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GIEMS (Global Inundation Extent from Multi-Satellites)

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The Global Inundation Extent from Multi-Satellites (GIEMS) is a unique dataset that provides the surface water extent and dynamics over the globe and over a long time record (1993-2007), based on a collection of satellite observations. The percentage of inundation is estimated over an equal-area grid (pixels of 0.25°x0.25° at the equator, i.e., roughly 28kmx28km), at a monthly time-scale.

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Figure: Annual mean surface water extent, as estimated from satellites, between 1993 and 2007, in km² for each 773km² pixel.

The data set is available upon request to Catherine Prigent (catherine.prigent@obspm.fr).

Methodology - Global wetland extent and dynamics are estimated from a remote-sensing technique employing a suite of complementary satellite observations: it uses both passive and active microwave measurements, along with visible and near-infrared reflectances. Combining observations from different instruments makes it possible to capitalize on their complementary strengths, to extract maximum information about inundation characteristics, and to minimize problems related to one instrument only. The technique is globally applicable without any tuning for particular environments. The satellite data are used to calculate monthly-mean inundated fractions of equal-area grid cells (0.25°x0.25° at the equator), taking into account the contribution of vegetation (Prigent et al., 2001, 2007, 2012; Papa et al., 2010). The resulting GIEMS data set covers 1993 to 2007.

Evaluation - The variability of GIEMS (intra- and inter-annual) has been analyzed, under different environments. These variations have been compared to other hydrological variables such as river height (from gages and altimeters), precipitation, water runoff, or granmetric data Grace, for evaluation of the GIEMS database (Papa et al., 2007, 2008, 2010).

Applications - The GIEMS database has been widely distributed around the world, for multiple applications. The natural wetlands being the world’s largest source of atmospheric methane (a very powerful green-house gas), our data set provides a unique resource for modelling the methane emissions and for reducing uncertainties in the role of natural wetlands in the inter-annual variability of the growth rate of atmospheric methane (e.g., Bousquet et al., 2006; Ringeval et al., 2010; Petrescu et al., 2010; Hodson et al., 2011; Beck et al., 2013 ; Pison et al., 2013 : Wania et al., 2013). GIEMS is also used to evaluate hydrological modelling at continental to global scale (e.g., Decharme et al., 2008, 2011). The GIEMS water extent has also been combined with altimetric water levels to estimate the water volume changes (Frappart et al., 2008, 2010; Papa et al., 2013).

Climate trends - Results for 1993 to 2007 exhibit a large seasonal and inter-annual variability of the inundation extent with an overall decline in global average maximum inundated area of 6% during the fifteen-year period, primarily in tropical and subtropical South America and in South Asia. The largest declines of open water are found where large increases in population have occurred over the last two decades, suggesting a global scale effect of human activities on continental surface freshwater: denser population can impact local hydrology by reducing freshwater extent, by draining marshes and wetlands, and by increasing water withdrawals (Prigent et al., 2012).

High-spatial resolution – GIEMS dataset is being downscaled to provide the same global coverage and time record, but with a spatial resolution of about 100 m (http://www.estellus.fr/index.php?static13/giems-d15). The downscaling methodologies use auxiliary high-resolution information such as Digital Elevation Models (Fluet-Chouinard et al., 2015), satellite SAR measurements (Aires et al., 2013), or visible/ infrared satellite observations (Aires et al., 2014).


GIEMS methodology and evaluation:

  • Prigent, C., E. Matthews, F. Aires, and W. B. Rossow, Remote sensing of global wetland dynamics with multiple satellite data sets, Geo. Res. Lett., 28 , 4631-4634, 2001.
  • Prigent, C., F. Papa, F. Aires, W. B. Rossow, and E. Matthews, Global inundation dynamics inferred from multiple satellite observations, 1993-2000, J. Geophys. Res., 112, D12107, doi:10.1029/2006JD007847, 2007.
  • Papa, F., C. Prigent, and W.B. Rossow, Ob’ River flood inundations from satellite observations: A relationship with winter snow parameters and river runoff. J. Geophys. Res., 112, D18103, doi:10.1029/2007JD008451, 2007.
  • Papa, F., C. Prigent, and W. B. Rossow, Monitoring flood and discharge variations in the large Siberian Rivers from a multi-satellite technique, Surv. Geophys., doi:10.1007/s10712-008-9036-0, 2008.
  • Papa, F., C. Prigent, C. Jimenez, F. Aires, and W. B. Rossow, Interannual variability of surface water extent at global scale, 1993-2004, J. Geophys. Res., 115, D12111, doi:10.1029/2009JD012674, 2010.
  • Prigent, C., F. Papa, F. Aires, C. Jimenez, W. Rossow, and E. Matthews, Changes in land surface water dynamics since the 1990s and relation to population pressure, Geophys. Res. Lett., 39, L08403, doi:10.1029/2012GL051276, 2012.

