Drought self-propagation and its imprint on ecosystem productivity

Abstract:

The local effects of drought on the terrestrial biosphere has advanced dramatically in recent years. However, the influence of remote drought conditions on downwind ecosystems remains less explored. To better predict and anticipate the consequences of drought on our biosphere, the spatial reach of droughts via atmospheric energy and moisture transport needs to be better understood. The fact that land evaporation in upwind (source) areas contributes moisture for precipitation to downwind (sink) regions has long been acknowledged. For instance, recent studies have pointed to the importance of forest evaporation for downwind rainfed agriculture and natural ecosystem productivity. A priori, within-continent water vapor transport may lead to the expansion and concatenation of droughts: as the upwind source desiccates, the reduction in evaporation results in less moisture being transported into downwind locations, where in turn rainfall deficits may also occur.

Here, we study the consequences of drought propagation for ecosystem productivity using satellite data and a Lagrangian trajectory model driven by atmospheric reanalysis. We show how the advection of dry and hot air from drought regions worldwide leads to the downwind propagation of these events and a trail of downwind impacts on primary productivity. For water-limited regions, results show a net detrimental effect on ecosystem gross primary production (GPP) and net primary production (NPP). Our findings underline the vulnerability of our biosphere to the occurrence of upwind climatic extremes and highlight the importance of spatiotemporal connections to understand ecosystem disturbances. These feedback pathways may be exploited to develop geo-engineering mitigation strategies that can help prevent events from aggravating during their early stages, or even propagating to other regions.