Data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are used to estimate monthly changes in total water storage across the Middle East during February 2003 to December 2012. The results show a large negative trend in total water storage centered over western Iran and eastern Iraq. Subtracting contributions from the Caspian Sea and two large lakes, Tharthar and Urmiah, and using output from a version of the CLM4.5 land surface model to remove contributions from soil moisture, snow, canopy storage, and river storage, we conclude that most of the long-term water loss is due to a decline in groundwater storage. By dividing the region into seven mascons outlined along national boundaries and fitting them to the data, we find that the largest groundwater depletion is occurring in Iran, with a mass loss rate of 25 6 3 Gt/yr during the study period. The conclusion of significant Iranian groundwater loss is further supported by in situ well data from across the country. Anthropogenic contributions to the groundwater loss are estimated by removing the natural variations in groundwater predicted by CLM4.5. These results indicate that over half of the groundwater loss in Iran (14 6 3 Gt/yr) may be attributed to human withdrawals.
The Gravity Recovery and Climate Experiment (GRACE) satellite data is used to estimate the rate of ice mass variability over Greenland. To do this, monthly GRACE level 2 Release-04 (RL04) data from three different processing centers, Center for Space Research (CSR), German Research Center for Geosciences (GFZ) and Jet Propulsion Laboratories (JPL) were used during the period April 2002 to February 2010. It should be noted that some months are missing for all three data sets. Results of computations provide a mass decrease of −163 ± 20 Gigaton per year (Gt/yr) based on CSR-RL04 data, −161 ± 21 Gt/yr based on GFZ-RL04 data and −84 ± 26 Gt/yr based on JPL RL04.1. The results are derived by the application of a nonisotropic filter whose degree of smoothing corresponds to a Gaussian filter with a radius of 340 km. Striping effects in the GRACE data, C20 effect, and leakage effects are taken into the consideration in the computations. There is some significant spread of the results among different processing centers of GRACE solutions; however, estimates achieved in this study are in agreement with the results obtained from alternative GRACE solutions.
We derive the mass balance of Greenland ice sheet from the Gravity Recovery and Climate Experiment (GRACE) for the period January 2003-October 2014. We have found an ice mass loss with peak amplitude of-15 cm/yr in the southeastern and northwestern parts, and an acceleration of-2.5 cm/yr 2 in the southwestern region. Global warming is a wellknown suspected triggering factor of ice melting. We use MODIS-derived Ice Surface Temperature (IST), and continuous and cross wavelet transforms have been determined to investigate the common power and relative phase between GRACE derived time-series of ice mass changes and IST time-series. Results indicate a high common power between the two time-series for the whole study period, but with different time patterns.
Mass balance and mass loss acceleration of the Greenland ice sheet (2002 - 2011) from GRACE gravity dataWe 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.
Abstract: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][2004][2005][2006][2007][2008][2009][2010][2011][2012]. We show that the well documented Greenland ice mass loss in the southern region spread to northwest Greenland in the period from 2007 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.
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