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Braun S.,Institute for Applied Plant Biology | Achermann B.,Federal Office for the Environment | De Marco A.,ENEA | Pleijel H.,Gothenburg University | And 4 more authors.
Science of the Total Environment | Year: 2017

For human health studies, epidemiology has been established as important tool to examine factors that affect the frequency and distribution of disease, injury, and other health-related events in a defined population, serving the purpose of establishing prevention and control programs. On the other hand, gradient studies have a long tradition in the research of air pollution effects on plants. While there is no principal difference between gradient and epidemiological studies, the former address more one-dimensional transects while the latter focus more on populations and include more experience in making quantitative predictions, in dealing with confounding factors and in taking into account the complex interplay of different factors acting at different levels. Epidemiological analyses may disentangle and quantify the contributions of different predictor variables to an overall effect, e.g. plant growth, and may generate hypotheses deserving further study in experiments. Therefore, their use in ecosystem research is encouraged. This article provides a number of recommendations on: (1) spatial and temporal aspects in preparing predictor maps of nitrogen deposition, ozone exposure and meteorological covariates; (2) extent of a dataset required for an analysis; (3) choice of the appropriate regression model and conditions to be satisfied by the data; (4) selection of the relevant explanatory variables; (5) treatment of interactions and confounding factors; and (6) assessment of model validity. © 2017 Elsevier B.V.

Braun S.,Institute for Applied Plant Biology | Schindler C.,Swiss Tropical and Public Health Institute | Rihm B.,Meteotest
Science of the Total Environment | Year: 2017

Understanding the effects of nitrogen deposition, ozone and climate on tree growth is important for planning sustainable forest management also in the future. The complex interplay of all these factors cannot be covered by experiments. Here we use observational data of mature forests for studying associations of various biotic and abiotic factors with tree growth. A 30 year time series on basal area increment of Fagus sylvatica L. and Picea abies Karst. in Switzerland was analyzed to evaluate the development in relation to a variety of predictors. Basal area increment of Fagus sylvatica has clearly decreased during the observation period. For Picea abies no trend was observed. N deposition of more than 26 (beech) or 20–22 kg N ha− 1 year− 1 (Norway spruce) was negatively related with basal area increment, in beech stronger than in Norway spruce. High N deposition loads and low foliar K concentrations in Fagus were correlated with increased drought sensitivity. High air temperatures in winter were negatively related with basal area increment in Norway spruce in general and in beech at high N:Mg ratio or high N deposition while on an average the relation was positive in beech. Fructification in beech was negatively related to basal area increment. The increase of fructification observed during the last decades contributed thus to the growth decrease. Ozone flux was significantly and negatively correlated with basal area increment both in beech and Norway spruce. The results show clear non-linear effects of N deposition on stem increment of European beech and Norway spruce as well as strong interactions with climate which have contributed to the growth decrease in beech and may get more important in future. The results not only give suggestions for ecological processes but also show the potential of an integral evaluation of observational data. © 2017 Elsevier B.V.

Braun S.,Institute for Applied Plant Biology | Schindler C.,Swiss Tropical and Public Health Institute | Rihm B.,Meteotest
Environmental Pollution | Year: 2014

The estimate of growth losses by ozone exposure of forest trees is a significant part in current C sequestration calculations and will also be important in future modeling. It is therefore important to know if the relationship between ozone flux and growth reduction of young trees, used to derive a Critical Level for ozone, is also valid for mature trees. Epidemiological analysis of stem increment data from Fagus sylvatica L. and Picea abies Karst. observed in Swiss forest plots was used to test this hypothesis. The results confirm the validity of the flux-response relationship at least for beech and therefore enable estimating forest growth losses by ozone on a country-wide scale. For Switzerland, these estimates amount to 19.5% growth reduction for deciduous forests, 6.6% for coniferous forests and 11.0% for all forested areas based on annual ozone stomatal uptake during the time period 1991-2011. © 2014 Elsevier Ltd. All rights reserved.

Sprenger M.,ETH Zurich | Schemm S.,University of Bergen | Schemm S.,Bjerknes Center for Climate Research | Oechslin R.,Meteotest | Jenkner J.,UBIMET GmbH
Weather and Forecasting | Year: 2017

