Cyrus Samimi

Prof. Cyrus Samimi

Climatology, University of Bayreuth, Universitaetsstr. 30, 95447 Bayreuth, Germany
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Research Focus & Metrics

Academic Career Length

25Years (2002-Present)

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

Representative Publications

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4 February 2019 in Journal of Vegetation Science
Verified
Journal Article
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HBHelge Bruelheide
Helge Bruelheide
JDJürgen Dengler
Jürgen Dengler
BJBorja Jiménez‐Alfaro
Borja Jiménez‐Alfaro
OPOliver Purschke
Oliver Purschke
SHStephan M. Hennekens
Stephan M. Hennekens
AZAndrei Zverev
Andrei Zverev
Aims: Vegetation‐plot records provide information on the presence and cover or abundance of plants co‐occurring in the same community. Vegetation‐plot data are spread across research groups, environmental agencies and biodiversity research centers and, thus, are rarely accessible at continental or global scales. Here we present the sPlot database, which collates vegetation plots worldwide to allow for the exploration of global patterns in taxonomic, functional and phylogenetic diversity at the plant community level.Results: sPlot version 2.1 contains records from 1,121,244 vegetation plots, which comprise 23,586,216 records of plant species and their relative cover or abundance in plots collected worldwide between 1885 and 2015. We complemented the information for each plot by retrieving climate and soil conditions and the biogeographic context (e.g., biomes) from external sources, and by calculating community‐weighted means and variances of traits using gap‐filled data from the global plant trait database TRY. Moreover, we created a phylogenetic tree for 50,167 out of the 54,519 species identified in the plots. We present the first maps of global patterns of community richness and community‐weighted means of key traits.Conclusions: The availability of vegetation plot data in sPlot offers new avenues for vegetation analysis at the global scale.

21 June 2021 in Global Ecology and Biogeography
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Journal Article
Open access
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FSFrancesco Maria Sabatini
Francesco Maria Sabatini
JLJonathan Lenoir
Jonathan Lenoir
THTarek Hattab
Tarek Hattab
EAElise Aimee Arnst
Elise Aimee Arnst
MCMilan Chytrý
Milan Chytrý
HBHelge Bruelheide
Helge Bruelheide
Motivation: Assessing biodiversity status and trends in plant communities is critical for understanding, quantifying and predicting the effects of global change on ecosystems. Vegetation plots record the occurrence or abundance of all plant species co‐occurring within delimited local areas. This allows species absences to be inferred, information seldom provided by existing global plant datasets. Although many vegetation plots have been recorded, most are not available to the global research community. A recent initiative, called ‘sPlot’, compiled the first global vegetation plot database, and continues to grow and curate it. The sPlot database, however, is extremely unbalanced spatially and environmentally, and is not open‐access. Here, we address both these issues by (a) resampling the vegetation plots using several environmental variables as sampling strata and (b) securing permission from data holders of 105 local‐to‐regional datasets to openly release data. We thus present sPlotOpen, the largest open‐access dataset of vegetation plots ever released. sPlotOpen can be used to explore global diversity at the plant community level, as ground truth data in remote sensing applications, or as a baseline for biodiversity monitoring.Main types of variable contained: Vegetation plots (n = 95,104) recording cover or abundance of naturally co‐occurring vascular plant species within delimited areas. sPlotOpen contains three partially overlapping resampled datasets (c. 50,000 plots each), to be used as replicates in global analyses. Besides geographical location, date, plot size, biome, elevation, slope, aspect, vegetation type, naturalness, coverage of various vegetation layers, and source dataset, plot‐level data also include community‐weighted means and variances of 18 plant functional traits from the TRY Plant Trait Database.Spatial location and grain: Global, 0.01–40,000 m².Time period and grain: 1888–2015, recording dates.Major taxa and level of measurement: 42,677 vascular plant taxa, plot‐level records.Software format: Three main matrices (.csv), relationally linked.

