Ob' River flood inundations from satellite observations: A relationship with winter snow parameters and river runoff

Using a multisatellite method, including passive microwave land surface emissivities, along with active microwave, visible and near infrared observations developed to estimate global inundated area, we examine the spatial and temporal variations of the 1993 2000 monthly inundation extents over a Boreal environment, the Ob River basin. Over the entire watershed, the mean extent of inundation during the snow-free months is 2.6 x 10(5) km(2), consistent with previous independent static or satellites-derived estimates. The maximum in yearly inundation, showing propagation from south to north between April and June, exhibits strong seasonal and inter-annual variations. The consistency of the inundation estimates is then analyzed at local or basin-wide scale using different in situ or satellite-derived snow and runoff parameters. The results show a strong relationship between the inundation extent and the snowmelt date, the snowpack depth at three in situ stations located in the southern part of the basin. Over the northern part, results show that flooding is more closely linked to the amount of water coming downstream from the southern part of the basin. A close systematic relationship is also found between the inundation extent and the local in situ runoff at six locations as well as with the altimeter-derived discharge measured at the Ob estuary. This case study evaluation shows the potential of these data sets to provide consistent information about the seasonal and inter-annual variations of inundation over a major Boreal river basin. These results also suggest new potential to improve the description of the snow-inundation-runoff relationship that are fundamental for climate and hydrological models.