Disappearing cities on US coasts.

The sea level along the US coastlines is projected to rise by 0.25-0.3 m by 2050, increasing the probability of more destructive flooding and inundation in major cities1-3. However, these impacts may be exacerbated by coastal subsidence-the sinking of coastal land areas4-a factor that is often underrepresented in coastal-management policies and long-term urban planning2,5. In this study, we combine high-resolution vertical land motion (that is, raising or lowering of land) and elevation datasets with projections of sea-level rise to quantify the potential inundated areas in 32 major US coastal cities. Here we show that, even when considering the current coastal-defence structures, further land area of between 1,006 and 1,389 km2 is threatened by relative sea-level rise by 2050, posing a threat to a population of 55,000-273,000 people and 31,000-171,000 properties. Our analysis shows that not accounting for spatially variable land subsidence within the cities may lead to inaccurate projections of expected exposure. These potential consequences show the scale of the adaptation challenge, which is not appreciated in most US coastal cities.

Interferometric SAR Phase Denoising Using Proximity-Based K-SVD Technique.

This paper addresses the problem of interferometric noise reduction in Synthetic Aperture Radar (SAR) interferometry based on sparse and redundant representations over a trained dictionary. The idea is to use a Proximity-based K-SVD (ProK-SVD) algorithm on interferometric data for obtaining a suitable dictionary, in order to extract the phase image content effectively. We implemented this strategy on both simulated as well as real interferometric data for the validation of our approach. For synthetic data, three different training dictionaries have been compared, namely, a dictionary extracted from the data, a dictionary obtained by a uniform random distribution in [ - π , π ] , and a dictionary built from discrete cosine transform. Further, a similar strategy plan has been applied to real interferograms. We used interferometric data of various SAR sensors, including low resolution C-band ERS/ENVISAT, medium L-band ALOS, and high resolution X-band COSMO-SkyMed, all over an area of Mt. Etna, Italy. Both on simulated and real interferometric phase images, the proposed approach shows significant noise reduction within the fringe pattern, without any considerable loss of useful information.

Sustained Groundwater Loss in California's Central Valley Exacerbated by Intense Drought Periods.

The accelerated rate of decline in groundwater levels across California's Central Valley results from overdrafting and low rates of natural recharge and is exacerbated by droughts. The lack of observations with an adequate spatiotemporal resolution to constrain the evolution of groundwater resources poses severe challenges to water management efforts. Here we present SAR interferometric measurements of high-resolution vertical land motion across the valley, revealing multiscale patterns of aquifer hydrogeological properties and groundwater storage change. Investigating the depletion and degradation of the aquifer-system during 2007-2010, when the entire valley experienced a severe drought, we find that ~2% of total aquifer-system storage was permanently lost, owing to irreversible compaction of the system. Over this period, the seasonal groundwater storage change amplitude of 10.11 ± 2.5 km3 modulates a long-term groundwater storage decline of 21.32 ± 7.2 km3. Estimates for subbasins show more complex patterns, most likely associated with local hydrogeology, recharge, demand, and underground flow. Presented measurements of aquifer-system compaction provide a more complete understanding of groundwater dynamics and can potentially be used to improve water security.

Identifying susceptible groundwater contamination zones in western Odisha of India using hydro-geochemical and geospatial approaches.

Nuapada is one of the most drought-affected and fluoride-contaminated districts in Odisha, India. The presence of various dissolved substances, evapotranspiration, and lowering water table during pre- and post-monsoon (PRM and POM) seasons are responsible for declining groundwater (GW) quality over the Nuapada region. To comprehend the contaminated GW zones over the Nuapada and Komna blocks of the northern Nuapada district during the seasons, integration of hydrogeochemistry and statistical approaches using GW sample data on a geospatial platform have been done. The analysis exhibits that the major source of groundwater contamination is mostly geogenic with little anthropogenic impact. The cumulative impact of fluoride (F-), iron (Fe2+), and nitrate (NO3-) contents are noticed in great-depth zones of the water table in the north and south parts of Nuapada and Komna blocks, respectively. The dominant hydro facies, such as Na-Cl (41.77%) and Ca-Cl (25.31%) types exist over both blocks during PRM and POM seasons, respectively. Demarcation of contaminant and susceptible zones over the study area using geospatial analysis and groundwater quality indices (GWQI) were done. About 3% of the total area, in the north and middle parts of the Nuapada and Komna blocks, falls under contamination zones and is unfit for drinking purposes, and about 35% of the region is susceptible to future contamination. The outcome of the result analysis will enhance the scope for researchers, policymakers, and water managers to regulate emerging health, agricultural, and industrial issues in the stressed aquifer system in India and the world.

Hidden vulnerability of US Atlantic coast to sea-level rise due to vertical land motion.

The vulnerability of coastal environments to sea-level rise varies spatially, particularly due to local land subsidence. However, high-resolution observations and models of coastal subsidence are scarce, hindering an accurate vulnerability assessment. We use satellite data from 2007 to 2020 to create high-resolution map of subsidence rate at mm-level accuracy for different land covers along the ~3,500 km long US Atlantic coast. Here, we show that subsidence rate exceeding 3 mm per year affects most coastal areas, including wetlands, forests, agricultural areas, and developed regions. Coastal marshes represent the dominant land cover type along the US Atlantic coast and are particularly vulnerable to subsidence. We estimate that 58 to 100% of coastal marshes are losing elevation relative to sea level and show that previous studies substantially underestimate marsh vulnerability by not fully accounting for subsidence.

