Andreas Christen
LightNews LightNews
banner
envmet.bsky.social
Andreas Christen
@envmet.bsky.social
260 followers 180 following 25 posts
Professor of Environmental Meteorology at University of Freiburg | Observing and modelling airflow, greenhouse gases, climate change in urban & forest systems. https://www.meteo.uni-freiburg.de/en/team/andreas-christen
Posts Replies Media Videos
envmet.bsky.social
In our ECOSENSE forest we are monitoring ecosystem processes and stresses in real-time using distributed sensor networks: Our new @egu.eu preprint discusses the implementation of this major technical infrastructure and its data management @ecosense-sfb-1537.bsky.social - doi.org/10.5194/egus...
October 24, 2025 at 9:18 AM
envmet.bsky.social
Is satellite land surface temperature (LST) a good proxy for urban heat stress? In our new article led by Ferdinand Briegel @kit.edu and @uni-freiburg.de in RSE we conclude "no" - comparing nearly 100 LST scenes to detailed 1-m heat stress modelling at pedestrian level. doi.org/10.1016/j.rs...
Maps of averaged LST (a) and UTCI (b) for 46 timesteps in summer in Freiburg, Germany. The difference between LST and UTCI is shown in (c), and the land cover classes are shown in (d).
October 4, 2025 at 8:23 PM
envmet.bsky.social
Summer 2025 was unusually warm and wet. At our at Hartheim @icos-ri.eu station of @uni-freiburg.de in the Upper Rhine Valley JJA was 1°C warmer and +25% precipitation vs. 1991–2020 (June +2.7°C). Only 4 years since 1978 were both wetter and warmer, but 2025 stands out as most extreme yet.
September 9, 2025 at 5:59 AM
envmet.bsky.social
Years of drought turn forest into source of CO₂ - Press release on our research with @simonhaber.bsky.social and @chriswernerlab.bsky.social at @icos-ri.eu site DE-Har, showing tree mortality following droughts has fundamentally shifted forest structure & functioning uni-freiburg.de/en/years-of-...
Aerial view of the experimental forest near Hartheim with the 30-metre-high crown access tower in September 2023. Dead Scots pines and gaps in the canopy are visible throughout the forest. Photo: Fabio Scarpa
July 14, 2025 at 10:14 AM
envmet.bsky.social
Great presence of @icos-ri.eu at the International Conference on Urban Climate (#ICUC12) today in Rotterdam. Presenting latest science on modelling, observing, and attributing urban greenhouse gas emission reductions using ICOS infrastructure in Paris, Munich, Zurich Berlin, Heidelberg & Heraklion.
July 8, 2025 at 3:55 PM
envmet.bsky.social
Today was another unusually hot day in Freiburg, with temperatures above 38°C. Our urban weather station network operated by @uni-freiburg.de and funded by @erc.europa.eu reveals intra-urban differences and where it was coolest (in a forest). Explore the map weather.uni-freiburg.de/map/freiburg...
July 2, 2025 at 4:33 PM
envmet.bsky.social
During the current #UKHeatWave we measured for the first time a #TropicalNight across our Bristol street-level weather network. Stations outside the city and on hills cooled down to < 20°C while the urban heat island kept the city core above 20°C last night. weather.uni-freiburg.de/map/bristol/...
Stations colored in red show a tropical night, i.e. that air temperature at those weather stations did no drop below 20°C all night on Jun 21, 2025.
June 21, 2025 at 7:29 PM
envmet.bsky.social
New weather stations on lamp-posts across Bristol, UK reveal interacting urban, orographic and coastal effects in real time. Last night, we observed an urban heat island of 5ºC. Multi-institutional effort between urbisphere ‪@erc.europa.eu‬, @urbanair.bsky.social‬ and ASSURE: doi.org/10.5281/zeno...
