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A method is presented to obtain dynamic estimates of basin wetness (BWI) and fractional water surface (FWS) indices at the scale of the Mackenzie River Basin using SSM/I remotely sensed brightness temperature measurements. The approach accounts for the seasonal evolution of the vegetation state and the basin surface heterogeneity. Results demonstrate that the approach can filter out the vegetation effect and produce reasonable estimates of FWS at the basin scale. However, the low resolution of SSM/I and other passive microwave sensors precludes the use of this approach for monitoring soil wetness at a smaller scale. Also, the FWS cannot distinguish moisture effects from open water bodies from that of soil surface. A methodology based on the combined use of passive microwave and visible data, along with topographic information, has been developed to separate the open water from the soil surface component in estimating the BWI, and to downscale the index at the digital elevation models scale using a topographic index (TI) which is continuously adjusted to account for vegetation growth. When applied to the Peace-Athabasca-Delta area, this method improved the correlation between soil wetness and precipitation measured at a meteorological station, compared to an approach based on a time invariant TI. [ABSTRACT FROM AUTHOR]