Browsing by Subject "CARBON-DIOXIDE EXCHANGE"

Sort by: Order: Results:

Now showing items 1-17 of 17
  • Gielen, Bert; Acosta, Manuel; Altimir, Nuria; Buchmann, Nina; Cescatte, Alessandro; Ceschia, Eric; Fleck, Stefan; Hortnagal, Lukas; Klumpp, Katja; Kolari, Pasi; Lohile, Annalea; Loustau, Denis; Maranon-Jimenez, Sara; Manisp, Languy; Matteucci, Giorgio; Merbold, Lutz; Metzger, Christine; Moureaux, Christine; Montagnani, Leonardo; Nilsson, Mats B.; Osborne, Bruce; Papale, Dario; Pavelka, Marian; Saunders, Matthew; Simioni, Guillaume; Soudani, Kamel; Sonnentag, Oliver; Tallec, Tiphaine; Tuittila, Eeva-Stiina; Peichl, Matthias; Pokorny, Radek; Vincke, Caroline; Wohljahrt, Georg (2018)
    The Integrated Carbon Observation System is a Pan-European distributed research infrastructure that has as its main goal to monitor the greenhouse gas balance of Europe. The ecosystem component of Integrated Carbon Observation System consists of a multitude of stations where the net greenhouse gas exchange is monitored continuously by eddy covariance measurements while, in addition many other measurements are carried out that are a key to an understanding of the greenhouse gas balance. Amongst them are the continuous meteorological measurements and a set of non-continuous measurements related to vegetation. The latter include Green Area Index, aboveground biomass and litter biomass. The standardized methodology that is used at the Integrated Carbon Observation System ecosystem stations to monitor these vegetation related variables differs between the ecosystem types that are represented within the network, whereby in this paper we focus on forests, grasslands, croplands and mires. For each of the variables and ecosystems a spatial and temporal sampling design was developed so that the variables can be monitored in a consistent way within the ICOS network. The standardisation of the methodology to collect Green Area Index, above ground biomass and litter biomass and the methods to evaluate the quality of the collected data ensures that all stations within the ICOS ecosystem network produce data sets with small and similar errors, which allows for inter-comparison comparisons across the Integrated Carbon Observation System ecosystem network.
  • Makela, Jarmo; Susiluoto, Jouni; Markkanen, Tiina; Aurela, Mika; Järvinen, Heikki; Mammarella, Ivan; Hagemann, Stefan; Aalto, Tuula (2016)
    We examined parameter optimisation in the JSBACH (Kaminski et al., 2013; Knorr and Kattge, 2005; Reick et al., 2013) ecosystem model, applied to two boreal forest sites (Hyytiala and Sodankyla) in Finland. We identified and tested key parameters in soil hydrology and forest water and carbon-exchange-related formulations, and optimised them using the adaptive Metropolis (AM) algorithm for Hyytil with a 5-year calibration period (2000-2004) followed by a 4-year validation period (2005-2008). Sodankyla acted as an independent validation site, where optimisations were not made. The tuning provided estimates for full distribution of possible parameters, along with information about correlation, sensitivity and identifiability. Some parameters were correlated with each other due to a phenomenological connection between carbon uptake and water stress or other connections due to the set-up of the model formulations. The latter holds especially for vegetation phenology parameters. The least identifiable parameters include phenology parameters, parameters connecting relative humidity and soil dryness, and the field capacity of the skin reservoir. These soil parameters were masked by the large contribution from vegetation transpiration. In addition to leaf area index and the maximum carboxylation rate, the most effective parameters adjusting the gross primary production (GPP) and evapotranspiration (ET) fluxes in seasonal tuning were related to soil wilting point, drainage and moisture stress imposed on vegetation. For daily and half-hourly tunings the most important parameters were the ratio of leaf internal CO2 concentration to external CO2 and the parameter connecting relative humidity and soil dryness. Effectively the seasonal tuning transferred water from soil moisture into ET, and daily and half-hourly tunings reversed this process. The seasonal tuning improved the month-to-month development of GPP and ET, and produced the most stable estimates of water use efficiency. When compared to the seasonal tuning, the daily tuning is worse on the seasonal scale. However, daily parametrisation reproduced the observations for average diurnal cycle best, except for the GPP for Sodankyla validation period, where half-hourly tuned parameters were better. In general, the daily tuning provided the largest reduction in model-data mismatch. The models response to drought was unaffected by our parametrisations and further studies are needed into enhancing the dry response in JSBACH.
