Abstract
Abstract. A flash drought is characterized by its rapid onset and arouses widespread concerns due to its devastating impacts on the environment and society without sufficient early warnings. The increasing frequency of soil moisture flash droughts in a warming climate highlights the importance of understanding its impact on terrestrial ecosystems. Previous studies investigated the vegetation dynamics during several extreme cases of flash drought, but there is no quantitative assessment on how fast the carbon fluxes respond to flash droughts based on decade-long records with different climates and vegetation conditions. Here we identify soil moisture flash drought events by considering decline rate of soil moisture and the drought persistency, and we detect the response of ecosystem carbon and water fluxes to a soil moisture flash drought during its onset and recovery stages based on observations at 29 FLUXNET stations from croplands to forests. Corresponding to the sharp decline in soil moisture and higher vapor pressure deficit (VPD), gross primary productivity (GPP) drops below its normal conditions in the first 16 d and decreases to its minimum within 24 d for more than 50 % of the 151 identified flash drought events, and savannas show highest sensitivity to flash drought. Water use efficiency increases for forests but decreases for cropland and savanna during the recovery stage of flash droughts. These results demonstrate the rapid responses of vegetation productivity and resistance of forest ecosystems to flash drought.
Highlights
Terrestrial ecosystems play a key role in the global carbon cycle and absorb about 30 % of anthropogenic carbon dioxide emissions during the past five decades (Le Quéré et al, 2018)
Based on FLUXNET data, we have identified 151 soil moisture flash drought events with durations longer than or equal to 24 d using soil moisture observations of 371 site years
This study presents how carbon and water fluxes respond to soil moisture flash droughts during the 8 d before flash droughts, the onset and recovery stages, and the 8 d after flash droughts through analyzing decade-long observations from FLUXNET
Summary
Terrestrial ecosystems play a key role in the global carbon cycle and absorb about 30 % of anthropogenic carbon dioxide emissions during the past five decades (Le Quéré et al, 2018). Terrestrial ecosystems can even turn to carbon sources during extreme drought events (Ciais et al, 2005). Record-breaking drought events have caused enormous reductions of the ecosystem gross primary productivity (GPP), e.g., the European 2003 drought (Ciais et al, 2005; Reichstein et al, 2007), USA 2012 drought (Wolf et al, 2016), China 2013 drought (Xie et al, 2016; Yuan et al, 2016), southern Africa 2015–2016 drought (Yuan et al, 2017) and Australia millennium drought (Banerjee et al, 2013). The 2012 summertime drought in the USA was classified as a flash drought with rapid intensification and insufficient early warning, which caused a 26 % reduction in crop yield (Hoerling et al, 2014; Otkin et al, 2016). Several extreme flash droughts would propagate into long-term droughts due to persistent precipitation deficits, e.g., the 2012 flash
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