Papa, F., C. Prigent, W.B. Rossow, and E. Matthews, 2008: Interannual variability of surface water extent at global scale, 1993-2004. J. Geophys. Res., submitted.
Land surface waters play a primary role in the global water cycle and climate. As a consequence, there is a widespread demand for accurate and long-term quantitative observations of their distribution over the whole globe. This study presents the first global dataset that quantifies the monthly distribution of surface water extent at ~25km sampling intervals over 12 years (1993-2004). These estimates, generated from complementary multiple satellite observations, including passive microwave (SSM/I), scatterometer (ERS) along with visible and near-infrared (AVHRR), were first developed over 1993-2000. ERS encountered technical problems in 2001 and the processing scheme had to be adapted to extend the time series. We investigate and discuss here the adjustments of the methodology, compare the various options and show that the data set can be extended with good confidence beyond 2000, using ERS and AVHRR mean-monthly climatologies. In addition to a strong seasonal and inter-annual variability, the 12-year record dataset shows a systematic decrease in the surface water extents, especially over the tropics and the northern mid-latitudes, with patterns of stronger decline in the coastal regions. Over inland water bodies and large river basins, we assess the seasonal and inter-annual variations of the surface water extent, as well as their trends, against related variables such as altimeter-derived rivers / floodplains water level heights, rain rate estimates, air temperatures and in situ river discharges. Over the coastal regions, we show that areas with large population increase over the last 15 years underwent stronger extent decrease than the other regions.
