Water balance and hydrologic characteristics of a rain forest catchment in the Central Amazon Basin

Abstract

The water balance and hydrologic characteristics of streamflow and subsurface outflow were measured for a first‐order catchment draining a 23.4‐ha stand of undisturbed terra firme rain forest in the central Amazon Basin over a 1 year period. Total rainfall during the study period, representing a 1 in 10 wet year, was 2870 mm of which 1650 mm and 42 mm respectively were exported from the catchment as streamflow and subsurface outflow. A hydrograph separation technique applied to the entire streamflow record distinguished 173 storms. The storm flow volume was 88 mm, which represented only 5% of overall streamflow and less than 3% of the rainfall. The 20% of least frequent, large‐volume storms accounted for 75% of the rainfall volume and 80% of the storm flow volume. The fraction of the catchment that could account for the volume of storm flow runoff in a given storm as overland flow never exceeded 4%, even for the largest storms. The change in soil water storage from the previous year was equivalent to about 57 mm of water. Evapotranspiration, estimated as the water balance residual, was equivalent to 1120 mm per year with an uncertainty, estimated by propagating measurement errors, of ±16–21%. Evapotranspiration is significantly less than values previously reported from catchment‐scale water balance studies in the central Amazon, and is slightly lower than recent estimates derived from micrometeorologieal techniques, though differences in the latter case are within measurement error.