Drought, Heat, and the Carbon Cycle: a Review

Abstract

Purpose of the Review Weather and climate extremes substantially affect global-and regional-scale carbon (C) cycling, and thus spatially or temporally extended climatic extreme events jeopardize terrestrial ecosystem carbon sequestration. We illustrate the relevance of drought and/or heat events (BDHE^) for the carbon cycle and highlight underlying concepts and complex impact mechanisms. We review recent results, discuss current research needs and emerging research topics. Recent Findings Our review covers topics critical to understanding, attributing and predicting the effects of DHE on the terrestrial carbon cycle: (1) ecophysiological impact mechanisms and mediating factors, (2) the role of timing, duration and dynamical effects through which DHE impacts on regional-scale carbon cycling are either attenuated or enhanced, and (3) large-scale atmospheric conditions under which DHE are likely to unfold and to affect the terrestrial carbon cycle. Recent research thus shows the need to view these events in a broader spatial and temporal perspective that extends assessments beyond local and concurrent C cycle impacts of DHE. Summary Novel data streams, model (ensemble) simulations, and analyses allow to better understand carbon cycle impacts not only in response to their proximate drivers (drought, heat, etc.) but also attributing them to underlying changes in drivers and large-scale atmospheric conditions. These attribution-type analyses increasingly address and disentangle various sequences or dynamical interactions of events and their impacts, including compensating or amplifying effects on terrestrial carbon cycling.

Drought: Progress in broadening its understanding

“…This demonstrated that losses in net carbon uptake during the summer were largely offset by carbon gains in the extremely warm spring. This suggests that the warm spring reduced the carbon cycle dependence on timing (Sippel et al, ).…”

“…With increasing climate change, the intensity and frequency of droughts will likely increase (Brando et al, 2019;Sippel et al, 2018). As a result, forests may lose their role as a robust sink of carbon, which will exacerbate potential warming trends (Yang et al, 2018).…”

Coupling between the terrestrial carbon and water cycles—a review

“…from ESMs(Anderegg et al 2013, 2015c, Kaisermann et al 2017, Sippel et al 2018. Soil moisture also regulates plant growth, and especially sap area and tree ring size on interannual time scales, with wet years leading to larger tree rings (Gao et al 2018).…”

Contrasting responses in dissolved organic carbon to extreme climate events from adjacent boreal landscapes in Northern Sweden

“…Soil freezing may also promote DOC losses (Haei et al 2010, Hagemann et al 2016 by physically disrupting soil aggregates (Kalbitz and Kaiser 2008), damaging plant roots (Cleavitt et al 2008), and lysing microbial cells (Yanai et al 2004). Similarly, drought has been linked to increased aeration of otherwise waterlogged soils, facilitating the decomposition of soil carbon and eventual DOC release (Freeman et al 2001b, Sippel et al 2018, while increased precipitation has been shown to enhance the mobilization of organic carbon from soils to streams (Ågren et al 2010(Ågren et al , de Wit et al 2016. Although these studies have shed important light on our understanding of soil carbon responses to individual drivers, they have not addressed the combined, interactive, and potentially lagged and legacy effects (Smith et al 2009) of climate extremes that typify seasonal transitions in ecosystems.…”