Analyzing the discharge regime of a large tropical river through remote sensing, ground-based climatic data, and modeling

This study demonstrates the potential for applying passive microwave satellite sensor data to infer the discharge dynamics of large river systems, using the mainstem Amazon as a test case. The methodology combines a) interpolated ground-based meteorological station data, b) horizontally and vertically-polarized temperature differences (HVPTD) from the 37 GHz Scanning Multichannel Microwave Radiometer (SMMR) aboard the Nimbus-7 satellite and c) a calibrated Water Balance/Water Transport Model (WBM/WTM). Monthly HVPTD values at 0.25 degree latitude/spl times/longitude resolution were re-sampled spatially and temporally to produce an enhanced HVPTD time series at 0.5 degree grid-cell resolution for the period May 1979 through February 1985. Enhanced HVPTD values were regressed against monthly discharge derived from the WBM/WTM for each of 40 grid-cells along the mainstem over a calibration period from May 1979 to February 1983 to provide a spatially-contiguous estimate of time-varying discharge. HVPTD-estimated flows generated for a validation period from March 1983 to February 1985 were found to be in good agreement with both observed and modeled discharges over a 1400 km section of the mainstem Amazon. Both the WBM/WTM and HVPTD-derived flow rates reflect the significant impact of the 1982-83 ENSO event on water balances within the basin.