Land Water Mass Research Articles

Study of water storage variations at the Pantanal wetlands area from GRACE monthly mass grids

Abstract The continental water storage is significantly in-fluenced by wetlands, which are highly affected by climate change and anthropogenic influences. The Pantanal, located in the Paraguay river basin, is one of the world’s largest and most important wetlands because of the environmental biodiversity that represents. The satellite gravity mission GRACE (Gravity Recovery And Climate Experiment) provided until 2017 time-variable Earth’s gravity field models that reflected the variations due to mass transport processes-like continental water storage changes-which allowed to study environments such as wetlands, at large spatial scales. The water storage variations for the period 2002-2016, by using monthly land water mass grids of Total Water Storage (TWS) derived from GRACE solutions, were evaluated in the Pantanal area. The capability of the GRACE mission for monitoring this particular environment is analyzed, and the comparison of the water mass changes with rainfall and hydrometric heights data at different stations distributed over the Pantanal region was carried out. Additionally, the correlation between the TWS and river gauge measurements, and the phase differences for these variables, were also evaluated. Results show two distinct zones: high correlations and low phase shifts at the north, and smaller correlation values and consequently significant phase differences towards the south. This situation is mainly related to the hydrogeological domains of the area.

Global mean sea level variations and the land water cycle at the inter-annual scale during the 2014–2016 El Niño episode

Since 1993, the global mean sea level (GMSL) has been rising at a rate of about 3 mm/a detected by multi-satellite radar altimetry. The spaceborne gravimetry satellite, Gravity Recovery and Climate Experiment (GRACE), has been monitoring Earth’s surface water mass variations since 2002. La Nina and El Nino events induces inter-annual variations of the GMSL manifest in ocean mass and steric sea level changes, linked with corresponding changes in land water cycle. Here we study the GMSL inter-annual variations and global land water mass changes integrating satellite altimetry, GRACE and Argo data, 2010–2016, during which strong La Nina and El Nino events occurred. First, we quantify the evolutions of GMSL during the study time period. The results show that during the 2010–2011 La Nina episode, the GMSL dropped rapidly to 7.6 mm, with the ocean mass and the steric sea level decreased to 5.1 mm and to 1.8 mm, respectively. GMSL then increased to 19.2 mm, with ocean mass increased to 12.3 mm during 2011–2013. From 2013 to 2014, the steric GMSL increased by 2.1 mm, and the ocean mass variations dropped by 2.3 mm, thus the total GMSL remains nearly unchanged. During the strong 2014–2016 El Nino, ocean mass variations increased by 13.1 mm and contributed over 90% of GMSL change, which rises up by 15.1 mm. Next, we analyze land water mass changes in four regions, namely Australia and Southeast Asia, South America, North America, Antartica and Greenland, and investigate their linkage to the GMSL inter-annual variations. Here, we used the Forward Modelling (FM) method for GRACE data post-processing to reduce signal leakage problem to estimate land water storage mass changes. The results show that during the 2014–2016 El Nino episode, the global ocean mass increasing is mainly due to the total land water storage decreasing in Australia and Southeast Asia, South America, and Antartica and Greenland. The inter-annual variations of global ocean mass variation during 2003–2016 is closely linked with the land water storage changes from Australia and Southeast Asia and the South America regions, which are strongly affected by La Nina and El Nino events. During 2003–2016, the ice ablations from the Antartica and Greenland ice sheets directly contributed to GMSL rising, as opposed to the land water mass increase in the North America region, which has a negative effect on GMSL trend. Finally, we estimated the GMSL, ocean mass and steric sea level trends at 3.4±0.4, 2.1±0.3, and 1.1±0.2 mm/a, respectively during 2003–2016, and 6.5±1.2, 4.1±1.0, and 1.9±0.4 mm/a, respectively during 2010–2016. We concluded that the ocean mass variation contributed to the GMSL trend two times larger than that of the steric sea level contribution during these two time periods. However the ocean mass variation is roughly equivalent to the steric sea level variation during 2003–2010.