Analysis of the methane emission:

  • Bousquet, P., P. Ciais, J.B. Miller, E.J. Dlugokencky, D. A. Hauglustaine, C. Prigent, G.R. Van der Werf, P. Peylin, E.G. Brunke, C. Carouge, R. L. Langenfelds, J Lathière, F. Papa, M. Ramonet, M. Schmidt, L. P. Steele, S.C. Tyler, and J. White, Contribution of anthropogenic and natural sources to atmospheric methane variability, Nature, 443, 439-443, doi:10.1038/nature05132, 2006.
  • Petrescu, A. M. R., R. L.P.H. van Beek, J. Van Huissteden, C. Prigent, T. Sachs, C. A.R. Corradi, F. W. Parmentier, A. J. Dolman, Modeling regional to global CH4 emissions of boreal and arctic wetlands, Global Biogeochemical Cycles, 24, 4, 10.1029/2009GB003610, 2010.
  • Ringeval, B., N. de Noblet-Ducoudre, P. Ciais, P. Bousquet, C. Prigent, F. Papa, W. B. Rossow, An attemp to quantify the impact of changes in wetland extent on methane emissions at the seasonal and interannual time scales, Global Biogeochemical Cycles, 24, GB2003, doi:10/1029/2008GB003354, 2010.
  • Hodson, E. L., B. Poulter, N. E. Zimmermann, C. Prigent, and J. O. Kaplan, The El Niño–Southern Oscillation and wetland methane interannual variability, Geophys. Res. Lett., 38, L08810, doi:10.1029/2011GL04686, 2011.
  • Beck, V. C. Gerbig, T. Koch, M. M. Bela, K. M. Longo, S. R. Freitas, J. O. Kaplan, C. Prigent, P. Bergamaschi, and M. Heimann, WRF−Chem simulations in the Amazon region during wet and dry season transitions: evaluation of methane models and wetland inundation maps, Atmos. Chem. Phys., 13, 7961−7982, 2013.
  • Wania, R., Melton, J. R., Hodson, E. L., Poulter, B., Ringeval, B., Spahni, R., Bohn, T., Avis, C. A., Chen, G., Eliseev, A. V., Hopcroft, P. O., Riley, W. J., Subin, Z. M., Tian, H., van Bodegom, P. M., Kleinen, T., Yu, Z. C., Singarayer, J. S., Zürcher, S., Lettenmaier, D. P., Beerling, D. J., Denisov, S. N., Prigent, C., Papa, F., and Kaplan, J. O.: Present state of global wetland extent and wetland methane modelling: methodology of a model inter−comparison project (WETCHIMP), Geosci. Model Dev., 6, 617−641, doi:10.5194/gmd−6−617−2013, 2013.
  • Pison, I., B. Ringeval, P. Bousquet, C. Prigent, and F. Papa, Stable atmospheric methane in the 2000s: key−role of emissions from natural wetlands, Atmos. Chem. Phys. Discuss., 13, 9017−9049, 2013.

Evaluation of hydrological models:

  • Decharme B., H. Douville, C. Prigent, F. Papa, and F. Aires, A new river flooding scheme for global climate applications: Off-line evaluation over South America, J. Geophys. Res., 113, D11110, doi:10.1029/2007JD009376, 2008.
  • Decharme, B., R. Alkama F. Papa, S. Faroux, H. Douville, C. Prigent, Global off-line evaluation of the ISBA-TRIP flood model, Clim. Dyn., DOI 10.1007/s00382-011-1054-9, 2011.

