Plants link the carbon and water cycles through photosynthesis and evapotranspiration (ET). When plants take in CO2 for photosynthesis, water evaporates to the atmosphere. This exchange of carbon and water is sensitive to a number of environmental variables including: soil water availability, temperature, atmospheric water vapor, and radiation. When the atmospheric demand for water is high, plants avoid hydraulic failure by regulating the amount of water exiting leaves at the expense of inhibiting carbon uptake. Over time, stress caused by this response limits plant growth and can even result in death by carbon starvation. With increasing atmospheric demand for water, impending expansion of arid regions, and more frequent droughts, understanding how vegetation responds to regulate photosynthesis and ET is important to quantify potential feedbacks between the carbon and water cycles. Despite its importance, to what extent plants respond to stressful conditions is an open science question. An important step forward is to characterize the dominant controls in these stress events and identify geographic areas that are vulnerable to climate change. The 2015-2016 El Nino and subsequent 2016-2017 La Nina transition provides an opportunity to quantify the extent and magnitude of vegetation regulation of these carbon and water variables in response to changes in environmental conditions. We present results from a space-based analysis using global observations of solar induced fluorescence (SIF) from the Orbiting Carbon Observatory-2 (OCO-2), soil moisture from Soil Moisture Active Passive (SMAP), and two widely used ET models (PT-JPL and MOD-16) to characterize the dominant controls on gross primary production and ET.
Purdy, A. J.; Fisher, J.; Goulden, M.; Randerson, J. T.; Famiglietti, J. S. (2017): Water vs carbon: An evaluation of SMAP soil moisture and OCO-2 solar-induced fluorescence to characterize global plant stress. Fall Meeting, American Geophysical Union, December 2017. Abstract B23E-2116..