Climate analogs are locations on a landscape that share similar climatic characteristics to a site of interest. In the context of climate change, climate analogs use a space for time substitution and are increasingly used to evaluate climate change exposure, contextualize what a future climate may look like in a given location, and evaluate ecological impacts of climate change, such as shifting vegetation types. The use of climate analogs assumes that areas with similar climate also share similar ecological processes, yet there have been no formal evaluations of this assumption. Above-ground carbon storage at a location integrates growing conditions but is also sensitive to a range of non-climatic processes including disturbance and historical contingencies. This study attempts to validate a climate analog approach for forecasting climate change impacts using a retrospective analysis. We identify climate analogs under current conditions and use them to estimate above-ground carbon storage at twenty nine thousand Forest Inventory and Analysis (FIA) plots in the western US. To identify analogs, we use four climatic variables, mean minimum and maximum temperature, climatic water deficit and actual evapotranspiration, over the 1960-1990 reference period. We assess bias and precision in analog estimates of carbon storage and examine the relationship between these metrics and climatic and geographic distance between target sites and their analog sites.
Results/Conclusions
The number of analogs for an FIA plot ranges from 1 to 3609, with a median of 534. Mean difference between focal plot carbon and the mean of its analogs is -0.16 Mg/ha, suggesting that there is little overall bias in carbon estimate using the climate analog approach (mean plot carbon is 52.02 Mg/ha). We find varying relationships between carbon bias and geographic distance and expand on the implications of these results for using an analog approach . We expect that these findings will test ecological validity and provide support for the utility of climate analogs as a climate impact assessment tool.