Freshwater availability is changing worldwide. Here we quantify 34 trends in terrestrial water storage observed by the Gravity Recovery and Climate Experiment (GRACE) satellites during 2002–2016 and categorize their drivers as natural interannual variability, unsustainable groundwater consumption, climate change or combinations thereof. Several of these trends had been lacking thorough investigation and attribution, including massive changes in northwestern China and the Okavango Delta. Others are consistent with climate model predictions. This observation-based assessment of how the world’s water landscape is responding to human impacts and climate variations provides a blueprint for evaluating and predicting emerging threats to water and food security.

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Emerging trends in global freshwater availability.

We discuss several classes of improvements to gravity solutions from the Gravity Recovery and Climate Experiment (GRACE) mission. These include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution JPL RL05, and an alternate JPL RL05M mass concentration (mascon) solution benefitting from those same improvements but derived in surface spherical cap mascons. The mascon basis functions allow for convenient application of a priori information derived from near-global geophysical models to prevent striping in the solutions. The resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions, and do not necessitate empirical filters to remove north-south stripes, lowering the dependence on using scale factors (the global mean scale factor decreases by 0.17) to gain accurate mass estimates. Ocean bottom pressure (OBP) time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions (increase in correlation coefficient of 0.08 globally), particularly in low-latitude regions with small signal power (increase in correlation coefficient of 0.35 regionally), in addition to reducing the error RMS with respect to the in situ data (reduction of 0.37 cm globally, and as much as 1 cm regionally). Greenland and Antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results. Computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins; however, mascon solutions typically have greater resolution for smaller spatial regions, in particular when studying secular signals.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JB011547

Improved methods for observing Earth's time variable mass distribution with GRACE using spherical cap mascons

Groundwater depletion (GWD) compromises crop production in major global agricultural areas and has negative ecological consequences. To derive GWD at the grid cell, country, and global levels, we applied a new version of the global hydrological model WaterGAP that simulates not only net groundwater abstractions and groundwater recharge from soils but also groundwater recharge from surface water bodies in dry regions. A large number of independent estimates of GWD as well as total water storage (TWS) trends determined from GRACE satellite data by three analysis centers were compared to model results. GWD and TWS trends are simulated best assuming that farmers in GWD areas irrigate at 70% of optimal water requirement. India, United States, Iran, Saudi Arabia, and China had the highest GWD rates in the first decade of the 21st century. On the Arabian Peninsula, in Libya, Egypt, Mali, Mozambique, and Mongolia, at least 30% of the abstracted groundwater was taken from nonrenewable groundwater during this time period. The rate of global GWD has likely more than doubled since the period 1960–2000. Estimated GWD of 113 km3/yr during 2000–2009, corresponding to a sea level rise of 0.31 mm/yr, is much smaller than most previous estimates. About 15% of the globally abstracted groundwater was taken from nonrenewable groundwater during this period. To monitor recent temporal dynamics of GWD and related water abstractions, GRACE data are best evaluated with a hydrological model that, like WaterGAP, simulates the impact of abstractions on water storage, but the low spatial resolution of GRACE remains a challenge.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014WR015595

Global-scale assessment of groundwater depletion and related groundwater abstractions: Combining hydrological modeling with information from well observations and GRACE satellites

Do Not Cite, Quote or Distribute 4-1 Total pages: 139 1 Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities 2 3 Coordinating Lead Authors: Michael Oppenheimer (USA), Bruce Glavovic (New Zealand), Tuhin Ghosh 4 (India) 5 6 Lead Authors: Amro Abd-Elgawad (Egypt), Rongshuo Cai (China), Miguel Cifuentes-Jara (Costa Rica), 7 Rob Deconto (USA), John Hay (Cook Islands), Jochen Hinkel (Germany), Federico Isla (Argentina), 8 Alexandre K. Magnan (France), Ben Marzeion (Germany), Benoit Meyssignac (France), Zita Sebesvari 9 (Hungary), AJ Smit (South Africa), Roderik van de Wal (Netherlands) 10 11 Contributing Authors: Maya Buchanan (USA), Gonéri Le Cozannet (France), Catia Domingues 12 (Australia), Virginie Duvat (France), Tamsin Edwards (UK), Miguel D. Fortes (Philippines), Thomas 13 Frederikse (Netherlands), Jean-Pierre Gattuso (France), Robert Kopp (USA), Erwin Lambert (Netherlands), 14 Elizabeth McLeod (USA), Mark Merrifield (USA), Siddharth Narayan (US), Robert J. Nicholls (UK), 15 Fabrice Renaud (UK), Jonathan Simm (UK), Jon Woodruff (USA), Poh Poh Wong (Singapore), Siyuan Xian 16 (USA) 17 18 Review Editors: Ayako Abe-Ouchi (Japan), Kapil Gupta (India), Joy Pereira (Malaysia) 19 20 Chapter Scientist Maya Buchanan (USA) 21 22 Date of Draft: 20 April 2018 23 24 Notes: TSU Compiled Version 25 26

