Harnessing the Power of an Environmental Observation Network to Understand Land-Atmosphere Interactions During Drought (Invited Presentation)

Land-atmosphere exchanges of carbon and water are highly sensitive to drought stress. Declining soil moisture during drought can limit the supply of water to leaf, reducing stomatal conductance, transpiration, and photosynthetic capacity. At the same time, rising vapor pressure deficit (VPD) can further impact carbon and water exchanges as plants close their stomates to prevent excessive water loss to an increasingly dessicating atmosphere. Our ability to detect, classify, and project drought will benefit from new frameworks to understand how both water supply (from the soil) and demand (in the atmosphere) affect plant carbon and water exchange. It is particularly important to understand how stomatal response to these drivers decouples evapotranspiration from its potential rate, which has historically been a key input into widely-used drought indices.

Here, I will present a conceptual framework describing the sensitivity of stomatal conductance, ET, and carbon uptake to soil moisture and VPD across climate gradients, now and in the future. The framework’s predictions will be tested using a global network database of the same variables (e.g. FLUXNET), and finally model projects for future climate conditions (CMIP5) will be leveraged to understand how the relative importance of VPD versus soil moisture constraints may shift in the future. I’ll end by comparing how well standard drought indices (e.g. PSDI) capture the observed limitations to carbon and water exchange, and discuss some practical considerations for incorporating land-atmosphere feedbacks into drought metrics.