Vertical Displacements of the Amazon Basin From GRACE and GPS

Abstract

The extent to which Gravity Recovery and Climate Experiment (GRACE)‐recovered gravity anomalies can improve our understanding of Global Positioning System (GPS)‐measured vertical displacements is currently uncertain. To address this issue, we compared vertical displacements measured by 23 GPS stations in the Amazon basin with displacements estimated from GRACE geopotential fields. We show that despite poor correlation ( r2=0.15) between rate estimates in GPS and GRACE‐derived displacement time series, further analyses reveal low bias between annual amplitude estimates and a scaling near 1. There is higher correlation ( r2=0.78) between annual periodic motions, with near 1 to 1 agreement, but there is poor correlation ( r2=0.02) and little agreement between semiannual amplitude estimates. Subtracting GRACE displacements from the GPS time series flattens the GPS power spectra, reducing the spectral index magnitude, on average, from −1.2759±0.0007 (“fractional Brownian motion”) to −0.3346±0.0006 (“fractional Gaussian noise”), suggesting that some fraction of the apparent GPS error correlation derives from mass loading signals that are not completely characterized by secular trends or seasonal periodic motions. From March 2011 to November 2016, we find a GPS and GRACE‐derived displacement combined average uplift of the Amazon basin of 1.20±0.26 mm/yr and combined average annual periodic motion of 10.22±0.57 mm. Deviations from a standard trajectory model for site motion are apparent in both data sets and appear to coincide with various flooding and drought events between 2011 and 2016, which suggests that the GPS coordinate time series record displacements driven by large‐scale climate oscillations.

GPS Imaging of Global Vertical Land Motion for Studies of Sea Level Rise

“…This may explain why when considering overall trends Knowles et al. (2020) found an uplift trend in the Amazon, while our results show a combination of uplift and subsidence. This is consistent with the imaged temporal variability and indicates that the trends in the Amazon Basin are likely not permanent features of the vertical GPS rate field, and the sign of uplift depends on the time period of observation.…”

“…This indicates that changes in rates in the Amazon are not only seasonal but also have trends that inflect upward and downward, changing sign on multi-annual time scales between drought and wet periods. This may explain why when considering overall trends Knowles et al, (2020) found an uplift trend in the Amazon, while our results show a combination of uplift and subsidence. This is consistent with the imaged temporal variability and indicates that the trends in the Amazon Basin are likely not permanent features of the vertical GPS rate field, and the sign of uplift depends on the time period of observation.…”

Improved Hydrological Loading Models in South America: Analysis of GPS Displacements Using M-SSA

“…Previous studies analyzed the loading signal in South America using space geodesy time series. It has been demonstrated that GRACE signal is consistent with in situ water level and discharge data [31] and that GRACE and GPS give complementary estimates of vertical displacement in the Amazon basin [32]. The observed displacement includes seasonal, interannual and secular variations in mass loading.…”

“…Despite the GRACE hydrological signal being dominated by seasonal and long-term variability, recent changes in terrestrial water storage in South American river basins have been evidenced [33]. In particular it concerns drought in 2010 in the Amazon area, in 2012-2014 in the Sao Paulo region [34] or the 2015-2016 severe drought, as well as extreme floods in 2011-2012 and 2013-2014 [32]. GPS time series analysis is also useful to monitor hydrological hazard, as it was performed on the vertical loading signal induced by drought in Brazil [35].…”

Assessment of Temporal Variations of Orthometric/Normal Heights Induced by Hydrological Mass Variations over Large River Basins Using GRACE Mission Data

“…Several authors demonstrated the usefulness of GRACE satellite mission data for investigating temporal variations of geoid/quasigeoid heights, e.g., [13][14][15][16][17][18][19]. Moreover, many authors have proved that the estimated vertical deformations of the Earth's surface using GRACE satellite mission data are in a good agreement with the corresponding ones determined from other space geodetic techniques such as GNSS on a global scale, e.g., [20][21][22], on a continental scale, e.g., [23,24] in Europe, as well as on a local/regional scale, e.g., [25,26] in the Amazon basin, [27] in the West Africa, [28] in the East Africa, [29] in Japan, [30] in Bangladesh, [31][32][33] in China, [34,35] in Tibet, [36,37] in Poland, [38] in Greenland, and [39][40][41][42] in the North America, and Very Long Baseline Interferometry (VLBI) (e.g., [43]). The use of GRACE satellite mission data for estimating physical height changes, i.e., temporal variations of orthometric/normal heights, was investigated on local and regional scales for the area of Turkey, Poland, Central Europe and Greenland [7][8][9][10]44].…”