IPCC:AR6/WGI/Chapter-8 - Revision history

Laura at 08:36, 22 May 2026

2026-05-22T08:36:02Z

← Older revision		Revision as of 08:36, 22 May 2026
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			{{ChapterNavigation
			\| cover = Cover-WGI.jpg
			\| reporturl = IPCC:AR6/WGI
			\| reporttitle = WGI
			\| prevurl = IPCC:AR6/WGI/Chapter-7
			\| nexturl = IPCC:AR6/WGI/Chapter-9
			}}

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Laura: Laura moved page IPCC:Wg1:Chapter:Chapter-8 to IPCC:AR6/WGI/Chapter-8 without leaving a redirect

2026-05-18T16:18:02Z

Laura moved page IPCC:Wg1:Chapter:Chapter-8 to IPCC:AR6/WGI/Chapter-8 without leaving a redirect

← Older revision	Revision as of 16:18, 18 May 2026
(No difference)

Laura: #119

2026-05-15T12:00:21Z

#119

← Older revision		Revision as of 12:00, 15 May 2026
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	'''Schematic depiction of the atmospheric effects of light-absorbing aerosols on convection and cloud formation: (a) without and (b) with the presence of absorbing aerosols in the planetary boundary layer.''' The dashed and solid blue lines correspond to the vertical temperature profiles in the absence and presence of the absorbing aerosol layer, respectively, and the solid and dashed red lines denote the dry and moist adiabats, respectively. Absorbing aerosols result in an increasing temperature in the atmosphere but a reduced temperature at the surface. The reduced surface temperature and the increased temperature aloft led to a larger negative energy associated with convective inhibition (–) and a higher convection condensation level (CCL) under the polluted conditions. On the other hand, the absorbing aerosol layer induces a larger convective available potential energy (+) above CCL, facilitating more intensive vertical development of clouds, if lifting is sufficient to overcome the larger convective inhibition. Figure from Y. [[#Wang--2013\|Wang et al. (2013)]] .		'''Schematic depiction of the atmospheric effects of light-absorbing aerosols on convection and cloud formation: (a) without and (b) with the presence of absorbing aerosols in the planetary boundary layer.''' The dashed and solid blue lines correspond to the vertical temperature profiles in the absence and presence of the absorbing aerosol layer, respectively, and the solid and dashed red lines denote the dry and moist adiabats, respectively. Absorbing aerosols result in an increasing temperature in the atmosphere but a reduced temperature at the surface. The reduced surface temperature and the increased temperature aloft led to a larger negative energy associated with convective inhibition (–) and a higher convection condensation level (CCL) under the polluted conditions. On the other hand, the absorbing aerosol layer induces a larger convective available potential energy (+) above CCL, facilitating more intensive vertical development of clouds, if lifting is sufficient to overcome the larger convective inhibition. Figure from Y. [[#Wang--2013\|Wang et al. (2013)]] .

	~~'''~~'''Aerosol cloud microphysical effects'''~~'''~~		'''Aerosol cloud microphysical effects'''