The city centre of Bristol has the highest nocturnal air temperatures measures, 5K warmer than a rural site to the west of the city at same elevation. Note also that the station in the NW near the coast stays even warmer (12.2ºC), while the Avon Gorge is relatively cool (8.8ºC). A weather station on a lamp-post measures at 3 m in a typical street canyon, here in the Windmill Hill neighborhood. Data are transmitted every 5 minutes over the cell-phone network and shared as open-data as part of several UK and EU research projects enhancing urban-scale weather and climate modelling.
June 2, 2025 at 7:59 PM
envmet.bsky.social
Celebrating our successful new excellence cluster #FutureForests @uni-freiburg.de. Thanks @dfg.de, this will enable us to substantially invest in exciting and much-needed research for the next 7 years - predicting and transforming forest systems in a changing climate uni-freiburg.de/futureforest...
May 24, 2025 at 9:48 PM
envmet.bsky.social
Using high-resolution weather models and a network of 25 LiDAR-ceilometers over Berlin, Germany, we explore how large cities modify the atmospheric boundary layer. New preprint on collaborative work by @uniofreading.bsky.social‬, @metoffice.bsky.social‬ and @uni-freiburg.de
doi.org/10.5194/egus...
May 21, 2025 at 6:17 PM
envmet.bsky.social
Impressive time-lapse of leaf emergence during the last weeks recorded by phenocams at our research forest @uni-freiburg.de. In the @dfg.de funded @ecosense-sfb-1537.bsky.social we study forest ecosystem functioning, and species interactions with novel sensor technologies uni-freiburg.de/ecosense/
April 25, 2025 at 8:33 PM
envmet.bsky.social
New preprint on our harmonised wind dataset from 6 doppler wind lidars operated along a transect through Paris, France. This data supports urban weather and climate modeling in multiple @erc.europa.eu, @wmo-global.bsky.social, @icos-ri.eu and @horizoneu.bsky.social projects: doi.org/10.5194/essd...
Six Doppler Wind LIDARS (DWLs) operated across Paris concurrently are used to retrieve horizontal wind speed and direction through the ABL at 18–25 m vertical and 1–60 min temporal resolution. The six DWLs were deployed in a multi-institutional effort along a 40 km transect through the centre of Paris (France) in 2023 - 2024.
April 23, 2025 at 1:34 PM
envmet.bsky.social
Our new paper with @ubcgeography.bsky.social in Agric. For. Meteorol. investigates climatic sensitivity of evapotranspiration in an ombrotrophic bog on Canada's West Coast. The bog's water balance will be most sensitive to future increases in summer vapour pressure deficit. doi.org/10.1016/j.ag...
This study quantified surface energy balance and evapotranspiration in a Sphagnum-dominated ombrotrophic bog located near their southern limit in western North America on the Coast of British Columbia. We use ecohydrologicical and eddy-covariance measurements on a flux tower to assess the bog’s sensitivity to future climatic conditions, particularly to increasing severity and duration of drought conditions. Daily evapotranspiration from the bog 2014 - 2022 adjusted for lack of energy balance closure from all years versus equilibrium evapotranspiration Eeq. and color coded by month of year. The dashed line indicates the 1:1-line.
March 26, 2025 at 8:51 PM
envmet.bsky.social
New preprint at @egu.eu on greenhouse gas emission measurements from cities as part of @icos-ri.eu. Our group @uni-freiburg.de and partners propose a new method for attributing emissions to sources using multi-species eddy fluxes on a tall tower over Zurich. egusphere.copernicus.org/preprints/20...
An eddy-covariance system on a tall tower over Zurich, Switzerland. The system is equipped with an inlet to a multi-species fast gas analyzer measures simultaneously emissions and uptake of carbon dioxide (CO2), carbon monoxide (CO), nitrogen monoxide and -dioxide (NOx), methane (CH4) and nitrous oxide (N2O). The information on the correlation and flux ratios between species is used to attribute CO2, CO and NOx to major emission sectors (road transport, stationary combustion and biospheric sources / sinks) Correlation matrix of 30-min fluxes of measured species. The lower-left half is the summer months (Aug-Oct) and upper-right half is the winter months (Nov-Mar). Clearly, we see higher correlation between CO2 and combustion air pollutants CO / NOx, weaker correlation with non-CO2 greenhouse gases CH4 and N2O. Expectedly correlations are stronger in winter between CO2 and air pollutants, when biospheric CO2 fluxes are weaker.
