Guiping Feng

Uncertainty of grace-estimated land water and glaciers contributions to sea level change during 2003–2012

Global mean sea level change (GMSL) is one of the most significant effects of climate change. However the contribution of land water and glaciers to GMSL is difficult to quantify due to lack of in situ measurements and complex dynamics of galcier melting. In this study, we use the GRACE Release 5 (RL05) data from 2003.01 to 2012.12 to quantify the land water and glaciers contributions to the sea level rise as well as their uncertainties. The contribution of land water to the sea level change is 0.15±0.25 mm/yr, and the contribution of glaciers is 1.94±0.29 mm/yr. The impact of the degree 1 and degree 2 Stokes gravity field coefficients computed from different GRACE analysis centers (the Jet Propulsion Laboratory (JPL), the University of Texas, Center for Space Research (UTCSR) and the GeoForschungsZentrum (GFZ)) on the sea level change are investigated and discussed. The impact of first-order coefficient to the mass-induced sea level variations is 0.10±0.08 mm/yr, and the second-order coefficient to the mass-induced sea level variations is 0.16±0.04 mm/yr. The results from CSR are consistent with GFZ results, while the JPLs results are slightly smaller.

Global water cycle and climate change signals observed by satellite gravimetry

Terrestrial water storage (TWS) is an important parameter in water resource manages and research of land-surface processes and hydrological cycle. However, the traditional instruments are very difficult to monitor global high temporal-spatial terrestrial water storage and its variability without a comprehensive global monitoring network of hydrological parameters due to high cost and high labor intensity. The recent Gravity Recovery and Climate Experiment (GRACE) mission provides a unique opportunity to directly measure the global TWS and its change at multi-scales from August 2002 to February 2011. In this paper, the global terrestrial water storages with monthly resolution are derived from approximate 10 years of monthly GRACE measurements (2002 August-2011 February), and their changes at seasonal and long-term scales are investigated and compared with GLDAS (Global Land Data Assimilation System) model. Results show that significant annual variations of TWS are found at the globe, agreeing well with GLDAS model estimates. The secular trends are also observed at specific areas, reflecting extreme climate events, e.g., ice melting in Antarctica, Greenland, Canadian Islands, Alaska, Himalayan and Patagonia glaciers, La Plata drought in South American as well as floods in North Amazon, while the GLDAS model cannot capture these signals well.

Global groundwater cycles and extreme events responses observed by satellite gravimetry

The groundwater is one of key parameters in water resource management and hydrological cycle. However, the global groundwater and its changes are very difficultly monitored by traditional instruments. The recent Gravity Recovery and Climate Experiment (GRACE) mission launched in 2002 provided an opportunity to measure the global water storage and its changes. Some regional groundwater variations were well estimated and investigated from GRACE, however, global groundwater variations are not clear. In this paper, an approximate decade of the global groundwater is obtained after subtracting the soil moisture, snow, ice and canopy water from the hydrological model GLDAS (Global Land Data Assimilation System). Significant annual variations of global groundwater are found with the mean amplitude of 28.98 mm, while the semi-annual amplitude is almost half of annual amplitude in most parts of the world with the mean of 11.06 mm. The mean trend of global groundwater variations is 1.86 ± 0.36 mm/year. The trend mostly reflects the recent extreme events, e.g. groundwater depletion in Northwest India, California and North China, droughts in La Plata and Southeast USA, and flood in Amazon. In addition, the groundwater has an acceleration change in some areas with up to ±4 mm/year2.

Earth's surface fluid variations and deformations from GPS and GRACE in global warming

Global warming is affecting our Earths environment. For example, sea level is rising with thermal expansion of water and fresh water input from the melting of continental ice sheets due to human-induced global warming. However, observing and modeling Earths surface change has larger uncertainties in the changing rate and the scale and distribution of impacts due to the lack of direct measurements. Nowadays, the Earth observation from space provides a unique opportunity to monitor surface mass transfer and deformations related to climate change, particularly the global positioning system (GPS) and the Gravity Recovery and Climate Experiment (GRACE) with capability of estimating global land and ocean water mass. In this paper, the Earths surface fluid variations and deformations are derived and analyzed from global GPS and GRACE measurements. The fluids loading deformation and its interaction with Earth system, e.g., Earth Rotation, are further presented and discussed.