Calculation of water volumes:

  • Frappart, F., F. Papa, J. S. Famiglietti, C. Prigent, W. B. Rossow, F. Seyler, Interannual variations of river water storage from a multiple satellite approach: a case study for the Rio Negro River Basin, J. Geophys. Res., 113, D21104, doi:10.1029/2007JD009438, 2008.
  • Frappart, F., F. Papa, A. Güntner, S. Werth, G. Ramilien, C. Prigent, W. B. Rossow, M.-P. Bonnet, Interannual variations of the terrestrial water storage in the Lower Ob’ Basin from a multisatellite approach, Hydrology and Earth System Sciences, 14,12, 2010, 2443-2453, 2010.
  • Papa, F., F. Frappart, A. Güntner, C. Prigent, F. Aires, A. C. V. Getirana, and R. Maurer, Surface freshwater storage and variability in the Amazon basin from multi−satellite observations, 1993–2007, J. Geophys. Res. Atmos., 118, doi:10.1002/2013JD020500, 2013.

GIEMS downscaling:

  • Aires, F., F. Papa and C. Prigent, A long-term, high-resolution wetland dataset over the Amazon basin, downscaled from a multi-wavelength retrieval using SAR, J. Hydrometeorology, 14, 594-6007, 2013.
  • Aires, F., F. Papa, C. Prigent, J.-F. Cretaux and M. Berge-Nguyen, Characterization and downscaling of the inundation extent over the Inner Niger delta using a multi-wavelength retrievals and Modis data, J.. Hydrometeoroloy, 27, 1958-1979, doi: http://dx/doi.org/10.1175/JCLI-D-13-00161.1, 2014.
  • Fluet-Chouinard, E., B. Lehner, L-M Rebelo, F. Papa, S.K. Jamiston, Development of a global inundation map at high spatial resolution from topographic downscaling of coarse-scale remote sensing data, Remote Sensing of Environment, in press, 2015.

Séminaires à venir

Vendredi 23 octobre 2020, 14h00
téléconférence Zoom,
The role of molecular filaments in the origin of the IMF
Philippe ANDRÉ
CEA, Laboratoire d’Astrophysique AIM Paris-Saclay
résumé :
The origin of the stellar initial mass function (IMF) is one of the most debated
issues in astrophysics. I will discuss new insights into this problem based on a systematic census of prestellar cores and molecular filaments in nearby clouds taken as part of the Herschel Gould Belt survey, as well as higher-resolution observations with APEX/ArTéMiS and ALMA. Our results point to the key role of the quasi-universal filamentary structure pervading molecular clouds. They suggest that the dense cores making up the peak of the prestellar core mass function (CMF) - and indirectly the peak of the IMF - result from gravitational fragmentation of molecular filaments near the critical mass per unit length. The Salpeter power-law tail of the CMF/IMF may be at least partly inherited from the filament line mass function (FLMF), which is observed to follow a Salpeter-like power law in the regime of thermally supercritical filaments.

Vendredi 4 décembre 2020, 14h00
via Zoom, Paris
Simulating galaxies at high resolution in their cosmological context with NewHorizon: methods and some key results on galaxy properties and their morphology
Institut d'Astrophysique de Paris
résumé :
Hydrodynamical cosmological simulations are increasing their level of realism by considering more physical processes, having more resolution or larger statistics. However, one usually has to either sacrifice the statistical power of such simulations or the resolution reach within galaxies. I will introduce the NewHorizon project where a zoom-in region of ~(16 Mpc)^3, larger than a standard zoom-in region around a single halo, embedded in a larger box is simulated at high resolution. A resolution of up to 34 pc, typical of individual zoom-in state-of-the-art resimulated halos is reached within galaxies, allowing the simulation to capture the multi-phase nature of the interstellar medium and the clumpy nature of the star formation process in galaxies. I will present and discuss several key fundamental properties of galaxies and of their black holes. Due to its exquisite spatial resolution, NewHorizon captures the inefficient process of star formation in galaxies, which evolve over time from being more turbulent, gas-rich and star-bursting at high redshift. These high redshift galaxies are also more compact, and are more elliptical, disturbed and clumpier until the level of internal gas turbulence decays enough to allow for the formation of stable rotating discs. I will show the origin and persistence of the thin and thick disc components, and explain why the settling of discs ``magically’’ occurs at around a stellar mass of 1e10 Msun.

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