Not all droughts are created equal: the impacts of interannual drought pattern and magnitude on grassland carbon cycling

Abstract

Climate extremes, such as drought, may have immediate and potentially prolonged effects on carbon cycling. Grasslands store approximately one-third of all terrestrial carbon and may become carbon sources during droughts. However, the magnitude and duration of drought-induced disruptions to the carbon cycle, as well as the mechanisms responsible, remain poorly understood. Over the next century, global climate models predict an increase in two types of drought: chronic but subtle 'press-droughts', and shorter term but extreme 'pulse-droughts'. Much of our current understanding of the ecological impacts of drought comes from experimental rainfall manipulations. These studies have been highly valuable, but are often short term and rarely quantify carbon feedbacks. To address this knowledge gap, we used the Community Land Model 4.0 to examine the individual and interactive effects of pulse- and press-droughts on carbon cycling in a mesic grassland of the US Great Plains. A series of modeling experiments were imposed by varying drought magnitude (precipitation amount) and interannual pattern (press- vs. pulse-droughts) to examine the effects on carbon storage and cycling at annual to century timescales. We present three main findings. First, a single-year pulse-drought had immediate and prolonged effects on carbon storage due to differential sensitivities of ecosystem respiration and gross primary production. Second, short-term pulse-droughts caused greater carbon loss than chronic press-droughts when total precipitation reductions over a 20-year period were equivalent. Third, combining pulse- and press-droughts had intermediate effects on carbon loss compared to the independent drought types, except at high drought levels. Overall, these results suggest that interannual drought pattern may be as important for carbon dynamics as drought magnitude and that extreme droughts may have long-lasting carbon feedbacks in grassland ecosystems.

Extreme wildfire events are linked to global-change-type droughts in the northern Mediterranean

“…In this paper, we analyzed the weather conditions associated with the EWE that occurred during the 2003 and 2016 exceptional summer droughts in the northern Mediterranean. On the basis of this analysis, we introduce a novel con- ceptual scheme summarizing the response of wildfire to climate change droughts, which combines the FWT framework adapted from Ruffault et al (2016) and the drought classification from Hoover and Rogers (2016), which is depicted in Fig. 9.…”

“…Several types of droughts can be defined depending on their characteristics (Hoover et al, 2015;Hoover and Rogers, 2016). "Press droughts" are subtle but chronic reductions in water availability, driven by long-term (month to seasons) reductions in precipitation and/or warmer temperatures, which increase potential evapotranspiration and reduce soil moisture (Hoover and Rogers, 2016).…”

Asymmetric Responses of Primary Productivity to Altered Precipitation Simulated by Ecosystem Models across Three Longterm Grassland Sites

“…The dry SGS site is located in northern Colorado, USA Wilcox et al, 2015). The KNZ site is a native C4-dominated mesic tallgrass prairie in the Flint Hills of northeastern Kansas, USA (Heisler-White et al, 2009;Hoover et al, 2014). The moist site of STU is a subalpine meadow located in Austria Central Alps near the village of Neustift (Bahn et al, 2006;Bahn et al, 2008;Schmitt et al, 2010).…”

“…We recommend that models simulate SWC in the same soil layer as experiments in following studies, also considering the local soil textures. This will help in figuring out the bias of modeled sensitivities to precipitation and to check explicitly the sensitivity of vegetation productivity to change in SWC; (2) Responses of ANPP and BNPP to altered precipitation are different, however, there are still only few control 13 experiments for BNPP to be used for evaluating the corresponding processes in models Wilcox et al, 2017);(3) Consideration of other processes such as responses of primary productivity to irrigation or drought manipulations, and time-lag effects of droughts (Hoover and Rogers, 2016;Hoover et al, 2014;Sala et al, 2012;Wang et al, 2014). To study such effects, modelers will need to simulate the control experiments corresponding to the real local manipulations applied by field scientists, e.g., considering vegetation composition, root profiles, nutrient cycling, phenology and carbon allocation as 5 close as possible to local conditions.…”

“…(3) Consideration of other processes such as responses of primary productivity to irrigation or drought manipulations, and time-lag effects of droughts (Hoover and Rogers, 2016;Hoover et al, 2014;Sala et al, 2012;Wang et al, 2014). To study such effects, modelers will need to simulate the control experiments corresponding to the real local manipulations applied by field scientists, e.g., considering vegetation composition, root profiles, nutrient cycling, phenology and carbon allocation as 5 close as possible to local conditions.…”