Sabrina Hempel

Dr. Sabrina Hempel

Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB)
orcid

Research Focus & Metrics

Academic Career Length

16Years (2011-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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31 July 2013 in Earth System Dynamics
Verified
Journal Article
Open access
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Sabrina HempelSabrina Hempel
Sabrina Hempel
KFK. Frieler
K. Frieler
LWL. Warszawski
L. Warszawski
JSJ. Schewe
J. Schewe
FPF. Piontek
F. Piontek
Statistical bias correction is commonly applied within climate impact modelling to correct climate model data for systematic deviations of the simulated historical data from observations. Methods are based on transfer functions generated to map the distribution of the simulated historical data to that of the observations. Those are subsequently applied to correct the future projections. Here, we present the bias correction method that was developed within ISI-MIP, the first Inter-Sectoral Impact Model Intercomparison Project. ISI-MIP is designed to synthesise impact projections in the agriculture, water, biome, health, and infrastructure sectors at different levels of global warming. Bias-corrected climate data that are used as input for the impact simulations could be only provided over land areas. To ensure consistency with the global (land + ocean) temperature information the bias correction method has to preserve the warming signal. Here we present the applied method that preserves the absolute changes in monthly temperature, and relative changes in monthly values of precipitation and the other variables needed for ISI-MIP. The proposed methodology represents a modification of the transfer function approach applied in the Water Model Intercomparison Project (Water-MIP). Correction of the monthly mean is followed by correction of the daily variability about the monthly mean. Besides the general idea and technical details of the ISI-MIP method, we show and discuss the potential and limitations of the applied bias correction. In particular, while the trend and the long-term mean are well represented, limitations with regards to the adjustment of the variability persist which may affect, e.g. small scale features or extremes.

26 July 2011 in Physical Review Letters
Verified
Journal Article
Closed access
Sabrina HempelSabrina Hempel
Sabrina Hempel
AKA. Koseska
A. Koseska
JKJ. Kurths
J. Kurths
ZNZ. Nikoloski
Z. Nikoloski
Identifying causal links (couplings) is a fundamental problem that facilitates the understanding of emerging structures in complex networks. We propose and analyze inner composition alignment\char22{}a novel, permutation-based asymmetric association measure to detect regulatory links from very short time series, currently applied to gene expression. The measure can be used to infer the direction of couplings, detect indirect (superfluous) links, and account for autoregulation. Applications to the gene regulatory network of E.~coli are presented.

5 December 2019 in Earth System Dynamics
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Journal Article
Open access
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Sabrina HempelSabrina Hempel
Sabrina Hempel
CMChristoph Menz
Christoph Menz
SPSeverino Pinto
Severino Pinto
EGElena Galán
Elena Galán
David JankeDavid Janke
David Janke
Thomas AmonThomas Amon
Thomas Amon
In the last decades, a global warming trend was observed. Along with the temperature increase, modifications in the humidity and wind regime amplify the regional and local impacts on livestock husbandry. Direct impacts include the occurrence of climatic stress conditions. In Europe, cows are economically highly relevant and are mainly kept in naturally ventilated buildings that are most susceptible to climate change. The high-yielding cows are particularly vulnerable to heat stress. Modifications in housing management are the main measures taken to improve the ability of livestock to cope with these conditions. Measures are typically taken in direct reaction to uncomfortable conditions instead of in anticipation of a long-term risk for climatic stress. Measures that balance welfare, environmental and economic issues are barely investigated in the context of climate change and are thus almost not available for commercial farms. Quantitative analysis of the climate change impacts on animal welfare and linked economic and environmental factors is rare. Therefore, we used a numerical modeling approach to estimate the future heat stress risk in such dairy cattle husbandry systems. The indoor climate was monitored inside three reference barns in central Europe and the Mediterranean regions. An artificial neuronal network (ANN) was trained to relate the outdoor weather conditions provided by official meteorological weather stations to the measured indoor microclimate. Subsequently, this ANN model was driven by an ensemble of regional climate model projections with three different greenhouse gas concentration scenarios. For the evaluation of the heat stress risk, we considered the number and duration of heat stress events. Based on the changes in the heat stress events, various economic and environmental impacts were estimated. The impacts of the projected increase in heat stress risk varied among the barns due to different locations and designs as well as the anticipated climate change (considering different climate models and future greenhouse gas concentrations). There was an overall increasing trend in number and duration of heat stress events. At the end of the century, the number of annual stress events can be expected to increase by up to 2000, while the average duration of the events increases by up to 22 h compared to the end of the last century. This implies strong impacts on economics, environment and animal welfare and an urgent need for mid-term adaptation strategies. We anticipated that up to one-tenth of all hours of a year, correspondingly one-third of all days, will be classified as critical heat stress conditions. Due to heat stress, milk yield may decrease by about 2.8 % relative to the present European milk yield, and farmers may expect financial losses in the summer season of about 5.4 % of their monthly income. In addition, an increasing demand for emission reduction measures must be expected, as an emission increase of about 16 Gg of ammonia and 0.1 Gg of methane per year can be expected under the anticipated heat stress conditions. The cattle respiration rate increases by up to 60 %, and the standing time may be prolonged by 1 h. This causes health issues and increases the probability of medical treatments. The various impacts imply feedback loops in the climate system which are presently underexplored. Hence, future in-depth studies on the different impacts and adaptation options at different stress levels are highly recommended.

