Editing IPCC:AR6/WGI/Chapter-8 (section)

===== 8.3.1.7.3 Wetlands and lakes =====

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Wetlands and lakes affect the climate through their impact on carbon and methane budgets ( [[IPCC:Wg1:Chapter:Chapter-5#5.2.2|Section 5.2.2]] ; e.g., [[#Saunois--2016|Saunois et al., 2016]] ; [[#Zhan--2019|Zhan et al., 2019]] ) and on surface heat fluxes, with coupled weather and climate effects(e.g., [[#Zhan--2019|Zhan et al., 2019]] ). Although these features are also affected by human activities and by climate change, AR5 did not specifically report on wetlands and lakes.

Inventories of surface water bodies are not systematically produced at national or regional levels. However, assessments are undertaken at the global scale ( [[#Ramsar%20Convention%20on%20Wetlands--2018|Ramsar Convention on Wetlands, 2018]] ). Merging observations from multiple satellite sensors makes it possible to detect surface water even under vegetation and clouds over about 25 years, but with low spatial resolution ( [[#Prigent--2016|Prigent et al., 2016]] ). Most recent multi-satellite products from visible, infrared, and microwave measurements, estimate a surface water area of about 12 to 14 million km <sup>2</sup> (including permanent and transitory surfaces, e.g., [[#Aires--2018|Aires et al., 2018]] ; [[#Davidson--2018|Davidson et al., 2018]] ), which is much higher than those provided by optical imagery (about 3 million km <sup>2</sup> ). Inventories show a strong decrease in natural surface water of about 0.8% yr <sup>–1</sup> in total from 1970 to the present ( [[#Ramsar%20Convention%20on%20Wetlands--2018|Ramsar Convention on Wetlands, 2018]] ) but the sites are not evenly distributed. Multi-satellite estimates show a strong interannual variability in surface water extent over the period 1992 – 2015 with no clear long-term trend ( [[#Prigent--2020|Prigent et al., 2020]] ).

Human-made water bodies represent approximately 10% of the total continental water surfaces (Figure 8.1; [[#Ramsar%20Convention%20on%20Wetlands--2018|Ramsar Convention on Wetlands, 2018]] ) and consist mainly of reservoirs and rice paddies. High resolution optical imagery over the period 1984 – 2015 ( [[#Donchyts--2016|Donchyts et al., 2016]] ; [[#Pekel--2016|Pekel et al., 2016]] ) shows a net increase of about 0.1 million km <sup>2</sup> in artifical water surfaces, mainly due to the construction of reservoirs. Surfaces of rice paddies are also increasing, especially in South East Asia ( [[#Davidson--2018|Davidson et al., 2018]] ).

In summary, there is ''high confidence'' that the extent of human-made surface water has increased over the 20th and early 21st centuries. In contrast, due to ''low agreement'' in the observational records at the global scale, there is only ''low confidence'' in the observed decline of the natural surface water extent in recent years (see also SRCCL).

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