RII Track-4:NSF: Amplification of drought effects on vegetation by anthropogenic warming

Droughts are among the world’s costliest natural disasters, causing severe damage to both social and ecological systems. Human-caused warming increases the “dryness” of the atmosphere and, all other things being equal, increases evaporation rates from plant and soil surfaces, which in turn increases the loss of soil moisture and worsens naturally occurring precipitation deficits.

Drought reduces the photosynthesis and productivity of plants, including in both natural and agricultural ecosystems, but the extent to which human-caused ecological change has amplified the effects of drought on plant productivity still remains unclear. This EPSCoR RII Track-4:NSF Fellowship will combine state-of-the-art satellite and ground-based plant observations with observed and modeled climate data to examine how much the past century of climate change has worsened drought effects on plants, focusing specifically on the relative contributions of natural- vs. human-caused effects during two recent severe droughts: the 2012-2015 California drought and the 2012 Midwest drought.

The project will improve our understanding of the extent to which the effects of drought on Earth’s ecosystems are amplified by climate change, and it will also improve educational outcomes through training of a postdoctoral researcher and development of new climate change-related laboratory exercises for courses at the University of Iowa.

Droughts are among the world’s costliest natural disasters, causing severe damage to both social and ecological systems. Anthropogenic warming exacerbates natural precipitation deficits through heat-induced increases in evaporative demand, which further dries soils and stresses vegetation. Anthropogenic increases in the frequency and severity of droughts likely exert large, but still poorly constrained, impacts on ecosystem function, including photosynthesis and growth of plants (“primary production”).

While drought clearly reduces vegetation health and primary production, the relative contributions of natural variability and anthropogenic forcing remain unknown. Using the severe 2012-2015 California and 2012 Midwest droughts as case studies, this project will quantify the proportion of drought-induced primary production loss that was directly attributable to anthropogenic climate change, including attribution to specific climatic drivers (temperature, vapor pressure deficit, soil moisture, and solar radiation).

The primary hypothesis of this proposal is that anthropogenic contributions to drought-induced loss of primary production were even greater than anthropogenic contributions to loss of soil moisture due to the direct negative effects of higher temperatures and evaporative demand on stomatal conductance and photosynthesis. This hypothesis will be tested using state-of-the-art remote sensing techniques (e.g., solar-induced chlorophyll fluorescence) and climate change attribution methods.

The ultimate goal of this research is to develop an empirical “global change ecology” attribution framework that will be portable to other ecological systems and other impacts of climate change, including follow-up work focused on the effects of climate change on nationwide changes in primary production.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.