Variations and geophysical excitations of Earth’s dynamic oblateness estimated from GPS, OBP and GRACE

Planet Earth is a rotating flat ellipsoid and its dynamics oblateness (i.e. J 2 ) changes were mainly driven by the redistribution of Earth’s fluid mass and interaction of various spheres in the Earth system. Currently, the dynamics oblateness was determined from the satellite laser ranging (SLR) data. However, it was subject to the sparse SLR stations, uneven distribution in the Northern and Southern Hemispheres and non-continuous observation as well as dynamic models and constants in SLR data processing. Although the new generation of satellite gravity mission GRACE (gravity recovery and climate experiment) measurement has largely improved the lower-order coefficient estimates with one or two orders of magnitude, but the C 20 is not sensitive. In this paper, the high precise dynamics oblateness J 2 is derived from global continuous GPS loading displacements and GPS+OBP (ocean bottom pressure) as well as GPS+OBP+GRACE, respectively, which are analyzed and compared at multi-scales variations as well as their implications. It has shown that the annual variations of J 2 have a good agreement between GPS+OBP, GPS+OBP+GRACE, SLR and GRACE, while GPS alone has a smaller amplitude. For semi-annual variations, GRACE estimate is relatively worse due to the effect of about 161-day S 2 tide. Also the GPS+OBP and GPS+OBP+GRACE have a good correlation with SLR in intraseasonal and interannual J 2 variations, while GPS or GRACE alone is worse. Furthermore, the excitations of multi-scale J 2 variations are investigated and analyzed using geophysical models data. Results show that the variations of J 2 at seasonal, intraseasonal and interannual scales are mainly driven by the transfer and redistribution of Earth’s surface atmosphere, ocean and land water mass.

Global evapotranspiration over the past three decades: estimation based on the water balance equation combined with empirical models

We applied a land water mass balance equation over 59 major river basins during 2003–9 to estimate evapotranspiration (ET), using as input terrestrial water storage anomaly (TWSA) data from the GRACE satellites, precipitation and in situ runoff measurements. We found that the terrestrial water storage change cannot be neglected in the estimation of ET on an annual time step, especially in areas with relatively low ET values. We developed a spatial regression model of ET by integrating precipitation, temperature and satellite-derived normalized difference vegetation index (NDVI) data, and used this model to extrapolate the spatio-temporal patterns of changes in ET from 1982 to 2009. We found that the globally averaged land ET is about 604 mm yr−1 with a range of 558–650 mm yr−1. From 1982 to 2009, global land ET was found to increase at a rate of 1.10 mm yr−2, with the Amazon regions and Southeast Asia showing the highest ET increasing trend. Further analyses, however, show that the increase in global land ET mainly occurred between the 1980s and the 1990s. The trend over the 2000s, its magnitude or even the sign of change substantially depended on the choice of the beginning year. This suggests a non-significant trend in global land ET over the last decade.

Water balance of the Arctic drainage system using GRACE gravimetry products

Land water and snow mass anomalies versus time were computed from the inversion of 50 Gravity Recovery and Climate Experiment (GRACE) geoids (August 2002 to February 2007) from the RL04 GeoForschungZentrum (GFZ) release and used to characterize the hydrology of the Arctic drainage system. GRACE-based time series have been compared to snow water equivalent and snow depth climatologies, and snowfall for validation purpose. Time series of regional averages of water volume were estimated for the 11 largest Peri-Arctic basins. Strong correlations were found between the snow estimates and river discharges in the Arctic basins (0.49–0.8). Then changes in land water storage were compared to precipitation minus evapotranspiration fluxes to determine which flux of the hydrological budget controls the Arctic hydrology. Results are very contrasted according to the basin. Trends of snow and land water masses were also computed over the 2003–2006 period. Eurasian basins lose snow mass whereas North American basins are gaining mass.

A Revised Hydrology for the ECMWF Model: Verification from Field Site to Terrestrial Water Storage and Impact in the Integrated Forecast System

Abstract The Tiled ECMWF Scheme for Surface Exchanges over Land (TESSEL) is used operationally in the Integrated Forecast System (IFS) for describing the evolution of soil, vegetation, and snow over the continents at diverse spatial resolutions. A revised land surface hydrology (H-TESSEL) is introduced in the ECMWF operational model to address shortcomings of the land surface scheme, specifically the lack of surface runoff and the choice of a global uniform soil texture. New infiltration and runoff schemes are introduced with a dependency on the soil texture and standard deviation of orography. A set of experiments in stand-alone mode is used to assess the improved prediction of soil moisture at the local scale against field site observations. Comparison with basin-scale water balance (BSWB) and Global Runoff Data Centre (GRDC) datasets indicates a consistently larger dynamical range of land water mass over large continental areas and an improved prediction of river runoff, while the effect on atmospheric fluxes is fairly small. Finally, the ECMWF data assimilation and prediction systems are used to verify the effect on surface and near-surface quantities in the atmospheric-coupled mode. A midlatitude error reduction is seen both in soil moisture and in 2-m temperature.

