Shrinking freshwater availability increasing land contribution to sea level rise (opens in new tab)

Indeed!

The GRACE measurement of mass change is one of the more revolutionary advances in Earth science remote sensing in the last few decades. It has provided a unique and completely novel view of groundwater mass change. Grace is the main reason we know so much about the massive groundwater loss in the Oglala aquifer in the US Midwest, in the Central Basin in California, and in northern India. Water well data exists but it is very sparse and idiosyncratic.

It’s also our main window into mass losses in ice sheets in high latitudes (Greenland, Antarctica). We have radar altimetry data from Antarctica, but because of glacial rebound and other effects, it’s not easy to translate height changes into mass changes. Grace measures mass change directly.

Several authors of the cited study are on the science team. It is a JPL instrument.

The original Grace pair used radio to measure separation and velocity, while the follow-up Grace-FO uses a laser. I assume the small wavelength of the laser provides a more accurate measurement. It’s possible that Grace-FO has a slightly higher spatial resolution (I’ve worked with Grace but not Grace-FO); the horizontal resolution of Grace is about 100km or about 1 degree.

From an inference perspective the measurement is very interesting. They pool about a month’s worth of observations of the distance and velocity of a pair of satellites, and do a Bayesian inversion to obtain a parameterized gravitational potential for that month. The map from gravitational potential to observation is known analytically, so it’s readily possible to get a spatial covariance for the gravitational potential, as well as the point estimate.

The IPCC section “9.6.1.1 Global Mean Sea Level Change Budget in the Pre-satellite Era” says Since SROCC, a new ocean heat content reconstruction (Section 2.3.3.1; Zanna et al., 2019) has allowed global thermosteric sea level change to be estimated over the 20th century. As a result, the sea level budget for the 20th century can now be assessed for the first time. For the periods 1901–1990 and 1901–2018, the assessed very likely range for the sum of components is found to be consistent with the assessed very likely range of observed GMSL change (medium confidence), in agreement with Frederikse et al. (2020b; Table 9.5). This represents a major step forward in the understanding of observed GMSL change over the 20th century, which is dominated by glacier (52%) and Greenland Ice Sheet mass loss (29%) and the effect of ocean thermal expansion (32%), with a negative contribution from the LWS change (–14%). While the combined mass loss for Greenland and glaciers is consistent with SROCC, updates in the underlying datasets lead to differences in partitioning of the mass loss.”

Edit: by a different story I mean a different story from what is the leading driver of sea level rise. Sea level rise from ice melt was larger since 1900 because sea level rise in general was less fast back then and global mean temperature rise was much smaller so thermosteric sea level rise played less of a role. Thermosteric sea level rise is larger than ground water factors, both will be eclipsed by ice melt in the upcoming century.

I would note the authors pointedly do not call it the leading driver of sea level rise.

It wasn't that there is a contradiction. If the over use has been happening for decades, and it's at a rate faster than historical replenishment could happen anyways (before "climate change), then this would indicate that over use is the primary cause. Drier weather is a contributing factor in the pace of depletion, but in no way could be the solitary cause nor cure. Even in the article they mention the demands related to a growing population and industrial agriculture (article also mentions potential food scarcity).