	Cloud droplets nucleate on pre-existing aerosol particles which act as cloud condensation nuclei (CCN). Anthropogenic aerosols add CCN, compared to a pristine background, and produce clouds with more numerous and smaller droplets, slower to coalesce into raindrops and to freeze into ice hydrometeors at temperatures below 0°C. Adding CCN suppresses light rainfall from shallow and short-lived clouds, but it is compensated by heavier rainfall from deep clouds. Adding aerosols to clouds in extremely clean air invigorates them by more efficient vapour condensation on the added drop surfaces ( [[#Koren--2014\|Koren et al., 2014]] ; [[#Fan--2018\|Fan et al., 2018]] ). Clouds forming in more polluted air masses (hence with more numerous and smaller drops) need to grow deeper to initiate rain ( [[#Freud--2012\|Freud and Rosenfeld, 2012]] ; [[#Konwar--2012\|Konwar et al., 2012]] ; [[#Campos%20Braga--2017\|Campos Braga et al., 2017]] ). This leads to larger amount of cloud water evaporating aloft while cooling and moistening the air there at the expense of the lower levels, which leads to convective invigoration ( [[#Dagan--2017\|Dagan et al., 2017]] ; [[#Chua--2020\|Chua and Ming, 2020]] ), followed by convergence, air mass destabilization and added rainfall in an amplifying feedback loop		Cloud droplets nucleate on pre-existing aerosol particles which act as cloud condensation nuclei (CCN). Anthropogenic aerosols add CCN, compared to a pristine background, and produce clouds with more numerous and smaller droplets, slower to coalesce into raindrops and to freeze into ice hydrometeors at temperatures below 0°C. Adding CCN suppresses light rainfall from shallow and short-lived clouds, but it is compensated by heavier rainfall from deep clouds. Adding aerosols to clouds in extremely clean air invigorates them by more efficient vapour condensation on the added drop surfaces ( [[#Koren--2014\|Koren et al., 2014]] ; [[#Fan--2018\|Fan et al., 2018]] ). Clouds forming in more polluted air masses (hence with more numerous and smaller drops) need to grow deeper to initiate rain ( [[#Freud--2012\|Freud and Rosenfeld, 2012]] ; [[#Konwar--2012\|Konwar et al., 2012]] ; [[#Campos%20Braga--2017\|Campos Braga et al., 2017]] ). This leads to larger amount of cloud water evaporating aloft while cooling and moistening the air there at the expense of the lower levels, which leads to convective invigoration ( [[#Dagan--2017\|Dagan et al., 2017]] ; [[#Chua--2020\|Chua and Ming, 2020]] ), followed by convergence, air mass destabilization and added rainfall in an amplifying feedback loop

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	~~'''~~'''Observed changes'''~~'''~~		'''Observed changes'''

	The AR5 did not highlight observed changes in water cycle seasonality and SRCCL mostly emphasized changes in vegetation seasonality. Since AR5, a number of relevant studies have been published, but often with conflicting results. Based on three ''in situ'' datasets, reduced precipitation seasonality was identified over 62% of the terrestrial ecosystems analysed from 1950 – 2009 (Murray-Tortarolo et al. 2017). In contrast, both ''in situ'' and satellite data show a general increase in the annual range of precipitation from 1979 to 2010, which is dominated by wetter wet seasons ( [[#Chou--2013\|Chou et al., 2013]] ). This paradox may be partly explained by a larger aerosol radiative forcing in the middle of the 20th century as well as by internal variability ( [[#Kumar--2015\|Kumar et al., 2015]] ; see also Box 8.1). For instance, the ‘long rains’ over East Africa experienced declining trends in the 1980s and 1990s ( [[#Nicholson--2017\|Nicholson, 2017]] ), which was linked to anthropogenic aerosols and SST patterns ( [[#Rowell--2015\|Rowell et al., 2015]] ), followed by a recent recovery that was linked to internal variability ( [[#Wainwright--2019\|Wainwright et al., 2019]] ). Two satellite datasets revealed decreased rainfall seasonality in the tropics but an increased seasonality in the subtropics and mid-latitudes since 1979, without clear attribution ( [[#Marvel--2017\|Marvel et al., 2017]] ).		The AR5 did not highlight observed changes in water cycle seasonality and SRCCL mostly emphasized changes in vegetation seasonality. Since AR5, a number of relevant studies have been published, but often with conflicting results. Based on three ''in situ'' datasets, reduced precipitation seasonality was identified over 62% of the terrestrial ecosystems analysed from 1950 – 2009 (Murray-Tortarolo et al. 2017). In contrast, both ''in situ'' and satellite data show a general increase in the annual range of precipitation from 1979 to 2010, which is dominated by wetter wet seasons ( [[#Chou--2013\|Chou et al., 2013]] ). This paradox may be partly explained by a larger aerosol radiative forcing in the middle of the 20th century as well as by internal variability ( [[#Kumar--2015\|Kumar et al., 2015]] ; see also Box 8.1). For instance, the ‘long rains’ over East Africa experienced declining trends in the 1980s and 1990s ( [[#Nicholson--2017\|Nicholson, 2017]] ), which was linked to anthropogenic aerosols and SST patterns ( [[#Rowell--2015\|Rowell et al., 2015]] ), followed by a recent recovery that was linked to internal variability ( [[#Wainwright--2019\|Wainwright et al., 2019]] ). Two satellite datasets revealed decreased rainfall seasonality in the tropics but an increased seasonality in the subtropics and mid-latitudes since 1979, without clear attribution ( [[#Marvel--2017\|Marvel et al., 2017]] ).

