Editing IPCC:AR6/WGI/Chapter-9 (section)

===== 9.6.3.2.6 Land-water storage =====

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In AR5 and SROCC, the groundwater depletion contribution to GMSL rise was based on combining results from two approaches: one assuming a continuation of early 21st-century trends ( [[#Konikow--2011|Konikow, 2011]] ); and the other using land-surface hydrology models ( [[#Wada--2012|Wada et al., 2012]] ). Together, these yielded a range of about 0.02–0.09 m of GMSL rise by 2080–2099. The rate of water impoundment in reservoirs was likewise based on two approaches: one assuming the continuation of the average rate over 1971–2010 (and thus –0.01 to –0.03 m by 2080–2099; [[#Chao--2008|Chao et al., 2008]] ); and the other assuming no net impoundment after 2010 ( [[#Lettenmaier--2009|Lettenmaier and Milly, 2009]] ). Together, these yield a GMSL contribution from groundwater impoundment of –0.03 to 0 m. Combining groundwater depletion and water impoundment led AR5 and SROCC to infer a projected range of –0.01 to +0.11 m by 2100.

In the updated projections, a statistical relationship is applied, linking historical and future SSP global population to dam impoundment and groundwater extraction ( [[#Rahmstorf--2012|Rahmstorf et al., 2012]] ; [[#Kopp--2014|Kopp et al., 2014]] ). The population/groundwater depletion relationship is calibrated based on the same studies used in AR5 ( [[#Konikow--2011|Konikow, 2011]] ; [[#Wada--2012|Wada et al., 2012]] ), reduced by about 20% to account for water retained on land ( [[#Wada--2016|Wada et al., 2016]] ). The population/dam impoundment relationship is calibrated based on [[#Chao--2008|Chao et al. (2008)]] . However, while historically dam impoundment has been declining with population, recent literature shows that planned dam construction considerably exceeds the historical trend ( [[#Zarfl--2015|Zarfl et al., 2015]] ; [[#Hawley--2020|Hawley et al., 2020]] ). Over 2020–2040, the impoundment contribution to GMSL rise based on past trends would be about –0.1 mm yr <sup>–1</sup> , compared to about –0.5 mm yr <sup>–1</sup> if all currently planned dams are built ( [[#Hawley--2020|Hawley et al., 2020]] ) and the statistical projection is therefore augmented by an additional –0.4 to 0.0 mm yr <sup>–1</sup> over 2020–2040 to account for the possible effects of planned dam construction. As in AR5 and SROCC, climatically driven changes to land-water storage (LWS) have not been included in published sea level projections, as they are not well quantified (e.g., [[#Jensen--2019|Jensen et al., 2019]] ) or are considered negligible (e.g., permafrost, [[#9.5.2|Section 9.5.2]] ). This approach yields a ''likely'' global-mean land-water storage contribution (Figure 9.27, Table 9.8) that is slightly lower and narrower than the AR5 and SROCC ''likely'' ranges. Since the projections are explicitly population driven, these projections also exhibit a weak scenario dependence, with a contribution around 0.01 m higher under SSP3 than under other scenarios.

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'''Table 9.8''' '''|''' '''Global mean sea level projections between 199''' '''5–2''' '''014 and 2100 for total change and individual contributions, median values, (likely ) ranges of the process-based model ensemble''' for RCP 2.6 (from AR5 ( [[#Church--2013a|Church et al., 2013a]] ) and SROCC ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] )) and SSP1-2.6 (this Report), and for RCP8.5 (from AR5 ( [[#Church--2013a|Church et al., 2013a]] ) and SROCC ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] )) and SSP5-8.5 (this Report). Values for AR5 ( [[#Church--2013a|Church et al., 2013a]] ) and SROCC ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ) are adjusted from the 1986–2005 baseline used in past reports. Only the Antarctic contribution changed between AR5 ( [[#Church--2013a|Church et al., 2013a]] ) and SROCC ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Unshaded cells represent processes in which there is ''medium confidence'' ; shading indicates the inclusion of processes in which there is ''low confidence'' . For the MICI- and SEJ-based projections, parenthetical numbers represent the 17th–83rd percentile of the associated probability distributions, not assessed ''likely'' ranges.

