VERTICAL LAND MOTION ALONG THE COAST OF CALIFORNIA: IMPLICATIONS FOR FLOODING AND INUNDATION HAZARDS

The current estimates of damage in California due to sea level rise amount to nearly $100 billion in property losses, 8,750 km² of inundated wetlands, and 480,000 displaced people by the year 2100. The accuracy of these estimates is highly sensitive to variations in land subsidence along the coast. Hydrologic, tectonic, and morphological forces combine to drive spatially and temporally variable land motion along the California coast, and these variations alter expected flood extents and erosion rates. While California has an extensive network of ground monitoring stations to track these motions, the stations’ distribution is not dense enough to provide spatially continuous information on the state’s uplift and subsidence trends, thus failing to elucidate small-scale variability in vertical land motion rates. Here we present the first high-resolution (~100 m) state-wide map of the vertical land motion rates along the coast of California. We performed an advanced multitemporal interferometric analysis of all synthetic aperture radar data collected by ALOS L-band and Sentinel-1A/B C-band satellites combined with the horizontal velocity measurements from Global Navigation Satellite System. The validation test yields a standard deviation of 0.98 mm/year for the difference between the InSAR-derived vertical land motion rates and the vertical rates from Global Navigation Satellite System measurements. Thus, these results are reliable and this interferometric analysis is translatable to other regions with good synthetic aperture radar coverage. These results can be used to improve estimates of relative sea level rise and the related damages. They can be leveraged in many applications, including coastal planning, resource management, and improving geologic understanding for the state of California.