  • Wang, T.; Ciais, P.; Piao, S. L.; Ottle, C.; Brender, P.; Maignan, F.; Arain, A.; Cescatti, A.; Gianelle, D.; Gough, C.; Gu, L.; Lafleur, P.; Laurila, T.; Marcolla, B.; Margolis, H.; Montagnani, L.; Moors, E.; Saigusa, N.; Vesala, T.; Wohlfahrt, G.; Koven, C.; Black, A.; Dellwik, E.; Don, A.; Hollinger, D.; Knohl, A.; Monson, R.; Munger, J.; Suyker, A.; Varlagin, A.; Verma, S. (2011)
  • Linkosalmi, Maiju; Aurela, Mika; Tuovinen, Juha-Pekka; Peltoniemi, Mikko; Tanis, Cemal M.; Arslan, Ali N.; Kolari, Pasi; Bottcher, Kristin; Aalto, Tuula; Rainne, Juuso; Hatakka, Juha; Laurila, Tuomas (2016)
    Digital repeat photography has become a widely used tool for assessing the annual course of vegetation phenology of different ecosystems. By using the green chromatic coordinate (GCC) as a greenness measure, we examined the feasibility of digital repeat photography for assessing the vegetation phenology in two contrasting high-latitude ecosystems. Ecosystem-atmosphere CO2 fluxes and various meteorological variables were continuously measured at both sites. While the seasonal changes in GCC were more obvious for the ecosystem that is dominated by annual plants (open wetland), clear seasonal patterns were also observed for the evergreen ecosystem (coniferous forest). Daily and seasonal time periods with sufficient solar radiation were determined based on images of a grey reference plate. The variability in cloudiness had only a minor effect on GCC, and GCC did not depend on the sun angle and direction either. The daily GCC of wetland correlated well with the daily photosynthetic capacity estimated from the CO2 flux measurements. At the forest site, the correlation was high in 2015 but there were discernible deviations during the course of the summer of 2014. The year-to-year differences were most likely generated by meteorological conditions, with higher temperatures coinciding with higher GCCs. In addition to depicting the seasonal course of ecosystem functioning, GCC was shown to respond to environmental changes on a timescale of days. Overall, monitoring of phenological variations with digital images provides a powerful tool for linking gross primary production and phenology.
  • Vernay, Antoine; Tian, Xianglin; Chi, Jinshu; Linder, Sune; Makela, Annikki; Oren, Ram; Peichl, Matthias; Stangl, Zsofia R.; Tor-Ngern, Pantana; Marshall, John D. (2020)
    Gross primary production (GPP) is a key component of the forest carbon cycle. However, our knowledge of GPP at the stand scale remains uncertain, because estimates derived from eddy covariance (EC) rely on semi-empirical modelling and the assumptions of the EC technique are sometimes not fully met. We propose using the sap flux/isotope method as an alternative way to estimate canopy GPP, termed GPP(iso/SF), at the stand scale and at daily resolution. It is based on canopy conductance inferred from sap flux and intrinsic water-use efficiency estimated from the stable carbon isotope composition of phloem contents. The GPP(iso/SF)estimate was further corrected for seasonal variations in photosynthetic capacity and mesophyll conductance. We compared our estimate of GPP(iso/SF)to the GPP derived from PRELES, a model parameterized with EC data. The comparisons were performed in a highly instrumented, boreal Scots pine forest in northern Sweden, including a nitrogen fertilized and a reference plot. The resulting annual and daily GPP(iso/SF)estimates agreed well with PRELES, in the fertilized plot and the reference plot. We discuss the GPP(iso/SF)method as an alternative which can be widely applied without terrain restrictions, where the assumptions of EC are not met.
