Sea level rise is frequently mentioned in terms of melting glaciers and ice sheets, as well as the thermal expansion of seawater. However, tracking and predicting sea level rise is much more complex than simply measuring the height of our oceans. The land near coastlines is also constantly moving, rising, or sinking due to natural and human-caused processes. A recent NASA-led study focused on coastal land shifts along California found that even minor vertical land motion can majorly impact local sea levels in the future decades. Researchers used precise satellite measurements to identify how subsidence and uplift affect sea level estimates, giving vital insights for coastal adaptation techniques.

Understanding Vertical Land Motion’s Impact on Sea-Level Rise

By 2050, California’s sea levels are expected to rise between 6 and 14.5 inches (15 and 37 centimetres) above 2000 levels. While this increase is mainly caused by global warming-related processes such as ice sheet melting and ocean expansion, vertical land motion (VLM) is an essential but frequently disregarded factor in driving localized sea-level fluctuations.

According to Marin Govorcin, a remote sensing scientist at NASA’s Jet Propulsion Laboratory (JPL), many coastal locations, such as the reclaimed ground beneath San Francisco, are sinking faster than global sea levels rise. This means that local sea level rises can be far higher than global averages, posing serious threats to infrastructure, ecosystems, and communities.

The study in Science Advances demonstrates how unpredictable vertical coastal land shifts along California coast may be in terms of scale and speed. A combination of natural processes, including tectonic activity and sediment compaction, and human-induced impacts like groundwater extraction, wastewater injection, and hydrocarbon production causes this motion. Understanding these land processes is critical for improving sea-level rise estimates and guiding governments’ adaptation plans.

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Mapping California’s Coastal Changes Using Advanced Satellite Technology

JPL and NOAA researchers used satellite radar to gather high-resolution measurements of vertical coastal land shifts along California. They used data from ESA’s Sentinel-1 satellites and ground-based Global Navigation Satellite System (GNSS) stations to map over a thousand miles of coastline, pinpointing areas where land rises or sinks.

One of the primary tools used in the study was interferometric synthetic aperture radar (InSAR), which allows scientists to measure changes in land elevation down to a fraction of an inch. By analyzing data acquired between 2015 and 2023, the scientists discovered certain coastal regions experiencing significant vertical migration.

Key Findings: Subsidence Hotspots and Localized Sea Level Risks

• San Francisco Bay Area: Researchers detected ground settling at rates surpassing 0.4 inches (10 millimetres) per year in San Rafael, Corte Madera, Foster City, and Bay Farm Island, mainly owing to sediment compaction. If current rates continue, sea levels in these places might increase more than 17 inches (45 centimetres) by 2050, more than double the regional estimate of 7.4 inches (19 centimetres) based on tide gauge estimates.
• Southern California: Human activities such as groundwater extraction and hydrocarbon production have caused unpredictable vertical land motion in Los Angeles and San Diego counties. These factors cause uncertainty of up to 15 inches (40 centimetres) in sea level estimates in some regions.
• Santa Barbara and Long Beach: Although many coastal locations are sinking, some are rising. The Santa Barbara groundwater basin has been steadily increasing since 2018, whereas Long Beach has experienced elevation due to fluid extraction and injection associated with oil and gas operations.

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The Impact of Groundwater Withdrawal, Landslides, and Erosion

Coastal land shifts along California are not homogeneous throughout. While some places progressively subside, others endure oscillations caused by groundwater withdrawal, slow-moving landslides, and coastal erosion.

• Fluctuating Aquifers and Their Effect on Land Elevation

Groundwater depletion is a key contributor to land subsidence in central California’s Central Valley, where it can be up to 8 inches (20 centimetres) each year. Drought exacerbates the problem, forcing land to sink when subsurface water is drained. Conversely, aquifers can briefly rebound during wet periods, resulting in short-term elevation.

Similar patterns have been found in other sections of the state, such as Santa Clara in the San Francisco Bay Area, Santa Ana in Orange County, and Chula Vista in San Diego County. These variations challenge efforts to predict long-term sea level rises effectively.

• Landslides and Coastal Erosion: Unexpected Contributors to Land Motion

Researchers discovered downhill ground motion related to slow-moving landslides in mountainous coastal areas such as the Big Sur Mountains and the Palos Verdes Peninsula. Sinking tendencies were also noted in Northern California’s marshlands, lagoons, and estuaries, particularly in the Russian River estuary, Monterey Bay, and San Francisco Bay. Coastal erosion contributes significantly to these patterns, progressively changing the landscape and amplifying the consequences of sea-level rise.

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The Future of Sea-Level Monitoring: Using Advanced Satellite Data

NASA’s OPERA (Observational Products for End-Users from Remote Sensing Analysis) initiative provides scientists, policymakers, and the general public with precise data on land surface changes to aid in continuous monitoring activities. This effort gives extensive insights into North American land elevation changes, allowing for near-real-time tracking of subsidence, tectonic activity, and landslides.

In the near future, the OPERA project will combine data from the highly anticipated NISAR (NASA-Indian Space Research Organisation Synthetic Aperture Radar) mission, which is scheduled to launch in the coming months. This cutting-edge satellite technology will give even more exact and regular measurements of vertical land motion, improving our capacity to forecast localized sea level rise and enhance coastal resilience planning efforts.

Conclusion: The Need for a Comprehensive Approach to Sea Level Rise

As sea levels rise, coastal towns must consider marine changes and the shifting terrain beneath their feet. The findings of this NASA-led study highlight the need to include vertical land motion in sea-level rise estimates to generate more accurate and actionable adaptation methods.

By utilizing advanced satellite technologies and continual monitoring activities, researchers can improve their awareness of local risks and assist decision-makers in implementing policies to limit the effects of rising seas. A comprehensive strategy for sea level rise, whether through improved land-use planning, tougher groundwater extraction rules, or enhanced coastal defenses, is critical for preserving vulnerable regions from potential inundations.

Using cutting-edge satellite data in public planning and infrastructure projects will be critical to guaranteeing coastal resilience in California and elsewhere. As technology evolves, so should our plans for protecting communities from the ever-changing forces of land and water.

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