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	In summary, there is ''medium confidence'' that the annual range of precipitation has increased since the 1980s, at least in subtropical regions and over the Amazon. There is ''low confidence'' that this increase is due to human influence and that GHG forcing has already altered the timing or duration of wet seasons ''.'' There is ''high confidence'' that the human-induced retreat of the springtime snow cover and melting of glaciers have already contributed to changes in streamflow seasonality in high-latitude and low-elevation mountain catchments, and ''medium confidence'' that human activities have also contributed to an increased seasonality of water availability, including a drier dry season, in the extratropics.		In summary, there is ''medium confidence'' that the annual range of precipitation has increased since the 1980s, at least in subtropical regions and over the Amazon. There is ''low confidence'' that this increase is due to human influence and that GHG forcing has already altered the timing or duration of wet seasons ''.'' There is ''high confidence'' that the human-induced retreat of the springtime snow cover and melting of glaciers have already contributed to changes in streamflow seasonality in high-latitude and low-elevation mountain catchments, and ''medium confidence'' that human activities have also contributed to an increased seasonality of water availability, including a drier dry season, in the extratropics.

	'''~~'''Project''' '''ed~~ changes'''~~'''~~		'''Projected changes'''

	The AR5 reported with ''high confidence'' that the contrast between wet and dry seasons will generally increase with global warming and that monsoon onset dates will ''likely'' become earlier or show little change, while monsoon retreat dates will ''likely'' be delayed, resulting in a lengthening of the wet season in many regions.		The AR5 reported with ''high confidence'' that the contrast between wet and dry seasons will generally increase with global warming and that monsoon onset dates will ''likely'' become earlier or show little change, while monsoon retreat dates will ''likely'' be delayed, resulting in a lengthening of the wet season in many regions.

Laura: /* Chapter 8: Water Cycle Changes */

2026-05-13T14:05:26Z

Chapter 8: Water Cycle Changes

← Older revision		Revision as of 14:05, 13 May 2026
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	Richard P. Allan (United Kingdom), Paola A. Arias (Colombia), Mathew Barlow (United States of America), Ruth Cerezo-Mota (Mexico), Annalisa Cherchi (Italy), ThianY. Gan (Canada/Malaysia), Joëlle Gergis (Australia), Dabang Jiang (China), Asif Khan (Pakistan), Wilfried Pokam Mba (Cameroon), Daniel Rosenfeld (Israel), Jessica Tierney (United States of America), Olga Zolina (The Russian Federation/France, The Russian Federation)		Richard P. Allan (United Kingdom), Paola A. Arias (Colombia), Mathew Barlow (United States of America), Ruth Cerezo-Mota (Mexico), Annalisa Cherchi (Italy), ThianY. Gan (Canada/Malaysia), Joëlle Gergis (Australia), Dabang Jiang (China), Asif Khan (Pakistan), Wilfried Pokam Mba (Cameroon), Daniel Rosenfeld (Israel), Jessica Tierney (United States of America), Olga Zolina (The Russian Federation/France, The Russian Federation)

	'''Review~~''' '''~~Editors:'''		'''Review Editors:'''

	Pascale Braconnot (France), Arona Diedhiou (Côte d’Ivoire/Senegal)		Pascale Braconnot (France), Arona Diedhiou (Côte d’Ivoire/Senegal)

	'''Contributing~~''' '''~~Authors:'''		'''Contributing Authors:'''