  • Pihlatie, Mari; Kiese, Ralf; Brueggemann, Nicholas; Butterbach-Bahl, Klaus; Kieloaho, Antti-Jussi; Laurila, Tuomas; Lohila, Annalea; Mammarella, Ivan; Minkkinen, K.; Penttila, Timo; Schoenborn, Jochen; Vesala, Timo (2010)
  • Juutinen, Sari; Moore, Tim R.; Bubier, Jill L.; Arnkil, Sini; Humphreys, Elyn; Marincak, Brenden; Roy, Cameron; Larmola, Tuula (2018)
    Peatlands are globally significant sources of atmospheric methane (CH4). While several studies have examined the effects of nutrient addition on CH4 dynamics, there are few long-term peatland fertilization experiments, which are needed to understand the aggregated effects of nutrient deposition on ecosystem functioning. We investigated responses of CH4 flux and production to long-term field treatments with three levels of N (1.6-6.4 g m(-2) yr(-1) as NH4NO3), potassium and phosphorus (PK, 5.0 g P and 6.3 g K m(-2) yr(-1) as KH2PO4), and NPK in a temperate bog. Methane fluxes were measured in the field from May to August in 2005 and 2015. In 2015 CH4 flux was higher in the NPK treatment with 16 years of 6.4 g N m(-2) yr(-1) than in the control (50.5 vs. 8.6 mg CH4 m(-2) d(-1)). The increase in CH4 flux was associated with wetter conditions derived from peat subsidence. Incubation of peat samples, with and without short-term PK amendment, showed that potential CH4 production was enhanced in the PK treatments, both from field application and by amending the incubation. We suggest that changes in this bog ecosystem originate from long-term vegetation change, increased decomposition and direct nutrient effects on microbial dynamics.
  • Alekseychik, Pavel; Mammarella, Ivan; Karpov, Dmitry; Dengel, Sigrid; Terentieva, Irina; Sabrekov, Alexander; Glagolev, Mikhail; Lapshina, Elena (2017)
    Very few studies of ecosystem-atmosphere exchange involving eddy covariance data have been conducted in Siberia, with none in the western Siberian middle taiga. This work provides the first estimates of carbon dioxide (CO2) and energy budgets in a typical bog of the western Siberian middle taiga based on May-August measurements in 2015. The footprint of measured fluxes consisted of a homogeneous mixture of tree-covered ridges and hollows with the vegetation represented by typical sedges and shrubs. Generally, the surface exchange rates resembled those of pinecovered bogs elsewhere. The surface energy balance closure approached 100 %. Net CO2 uptake was comparatively high, summing up to CO2 gCm(-2) for the four measurement months, while the Bowen ratio was seasonally stable at 28 %. The ecosystem turned into a net CO2 source during several front passage events in June and July. The periods of heavy rain helped keep the water table at a sustainably high level, preventing a usual drawdown in summer. However, because of the cloudy and rainy weather, the observed fluxes might rather represent the special weather conditions of 2015 than their typical magnitudes.
  • Qiu, Chunjing; Zhu, Dan; Ciais, Philippe; Guenet, Bertrand; Krinner, Gerhard; Peng, Shushi; Aurela, Mika; Bernhofer, Christian; Bruemmer, Christian; Bret-Harte, Syndonia; Chu, Housen; Chen, Jiquan; Desai, Ankur R.; Dusek, Jiri; Euskirchen, Eugenie S.; Fortuniak, Krzysztof; Flanagan, Lawrence B.; Friborg, Thomas; Grygoruk, Mateusz; Gogo, Sebastien; Gruenwald, Thomas; Hansen, Birger U.; Holl, David; Humphreys, Elyn; Hurkuck, Miriam; Kiely, Gerard; Klatt, Janina; Kutzbach, Lars; Largeron, Chloe; Laggoun-Defarge, Fatima; Lund, Magnus; Lafleur, Peter M.; Li, Xuefei; Mammarella, Ivan; Merbold, Lutz; Nilsson, Mats B.; Olejnik, Janusz; Ottosson-Lofvenius, Mikaell; Oechel, Walter; Parmentier, Frans-Jan W.; Peichl, Matthias; Pirk, Norbert; Peltola, Olli; Pawlak, Wlodzimierz; Rasse, Daniel; Rinne, Janne; Shaver, Gaius; Schmid, Hans Peter; Sottocornola, Matteo; Steinbrecher, Rainer; Sachs, Torsten; Urbaniak, Marek; Zona, Donatella; Ziemblinska, Klaudia (2018)
    Peatlands store substantial amounts of carbon and are vulnerable to climate change. We present a modified version of the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model for simulating the hydrology, surface energy, and CO2 fluxes of peatlands on daily to annual timescales. The model includes a separate soil tile in each 0.5 degrees grid cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation within a grid cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model was evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (V-cmax) being optimized at each site. Regarding short-term day-to-day variations, the model performance was good for gross primary production (GPP) (r(2) = 0.76; Nash-Sutcliffe modeling efficiency, MEF = 0.76) and ecosystem respiration (ER, r(2) = 0.78, MEF = 0.75), with lesser accuracy for latent heat fluxes (LE, r(2) = 0.42, MEF = 0.14) and and net ecosystem CO2 exchange (NEE, r(2) = 0.38, MEF = 0.26). Seasonal variations in GPP, ER, NEE, and energy fluxes on monthly scales showed moderate to high r(2) values (0.57-0.86). For spatial across-site gradients of annual mean GPP, ER, NEE, and LE, r(2) values of 0.93, 0.89, 0.27, and 0.71 were achieved, respectively. Water table (WT) variation was not well predicted (r(2) <0.1), likely due to the uncertain water input to the peat from surrounding areas. However, the poor performance of WT simulation did not greatly affect predictions of ER and NEE. We found a significant relationship between optimized V-cmax and latitude (temperature), which better reflects the spatial gradients of annual NEE than using an average V-cmax value.
