Quantification of record-breaking subsidence in California’s San Joaquin Valley
Communications Earth & Environment volume 5, Article number: 677 (2024 ) Cite this article
In California’s San Joaquin Valley, groundwater overdraft has caused dramatic and continued land subsidence during two main periods, 1925–1970 (“the historic period”) and post-2006. The impacts of the subsidence are severe, with modified flood risks, damaged aqueducts, and permanently altered aquifer dynamics. However, we do not have a complete record of the post-2006 subsidence due to a 2011–2015 gap in Valley-wide observations, and this makes it difficult to develop an appropriate management response. Here, we used satellite geodetic subsidence measurements to quantify the Valley-wide subsidence volume during 2006–2022. We found a total subsidence volume of 14 km3 over the 16 years, the same as was measured during 24 years of monitoring in the historic period. Considering the extraordinary 2006–2022 Valley-wide subsidence, we make high-level recommendations for subsidence mitigation, highlighting the importance of focusing groundwater overdraft reductions on the deeper aquifers where subsidence originates, and on localities where subsidence impacts are greatest.
In the arid climate of California’s San Joaquin Valley, over a cubic kilometer of groundwater is pumped each year to support some of the United States’ most productive agricultural land1. A dramatic effect of this pumping is land subsidence, which has occurred during two main periods. The first, here referred to as the historic period, started in the 1920s and continued until the 1970s, with the greatest subsidence rates occurring between 1945 and 19702. During this period, 11000 km2 of the Valley sank by over 30 cm and total subsidence locally reached 9 m, an event described as “one of the single largest alterations of the land surface attributed to humankind”3. Subsidence rates fell in the 1970s and 1980s following the mass importation of surface water through new aqueducts4 and, between 1980-2006, greatly reduced groundwater use meant that subsidence was mostly absent5,6. However, following a series of droughts (2007-2009, 2012-2016 and 2020-2022) and the prioritization of water for environmental purposes, surface water imports have fallen which, coupled with land-use changes, have led to renewed subsidence in the post-2006 period, when rates have locally exceeded 30 cm/yr7.
