Editing IPCC:AR6/WGI/Chapter-11 (section)

==== 11.6.4.4 Atmospheric-based Drought Indices ====

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Different studies using atmospheric-based drought indices suggest an attributable anthropogenic signal, characterized by the increased frequency and severity of droughts ( [[#Cook--2018|Cook et al., 2018]] ), associated to increased AED ( [[#11.6.4.2|Section 11.6.4.2]] ). The majority of studies are based on the PDSI-PM. [[#Williams--2015|Williams et al. (2015)]] and [[#Griffin--2014|Griffin and Anchukaitis (2014)]] concluded that increased AED has had an increased contribution to drought severity over the last decades, and played a dominant role in the intensification of the 2012–2014 drought in California. The same temporal pattern and physical mechanism was stressed by Z. [[#Li--2017|]] [[#Li--2017|]] [[#Li--2017|]] [[#Li--2017|Li et al. (2017)]] in central Asia. [[#Marvel--2019|Marvel et al. (2019)]] compared tree ring-based reconstructions of the PDSI-PM over the past millennium with PDSI-PM estimates based on output from CMIP5 models. The comparisons suggested a contribution of greenhouse gas forcing to the changes since the beginning of the 20th century, although characterized with temporal differences that could be driven by temporal variations in the aerosol forcing. This was in agreement with the dominant external forcings of aridification at global scale between 1950 and 2014 ( [[#Bonfils--2020|Bonfils et al., 2020]] ). In the Mediterranean region, there is ''medium confidence'' of drying attributable to antropogenic forcing as a consequence of the strong AED increase ( [[#Gocic--2014|Gocic and Trajkovic, 2014]] ; [[#Azorin-Molina--2015|Azorin-Molina et al., 2015]] ; [[#Liuzzo--2016|Liuzzo et al., 2016]] ; [[#Maček--2018|Maček et al., 2018]] ), which has enhanced the severity of drought events ( [[#Vicente-Serrano--2014|Vicente-Serrano et al., 2014]] ; [[#Stagge--2017|Stagge et al., 2017]] ; [[#González-Hidalgo--2018|González-Hidalgo et al., 2018]] ). In particular, this effect was identified to be the main driver of the intensification of the 2017 drought that affected south-western Europe, and was attributed to the human forcing ( [[#García-Herrera--2019|García-Herrera et al., 2019]] ). [[#Nangombe--2020|Nangombe et al. (2020)]] and L. [[#Zhang--2020|]] [[#Zhang--2020|]] [[#Zhang--2020|]] [[#Zhang--2020|Zhang et al. (2020)]] concluded from differences between precipitation and AED that anthropogenic forcing contributed to the 2018 droughts that affected southern Africa and south-eastern China, respectively, principally as consequence of the high AED that characterized these two events.

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