  • Koebsch, Franziska; Sonnentag, Oliver; Järveoja, Järvi; Peltoniemi, Mikko; Alekseychik, Pavel; Aurela, Mika; Arslan, Ali Nadir; Dinsmore, Kerry; Gianelle, Damiano; Helfter, Carole; Jackowicz-Korczynski, Marcin; Korrensalo, Aino; Leith, Fraser; Linkosalmi, Maiju; Lohila, Annalea; Lund, Magnus; Maddison, Martin; Mammarella, Ivan; Mander, Ülo; Minkkinen, Kari; Pickard, Amy; Pullens, Johannes W.M.; Tuittila, Eeva-Stiina; Nilsson, Mats B.; Peichl, Matthias (2020)
    Abstract The role of plant phenology as regulator for gross ecosystem productivity (GEP) in peatlands is empirically not well constrained. This is because proxies to track vegetation development with daily coverage at the ecosystem scale have only recently become available and the lack of such data has hampered the disentangling of biotic and abiotic effects. This study aimed at unraveling the mechanisms that regulate the seasonal variation in GEP across a network of eight European peatlands. Therefore, we described phenology with canopy greenness derived from digital repeat photography and disentangled the effects of radiation, temperature and phenology on GEP with commonality analysis and structural equation modeling. The resulting relational network could not only delineate direct effects but also accounted for possible effect combinations such as interdependencies (mediation) and interactions (moderation). We found that peatland GEP was controlled by the same mechanisms across all sites: phenology constituted a key predictor for the seasonal variation in GEP and further acted as distinct mediator for temperature and radiation effects on GEP. In particular, the effect of air temperature on GEP was fully mediated through phenology, implying that direct temperature effects representing the thermoregulation of photosynthesis were negligible. The tight coupling between temperature, phenology and GEP applied especially to high latitude and high altitude peatlands and during phenological transition phases. Our study highlights the importance of phenological effects when evaluating the future response of peatland GEP to climate change. Climate change will affect peatland GEP especially through changing temperature patterns during plant-phenologically sensitive phases in high latitude and high altitude regions.
  • Matkala, Laura; Kulmala, Liisa; Kolari, Pasi; Aurela, Mika; Bäck, Jaana (2021)
    We studied the occurrence of extreme weather events and their effects on the carbon dioxide and water exchange of two subarctic forest stands. One study site was a Scots pine site in eastern Finnish Lapland (VarriO), and the other was a Norway spruce site in western Finnish Lapland (Kenttarova). We compared short-term meteorological data with long-term data and found that the pine forest had experienced extremely warm, wet and dry years as well as cold spells during the growing season in the studied period of 2012-2018. The spruce forest was studied during the period 2003-2013, during which time it experienced extremely warm and wet summers, and dry periods, although the dry times were not statistically defined as such. The spruce forest was less resilient to warm and dry periods, as its total ecosystem respiration and respiration potential decreased during warm and dry summers, while the same effect was not seen in the pine forest. The decreased respiration values may have occurred due to slowed decomposition of organic matter. The pine forest experienced two cold spells during the studied period. One of these cold periods was more of a continuation of the previous cold spring and late start of the growing season in 2017, while the other one occurred after a warm period in 2014. The ecosystem respiration rates and gross primary production in 2017 remained low for the whole July-August time period likely due to cold-inhibited growth of ground vegetation, while in 2014 no such effect could be seen. We saw no effect of extreme weather events in the water exchange related measurements in either of the forests. Overall, both forests, especially the trees, were resilient to the weather extremes and experienced no long-term damage.