The south foehn is a characteristic downslope windstorm in the valleys of the northern Alps in Europe that demands reliable forecasts because of its substantial economic and societal impacts. Traditionally, a foehn is predicted based on pressure differences and tendencies across the Alpine ridge. Here, a new objective method for foehn prediction is proposed based on a machine learning algorithm (called AdaBoost, short for adaptive boosting). Three years (2000-02) of hourly simulations of the Consortium for Small-Scale Modeling's (COSMO) numerical weather prediction (NWP) model and corresponding foehn wind observations are used to train the algorithm to distinguish between foehn and nonfoehn events. The predictors (133 in total) are subjectively extracted from the 7-km COSMO reanalysis dataset based on the main characteristics of foehn flows. The performance of the algorithm is then assessed with a validation dataset based on a contingency table that concisely summarizes the cooccurrence of observed and predicted (non)foehn events. The main performance measures are probability of detection (88.2%), probability of false detection (2.9%), missing rate (11.8%), correct alarm ratio (66.2%), false alarm ratio (33.8%), and missed alarm ratio (0.8%). To gain insight into the prediction model, the relevance of the single predictors is determined, resulting in a predominance of pressure differences across the Alpine ridge (i.e., similar to the traditional methods) and wind speeds at the foehn stations. The predominance of pressure-related predictors is further established in a sensitivity experiment where ~2500 predictors are objectively incorporated into the prediction model using the AdaBoost algorithm. The performance is very similar to the run with the subjectively determined predictors. Finally, some practical aspects of the new foehn index are discussed (e.g., the predictability of foehn events during the four seasons). The correct alarm rate is highest in winter (86.5%), followed by spring (79.6%), and then autumn (69.2%). The lowest rates are found in summer (51.2%). © 2017 American Meteorological Society.

Baumgartner F.P.,ZHAW Zurich University of Applied Sciences | Achtnich T.,ZHAW Zurich University of Applied Sciences | Remund J.,Meteotest | Gnos S.,NET Nowak Energie and Technology AG | Nowak S.,NET Nowak Energie and Technology AG
Progress in Photovoltaics: Research and Applications | Year: 2011

The high growth rate of photovoltaic (PV) installations leads to the question about the consequences for grid integration and management. As a case study, we present an analysis of the first limits for the amount of PV electricity in the utility grid of the greater Zurich area. The first limit is found at an amount of 6% of the yearly electricity generation from PV, where the PV generation capacity begins to exceed the daytime increase of the load profile. This scenario assumes no changes of the daily constant base load generation. If the PV power is further increased to an amount of 10% of the overall electricity generation, about 8% of the PV electricity production could find no demand, starting with a surplus of PV production at noon at sunny weekends in summer time. This would reduce the nominal working hours of the PV plants by 8%, increasing the PV generation costs by the same factor. An amount of 17% of PV generation can be reached in the Zurich utility grid by storing the surplus of unused PV electricity as produced, by the widely available pumped hydro plants in the Swiss Alps. The 17% PV target would also be possible without storage, but it would require reducing the base load power production in favour of PV electricity generation. To further increase the amount of PV electricity generation above 20%, low cost storage means or changes of the load profile would be required. © 2010 John Wiley & Sons, Ltd.

Belyazid S.,Belyazid Consulting and Communication | Kurz D.,EKG Geoscience | Braun S.,Institute For Angewandte Planzenbiologie | Sverdrup H.,Lund University | And 2 more authors.
Environmental Pollution | Year: 2011

A dynamic model of forest ecosystems was used to investigate the effects of climate change, atmospheric deposition and harvest intensity on 48 forest sites in Sweden (n = 16) and Switzerland (n = 32). The model was used to investigate the feasibility of deriving critical loads for nitrogen (N) deposition based on changes in plant community composition. The simulations show that climate and atmospheric deposition have comparably important effects on N mobilization in the soil, as climate triggers the release of organically bound nitrogen stored in the soil during the elevated deposition period. Climate has the most important effect on plant community composition, underlining the fact that this cannot be ignored in future simulations of vegetation dynamics. Harvest intensity has comparatively little effect on the plant community in the long term, while it may be detrimental in the short term following cutting. This study shows: that critical loads of N deposition can be estimated using the plant community as an indicator; that future climatic changes must be taken into account; and that the definition of the reference deposition is critical for the outcome of this estimate. © 2010 Elsevier Ltd. All rights reserved.

Roth T.,Hintermann and Weber AG | Roth T.,University of Basel | Kohli L.,Hintermann and Weber AG | Rihm B.,Meteotest | Achermann B.,Federal Office for the Environment FOEN
Agriculture, Ecosystems and Environment | Year: 2013

Nitrogen (N) deposition is a major threat to biodiversity of many habitats in the lowlands. In mountain habitats, however, the effect of N deposition on biodiversity is not well understood. Here, data from the biodiversity monitoring of Switzerland were used to investigate whether high N deposition is negatively related to species richness and community uniqueness of vascular plants and bryophytes in mountain grassland. The total species diversity, as well as the diversity of three subsets of species (i.e. oligotrophic species, eutrophic species and targeted grassland species according to conservation objectives of the Swiss authorities) were analyzed. Overall, the empirical data from the present study indicate that the currently expert-based range of the critical load of N deposition below which harmful effects on sensitive ecosystems should not occur (upper bound is currently at 20kg Nha-1yr-1) is set too large for mountain hay meadows. Negative relations between N deposition and species richness and community uniqueness in mountain grassland were found already at 10-15kg Nha-1yr-1. The results suggest that the negative effect of N deposition on plant diversity is mainly due to a decrease of oligotrophic plant species and to a lesser extent to an increase in eutrophic plant species. While for bryophytes, the decrease of community uniqueness is related to changes in both oligotrophic and eutrophic species. Furthermore, because plant species richness of target species for conservation was negatively related to N deposition, airborne N deposition is likely to defeat conservation efforts in mountain grassland. © 2013 Elsevier B.V.

