Defining ecological drought for the twenty-first century

This situation increases the vulnerability of ecosystems to drought, including a rise in drought-driven tree mortality globally (Allen et al. 2015) and anticipated ecosystem transformations from one state to another -- for example, forest to a shrubland (Jiang et al. 2013).

When a drought drives changes within ecosystems, there can be a ripple effect through human communities that depend on those ecosystems for critical goods and services (Millar and Stephenson 2015). For example, the "Millennium Drought" (2002–10) in Australia caused unanticipated losses to key services provided by hydrological ecosystems in the Murray-Darling basin -- including air quality regulation, waste treatment, erosion prevention, and recreation.