  • Park, Sung-Bin; Knohl, Alexander; Lucas-Moffat, Antje M.; Migliavacca, Mirco; Gerbig, Christoph; Vesala, Timo; Peltola, Oli; Mammarella, Ivan; Kolle, Olaf; Lavric, Jost Valentin; Prokushkin, Anatoly; Heimann, Martin (2018)
    Aerosols produced by wildfires are a common phenomenon in boreal regions. For the Siberian taiga, it is still an open question if the effects of aerosols on atmospheric conditions increase net CO2 uptake or photosynthesis. We investigated the factors controlling forest net ecosystem productivity (NEP) and explored how clouds and smoke modulate radiation as a major factor controlling NEP during fire events in the years 2012 and 2013. To characterize the underlying mechanisms of the NEP response to environmental drivers, Artificial Neural Networks (ANNs) were trained by eddy covariance flux measurements nearby the Zotino Tall Tower Observatory (ZOTTO). Total photosynthetically active radiation, vapour pressure deficit, and diffuse fraction explain at about 54-58% of NEP variability. NEP shows a strong negative sensitivity to VPD, and a small positive to f(dlf). A strong diffuse radiation fertilization effect does not exist at ZOTTO forest due to the combined effects of low light intensity, sparse canopy and low leaf area index. Results suggests that light intensity and canopy structure are important factors of the overall diffuse radiation fertilization effect.
  • Ducker, Jason A.; Holmes, Christopher D.; Keenan, Trevor F.; Fares, Silvano; Goldstein, Allen H.; Mammarella, Ivan; Munger, J. William; Schnell, Jordan (2018)
    We develop and evaluate a method to estimate O-3 deposition and stomatal O-3 uptake across networks of eddy covariance flux tower sites where O-3 concentrations and O-3 fluxes have not been measured. The method combines standard micrometeorological flux measurements, which constrain O-3 deposition velocity and stomatal conductance, with a gridded dataset of observed surface O-3 concentrations. Measurement errors are propagated through all calculations to quantify O-3 flux uncertainties. We evaluate the method at three sites with O(3 )flux measurements: Harvard Forest, Blodgett Forest, and Hyytiala Forest. The method reproduces 83 % or more of the variability in daily stomatal uptake at these sites with modest mean bias (21 % or less). At least 95 % of daily average values agree with measurements within a factor of 2 and, according to the error analysis, the residual differences from measured O-3 fluxes are consistent with the uncertainty in the underlying measurements. The product, called synthetic O-3 flux or SynFlux, includes 43 FLUXNET sites in the United States and 60 sites in Europe, totaling 926 site years of data. This dataset, which is now public, dramatically expands the number and types of sites where O-3 fluxes can be used for ecosystem impact studies and evaluation of air quality and climate models. Across these sites, the mean stomatal conductance and O-3 deposition velocity is 0.03-1.0 cm s(-1). The stomatal O-3 flux during the growing season (typically April-September) is 0.5-11.0 nmol O-3 m(-2) s(-1) with a mean of 4.5 nmol O(3 )m(-2) s(-1) and the largest fluxes generally occur where stomatal conductance is high, rather than where O-3 concentrations are high. The conductance differences across sites can be explained by atmospheric humidity, soil moisture, vegetation type, irrigation, and land management. These stomatal fluxes suggest that ambient O-3 degrades biomass production and CO2 sequestration by 20 %-24 % at crop sites, 6 %-29 % at deciduous broadleaf forests, and 4 %-20 % at evergreen needleleaf forests in the United States and Europe.
