Projections of Rangeland Fractional Component Cover Across Western US Rangelands for Representative Concentration Pathways (RCP) 4.5 and 8.5 Scenarios for the 2020s, 2050s, and 2080s Time-Periods

Climate change over the past century has altered vegetation community composition and species distributions across rangelands in the western United States. The scale and magnitude of climatic influences are largely unknown. While a number of studies have projected the impacts of climate change using several modeling approaches, none has evaluated impacts to fractional component cover at a 30-m resolution across rangelands of the Western U.S. We used fractional component cover data for rangeland functional groups and weather data from the 1985 to 2021 reference period in conjunction with soils and topography data to develop empirical models describing the spatio-temporal variation in component cover. To investigate the ramifications of future change across the western US, we extended models based on historical relationships over the reference period to model landscape effects based on future weather conditions from two emissions scenarios (Representative Concentration Pathways [RCP] 4.5 and 8.5) and three time periods (2020s, 2050s, and 2080s). We tested both Generalized Additive Models (GAMs) and Deep Neural Network (DNN) models, finding that the latter led to superior spatial and statistical results. We build upon the projections of Rigge 2022, expanding our study area to include the entire Rangeland Condition Monitoring Assessment and Projection (RCMAP) study area (including all the sagebrush biome), using updated climate projections (Mahony et al. 2022), and applying a DNN classifier. Our results suggest more xeric vegetation across most of the study area, with an increasing dominance of non-sagebrush shrubs, annual herbaceous, and bare ground over herbaceous and sagebrush cover in both RCP scenarios. In general, both scenarios yielded similar results, but RCP 8.5 tended to be more extreme, with greater change relative to the reference period. Results demonstrate that in cool sites some degree of warming to growing season maximum temperature or non-growing season minimum temperature could be beneficial to sagebrush and shrub growth. This is not the case, regardless of temperature, for non-growing season maximum temperature. This information can be used to inform management to prepare for future vegetation composition and cover through the prioritization of conservation and restoration and shed light on species’ range shifts.

Users are encouraged to utilize this newest generations of projections due to lower error and broader geographic extent relative to (Rigge et al. 2022).