8 January 2015 in Global Change Biology
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Journal Article
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MBMartin Brandt
Martin Brandt
CMCheikh Mbow
Cheikh Mbow
ADAbdoul Aziz Diouf
Abdoul Aziz Diouf
Aleixandre VergerAleixandre Verger
Aleixandre Verger
CSCyrus Samimi
Cyrus Samimi
RFRasmus Fensholt
Rasmus Fensholt

22 October 2019 in Scientific Reports
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Journal Article
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HZHarald Zandler
Harald Zandler
IHIsabell Haag
Isabell Haag
CSCyrus Samimi
Cyrus Samimi
Gridded datasets are of paramount importance to globally derive precipitation quantities for a multitude of scientific and practical applications. However, as most studies do not consider the impacts of temporal and spatial variations of included measurements in the utilized datasets, we conducted a quantitative assessment of the ability of several state of the art gridded precipitation products (CRU, GPCC Full Data Product, GPCC Monitoring Product, ERA-interim, ERA5, MERRA-2, MERRA-2 bias corrected, PERSIANN-CDR) to reproduce monthly precipitation values at climate stations in the Pamir mountains during two 15 year periods (1980–1994, 1998–2012) that are characterized by considerable differences in incorporated observation data. Results regarding the GPCC products illustrated a substantial and significant performance decrease with up to four times higher errors during periods with low observation inputs (1998–2012 with 2 stations on average per 124,000 km2) compared to periods with high quantities of regionally incorporated station data (1980–1994 with 14 stations on average per 124,000 km2). If independent stations were considered, the coefficient of efficiency indicated that only three of the gridded datasets (MERRA–2 bias corrected, GPCC, GPCC MP) performed better than the long term station mean for characterizing surface precipitation. Error patterns and magnitudes show that in complex terrain, evaluation of temporal and spatial variations of included observations is a prerequisite for using gridded precipitation products for scientific applications and to avoid overly optimistic performance assessments.

1 March 2015 in Remote Sensing of Environment
Verified
Journal Article
Closed access
HZHarald Zandler
Harald Zandler
Alexander BrenningAlexander Brenning
Alexander Brenning
CSCyrus Samimi
Cyrus Samimi

20 October 2011 in International Journal of Climatology
Verified
Journal Article
Open access
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HPHeiko Paeth
Heiko Paeth
AFAndreas H. Fink
Andreas H. Fink
SPSusan Pohle
Susan Pohle
FKFelix Keis
Felix Keis
HMHermann Mächel
Hermann Mächel
CSCyrus Samimi
Cyrus Samimi
In August and September 2007 media and aid organizations reported on a severe flood in large parts of sub‐Saharan Africa caused by a sequence of extreme rain events. However, the reporting was partly controversial and much was speculated about how unusual the flood event was. Here, we analyse various observational data sets in order to assess and to compare the spatio‐temporal characteristics and intensity of the flood and the associated rain events. The return times are estimated from daily precipitation time series at fine spatial resolution, and the potential causes are disclosed in a global and regional context.Satellite data reveal that the flood was not large scale but confined to the main river basins in sub‐Saharan West Africa. Nonetheless, abundant rainfall prevailed over large parts of Western Africa extending north into the Western Sahara, particularly during the second half of August and the beginning of September 2007. In detail, various precipitation data sets differ considerably in terms of the monthly anomalies, demonstrating the difficulty to delineate meteorological extreme events even at a sub‐continental scale and during the most recent past. Return times typically range between 1 and 50 years with high spatial heterogeneity but amount to 1200 years in the regional mean over the Upper Volta Basin. Among the potential causes we identify a La Niña event in the tropical Pacific, anomalous heating in the tropical Atlantic coming along with a greater depth of the monsoonal westerlies, and enhanced activity of African easterly waves, both evident in 2–6 day zonal wind and outgoing longwave radiation variance anomalies. Copyright © 2010 Royal Meteorological Society