  • Park, Sung-Bin; Knohl, Alexander; Migliavacca, Mirco; Thum, Tea; Vesala, Timo; Peltola, Olli; Mammarella, Ivan; Prokushkin, Anatoly; Kolle, Olaf; Lavric, Jost; Park, Sang Seo; Heimann, Martin (2021)
    Climate change impacts the characteristics of the vegetation carbon-uptake process in the northern Eurasian terrestrial ecosystem. However, the currently available direct CO2 flux measurement datasets, particularly for central Siberia, are insufficient for understanding the current condition in the northern Eurasian carbon cycle. Here, we report daily and seasonal interannual variations in CO2 fluxes and associated abiotic factors measured using eddy covariance in a coniferous forest and a bog near Zotino, Krasnoyarsk Krai, Russia, for April to early June, 2013-2017. Despite the snow not being completely melted, both ecosystems became weak net CO2 sinks if the air temperature was warm enough for photosynthesis. The forest became a net CO2 sink 7-16 days earlier than the bog. After the surface soil temperature exceeded similar to 1 degrees C, the ecosystems became persistent net CO2 sinks. Net ecosystem productivity was highest in 2015 for both ecosystems because of the anomalously high air temperature in May compared with other years. Our findings demonstrate that long-term monitoring of flux measurements at the site level, particularly during winter and its transition to spring, is essential for understanding the responses of the northern Eurasian ecosystem to spring warming.
  • Dengel, S.; Zona, D.; Sachs, T.; Aurela, M.; Jammet, M.; Parmentier, F. J. W.; Oechel, W.; Vesala, T. (2013)
  • Virkkala, Anna-Maria; Virtanen, Tarmo; Lehtonen, Aleksi; Rinne, Janne; Luoto, Miska (2018)
    The Arctic tundra plays an important role in the carbon cycle as it stores 50% of global soil organic carbon reservoirs. The processes (fluxes) regulating these stocks are predicted to change due to direct and indirect effects of climate change. Understanding the current and future carbon balance calls for a summary of the level of knowledge regarding chamber-derived carbon dioxide (CO2) flux studies. Here, we describe progress from recently (2000-2016) published studies of growing-season CO2 flux chamber measurements, namely GPP (gross primary production), ER (ecosystem respiration), and NEE (net ecosystem exchange), in the tundra region. We review the study areas and designs along with the explanatory environmental drivers used. Most of the studies were conducted in Alaska and Fennoscandia, and we stress the need for measuring fluxes in other tundra regions, particularly in more extreme climatic, productivity, and soil conditions. Soil respiration and other greenhouse gas measurements were seldom included in the studies. Although most of the environmental drivers of CO2 fluxes have been relatively well investigated (such as the effect of vegetation type and soil microclimate on fluxes), soil nutrients, other greenhouse gases and disturbance regimes require more research as they might define the future carbon balance. Particular attention should be paid to the effects of shrubification, geomorphology, and other disturbance effects such as fire events, and disease and herbivore outbreaks. An improved conceptual framework and understanding of underlying processes of biosphere-atmosphere CO2 exchange will provide more information on carbon cycling in the tundra.
  • Peltoniemi, Mikko; Aurela, Mika; Bottcher, Kristin; Kolari, Pasi; Loehr, John; Karhu, Jouni; Linkosalmi, Maiju; Tanis, Cemal Melih; Tuovinen, Juha-Pekka; Arslan, Ali Nadir (2018)
    In recent years, monitoring of the status of ecosystems using low-cost web (IP) or time lapse cameras has received wide interest. With broad spatial coverage and high temporal resolution, networked cameras can provide information about snow cover and vegetation status, serve as ground truths to Earth observations and be useful for gap-filling of cloudy areas in Earth observation time series. Networked cameras can also play an important role in supplementing laborious phenological field surveys and citizen science projects, which also suffer from observer-dependent observation bias. We established a network of digital surveillance cameras for automated monitoring of phenological activity of vegetation and snow cover in the boreal ecosystems of Finland. Cameras were mounted at 14 sites, each site having 1-3 cameras. Here, we document the network, basic camera information and access to images in the permanent data repository (http://www.zenodo.org/communities/phenology_camera/). Individual DOI-referenced image time series consist of half-hourly images collected between 2014 and 2016 (https://doi.org/10.5281/zenodo.1066862). Additionally, we present an example of a colour index time series derived from images from two contrasting sites.