A new framework to quantitatively disentangle the impacts of soil water stress and high vapor pressure deficit on vegetation productivity

Abstract:

Vegetation represents one of the largest carbon sinks on Earth and vegetation productivity is significantly affected by drought. Drought stress in plants manifests as a result of low soil water content (SWC), high vapor pressure deficit (VPD), or a combination of both known as compound drought. Climate change is expected to cause many ecosystems to transition to conditions where low SWC and high VPD are more common possibly having a significant impact on productivity. However, to what extent each drought type can limit productivity is currently unknown and is challenging to directly quantify. We developed a new framework that is capable of quantifying the impacts of SWC and VPD on ecosystem-level productivity either individually or in combination. We approached the process with consideration of both drought timing and drought severity by proposing two methodologies that consider the magnitude of a drought event and the seasonal relevance of it. Our results indicate that compound drought events generally cause more severe limitations than dry soil or dry air alone, however, there is substantial overlap between each drought type throughout the growing season. This new framework will be useful to predict drought impacts on vegetation productivity under future climates.