The 2000-2003 drought in the American southwest triggered a widespread die-off of forests around the region. A Carnegie-led team of scientists developed a new modeling tool to explain how and where trembling aspen forests died as a result of this drought. It is based on damage to an individual trees' ability to transport water under water-stressed conditions. If the same processes and threshold govern the future, their results suggest that more widespread die-offs of aspen forests triggered by climate change are likely by the 2050s.