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* Metric Name: Potential Climate Refugia -Baseline (Historical) Conditions  

* Tier: 3  

* Data Vintage: 1981 - 2010  

* Unit Of Measure: 0- 1. Low values indicate higher resilience to threats. High values indicate significant exposure to climate change. -1 represents ‘non analog’ areas, i.e. locations that are outside the historic climate envelope of a given vegetation type.  

* Metric Definition and Relevance: This raster dataset represents habitat types (natural vegetation communities) and their distribution across the array of climate conditions that each separate habitat type is found in under the baseline climate conditions. A 2015 map of the state’s natural vegetation compiled from multiple sources was classified to the National Vegetation Classification Standard’s mid-level classification, called “Macrogroup”. Thirty one natural vegetation macrogroups are identified in the map, covering 99.87% of the state’s natural terrestrial vegetation, and occupying 353,271 km2.

This serves as the foundation from which habitat types will be exposed to
predicted changes in climate. Data are arrayed across 0 to 1 in terms of their
exposure to current climate conditions. This data layer provides a baseline of
vegetation adapted to “historic” conditions; i.e. climate conditions from the
recent past; 1981-2010.

  

* Creation Method: The vegetation climate exposure analysis takes advantage of the 2015 vegetation map compiled for California by CALFIRE. Each Macrogroup (MG) was analyzed to determine which California habitats and associated dominant plant species make up its definition. California habitats are defined by the California Department of Fish and Wildlife (CDFW) through their California Wildlife Habitat Relationship (WHR) models9. WHR types are made up of plant species, such as the dominant trees, shrubs, and smaller plants. CDFW experts determined which WHR types correspond to each individual macrogroup; this cross-walk was used to develop a list of the dominant plant species that comprise each macrogroup.

The climate space occupied by each distinct vegetation macrogroup (largely
equivalent to a CWHR habitat type) from the current time period was
identified. This was done by using the points for each type and applying a
kernel density estimator on a 2-d surface composed of the first two principal
components of the climate conditions. The result is a smoothed continuous
point density surface, showing the prevalence of each vegetation type across
the range of sampled climatic conditions. This surface was partitioned by
fitting contour lines so that they enclose a proportion of the original points
from the current time period. Contours were calculated at 5% increments. For
example the innermost 5% contour line encloses the 5% of pixels for the given
vegetation type which are at the core of the climate space for that type, as
determined by its density in the climate space. Cells further away from the
dense central core, are considered to be more marginal in the vegetation
type’s distribution. The outer contours are fit to enclose the 95-99% of
climatically marginal points, with the last 1% of cells (beyond the 99%
contour) being the most marginal. In addition, if a cell lies outside the
space defined by the 99% contour of any vegetation type, it is considered to
be “non-analog,” which means that it experiences climatic conditions outside
of the conditions where we have a good sample in the initial time period.
Excluded from this assessment are non-vegetated types such as snow, open
water, and ice; and non-natural landcover types mapped as vineyards, tilled
earth, orchards and Urban.

For more information on methods for the development of these climate refugia
data see:

Thorne et al. 2015

Thorne et al. 2016

Thorne et al. 2017

Thorne et al. 2020

  

* Credits: Information Center for the Environment, UC Davis \--Jim Thorne