Subsidence-Derived Volumetric Strain Models for Mapping Extensional Fissures and Constraining Rock Mechanical Properties in the San Joaquin Valley, California.

Large-scale subsidence due to aquifer-overdraft is an ongoing hazard in the San Joaquin Valley. Subsidence continues to cause damage to infrastructure and increases the risk of extensional fissures.Here, we use InSAR-derived vertical land motion (VLM) to model the volumetric strain rate due to groundwater storage change during the 2007-2010 drought in the San Joaquin Valley, Central Valley, California. We then use this volumetric strain rate model to calculate surface tensile stress in order to predict regions that are at the highest risk for hazardous tensile surface fissures. We find a maximum volumetric strain rate of -232 microstrain/yr at a depth of 0 to 200 m in Tulare and Kings County, California. The highest risk of tensile fissure development occurs at the periphery of the largest subsiding zones, particularly in Tulare County and Merced County. Finally, we assume that subsidence is likely due to aquifer pressure change, which is calculated using groundwater level changes observed at 300 wells during this drought. We combine pressure data from selected wells with our volumetric strain maps to estimate the quasi-static bulk modulus, K, a poroelastic parameter applicable when pressure change within the aquifer is inducing volumetric strain. This parameter is reflective of a slow deformation process and is one to two orders of magnitude lower than typical values for the bulk modulus found using seismic velocity data. The results of this study highlight the importance of large-scale, high-resolution VLM measurements in evaluating aquifer system dynamics, hazards associated with overdraft, and in estimating important poroelastic parameters.

Tracking California's sinking coast from space: Implications for relative sea-level rise.

Coastal vertical land motion affects projections of sea-level rise, and subsidence exacerbates flooding hazards. Along the ~1350-km California coastline, records of high-resolution vertical land motion rates are scarce due to sparse instrumentation, and hazards to coastal communities are underestimated. Here, we considered a ~100-km-wide swath of land along California's coast and performed a multitemporal interferometric synthetic aperture radar (InSAR) analysis of large datasets, obtaining estimates of vertical land motion rates for California's entire coast at ~100-m dimensions-a ~1000-fold resolution improvement to the previous record. We estimate between 4.3 million and 8.7 million people in California's coastal communities, including 460,000 to 805,000 in San Francisco, 8000 to 2,300,00 in Los Angeles, and 2,000,000 to 2,300,000 in San Diego, are exposed to subsidence. The unprecedented detail and submillimeter accuracy resolved in our vertical land motion dataset can transform the analysis of natural and anthropogenic changes in relative sea-level and associated hazards.

Groundwater Loss and Aquifer System Compaction in San Joaquin Valley During 2012-2015 Drought.

California's millennium drought of 2012-2015 severely impacted the Central Valley aquifer system and caused permanent loss of groundwater and aquifer storage capacity. To quantify these impacts within the southern San Joaquin Valley, we analyze various complementary measurements, including gravity changes from Gravity Recovery and Climate Experiment (GRACE) satellites; vertical land motion from Global Positioning System, interferometric synthetic aperture radar, and extensometer; and groundwater level records. The interferometric data set acquired by the Sentinel-1 satellite only spans the period January 2015 and October 2017, while the other data sets span the entire drought period. Using GRACE observations, we find an average groundwater loss of 6.1 ± 2.3 km3/year as a lower bound estimate for the San Joaquin Valley, amounting to a total volume of 24.2 ± 9.3 km3 lost during the period October 2011 to September 2015. This is consistent with the total volume of 29.25 ± 8.7 km3, estimated using only Global Positioning System deformation data. Our results highlight the advantage of using vertical land motion data to evaluate groundwater loss and thus fill the gaps between GRACE and GRACE-Follow-On missions and complement their estimates. We further determine that 0.4-3.25% of the aquifer system storage capacity is permanently lost during this drought period. Comparing groundwater level and vertical land motion data following September 2015, we determine an equilibration time of 0.5-1.5 years for groundwater levels within aquitard and aquifer units, during which residual compaction of aquitard and land subsidence continues beyond the drought period. We suggest that such studies can advance the knowledge of evolving groundwater resources, enabling managers and decision makers to better assess water demand and supply during and in-between drought periods.

Comment on "Short-lived pause in Central California subsidence after heavy winter precipitation of 2017" by K. D. Murray and R. B. Lohman.

In a study by Murray and Lohman (M&L), the authors suggest that remote sensing data are useful for monitoring land subsidence due to aquifer system compaction. We agree. To infer aquifer dynamics, we provide a more detailed and joint analysis of deformation and groundwater data. Investigating well data in the Tulare Basin, we find that groundwater levels stabilized before 2015 and show that M&L's observed continued subsidence through July 2016 is likely caused by the delayed compaction of the aquitard. Our analysis suggests the observed 2017 transient uplift is not due to recharge of the aquifer system after heavy winter rainfall because it requires an unrealistic vertical hydraulic gradient nearly five orders of magnitude larger than that typical of Tulare Basin. We find that, regardless of the amount of rainfall, transient annual uplifts of ~3 cm occur in May to June. Using an elastic skeletal storage coefficient of 5 × 10-3, we link this ground uplift to annual groundwater level changes.