Global Patterns of Drought Recovery
Monday, 14 December 2015: 09:45
2010 (Moscone West)
Understanding the impacts of drought on carbon metabolism is crucial to elucidate how global environmental change will alter the climate regulation ecosystem service provided by terrestrial vegetation. Notwithstanding past and anticipated future changes in drought regime the interplay between hydrologic (amelioration of precipitation deficit) and functional (return to pre-drought levels of carbon metabolism) post-drought recovery is not well understood. Recovery time is however a prime determinant of whether ecosystems revert to their initial state or transition to a new equilibrium. Here we quantify post-drought recovery time of gross primary productivity (GPP) at grid cell (0.5° spatial resolution) to global scales using three reconstructions: MODIS, upscaled FLUXNET, and an ensemble of state-of-the-art standardized land surface model runs taken from MsTMIP (Multi-scale Synthesis and Terrestrial Model Intercomparison Project). Drought is tracked using the multiscalar Standardized Precipitation-Evapotranspiration Index drought metric where the integration period (the retrospective window used to calculate the metric) is varied from 1 to 24-months. We define recovery time as a function of both hydrologic and GPP recovery, i.e., both must attain pre-drought levels for recovery to occur. Despite the diverse provenance of the reconstructions, different reconstruction periods, and variable integration lengths several consistent patterns emerge across the c. 4 000 000 drought events and subsequent recovery times cataloged. Recovery time scales with drought severity and drought length. Biological productivity and biodiversity exhibit response surfaces with large amplitudes and clear thresholds whereas soil fertility is a weak constraint. In general, GPP-based descriptors of drought events serve as key boundary conditions for drought recovery. The longest recovery times occur on marginal lands--non-forested, mixed tree-grass, and boreal systems--with a slight uptick for tropical forests. Overall, recovery time is more controlled by GPP anomaly magnitude as opposed to the magnitude and duration of the hydrologic anomaly itself. At the extremes however prolonged hydrologic drought dominates post-drought recovery, indicating the presence of "triggering thresholds".