Editing IPCC:AR6/WGII/Chapter-2 (section)

=== 2.3.2 Projected Impacts of Increases in Extreme Events ===

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Understanding of the large-scale drivers and the local-to-regional feedback processes that lead to extreme events is still limited, and projections of extremes and coincident or compounding events remain uncertain ( [[#Prudhomme--2014|Prudhomme et al., 2014]] ; [[#Sillmann--2017|Sillmann et al., 2017]] ; [[#Hao--2018|Hao et al., 2018]] ; [[#Miralles--2019|Miralles et al., 2019]] ). Extreme events are challenging to model because they are, by definition, rare, and often occur at spatial and temporal scales much finer than the resolution of climate models ( [[#Sillmann--2017|Sillmann et al., 2017]] ; [[#Zscheischler--2018|Zscheischler et al., 2018]] ). Additionally, the processes that cause extreme events often interact, as is the case for drought and heat events, and they are spatially and temporally dependent, for example, soil moisture and temperature ( [[#Vogel--2017|Vogel et al., 2017]] ). Understanding feedbacks between land and atmosphere also remains limited. For example, positive feedbacks between soil and vegetation, or between evaporation, radiation and precipitation, are important in the preconditioning of extreme events such as heat waves and droughts, and can increase the severity and impact of such events ( [[#Miralles--2019|Miralles et al., 2019]] ).

Despite recent improvements in observational studies and climate modelling ( [[#Santanello--2015|Santanello et al., 2015]] ; [[#Stegehuis--2015|Stegehuis et al., 2015]] ; [[#PaiMazumder--2016|PaiMazumder and Done, 2016]] ; [[#Basara--2018|Basara and Christian, 2018]] ; [[#Knelman--2019|Knelman et al., 2019]] ), the potential to quantify or infer formal causal relationships between multiple drivers and/or hazards remains limited ( [[#Zscheischler--2017|Zscheischler and Seneviratne, 2017]] ; [[#Kleinman--2019|Kleinman et al., 2019]] ; [[#Miralles--2019|Miralles et al., 2019]] ; [[#Yokohata--2019|Yokohata et al., 2019]] ; [[#Harris--2020|Harris et al., 2020]] ). The mechanisms underlying the response are difficult to identify (e.g., responses to heat stress, drought and insects), effects vary among species and at different life stages, and an initial stress may influence the response to further stress ( [[#Nolet--2018|Nolet and Kneeshaw, 2018]] ). Additionally, hazards such as drought are often exacerbated by societal, industrial and agricultural water demands, requiring more sophisticated modelling of the physical and human systems ( [[#Mehran--2017|Mehran et al., 2017]] ; [[#Wan--2017|Wan et al., 2017]] ). Observations of past compound events may not provide reliable guides as to how future events may evolve, because human activity and recent climate change continue to interact to influence both system functioning and a climate state not previously experienced ( [[#Seneviratne--2021|Seneviratne et al., 2021]] )

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