Hiller R.V.,ETH Zurich | Hiller R.V.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Neininger B.,Airborne | Brunner D.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2014

For regional-scale investigations of greenhouse gas budgets the spatially explicit information from local emission sources is needed, which then can be compared with flux measurements. Here we present the first validation of a section of a spatially explicit CH4 emission inventory of Switzerland. The validation was done for the agriculturally dominated Reuss Valley using measurements from a low-flying aircraft (50-500 m above ground level). We distributed national emission estimates to a grid with 500 m cell size using available geostatistical data. Validation flux measurements were obtained using the eddy covariance (EC) technique and the boundary layer budgeting (BLB) approach that only uses the mean concentrations of the same aircraft transects. Inventory estimates for the flux footprint of the aircraft measurements were lowest (median 0.40 μg CH4m-2s -1), and BLB fluxes were highest (1.02 μg CH4m -2s-1) for the Reuss Valley, with EC fluxes in between (0.62 μg CH4m-2s-1). Flux estimates from measurements and inventory are within the same order of magnitude, but measured fluxes were significantly larger than the inventory emission estimates. The differences are larger than the uncertainties associated with storage of manure, temperature dependence of emissions, diurnal cycle of enteric fermentation by cattle, and the limitations of the inventory that only covers ≥90% of all expected methane emissions. From this we deduce that it is not unlikely that the Swiss CH4 emission inventory estimates are too low. Key Points CH4 emission inventory estimates from Swiss agriculture may be too low Cavity ring-down CH4 spectrometer works reliably on small aircraft (motorglider) Eddy covariance flux more reliable than the boundary layer budget approach. © 2014. American Geophysical Union. All Rights Reserved.

Stucki P.,University of Bern | Bronnimann S.,University of Bern | Martius O.,University of Bern | Welker C.,University of Bern | And 5 more authors.
Bulletin of the American Meteorological Society | Year: 2015

A high-impact foehn storm was reconstructed in the Swiss Alps that occurred on 15 February 1925. The weather event and the related impact patterns were analyzed by traditional documentary means. Then, we feed dynamically downscaled wind fields of the Twentieth Century Reanalysis (20CR) ensemble dataset into an open-source economic loss model. The 20CR sets the boundary conditions for the high-resolution downscaling. In the reanalysis, a deep surface low is located over Great Britain and surface air pressure increases toward southeastern Europe at 0000 UTC on 15 February 1925. Mean sea level pressure (MSLP) differences across the Alps are approximately 5.5 hPa. 20CR ensemble mean fields provide the initial and lateral boundary conditions that drive the regional, higher-resolution Weather Research and Forecasting (WRF) model for a limited domain over Europe. The generally accurate and dynamically consistent wind fields from WRF output provide an encouraging basis for modeling the storm-related losses. High damage is typically related to maximum wind gusts. For each municipality, the monetary damage is simulated based on the product between the respec?tive asset value and a nonlinear damage function.

PubMed | University of Basel, Federal Office for the Environment FOEN, Hintermann & Weber AG and Meteotest
Type: Journal Article | Journal: Environmental pollution (Barking, Essex : 1987) | Year: 2016

To protect ecosystems and their services, the critical load concept has been implemented under the framework of the Convention on Long-range Transboundary Air Pollution (UNECE) to develop effects-oriented air pollution abatement strategies. Critical loads are thresholds below which damaging effects on sensitive habitats do not occur according to current knowledge. Here we use change-point models applied in a Bayesian context to overcome some of the difficulties when estimating empirical critical loads for nitrogen (N) from empirical data. We tested the method using simulated data with varying sample sizes, varying effects of confounding variables, and with varying negative effects of N deposition on species richness. The method was applied to the national-scale plant species richness data from mountain hay meadows and (sub)alpine scrubs sites in Switzerland. Seven confounding factors (elevation, inclination, precipitation, calcareous content, aspect as well as indicator values for humidity and light) were selected based on earlier studies examining numerous environmental factors to explain Swiss vascular plant diversity. The estimated critical load confirmed the existing empirical critical load of 5-15kgN ha

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