After several years of debilitating drought, California experienced this year its wettest winter on record. Water returned to California's rivers and reservoirs, the Sierra Nevadas were buried beneath a near-record snowpack, and Governor Jerry Brown lifted the drought emergency across the majority of the state. But while the drought may have ended, recovery has likely just begun for the state's ecosystems. A new study, published today in Nature, is one of the first to zero in on the factors that determine how long it takes for an ecosystem to return to pre-drought levels of photosynthesis and growth.
"When we think about drought impacts on ecosystems or on forests, we tend to stop paying attention once the rainfall returns to normal, once the drought from a climate perspective is done," says William Anderegg, an assistant professor at the University of Utah and an author on the study. "We hadn't really zoomed in on the recovery period as a key piece of an ecosystem's resilience to changes in climate."
To fill in this gap, Anderegg and his colleagues used data collected from satellites and land-based observation sites to estimate photosynthesis rates around the globe and find out which ecosystems recovered faster after droughts. They also wanted to pinpoint which factors controlled the pace of recovery. The team found that temperature and precipitation had a large effect on recovery times. Wetter conditions, like those that followed California's most recent drought, sped up recovery, while both hot or cold temperature extremes slowed recovery down.
"As droughts get more frequent and severe due to climate change, multiple droughts could occur before an ecosystem has recovered."
There were also regional differences. While most of the globe recovered from drought in mere months, high latitude Arctic forests and those in the tropics often took two years or more.
"The big concern here is that, as droughts get more frequent and severe due to climate change, multiple droughts could occur before an ecosystem has recovered," Anderegg says. "That really increases the odds that you have a complete crash and loss of an ecosystem."
This is of particular concern in the tropics, which harbor a greater number of species of plants and animals than anywhere else on the planet and take in a significant amount of the carbon dioxide humans pump into the atmosphere. If droughts start to hit faster than these systems can recover, it could lead to an alarming feedback loop of increased warming and more extreme climates.
How are human beings supposed to prevent such a scenario? On a local scale, identifying species or ecosystems that are resilient to drought is one way to help land managers provide a buffer to an area. Of course, none of that will matter if climate change continues unchecked.
"The amount of climate change that occurs matters enormously," Anderegg says. "Slowing climate change is the single best strategy."