Changes in Plant Hardiness Zones under Climate Change Scenarios in the South-Central United States

Abstract Climate change scenarios have been developed for the south-central United States, indicating a minimum temperature change. These scenarios have combined multiple emission scenarios, global climate model simulations, and statistical downscaling techniques. The scenarios are for the midcentury (2036–65) and far-future (2070–99) period. Based on the USDA definitions, plant hardiness zones were delineated under different climate change scenarios. These zones divide the geography into zones by 10°F (5.56°C) increments from each zone. Climate projections developed from RCP4.5 and RCP8.5 emission scenarios project an increase in minimum temperature, while climate projections under the RCP2.6 emissions’ scenario (RCP2.6; 2070–99) project a decrease in minimum temperature. The increase in minimum temperature triggers an expansion of warm plant hardiness zones (PHZs). In the ensemble mean of climate projections under RCP8.5, 2070–99, 27% of the south-central United States will change from hardiness zones 9a and 9b to 10a and 10b, and 23% will change from PHZ10 (10a and 10b) to PHZ11 (11a and 11b). The most significant transition in all climate change scenarios occurs from PHZ9 to PHZ10. Plant hardiness zone mapping under diverse climate change scenarios corroborates that the southern region of Texas may experience heat stress, while Colorado and Kansas may benefit from an expansion of thermally suitable areas for plant growth.