Theeuwes NE, Thomson D, Voogt JA, Ward HC, Xie Z-T, Zhong J, 2017: Developing a Research Strategy to Better Understand, Observe, and Simulate Urban Atmospheric Processes at Kilometer to Subkilometer Scales. Bulletin of the American Meteorological Society, 98 (10): ES261-ES264.
• Giometto MG, Christen A, Egli PE, Schmid MF, Tooke RT, Coops NC, Parlange MB, 2017: Effects of trees on mean wind, turbulence and momentum exchange within and above a real urban environment. Advances in Water Resources, 106, 154-168.
• Järvi L, Grimmond CSB, McFadden JP, Christen A, Strachan IB, Taka M, Warsta L, Heimann M, 2017: Warming effects on the urban hydrology in cold climate regions. Scientific Reports, 7, 5833.
• Cassidy AE, Christen A, Henry GHR, 2017: Impacts of active retrogressive thaw slumps on vegetation, soil, and net ecosystem exchange of carbon dioxide in the Canadian High Arctic. Arctic Science, 10.1139/AS-2016-0034.
• Lee JK, Christen A, Ketler R, Nesic Z, 2017: A mobile sensor network to map carbon dioxide emissions in urban environments. Atmospheric Measurement Techniques, doi:10.5194/amt-2016-200, 2291-2303.
• Lee, S-C, Christen, A, Black, AT, Johnson, MS, Jassal, RS, Ketler, R, Nesic, Z, Merkens, M, 2017: Annual greenhouse gas budget for a bog ecosystem undergoing restoration by rewetting Biogeosciences, 14, 2799-2814.
• Meyer G, Black TA, Jassal RS, Nesic Z, Grant NJ, Spittlehouse DL, Fredeen AL, Christen A, Coops NC, Foord VN, Bowler R, 2017: Measurements and simulations using the 3-PG model of the water balance and water use efficiency of a lodgepole pine stand following mountain pine beetle attack. Forest Ecology and Management, 393, 89–104.
• Cassidy AE, Christen A, Henry GHR, 2016: The effect of a permafrost disturbance on growing-season carbon-dioxide fluxes in a high Arctic tundra ecosystem. Biogeosciences, 13, 2291-2303, doi:10.5194/bg-13-2291-2016.
• Chance CM, Coops NC, Plowright AA, Tooke TR, Christen A, Aven N, 2016: Invasive Shrub Mapping in an Urban Environment From Hyperspectral and LiDAR-Derived Attributes. Frontiers in Plant Science 07 (891534): 281–19.
• Christen A, Jassal RS, Black TA, Grant NJ, Hawthorne I, Johnson MS, Lee S-C, Merkens M, 2016: Summertime greenhouse gas fluxes from an urban bog undergoing restoration through rewetting. Mires and Peat, 17, Article 3, 1–24.
• Crawford B, Christen A, McKendry IG, 2016: Diurnal course of carbon dioxide mixing ratios in the urban boundary layer in response to surface emissions. Journal of Applied Meteorology and Climatology, 55, 507–529.
• Giometto MG, Christen A, Meneveau C, Fang J, Krafczyk M, Parlange MB, 2016: Spatial characteristics of roughness sublayer mean flow and turbulence over a realistic urban surface. Boundary Layer Meteorology, 160 (3), 425–452.
  
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