Evaluation of global land-to-ocean fresh water discharge and evapotranspiration using space-based observations

Summary We estimate global fresh water discharge from land-to-oceans ( Q ) and evapotranspiration ( ET ) on monthly time scales using a number of complimentary hydrologic data sets. This estimate is possible due to the new capability of measuring oceanic and land water mass changes from GRACE as well as the space-based measurements of oceanic and land precipitation ( P l ) and oceanic evaporation. Monthly time series of Q show peaks in July and January, and those of ET show peaks in March, May and August. Our estimates of Q and ET are correlated with P l indicating qualitatively that our estimates capture temporal patterns of Q and ET reasonably well. Comparison of our Q with two other previous estimates based on the Global Runoff Data Centre (GRDC) river gauges network shows that our maximum peak in Q occurs about a month later than previous estimates. In addition, we compare our estimation of Q and ET to 20th century simulations from the WCRP CMIP3 multi-model archive assessed in the IPCC 4th Assessment Report. Runoff ( R ) and ET from AOGCMs tend to only exhibit the annual cycle, but the Q estimated in this study exhibits additional semi-annual variations that exists in P l as well. In addition, R from the models shows a maximum peak 2 months earlier than the estimated Q , which is due partly to the river discharge time lag that most AOGCMs do not take into account. These results indicate that current AOGCMs exhibit basic shortcomings in simulating Q and ET accurately. The new method developed here can be a useful constraint on these models and can be useful to close budget of global water balance.

Trend of China land water storage redistribution at medi- and large-spatial scales in recent five years by satellite gravity observations

The GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission has provided a new method to study land water mass redistribution at medi- and long-spatial scales in recent years. We estimate continental water mass redistribution in China using GRACE observations during 2003 to 2007. The results show some large regions with increase or decrease of land water mass storage in the central northern region, Tibetan Plateau, the Three Gorges region, the place where Qinghai, Sichuan and Gansu provinces meet, and the Altun Mountains region in the Xinjiang Uygur Autonomous Region. In the first two regions, it is obvious that water (ice) mass storages are decreasing. Water mass in the central northern region decreases at a linear rate of 2.4 cm/a equivalent water height, equal to 5.2 billion cubic meters per year during the five years’ period, and water mass depletion in Hebei Province is ∼ 4.5 billion cubic meters per year in the same period, which is consistent with the average water mass depletion of 4.0 billion cubic meters per year of overused underground water in the recent 30 years estimated by Hebei Province Water Resources Bureau. Furthermore, GRACE can detect the water mass accumulation of ∼ 5 cm equivalent water height within the region spreading over about 0.12 million square kilometers due to the Three Gorges dam construction in June 2003. We also find a water mass gain of ∼ 1.1 cm/a in the areas where Qinghai, Sichuan and Gansu provinces meet. This indicates that the climate of these regions has been becoming gradually humid in recent years.

Time variations of the regional evapotranspiration rate from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry

Since its launch in March 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has been measuring the global time variations of the Earth's gravity field with a current resolution of ∼500 km. Especially over the continents, these measurements represent the integrated land water mass, including surface waters (lakes, wetlands and rivers), soil moisture, groundwater, and snow cover. In this study, we use the GRACE land water solutions computed by Ramillien et al. (2005a) through an iterative inversion of monthly geoids from April 2002 to May 2004 to estimate time series of basin‐scale regional evapotranspiration rate and associated uncertainties. Evapotranspiration is determined by integrating and solving the water mass balance equation, which relates land water storage (from GRACE), precipitation data (from the Global Precipitation Climatology Centre), runoff (from a global land surface model), and evapotranspiration (the unknown). We further examine the sensibility of the computation when using different model runoff. Evapotranspiration results are compared to outputs of four different global land surface models. The overall satisfactory agreement between GRACE‐derived and model‐based evapotranspiration prove the ability of GRACE to provide realistic estimates of this parameter.