Periodic Reporting for period 1 - GEOCLIME (Climate change and Geodetic deformation)
Reporting period: 2019-01-07 to 2021-01-06
Earth is a dynamic planet subject to many processes. Detectable changes in the shape of the solid Earth and its gravity field arise due to the varying mass distribution of the surface fluids (oceans, atmosphere and terrestrial water storage). These include variations related to climate change such as sea level changes, loss of ice sheets, post-glacial rebound, and changes in precipitation, water storage, and runoff. These shape changes are called loading effects and can reach significant amplitudes (several mm). Besides global climate changes, loads exhibit regional variations over all time scales.
Space geodesy provides unprecedented coverage of the Earth's surface and can contribute to monitoring the interaction between climate change and Earth’s time-dependent shape and gravity field. The Global Positioning System (GPS) has become the essential tool for the mm to cm level positioning requirements within the geosciences. Gravity satellite missions such as the Gravity Recovery and Climate Experiment (GRACE) can also observe the global movement of environmental fluids. These two techniques give very long time series of observations that are extremely complementary in spatial and temporal resolution, for monitoring loading effects and enhancing global understanding of the mass transport at the Earth’s surface. Loading effects can explain much of the annual signal in position time series. Nevertheless, the errors in the geophysical models are still significant and discrepancies exist between models and observations.
The GEOCLIME (Climate change and Geodetic deformation) project aimed to better infer crustal deformation processes related to the water cycle, and the impact of climate change on Earth’s shape via the study of loading effects. This project addressed key science questions related to surface deformation associated with water distribution and water cycle change, as well as the processes controlling variations in relative land and sea levels. It also contributed to other major unresolved scientific problems concerning the effective rheology and structure of the lithosphere and mantle. The main objective was to explore the impact of changing rheological properties in loading deformation models and to improve and validate these forward models. To achieve this, the project adopted a multi-disciplinary approach using highly accurate space geodesy datasets and state of the art modelling. This offered a unique opportunity to identify climate change signals, improving our understanding of how Earth responds to the water cycle. Better understanding this interaction is essential for applications such as how coasts react to relative sea level change and storms as well as natural hazard mitigation.
Space geodesy provides unprecedented coverage of the Earth's surface and can contribute to monitoring the interaction between climate change and Earth’s time-dependent shape and gravity field. The Global Positioning System (GPS) has become the essential tool for the mm to cm level positioning requirements within the geosciences. Gravity satellite missions such as the Gravity Recovery and Climate Experiment (GRACE) can also observe the global movement of environmental fluids. These two techniques give very long time series of observations that are extremely complementary in spatial and temporal resolution, for monitoring loading effects and enhancing global understanding of the mass transport at the Earth’s surface. Loading effects can explain much of the annual signal in position time series. Nevertheless, the errors in the geophysical models are still significant and discrepancies exist between models and observations.
The GEOCLIME (Climate change and Geodetic deformation) project aimed to better infer crustal deformation processes related to the water cycle, and the impact of climate change on Earth’s shape via the study of loading effects. This project addressed key science questions related to surface deformation associated with water distribution and water cycle change, as well as the processes controlling variations in relative land and sea levels. It also contributed to other major unresolved scientific problems concerning the effective rheology and structure of the lithosphere and mantle. The main objective was to explore the impact of changing rheological properties in loading deformation models and to improve and validate these forward models. To achieve this, the project adopted a multi-disciplinary approach using highly accurate space geodesy datasets and state of the art modelling. This offered a unique opportunity to identify climate change signals, improving our understanding of how Earth responds to the water cycle. Better understanding this interaction is essential for applications such as how coasts react to relative sea level change and storms as well as natural hazard mitigation.
