A Technical Note on Least Squares Mascon Fitting to GRACE Satellite Data to Estimate Total Water Storage Changes in the Middle East

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Estimation of Groundwater Depletion in Iran’s Catchments Using Well Data

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Earth Mass Change Tracking Using GRACE Satellite Gravity Data

This project is dealing with the estimation of present-day Earth’s mass transport and its redistribution by using observations from Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE measures the gravity fluctuations which are primarily related to redistribution of water around the globe. GRACE data has yield profound new insights into melting rates of ice sheets and mountain glaciers, land hydrology, ocean circulation, and sea level rise. In this project, first, the ice melting rate in the Greenlandic ice sheet is studied. This is done by analyzing the time series of monthly GRACE release 04 gravity field solutions from three different data sets, CSR (Center for Space Research), GFZ (Geoforschungszentrum), and JPL (Jet Propulsion Laboratory) with respect to their long-term temporal changes. The data are de-striped by applying a non-isotropic filter. Also, a method for reducing the leakage effects is developed. As an example, the ice mass balance is estimated of -163 ± 20 Gt/yr based on the CSR release 04 and smoothing by a parameter of a =1013 during April 2002 to February 2010. The results also show that the spatial distribution of the ice mass loss is changing with time and the ice mass loss is accelerating. For example, its acceleration is a rate of -32±6 Gt/yr2 during 2002 to 2011. The second part of this project is concern with the determination of water mass changes in the Nordic Seas. It is determined by analyzing the time series of monthly GRACE level 2 release 04 data from GFZ during October 2002 to October 2010. The striping errors are reduced by using a non-isotropic filter and the data are smoothed by a parameter of a =1014 according to Gaussian smoothing radius of 530 km. The time series of water mass changes are used to study the steric sea height variations over the Nordic Seas during the same period of study. This is done by analyzing the time series of monthly sea level anomaly from ENVISAT (Environmental Satellite) altimetry data, cycles 10 to 93, among the time series of water mass changes. The results show that the interdisciplinary nature of the GRACE measurements have opened up the unique opportunity to enhance our knowledge on the interaction between Earth system components and their response to climate variability. In the last part of this project, variations of the continental total water storage, total groundwater storage, and anthropogenic contributions across the Middle East are studied. By using a mascon analysis method and GRACE level 2 release 05 data from CSR during February 2003 to December 2012, the time series of total water storage, total ground water storage and anthropogenic contributions are estimated over this region. The region is subdivided to seven mascons including Iran, Iraq, Syria, eastern Turkey (east of 35º longitude), northern and southern Saudi Arabia (north and south of 25º latitude), and the region immediately west of Caspian Sea. The total groundwater storage, and anthropogenic contributions are separated from the total water storage by using the CLM4.5 (version 4.5 of the Community Land Model) hydrological model. The results show that Iran with a rate of 25±6 Gt/yr has the most groundwater loss rate during February 2003 to December 2012 in this region. The Iran’s rate of groundwater loss from the GRACE data is supported by an analysis of in situ well data from across Iran. The results also show that the GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 200,000 km2 or larger in area, and, can contribute to water management at regional and national scales, and to international policy discussions as well

Greenland mass balance estimation from satellite gravity measurements

The Gravity Recovery and Climate Experiment (GRACE) data is used to estimate the secular trend and periodic variations of ice mass variability over Greenland. To do this, we use 92 monthly GRACE level 2 Release-04 (RL04) data from the Center for Space Research at the University of Texas (UTCSR) during the period April 2002 to February 2010. The high frequency noise of data has been filtered out with three smoothing cap radius. For separation of leakage effects, the appropriate reduction model is used. Taking the average over all smoothing radius after the leakage effects correction, the annual ice-mass loss becomes -155±3 Gt/year. Note that these values are free of any GIA correction

Mass balance and mass loss acceleration of the Greenland ice sheet (2002 – 2011) from GRACE gravity data

