Extreme wet events as important as extreme dry events in controlling spatial patterns of vegetation greenness anomalies

Caroline A Famiglietti, Anna M Michalak, and 


Summary

To reduce uncertainties in future projections of the carbon cycle, it is important to understand how plants respond both to extreme wet and extreme dry events. While many studies have focused on the impact of droughts, less is known about the effects of extreme wet conditions. Using 34 years of satellite data, we found that regions more sensitive to extreme wet events than to extreme dry events are more prevalent than previously recognized. In addition, the greenness responses of those regions are not uniform. They are functions of multiple, often interacting mechanisms such as atmospheric moisture demand, average and preceding climate conditions, etc.

Figure: Strong sensitivity hotspots exist for both wet (a) and dry (b) extremes, indicating regions for which vegetation greenness anomalies are strongly coupled to extreme hydrological events. High-magnitude sensitivities to both extreme wet events and extreme dry events appear in northeastern Australia and southern Africa, while many northern boreal regions are significantly sensitive only to the former and parts of India are only to the latter.


Abstract

Understanding plant responses to hydrological extremes is critical for projections of the future terrestrial carbon uptake, but much more is known about the impacts of drought than of extreme wet conditions. However, the latter may control ecosystem-scale photosynthesis more strongly than the former in certain regions. Here we take a data-driven, location-based approach to evaluate where wet and dry extremes most affect photosynthesis. By comparing the sensitivity of vegetation greenness during extreme wetness to that during extreme dryness over a 34 year record, we find that regions where the impact of wet extremes dominates are nearly as common as regions where drought impacts dominate. We also demonstrate that the responses of wet-sensitive regions are not uniform and are instead controlled by multiple, often interacting, mechanisms. Given predicted increases in the frequency and intensity of extreme hydrological events with climate change, the consequences of extreme wet conditions on local and global carbon cycling will likely be amplified in future decades.

Famiglietti, C. A., A. M. Michalak, & A. G. Konings. (2021). Extreme wet events as important as extreme dry events in controlling spatial patterns of vegetation greenness anomalies. Environmental Research Letters. https://doi.org/10.1088/1748-9326/abfc78