/pdf/sea-level-rise-and-implications-for-low-lying-islands-coasts-1ptd3trc7d.pdf

Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities

https://www.uni-frankfurt.de/45217813/doell_et_al_2012_jgeodyn_impact_of_gw_and_sw_withdrawals.pdf

Impact of water withdrawals from groundwater and surface water on continental water storage variations

The geocenter motion can be inferred by evaluating Satellite Laser Ranging (SLR) observations to the LAGEOS satellites. Within the dynamic orbit determination process the degree 1 coefficients of a spherical harmonic expansion of the Earth’s gravity field are estimated. In a combined approach covering the years 2006–2011, GRACE mission GPS, K-band inter-satellite range-rate, and SLR observations are added to the LAGEOS solution via normal equations to examine possible improvements of the geocenter estimates. The particular effects on the estimates by each of the GRACE observation types are analyzed and the combined solutions are assessed and discussed. It turns out that adding GRACE data degrades the LAGEOS geocenter time series while at the same time consuming considerable computational resources.

A Geocenter Time Series from a Combination of LAGEOS and GRACE Observations


 <p>The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission were successfully launched in May-2018. The primary objective of the mission is to continue the 15-year GRACE (2002-2017) global data record of Earth&#8217;s monthly mass changes. These measurements have become an indispensable tool to quantify and track Earth&#8217;s water movement and surface mass changes across the planet. Monitoring changes in ice sheets and glaciers, near-surface and underground water storage, the amount of water in large lakes and rivers, as well as changes in sea level and ocean currents provides an integrated global view of how Earth&#8217;s water cycle and energy balance are evolving.</p><p>In this presentation we will present the current mission status, including instrument and flight system performance, discuss science data quality and performance as well as recent science results from the first two years of observations, and address data continuity from GRACE to GRACE Follow-On.</p>


NASA and GFZ GRACE Follow-On Mission: Status, Science, Advances

The official GFZ RL05 monthly GRACE gravity models were processed in a two-step approach. In the first step the orbits were determined. In the second step corrections to the gravity field parameters were estimated, while the orbits were kept fixed. This led to a significant de-noising of the resulting monthly models, but accidentally also to a regularization, i.e., the estimated gravity field coefficients were biased towards the a priori model. We compare the GFZ RL05 models to a revised version RL05a that was determined in a common estimation of orbit and force model parameters. A large number of gravity field coefficients is significantly affected. We relate this effect to the one-hourly stochastic accelerations estimated for orbit determination, and to ignoring the correlations. In the main part of this paper we study the interaction between pseudo-stochastic orbit parameters and gravity field coefficients. To explain this interaction we make use of a time-wise approach to gravity field determination. We apply the linear perturbation theory developed by Hill for circular orbits to compute lumped coefficients of the inter-satellite range-rate observations. We illustrate that the pseudo-stochastic orbit parameters act as a high-pass filter on the lumped coefficients spectra of the range-rates. Because the lumped coefficients are related to the spherical harmonics coefficients via a summation over all degrees, the whole range of gravity field coefficients is affected. This result is of relevance for all approaches to gravity field estimation from orbit observations, where dynamic orbits are introduced a priori and the arc-specific parameters are kept fixed.

The effect of stochastic orbit parameters on GRACE range-rate residuals and monthly gravity fields

As of the time of this abstract submission, the GRACE Follow-On satellites have been constructed and transferred to Ottobrunn near Munich for several months of operational testing in the IABG test centre. The Russian/Ukraine Dnepr launcher had to be exchanged and a corresponding new contract has been signed by GFZ and Iridium Satellite LLC. This includes a "Rideshare" between GRACE-FO and 5 Iridium-Next satellites on a Space-X Falcon-9 from Vandenberg Air Force Base in California within the launch period December 2017 till February 2018.

Current Status Of The GRACE Follow-On Mission

The official GFZ RL05 monthly GRACE gravity models were processed in a two-step approach. In the first step the orbits were determined. In the second step corrections to the gravity field parameters were estimated, while the orbits were kept fixed. This led to a significant de-noising of the resulting monthly models, but accidentally also to a regularization, i.e., the estimated gravity field coefficients were biased towards the a priori model. We compare the GFZ RL05 models to a revised version RL05a that was determined in a common estimation of orbit and force model parameters. A large number of gravity field coefficients is significantly affected. We relate this effect to the one-hourly stochastic accelerations estimated for orbit determination, and to ignoring the correlations.

Christoph Dahle

Papers

A Geocenter Time Series from a Combination of LAGEOS and GRACE Observations

NASA and GFZ GRACE Follow-On Mission: Status, Science, Advances

The effect of stochastic orbit parameters on GRACE range-rate residuals and monthly gravity fields

Current Status Of The GRACE Follow-On Mission

The Effect of Pseudo-Stochastic Orbit Parameters on GRACE Monthly Gravity Fields: Insights from Lumped Coefficients