Missing Hydrological Contribution to Sea Level Rise

• Published in: Geophysical research letters 2019-11, Vol.46 (21), p.12049-12055
• Main Authors: Kim, Jae‐Seung, Seo, Ki‐Weon, Jeon, Taehwan, Chen, Jianli, Wilson, Clark R.
• Format: Article
• Language: English
• Subjects: Antarctic ice; Budgets; Coefficients; Estimates; GRACE; GRACE (experiment); Gravity; Gravity data; Hydrology; Ice; Ice melting; Inflow; Mean sea level; Oceans; Sea level; Sea level rise; Spherical harmonics; Terrestrial environments; terrestrial water storage; Thermal expansion; Volume transport; Water; Water inflow; Water storage
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL085470

Over the past decade, the rate of global mean sea level (GMSL) rise is about 3.5 mm/year. Terrestrial water/ice mass loss to the oceans and ocean volume expansion explain about 3.1 mm/year, indicating that the GMSL budget is not been fully understood. Past estimates from Gravity Recovery and Climate Experiment (GRACE) data have indicated that terrestrial water storage (TWS) is increasing and is thus a mitigating contributor to GMSL rise. However, TWS estimates from GRACE are uncertain mostly due to limitations in GRACE estimates of degree‐1 and degree‐2 order‐0 spherical harmonic coefficients. We obtain an improved estimate of the TWS contribution to GMSL change using revised GRACE estimates of these low‐degree coefficients. For the period 2005–2015, we find that TWS makes an additional contribution to GMSL rise of about 0.32 ± 0.02 mm/year, mostly associated with a TWS decrease. This revised estimate is sufficient to nearly balance the budget of GMSL rise. Plain Language Summary During the last decade, the rate of global mean sea level (GMSL) rise is about 3.5 mm/year. Ocean volume increase due to thermal expansion has contributed to GMSL rise by about 1.3 mm/year. Recent estimates of terrestrial water and ice melt inflow to the oceans can explain about 1.8 mm/year, so the sum of ocean mass and volume increase (3.1 mm/year) does not explain the total observed GMSL rise (3.5 mm/year). The missing contribution to GMSL rise, about 0.4 mm/year, is a significant water volume, similar in size to the contribution from melting Antarctic ice. In this study, we show that loss of water stored on land (terrestrial water storage (TWS)) accounts for most of the missing contribution to GMSL rise (about 0.3 mm/year). Previous TWS estimates using satellite gravity data were flawed due to various limitations, which are corrected in this study. Key Points Sea level rise from terrestrial water storage (TWS) change has been underestimated in previous estimates using GRACE data During 2005–2015, TWS change has contributed to global mean sea level rise by about 0.32 ± 0.02 mm/year