	Gabriel Abramowitz (Australia), Guðfinna Adalgeirsdottir (Iceland), Andrea Alessandri (Italy), Robert J. Allen (United States of America), Kevin Anchukaitis (United States of America), Richard A. Betts (United Kingdom), Céline J. W. Bonfils (United States of America/ France), Michael Bosilovich (United States of America), Olivier Boucher (France), Josephine Brown (Australia), Michael P. Byrne (United Kingdom/Ireland), Robin Chadwick (United Kingdom), Sarah Connors (France/United Kingdom), Benjamin Cook (United States of America), Erika Coppola (Italy), Alejandro Di Luca (Australia, Canada/Argentina), Aïda Diongue Niang (Senegal), Petra Döll (Germany), Ellen Douglas (United States of America), Paul J. Durack (United States of America/Australia), Hayley J. Fowler (United Kingdom), Alexander Gershunov (United States of America), Nicholas R. Golledge (New Zealand/ United Kingdom), James Kossin (United States of America), Won-Tae Kwon (Republic of Korea), Flavio Lehner (United States of America/Switzerland), Eric Maloney (United States of America), Vimal Mishra (India), Angeline Pendergrass (United States of America), Stefan Pfahl (Germany), Catherine Prigent (France), Catherine Rio (France), Alex C. Ruane (United States of America), Benjamin Sanderson (United Kingdom), Sonia I. Seneviratne (Switzerland), Shoichi Shige (Japan), Vijay Singh (United States of America), Abigail Swann (United States of America), Richard G. Taylor (United Kingdom/Canada, United Kingdom), Laurent Terray (France), Natalia Tilinina (The Russian Federation), Bart van den Hurk (The Netherlands), Sergio M. Vicente-Serrano (Spain), Michael Wehner (United States of America), Laura J. Wilcox (United Kingdom), Cunde Xiao (China), Prodromos Zanis (Greece), Xuebin Zhang (Canada)		Gabriel Abramowitz (Australia), Guðfinna Adalgeirsdottir (Iceland), Andrea Alessandri (Italy), Robert J. Allen (United States of America), Kevin Anchukaitis (United States of America), Richard A. Betts (United Kingdom), Céline J. W. Bonfils (United States of America/ France), Michael Bosilovich (United States of America), Olivier Boucher (France), Josephine Brown (Australia), Michael P. Byrne (United Kingdom/Ireland), Robin Chadwick (United Kingdom), Sarah Connors (France/United Kingdom), Benjamin Cook (United States of America), Erika Coppola (Italy), Alejandro Di Luca (Australia, Canada/Argentina), Aïda Diongue Niang (Senegal), Petra Döll (Germany), Ellen Douglas (United States of America), Paul J. Durack (United States of America/Australia), Hayley J. Fowler (United Kingdom), Alexander Gershunov (United States of America), Nicholas R. Golledge (New Zealand/ United Kingdom), James Kossin (United States of America), Won-Tae Kwon (Republic of Korea), Flavio Lehner (United States of America/Switzerland), Eric Maloney (United States of America), Vimal Mishra (India), Angeline Pendergrass (United States of America), Stefan Pfahl (Germany), Catherine Prigent (France), Catherine Rio (France), Alex C. Ruane (United States of America), Benjamin Sanderson (United Kingdom), Sonia I. Seneviratne (Switzerland), Shoichi Shige (Japan), Vijay Singh (United States of America), Abigail Swann (United States of America), Richard G. Taylor (United Kingdom/Canada, United Kingdom), Laurent Terray (France), Natalia Tilinina (The Russian Federation), Bart van den Hurk (The Netherlands), Sergio M. Vicente-Serrano (Spain), Michael Wehner (United States of America), Laura J. Wilcox (United Kingdom), Cunde Xiao (China), Prodromos Zanis (Greece), Xuebin Zhang (Canada)
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	This chapter should be cited as:		'''This chapter should be cited as:'''

	Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, and O. Zolina, 2021: Water Cycle Changes. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1055–1210, doi: [https://doi.org/10.1017/9781009157896.010 '''10.1017/9781009157896.010'''] .		Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, and O. Zolina, 2021: Water Cycle Changes. In ''Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change'' [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1055–1210, doi: [https://doi.org/10.1017/9781009157896.010 '''10.1017/9781009157896.010'''] .

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imported>Design: /* References */

2026-05-11T08:47:23Z

References

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