We examine the magnitude and acceleration of the Greenland ice sheet mass loss between 2002 and 2011. We use monthly observations of time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission. The Greenland mass loss during this time period is not a constant, but accelerating with time. We have used a quadratic trend in addition to a linear trend, which is usually applied to the GRACE monthly time series of ice mass changes, to show that it better represents GRACE observations. Results of computations provide a mass decrease of -166±20 Gigatonne per year (Gt/yr) by using a linear trend and -111±21 Gt/yr by fitting a quadratic trend to the monthly time series. Quadratic fitting shows that the mass loss increases from -121 Gt/yr in 2002 - 2003 to -210 Gt/yr in 2006 - 2007 and -271 Gt/yr in 2010 - 2011 with an acceleration of -32±6 Gt/yr2 in 2002 - 2011. This implies that the Greenland ice sheet contribution to sea level rise becomes larger with time. Contrary to recent studies, we use a non-isotropic filter whose degree of smoothing corresponds to a Gaussian filter with a radius of 340 km. Stripping effects in the GRACE data, C20 effect, and leakage effects are applied

Estimation of Groundwater Depletion in Iran’s Catchments Using Well Data

Iran is experiencing significant water challenges that have now turned water security into a national priority. By estimating secular trend groundwater storage in Iran between 2002 and 2017, we see that there is an intensive negative trend, even −4400 Mm3 in some areas. These estimations show shifting in the climate and extra extraction from aquifers for agricultural use in some areas in Iran. The secular trend of groundwater storage changes across the whole of Iran inferred from observation well data is −20.08 GT/yr. The secular trends of GWS changes based on observation well data are: −11.55 GT/yr for the Central Plateau basin, −3.60 GT/yr for the Caspian Sea basin, −3.0 GT/yr for the Persian Gulf and Oman Sea basin, −0.53 GT/yr for the Urmieh Lake basin, −0.57 GT/yr for the Eastern Boundary basin, and −0.83 GT/yr for the Gharaghom basin. The most depleted sub-basin (Kavir Markazi) has secular trends of GWS changes of −4.503 GT/yr. This study suggests that groundwater depletion is the largest single contributor to the observed negative trend of groundwater storage changes in Iran, the majority of which occurred after the drought in 2007. The groundwater loss that has been accrued during the study period is particularly alarming for Iran, which is already facing severe water scarcity

GRACE-derived ice-mass loss spread over Greenland

The Gravity Recovery and Climate Experiment (GRACE) monthly satellite data is used to examine the extent and magnitude of Greenland ice sheet melting for 2003-2012. We show that the well documented Greenland ice mass loss in the southern region spread to northwest Greenland in the period from2007 to 2010 and 2010 to 2012 by estimating ice mass variability over time in Greenland. The ice-mass melting is estimated to –183±11 Gt/yr. This estimation means that Greenland is still losing much more ice than gained, and continuing to contribute to global sea level rise in a warming world. Unlike other recent studies, our method employs a non-isotropic filter. A nonisotropic filter is used to decorrelate the GRACE data, since the GRACE noise structure has a non-isotropic nature

Steric sea level changes from ENVISAT and GRACE in the Nordic Seas

Steric sea level changes are estimated over the Nordic Seas using ENVISAT (Environmental Satellite) altimetry and GRACE (Gravity Recovery and Climate Experiment) gravity data. We have used altimetry data from the ENVISAT during October 2002 to October 2010, cycles 10 to 93, and the GRACE level 2 RL04 data released by GFZ (German Research Center for Geosciences) processing center during October 2002 to October 2010. It should be noted that some months are missing for the GRACE data set. Correction terms are applied to properly combine the altimetry and GRACE data, including the inverted barometer term, dynamic ocean and atmospheric terms and GRACE coefficients with degrees 0, 1, and 2 (with order 0). Finally, the steric sea level changes are derived over the Nordic Seas for October 2002 to October 2010