Editing IPCC:AR6/SROCC/Chapter-4 (section)

===== 4.2.2.2.5 Contributions from water storage on land =====

Water is stored on land not only in the form of ice but snow, surface water, soil moisture and groundwater. Temporal changes in land water storage, defined as all forms of water stored on land excluding land ice, contribute to observed changes in ocean mass and thus sea level on annual to centennial time scales (Döll et al., 2016 <sup>[[#fn:r225|225]]</sup> ; Reager et al., 2016 <sup>[[#fn:r226|226]]</sup> ; Hamlington et al., 2017 <sup>[[#fn:r227|227]]</sup> ; Wada et al., 2017 <sup>[[#fn:r228|228]]</sup> ) . They are caused by both climate variability and direct human interventions, at the multi-decadal to centennial time scales. Over the past century, the main cause for land water storage changes are the groundwater depletion and impoundment of water behind dams in reservoirs (Döll et al., 2016 <sup>[[#fn:r229|229]]</sup> ; Wada et al., 2016 <sup>[[#fn:r230|230]]</sup> ) . While the rate of groundwater depletion and thus its contribution to SLR increased during the 20th century and up to today (Wada et al., 2016 <sup>[[#fn:r231|231]]</sup> ) , its effect on sea level was more than balanced by the increase in land water storage due to dam construction between 1950 and 2000 (Wada et al., 2016 <sup>[[#fn:r232|232]]</sup> ) . Since about 2000, based on hydrological models, the combined effect of both processes is a positive contribution to SLR (Wada et al., 2016 <sup>[[#fn:r233|233]]</sup> ) . Decreased water storage in lakes, wetlands and soils due to human activities are less important for ocean mass changes (Wada et al., 2016 <sup>[[#fn:r234|234]]</sup> ) . Overall, the integrated effects of the direct human intervention on land hydrology have reduced land water storage during the last decade, increasing the rate of SLR by 0.15–0.24 mm yr <sup>–</sup> <sup>1</sup> (Wada et al., 2016 <sup>[[#fn:r235|235]]</sup> ; Wada et al., 2017 <sup>[[#fn:r236|236]]</sup> ; Scanlon et al., 2018 <sup>[[#fn:r237|237]]</sup> ; WCRP Global Sea Level Budget Group, 2018 <sup>[[#fn:r238|238]]</sup> ) . Over periods of a few decades, land water storage was affected significantly by climate variability (Dieng et al., 2015a <sup>[[#fn:r239|239]]</sup> ; Reager et al., 2016 <sup>[[#fn:r240|240]]</sup> ; Dieng et al., 2017 <sup>[[#fn:r241|241]]</sup> ) . Net land water storage change driven by both climate and direct human interventions can be determined based on GRACE observations and global hydrological modelling. They indicate different estimates of the rate of SLR. Over the period 2002–2014 GRACE-based estimates of the net land water storage (i.e., not including glaciers) show a negative contribution to sea level (e.g., Scanlon et al., 2018) resulting in the negative value after 2006 in Table 1while hydrological models determined a slightly positive one. The reasons for this difference between estimates are not elucidated. There is scientific consensus that uncertainties of both net land water storage contribution to sea level and its individual contributions remain high (WCRP Global Sea Level Budget Group, 2018 <sup>[[#fn:r242|242]]</sup> ) . The differences in estimates and the lack of multiple consistent studies give ''low confidence'' in the net land water storage contribution to current SLR.

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