The impact of the 2009/2010 drought on vegetation growth and terrestrial carbon balance in Southwest China

The 2009/2010 drought in Southwest China was a once in a century drought event. This drought event had strong adverse impacts, such as water scarcity, crop failure, and economic loss, on ecosystems and the human society. Explicit representations of this drought event and associated changes in vegetation dynamics and carbon cycle, however, are still largely missed in literature. Here we used the standardized anomaly of 3-month Standard Precipitation-Evapotranspiration Index (SPEI) to characterize this 2009/2010 drought event, including its onset and end months, duration and severity. We examined the drought impacts on vegetation greenness using Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI); and assessed the terrestrial carbon flux responses to drought using data from satellite-based datasets, atmospheric inversion, one data-based model, and three ecosystem models. Our analysis showed that this autumn-winter-spring drought mostly suppressed vegetation growth in Yunnan, North Guangxi, Guizhou and East Sichuan. In comparisons to the same months of the reference period (2000-2015), the drought caused a large reduction in carbon uptake (4.4 +/- 5 gCm(-2) month(-1)) from the decrease in gross primary production (GPP, 5.7 +/- 9.5 gCm(-2) month(-1)), although ecosystem respiration (TER) also decreased by a smaller extent (1.3 +/- 5.1 gCm(-2) month(-1)). Nonetheless, more than 65% of the drought-impacted area recovered in both vegetation greenness and productivity within 3 months, while about 10% of the drought-affected area failed to recover even after 6 months post the drought event. Across different vegetation types, forests and shrubs had stronger capability of drought resistance and shorter post-drought recovery time than crops and grasses. Model comparison reveals that while data from different sources generally agreed on the sign of vegetation greenness and carbon flux responses to drought, they differ significantly in the extent of such responses.