Publications Published in Global and Planetary Change
Global physical effects of anthropogenic hydrological alterations: sea level and water redistribution. Sahagian, Dork.
Global and Planetary Change:
Human influence on the Earth System and hydrologic cycle has reached the point where it affects the hydrologic balance between ocean and continental storage reservoirs. The anthropogenic redistribution of water mass at a planetary scale even has an effect on Earth rotation parameters. Land use changes associated with expanding agriculture to support an increasing human population have already had a profound influence on basin-scale hydrology, and in extreme cases, on regional climate. Major human activities which lead to hydrologic alterations include irrigation (from ground water mining and surface water diversion), deforestation, wetland filling or drainage, and new dam construction. With the exception of the latter, these all contribute to the transfer of water from the continents to the ocean and a reduction of continental water resources. However, water impoundment behind dams may partially or completely counteract the cumulative effect of the others. Present compilations of reservoirs impounded by dams include only the results of major engineering projects. Smaller impoundments have largely been ignored. The cumulative volume of the literally millions of small reservoirs such as farm ponds and rice paddies may approach that of the larger documented reservoirs. Unfortunately it is not practical to make a global inventory of millions of small and unregistered reservoirs, so their volume may never be known precisely. The quantity of water stored in artifically raised water tables behind dams has also not yet been addressed. The issue of water impoundment or release from continental drainage basins affects global sea level. Recent estimates based solely on major dammed reservoirs suggest that if new dam construction is not maintained at the rates of the 1960s through 1980s, the rate of sea level rise could increase by about half a millimeter per year. If small impoundments are taken into account, this figure could be much greater.
Land water storage contribution to sea level from GRACE geoid data over 2003-2006. Ramillien, G.; Bouhours, S.; Lombard, A.; Cazenave, A.; Flechtner, F.; Schmidt, R..
Global and Planetary Change:
Seasonal and inter-annual change in land water storage (expressed in terms of water volume change) over 27 large river basins worldwide are estimated from monthly GRACE geoids solutions computed at GFZ from February 2003 to February 2006. The largest annual water volume change is found in the Amazon basin, followed by the Parana, Ob, Orinoco, Tocantins, Niger, Congo, Ganges, Mekong, and Brahmaputra. In terms of trend over the 3-year period, positive and negative values are observed but in a number of cases computed trends are at the noise level. However significant negative trends are found in the Amazon, Ganges, Mississippi, Nile, Parana, and Zambezi basins, indicating water mass loss over that period. Positive trends (water mass gain) are marginally significant. We have computed the land water contribution to sea level change. On average over the 3-year time span, we find that the net effect is positive (net loss of water in terrestrial reservoirs), on the order of 0.19 +/− 0.06 mm/yr. If sustained over a longer time span than considered here, such a value may become comparable to the ice sheets contribution to sea level rise.
Reconstruction of past decades sea level using thermosteric sea level, tide gauge, satellite altimetry and ocean reanalysis data. Berge-Nguyen, M.; Cazenave, A.; Lombard, A.; Llovel, W.; Viarre, J.; Cretaux, J. F..
Global and Planetary Change:
This study investigates past sea level reconstruction (over 1950–2003) based on tide gauge records and EOF spatial patterns from different 2-D fields. In a first step, we test the influence on the reconstructed signal of the 2-D fields temporal coverage. For that purpose we use global grids of thermosteric sea level data, available over 1950–2003. Different time spans (in the range 10–50 yr) for the EOF spatial patterns, and different geographical distributions for the 1-D thermosteric sea level time series (interpolated at specific locations from the 2-D grids), are successively used to reconstruct the 54-year long thermosteric sea level signal. In each case we compare the reconstructed trend map with the reference. The simulation indicates that the longer the time span covered by the spatial EOFs, the closer to the reference the reconstructed thermosteric sea level trends. In a second step, we apply the method to reconstructing 2-D sea level data over 1950–2003, combining sparse tide gauge records available since 1950, with EOF spatial patterns from different sources: (1) thermosteric sea level grids over 1955–2003, (2) sea level grids from Topex/Poseidon satellite altimetry over 1993–2003, and (3) dynamic height grids from the SODA reanalysis over 1958–2001. The reconstructed global mean sea level trend based on thermosteric EOFs (case 1) is significantly lower than the observed trend, while the interannual/decadal sea level fluctuations are well reproduced. Case 2 (Topex/Poseidon EOFs over 1993–2003) leads to a global mean sea level trend over the 54-year time interval very close to the observed trend. But the spatial trends of the reconstruction over 1950–2003 are significantly different from those obtained with thermosteric EOFs. Case 3 (SODA EOFs over 1958–2001) provides a reconstruction trend map over 1950–2003 that differs significantly from the previous two cases. We discuss possible causes for such differences. For the three cases, on the other hand, reconstructed spatial trends over 1993–2003 agree well with the regional sea level trends observed by Topex/Poseidon.