We used an innovative methodology for precise determination of crustal deformations induced by non-tidal loading effects. We tested the level of anelastic contribution to surface hydrological loading deformation at seasonal timescales. This study is one of the few to consider the full 3-d movement. To validate the methodology, we considered the Great Lakes region of North America, a region offering a high density of long-term GNSS sites at different distances and in different directions from the lakes as well as a well-constrained water mass variation, the only parameter being the crustal response. We produced daily load grids from in situ water level time series and shoreline dataset. We computed the Love numbers and Green’s functions of displacements for a reference Earth model, which express the surface response as a function of the angular distance between an observer and the mass load. Then, we simulated the 3D crustal loading deformations for daily and 21-year time series induced by each lake and the cumulative loading effect for all the lakes for regular grids and at hundreds of GPS sites. The next step was to generate and use five Earth models with different rheological parameters introducing anelasticity, reducing the shear modulus in the asthenosphere as well as dispersion at short or annual periods. We performed the time series analysis comparing the different models to the reference model and to GPS and GRACE observations.
Then, we computed the deformation induced by the full loading signal (cumulative effect of ocean, atmosphere and hydrology) inferred from 14 years of GRACE monthly mass concentration solutions (mascons). In addition, we applied the same methodology to Amazon area where the hydrological signal is very strong (both spatially and in amplitude), since the Amazon Basin has the world’s largest continental seasonal water variations. This area is of great interest concerning the Earth’s hydrological system understanding. We compared the loading deformation predicted with the different Earth models with respect to the reference model and to GPS time series for more than 600 and 200 GPS sites in the first and second areas, respectively. In both study areas, the large number of sites allows us to overcome the GPS time series noise and to validate the loading deformation models. Comparison with the GPS observations enables to select the most relevant model at daily and annual periods over different spatial scales for both regions. The spatial and temporal pattern analysis of the results helps to separate and quantify the different sources and frequencies from daily to decadal time scales and to infer hydrologic local/regional signals linked to recent climate change.
Then, we computed the deformation induced by the full loading signal (cumulative effect of ocean, atmosphere and hydrology) inferred from 14 years of GRACE monthly mass concentration solutions (mascons). In addition, we applied the same methodology to Amazon area where the hydrological signal is very strong (both spatially and in amplitude), since the Amazon Basin has the world’s largest continental seasonal water variations. This area is of great interest concerning the Earth’s hydrological system understanding. We compared the loading deformation predicted with the different Earth models with respect to the reference model and to GPS time series for more than 600 and 200 GPS sites in the first and second areas, respectively. In both study areas, the large number of sites allows us to overcome the GPS time series noise and to validate the loading deformation models. Comparison with the GPS observations enables to select the most relevant model at daily and annual periods over different spatial scales for both regions. The spatial and temporal pattern analysis of the results helps to separate and quantify the different sources and frequencies from daily to decadal time scales and to infer hydrologic local/regional signals linked to recent climate change.
The main novelty is the introduction of anelastic asthenosphere response for modelling 3D loading deformation. By creating different possible models, we learn more about the crustal deformation linked to environmental fluids and enhance water cycle understanding. More widely, better understanding the interaction between the solid Earth and the mass redistributions linked to natural climate variability and human activities gives insights on the processes that control local variation in relative land and sea levels. For instance, accurate crustal deformation modelling is required to measure sea level rise, which is not spatially uniform and is a complex function of different parameters including local land movement. Such answers are critical to assess the impacts on coastal infrastructure, human society, and ecosystems. A refined model of how the dynamic of Earth system responds to loading effects is also essential to infer the response of the solid Earth to present-day ice changes. In addition, such results can contribute to some WCRP (World Climate Research Program) Grand Challenges and are in line with the 2021-2030 United Nations Decade of Ocean Science for Sustainable Development.
Results dissemination through international conferences and publications will continue and will enable their exploitation by the scientific community. Engagement activities will also be performed for the public and schoolchildren to illustrate the importance of understanding the Earth system in the frame of climate change as well as to attract future scientists.
Results dissemination through international conferences and publications will continue and will enable their exploitation by the scientific community. Engagement activities will also be performed for the public and schoolchildren to illustrate the importance of understanding the Earth system in the frame of climate change as well as to attract future scientists.