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

==== 2.5.3.3 Feedbacks related to changes in soil moisture resulting from global warming ====

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There is medium evidence but ''high agreement'' that soil moisture conditions influence the frequency and magnitude of extremes such as drought and heatwaves. Observational evidence indicates that dry soil moisture conditions favour heatwaves, in particular in regions where evapotranspiration is limited by moisture availability (Mueller and Seneviratne 2012 <sup>[[#fn:r1290|1290]]</sup> ; Quesada et al. 2012 <sup>[[#fn:r1291|1291]]</sup> ; Miralles et al. 2018 <sup>[[#fn:r1292|1292]]</sup> ; Geirinhas et al. 2018 <sup>[[#fn:r1293|1293]]</sup> ; Miralles et al. 2014 <sup>[[#fn:r1294|1294]]</sup> ; Chiang et al. 2018 <sup>[[#fn:r1295|1295]]</sup> ; Dong and Crow 2019 <sup>[[#fn:r1296|1296]]</sup> ; Hirschi et al. 2014 <sup>[[#fn:r1297|1297]]</sup> ).

In future climate projections, soil moisture plays an important role in the projected amplification of extreme heatwaves and drought in many regions of the world ( ''medium confidence'' ) (Seneviratne et al. 2013 <sup>[[#fn:r1298|1298]]</sup> ; Vogel et al. 2017 <sup>[[#fn:r1299|1299]]</sup> ; Donat et al. 2018 <sup>[[#fn:r1300|1300]]</sup> ; Miralles et al. 2018 <sup>[[#fn:r1301|1301]]</sup> ). In addition, the areas where soil moisture affects heat extremes will not be located exactly where they are today. Changes in rainfall, temperature, and thus in evapotranspiration, will induce changes in soil moisture and therefore where temperature and latent heat flux will be negatively coupled (Seneviratne et al. 2006 <sup>[[#fn:r1302|1302]]</sup> ; Fischer et al. 2012 <sup>[[#fn:r1303|1303]]</sup> ). Quantitative estimates of the actual role of soil moisture feedbacks are, however, very uncertain due to the ''low confidence'' in projected soil moisture changes (IPCC 2013a <sup>[[#fn:r1304|1304]]</sup> ), to weaknesses in the representation of soil moisture–atmosphere interactions in climate models (Sippel et al. 2017 <sup>[[#fn:r1305|1305]]</sup> ; Ukkola et al. 2018 <sup>[[#fn:r1306|1306]]</sup> ; Donat et al. 2018 <sup>[[#fn:r1307|1307]]</sup> ; Miralles et al. 2018 <sup>[[#fn:r1308|1308]]</sup> ) and to methodological uncertainties associated with the soil moisture prescription framework commonly used to disentangle the effect of soil moisture on changes in temperature extremes (Hauser et al. 2017 <sup>[[#fn:r1309|1309]]</sup> ).

Where soil moisture is predicted to decrease in response to climate change in the subtropics and temperate latitudes, this drying could be enhanced by the existence of soil moisture feedbacks ( ''low confidence'' ) (Berg et al. 2016 <sup>[[#fn:r1310|1310]]</sup> ). The initial decrease in precipitation and increase in potential evapotranspiration and latent heat flux, in response to global climate change, leads to decreased soil moisture at those latitudes and can potentially amplify both. Such a feature is consistent with evidence that, in a warmer climate, land and atmosphere will be more strongly coupled via both the water and energy cycles (Dirmeyer et al. 2014 <sup>[[#fn:r1311|1311]]</sup> ; Guo et al. 2006 <sup>[[#fn:r1312|1312]]</sup> ). This increased sensitivity of atmospheric response to land perturbations implies that changes in land uses and cover are expected to have more impact on climate in the future than they do today.

Beyond temperature, it has been suggested that soil moisture feedbacks influence precipitation occurrence and intensity. But the importance, and even the sign of this feedback, is still largely uncertain and debated (Tuttle and Salvucci 2016 <sup>[[#fn:r1313|1313]]</sup> ; Yang et al. 2018 <sup>[[#fn:r1314|1314]]</sup> ; Froidevaux et al. 2014 <sup>[[#fn:r1315|1315]]</sup> ; Guillod et al. 2015 <sup>[[#fn:r1316|1316]]</sup> ).

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