We developed a FVI that identifies when and where forests have
been experiencing increasingly high surface temperatures and greater
growing season water deficits. Our method takes a direct approach to
monitoring concurrent changes in canopy water and energy exchange
processes that have clear mechanistic links to the effects of drought
and high temperatures on vegetation (Fig. 1). By directly linking LST
to WB for each month (April through October) across years (2003
through 2012), we have characterized how the monthly LST and WB
trajectories change in relation to one another over the growing season
to express the FVI. This has revealed that positive FVI slopes can result
frommultiple LST and WB slope combinations, such as occurred during
August and September in the PNW (Fig. 4).