Editing IPCC:AR6/SROCC/Chapter-6 (section)

==== 6.4.2.2 Impacts on the Physical System ====

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MHWs can impact weather patterns over land via teleconnections causing drought, heavy precipitation or heat wave events. For example, the Northeast Pacific 2013–2015 MHW and the associated persistent atmospheric high-pressure ridge prevented normal winter storms from reaching the West Coast of the US and may have contributed to the drought conditions across the entire West Coast (Seager et al., 2015 <sup>[[#fn:r443|443]]</sup> ; Di Lorenzo and Mantua, 2016). The Tasman Sea 2015–2016 MHW has increased the intensity of rainfall that caused flooding in northeast Tasmania in January 2016 (see Box 6.1) and the Coastal Peruvian 2017 MHW caused heavy rainfall and flooding on the west coast of tropical South America (ENFEN, 2017 <sup>[[#fn:r444|444]]</sup> ; Echevin et al., 2018 <sup>[[#fn:r445|445]]</sup> ; Garreaud, 2018 <sup>[[#fn:r446|446]]</sup> ; Takahashi et al., 2018 <sup>[[#fn:r447|447]]</sup> ). Similarly, MHWs in the Mediterranean Sea may have amplified heatwaves (Feudale and Shukla, 2007 <sup>[[#fn:r448|448]]</sup> ; García-Herrera et al., 2010 <sup>[[#fn:r449|449]]</sup> ) and heavy precipitation events over central Europe (Messmer et al., 2017 <sup>[[#fn:r450|450]]</sup> ), as well as trigger intense ETCs over the Mediterranean Sea (González ‐ Alemán et al., 2019 <sup>[[#fn:r451|451]]</sup> ). Such physical changes induced by MHWs may then also affect ecosystems and human systems on land (Reimer et al., 2015 <sup>[[#fn:r452|452]]</sup> ).

It should be noted that past and future impacts of MHWs on weather patterns over land depend not only on the duration and intensity of MHWs, but also on a wide range of different additional processes in the climate system such as the large-scale circulation of the atmosphere and oceans, and changes in the mean climate. Therefore, we conclude that there is currently ''low confidence'' in how MHWs impact the weather systems over land.

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