{| class="wikitable"
|-
|
| colspan="2"| '''RCP2.6'''

| colspan="3"| '''SSP1-2.6'''

|-
| m relative to 1995–2014

| '''AR5'''

| '''SROCC'''

| Medium confidence '''processes'''

| '''MICI'''

| '''SEJ'''

|-
| '''Thermal expansion ( [[#9.2.4.1|Section 9.2.4.1]] )'''

| colspan="2"| 0.14 (0.10–0.19) m

| colspan="3"| 0.14 (0.11–0.18) m

|-
| '''Greenland [[#9.4.1.3|Section 9.4.1.3]] )'''

| colspan="2"| 0.07 (0.03–0.11) m

| colspan="2"| 0.06 (0.01–0.10) m

| 0.13 (0.07–0.30) m

|-
| '''Antarctica ( [[#9.4.2.5|Section 9.4.2.5]] )'''

| 0.06 (–0.04 to +0.16) m

| 0.04 (0.01–0.11) m

| 0.11 (0.03–0.27) m

| 0.08 (0.06–0.12) m

| 0.09 (–0.01 to +0.25) m

|-
| '''Glaciers ( [[#9.5.1.3|Section 9.5.1.3]] )'''

| colspan="2"| 0.10 (0.04–0.16) m

| colspan="3"| 0.09 (0.07–0.11) m

|-
| '''Land-water storage ( [[#9.6.3.2|Section 9.6.3.2]] )'''

| colspan="2"| 0.05 (–0.01 to +0.11) m

| colspan="3"| 0.03 (0.01–0.04) m

|-
|
|-
| '''Total (2100)'''

| 0.41 (0.25–0.58) m

| 0.40 (0.26–0.56) m

| 0.44 (0.33–0.62) m

| 0.41 (0.35–0.48) m

| 0.53 (0.38–0.79) m

|-
| '''Total (2150)'''

| 0.29–0.63 m

| 0.56 (0.40–0.73) m

| 0.68 (0.46–0.99) m

| 0.74 (0.62–0.91) m

| 0.84 (0.56–1.34) m

|-
|
|-
| '''GMSL rate, 2080–2100 (mm''' '''yr''' <sup>–1</sup> ''')'''

| 4.4 (2.0–6.8) mm yr <sup>–1</sup>

| 4 (2–6) mm yr <sup>–1</sup>

| 5.2 (3.2–8.0) mm yr <sup>–1</sup>

| 5.1 (4.3–6.2) mm yr <sup>–1</sup>

| 5.9 (2.8–11.0) mm yr <sup>–1</sup>

|-
|
| colspan="2"|
| colspan="3"|
|-
|
| colspan="2"| '''RCP8.5'''

| colspan="3"| '''SSP5-8.5'''

|-
| m relative to 1995–2014

| '''AR5'''

| '''SROCC'''

| Medium confidence '''processes'''

| '''MICI'''

| '''SEJ'''

|-
| '''Thermal expansion ( [[#9.2.4.1|Section 9.2.4.1]] )'''

| colspan="2"| 0.31 (0.24–0.38) m

| colspan="3"| 0.30 (0.24–0.36) m

|-
| '''Greenland [[#9.4.1.3|Section 9.4.1.3]] )'''

| colspan="2"| 0.14 (0.08–0.27) m

| colspan="2"| 0.13 (0.09–0.18) m

| 0.23 (0.10–0.59) m

|-
| '''Antarctica ( [[#9.4.2.5|Section 9.4.2.5]] )'''

| 0.04 (–0.08 to +0.14) m

| 0.12 (0.03–0.28) m

| 0.12 (0.03–0.34) m

| 0.34 (0.19–0.53) m

| 0.21 (0.02–0.56) m

|-
| '''Glaciers ( [[#9.5.1.3|Section 9.5.1.3]] )'''

| colspan="2"| 0.17 (0.09–0.25) m

| colspan="3"| 0.18 (0.15–0.20) m

|-
| '''Land-water storage ( [[#9.6.3.2|Section 9.6.3.2]] )'''

| colspan="2"| 0.05 (–0.01 to +0.11) m

| colspan="3"| 0.03 (0.01–0.04) m

|-
|
|-
| '''Total (2100)'''

| 0.71 (0.49–0.95) m

| 0.81 (0.58–1.07) m

| 0.77 (0.63–1.01) m

| 0.99 (0.82–1.19) m

| 1.00 (0.70–1.60) m

|-
| '''Total (2150)'''

| 0.34–1.35 m

| 1.27 (0.80–1.79) m

| 1.32 (0.98–1.88) m

| 3.48 (2.57–4.82) m

| 1.79 (1.22–2.94) m

|-
|
|-
| '''GMSL rate, 2080–2100 (mm''' '''yr''' <sup>–1</sup> ''')'''

| 11.2 (7.5–15.7) mm yr <sup>–1</sup>

| 15 (10–20) mm yr <sup>–1</sup>

| 12.1 (8.6–17.6) mm yr <sup>–1</sup>

| 23.1 (17.5–30.1) mm yr <sup>–1</sup>

| 16.0 (9.8–28.9) mm yr <sup>–1</sup>

|}

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