Ocean-Atmosphere Influence on North American Ecosystems: Patterns and Predictability
Dr. Matthew Dannenberg
School of Natural Resources & the Environment
University of Arizona
Terrestrial vegetation provides vital services to humanity but is highly sensitive to climate variability and change. Understanding how synoptic-scale oceanic and atmospheric circulation patterns affect vegetation may allow short-term, seasonal forecasts of relevant ecosystem processes while also providing insight into long-term responses of ecosystems to future climate change. Using more than three decades of satellite imagery, I demonstrate the high sensitivity of North American ecosystems to coupled ocean-atmosphere circulation patterns over the Pacific Ocean. Following winters with El Niño conditions in the tropical Pacific, vegetation growing seasons in the western United States start earlier and last longer, with much greater carbon uptake than during La Niña years. This response is partly attributable to shifts in cool-season Pacific storm tracks, which tend to occur further south during El Niño years and further north during La Niña years. These storm track shifts have a strong influence on both water and vegetation in western North America, with opposing impacts on Canadian and U.S. ecosystems: while north-shifted storm tracks increase moisture delivery and vegetation productivity in western Canada, they decrease moisture delivery and vegetation productivity in the western United States. These findings demonstrate that North American ecosystem processes are partly predictable several months prior to the growing season by knowing the state of the atmosphere over the Pacific during winter. Further, future warming will likely shift the mean and/or variability of these coupled ocean-atmosphere circulation systems, which could pose novel threats to many North American ecosystems when combined with likely increases in temperature and evaporative demand.