1 May 2016 in Biosystems Engineering
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Journal Article
Open access
Sabrina HempelSabrina Hempel
Sabrina Hempel
Chayan SahaChayan Saha
Chayan Saha
MFMerike Fiedler
Merike Fiedler
WBWerner Berg
Werner Berg
CHChristiane Hansen
Christiane Hansen
Thomas AmonThomas Amon
Thomas Amon
Ammonia (NH3) and methane (CH4) emissions from naturally ventilated dairy barns affect the environment and the wellbeing of humans and animals. Our study improves the understanding of the dependency of emission rates on climatic conditions with a particular focus on temperature. Previous investigations of the relation between gas emission and temperature mainly rely on linear regression or correlation analysis.We take up a preceding study presenting a multilinear regression model based on NH3 and CH4 concentration and temperature measurements between 2010 and 2012 in a dairy barn for 360 cows in Northern Germany. We study scatter plots and non-linear regression models for a subset of these data and show that the linear approximation comes to its limits when large temperature ranges are considered. The functional dependency of the emission rates on temperature differs among the gases. For NH3, the exponential dependency assumed in previous studies was proven. For methane, a parabolic relation was found. The emissions show large daily and annual variations and environmental impact factors like wind and humidity superimpose the temperature dependency but the functional shape in general persists.Complementary to the former insight that high temperature increases emissions, we found that in the case of CH4, also temperatures below 10 °C lead to an increase in emissions from ruminal fermentation which is likely to be due to a change in animal activity. The improved prediction of emissions by the novel non-linear model may support more accurate economic and ecological assessments of smart barn concepts

19 July 2011 in BMC Bioinformatics
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Journal Article
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Sabrina HempelSabrina Hempel
Sabrina Hempel
AKAneta Koseska
Aneta Koseska
ZNZoran Nikoloski
Zoran Nikoloski
JKJürgen Kurths
Jürgen Kurths
Inferring regulatory interactions between genes from transcriptomics time-resolved data, yielding reverse engineered gene regulatory networks, is of paramount importance to systems biology and bioinformatics studies. Accurate methods to address this problem can ultimately provide a deeper insight into the complexity, behavior, and functions of the underlying biological systems. However, the large number of interacting genes coupled with short and often noisy time-resolved read-outs of the system renders the reverse engineering a challenging task. Therefore, the development and assessment of methods which are computationally efficient, robust against noise, applicable to short time series data, and preferably capable of reconstructing the directionality of the regulatory interactions remains a pressing research problem with valuable applications.

1 April 2018 in Energy and Buildings
Verified
Journal Article
Closed access
Qianying YiQianying Yi
Qianying Yi
GZGuoqiang Zhang
Guoqiang Zhang
MKMarcel König
Marcel König
David JankeDavid Janke
David Janke
Sabrina HempelSabrina Hempel
Sabrina Hempel
Thomas AmonThomas Amon
Thomas Amon