California Institute for Energy and Environment (CIEE)

Changes in ecosystems due to climate change or from climate mitigation measures may trigger follow-on changes in regional climate. These climate-ecosystem feedbacks are important because they may cause future climate change to be larger or smaller than predicted without considering these feedbacks. They also mean that climate mitigation involving land cover change, such as C sequestration by afforestation, may have local climate effects as well as global ones. This study uses a set of regional climate model (WRF-CLM3) simulations to quantify the climate effects of changes in ecosystem distribution under historical and future climate. The sensitivity of regional climate projections to vegetation change was investigated using three different vegetation distributions (Historic Native, Future Native, and Future Native + Afforestation) and two different global climate scenarios (GFDL 20th century and GFDL A2 Future). Results from 10-year model simulations suggest that vegetation change alone can lead to both increases and decreases in July midday temperatures of -1.5 to +5 °C, depending on subregion and vegetation-type change. Vegetation change accounts for up to 60% of statewide temperature change in snow-free regions due to the combination of large-scale (global) climate forcing and regional vegetation change. Afforestation may have effects on climate as well; the simulations indicate that a shift from shrubland to forest results in local temperature decreases of ~0.5-2 °C in snow-free regions. These temperature effects are the consequence of a complex set of changes to the surface energy budget and lower atmosphere.