March 24, 2025 at 1:54 PM
envmet.bsky.social
An arcus cloud passed over Freiburg earlier this evening. It was part of a convective system embedded in a cold front. A sharp increase in wind, a drop in air temperature and an unusual pressure jump +2 hPa in just 5 minutes measured @uni-freiburg.de weather station.
February 25, 2025 at 8:23 PM
envmet.bsky.social
We advertise a new Full Professorship (W3) in Fire Ecology @uni-freiburg.de. Do you work on effects of fires on vegetation biodiversity, functionality, dynamics and fire mitigation? Consider applying to join our vibrant Faculty of Environment and Natural Resources. uni-freiburg.de/en/job/00004...
February 17, 2025 at 10:53 AM
envmet.bsky.social
Urban Heat Islands are usually associated with heatwaves in summer. But during cold winter nights, they are equally present. Our street-level network @uni-freiburg.de reveals that frost is less likely to occur in the city of Freiburg (24 days per year) compared to the rural surrounding (50-60 days).
The map of Freiburg, Germany shows the number of frost days with a minimum air temperature below 0°C in the city of Freiburg and its surroundings as measured by a street-level sensor network in 2022-2023. Credits: Marvin Plein and Andreas Christen, Chair of Environmental Meteorology, University of Freiburg, sensor network supported and funded by ERC Grant urbisphere
February 6, 2025 at 8:17 PM
envmet.bsky.social
Our new paper in "Ecohydrology" led by @simonhaber.bsky.social describes dynamics of short-term droughts on tree water potentials. We were using new continuous stem water sensors at our @icos-ri.eu site in Hartheim @uni-freiburg.de as part of @ecosense-sfb-1537.bsky.social doi.org/10.1002/eco....
January 23, 2025 at 11:54 AM
envmet.bsky.social
New @eurogeosciences.bsky.social preprint on our @icos-ri.eu relaxed eddy accumulation system for measuring 14C fluxes. Developed by @uni-freiburg.de, @uniheidelberg.bsky.social and @maxplanck.de, it aims to partition city emissions into fossil fuel and biogenic contributions doi.org/10.5194/egus...
January 17, 2025 at 9:00 PM
envmet.bsky.social
Field trip with @uni-freiburg.de students to learn about urban climate activities in Basel - Meteoblue.com showcased their city climate services and city wide sensor networks. At @unibas.ch we learned how eddy covariance on towers is used to monitor GHG emission reductions.
University of Basel ICOS tower to measure GHG fluxes from the city. Students visit a black-globe weather station to measure human thermal comfort on a newly planned public plaza in Basel Meteoblue street-level weather station in Basel to test different weather sensors.
January 14, 2025 at 7:14 PM
envmet.bsky.social
New article in "Sustainable Cities and Society" documents custom-built weather stations to monitor pedestrian-level thermal comfort on street lights. They are part of our city-wide sensor network @uni-freiburg.de to evaluate urban climate models - funded by ERC @ec.europa.eu doi.org/10.1016/j.sc...
Weather station part of the Freiburg Sensor Network to monitor outdoor thermal comfort - Here in the neighbourhood of Vauban in Freiburg, Germany. The thermal comfort monitoring stations documented in the article in the city of Freiburg (blue symbols) are also complemented by regular commercial all-in one stations (yellow symbols) - together creating a network of 42 stations across the city and in its surrounding.
January 5, 2025 at 5:40 PM
envmet.bsky.social
Our new paper in Urban Climate presents a machine-learning approach to simulate airflow in real urban canopies based on large eddy simulations. Result from recent #I4C project on AI applications in environmental research and collaboration between @unifreiburg and Columbia U. doi.org/10.1016/j.uc...
December 2, 2024 at 9:16 PM