Robert https://desp.ucdavis.edu/people/robert-j-hijmans

Dr. Robert https://desp.ucdavis.edu/people/robert-j-hijmans

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Research Focus & Metrics

Academic Career Length

31Years (1996-Present)

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

Representative Publications

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30 November 2005 in International Journal of Climatology
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RHRobert https://desp.ucdavis.edu/people/robert-j-hijmans
Robert https://desp.ucdavis.edu/people/robert-j-hijmans
SCSusan E. Cameron
Susan E. Cameron
JPJuan L. Parra
Juan L. Parra
PJPeter G. Jones
Peter G. Jones
AJAndy Jarvis
Andy Jarvis
We developed interpolated climate surfaces for global land areas (excluding Antarctica) at a spatial resolution of 30 arc s (often referred to as 1‐km spatial resolution). The climate elements considered were monthly precipitation and mean, minimum, and maximum temperature. Input data were gathered from a variety of sources and, where possible, were restricted to records from the 1950–2000 period. We used the thin‐plate smoothing spline algorithm implemented in the ANUSPLIN package for interpolation, using latitude, longitude, and elevation as independent variables. We quantified uncertainty arising from the input data and the interpolation by mapping weather station density, elevation bias in the weather stations, and elevation variation within grid cells and through data partitioning and cross validation. Elevation bias tended to be negative (stations lower than expected) at high latitudes but positive in the tropics. Uncertainty is highest in mountainous and in poorly sampled areas. Data partitioning showed high uncertainty of the surfaces on isolated islands, e.g. in the Pacific. Aggregating the elevation and climate data to 10 arc min resolution showed an enormous variation within grid cells, illustrating the value of high‐resolution surfaces. A comparison with an existing data set at 10 arc min resolution showed overall agreement, but with significant variation in some regions. A comparison with two high‐resolution data sets for the United States also identified areas with large local differences, particularly in mountainous areas. Compared to previous global climatologies, ours has the following advantages: the data are at a higher spatial resolution (400 times greater or more); more weather station records were used; improved elevation data were used; and more information about spatial patterns of uncertainty in the data is available. Owing to the overall low density of available climate stations, our surfaces do not capture of all variation that may occur at a resolution of 1 km, particularly of precipitation in mountainous areas. In future work, such variation might be captured through knowledge‐based methods and inclusion of additional co‐variates, particularly layers obtained through remote sensing. Copyright © 2005 Royal Meteorological Society.

29 March 2006 in Ecography
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JEJane Elith
Jane Elith
CGCatherine H. Graham
Catherine H. Graham
RARobert P. Anderson
Robert P. Anderson
MDMiroslav Dudík
Miroslav Dudík
SFSimon Ferrier
Simon Ferrier
NZNiklaus Zimmermann
Niklaus Zimmermann
Prediction of species’ distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence‐only data to fit models, and independent presence‐absence data to evaluate the predictions. Along with well‐established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species’ distributions. These include machine‐learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species’ occurrence data. Presence‐only data were effective for modelling species’ distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.

12 August 2008 in Diversity and Distributions
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MWM. S. Wisz
M. S. Wisz
RHRobert https://desp.ucdavis.edu/people/robert-j-hijmans
Robert https://desp.ucdavis.edu/people/robert-j-hijmans
JLJ. Li
J. Li
APA. Townsend Peterson
A. Townsend Peterson
CGC. H. Graham
C. H. Graham
NGNCEAS Predicting Species Distributions Working Group
NCEAS Predicting Species Distributions Working Group
A wide range of modelling algorithms is used by ecologists, conservation practitioners, and others to predict species ranges from point locality data. Unfortunately, the amount of data available is limited for many taxa and regions, making it essential to quantify the sensitivity of these algorithms to sample size. This is the first study to address this need by rigorously evaluating a broad suite of algorithms with independent presence–absence data from multiple species and regions. We evaluated predictions from 12 algorithms for 46 species (from six different regions of the world) at three sample sizes (100, 30, and 10 records). We used data from natural history collections to run the models, and evaluated the quality of model predictions with area under the receiver operating characteristic curve (AUC). With decreasing sample size, model accuracy decreased and variability increased across species and between models. Novel modelling methods that incorporate both interactions between predictor variables and complex response shapes (i.e. GBM, MARS‐INT, BRUTO) performed better than most methods at large sample sizes but not at the smallest sample sizes. Other algorithms were much less sensitive to sample size, including an algorithm based on maximum entropy (MAXENT) that had among the best predictive power across all sample sizes. Relative to other algorithms, a distance metric algorithm (DOMAIN) and a genetic algorithm (OM‐GARP) had intermediate performance at the largest sample size and among the best performance at the lowest sample size. No algorithm predicted consistently well with small sample size (n < 30) and this should encourage highly conservative use of predictions based on small sample size and restrict their use to exploratory modelling.

20 October 2006 in Global Change Biology
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RHRobert https://desp.ucdavis.edu/people/robert-j-hijmans
Robert https://desp.ucdavis.edu/people/robert-j-hijmans
CGCatherine H. Graham
Catherine H. Graham

20 March 2010
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RHRobert https://desp.ucdavis.edu/people/robert-j-hijmans
Robert https://desp.ucdavis.edu/people/robert-j-hijmans

8 April 2013 in Proceedings of the National Academy of Sciences
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LHLee Hannah
Lee Hannah
PRPatrick R. Roehrdanz
Patrick R. Roehrdanz
IMIKEGAMI Makihiko
IKEGAMI Makihiko
ASAnderson V. Shepard
Anderson V. Shepard
MSM. Rebecca Shaw
M. Rebecca Shaw
RHRobert https://desp.ucdavis.edu/people/robert-j-hijmans
Robert https://desp.ucdavis.edu/people/robert-j-hijmans
Climate change is expected to impact ecosystems directly, such as through shifting climatic controls on species ranges, and indirectly, for example through changes in human land use that may result in habitat loss. Shifting patterns of agricultural production in response to climate change have received little attention as a potential impact pathway for ecosystems. Wine grape production provides a good test case for measuring indirect impacts mediated by changes in agriculture, because viticulture is sensitive to climate and is concentrated in Mediterranean climate regions that are global biodiversity hotspots. Here we demonstrate that, on a global scale, the impacts of climate change on viticultural suitability are substantial, leading to possible conservation conflicts in land use and freshwater ecosystems. Area suitable for viticulture decreases 25% to 73% in major wine producing regions by 2050 in the higher RCP 8.5 concentration pathway and 19% to 62% in the lower RCP 4.5. Climate change may cause establishment of vineyards at higher elevations that will increase impacts on upland ecosystems and may lead to conversion of natural vegetation as production shifts to higher latitudes in areas such as western North America. Attempts to maintain wine grape productivity and quality in the face of warming may be associated with increased water use for irrigation and to cool grapes through misting or sprinkling, creating potential for freshwater conservation impacts. Agricultural adaptation and conservation efforts are needed that anticipate these multiple possible indirect effects.