Catchments as filters: Understanding catchment processes through annual duration curves

Quantifying the response of a catchment to climate forcing and thereby linking this response to functional catchment properties can increase our understanding of the effects of climate change on water availability and identify those catchments most sensitive to climate. By viewing a catchment as a filter of the precipitation signal, we present a novel approach for comparing the annual variability in precipitation with the annual variability in streamflow using the concept of the annual duration curve (ADC). The ADC constructs a 365-day duration curve for each year of observed record, and has not previously been utilized to examine catchment behavior and understand similarity in catchment response. We compare the year-to-year changes in ADCs of precipitation to the year-to-year changes in the ADCs of streamflow for 42 unregulated catchments across the United States having at least 55 years of observed daily streamflow and precipitation records. We find that the annual variability in precipitation is relatively constant across the study catchments; however, the variability in streamflow can differ quite substantially. This result indicates that the extent to which annual variability in streamflow represents the annual variability in precipitation is likely related to the filtering process, which differs across catchments. Future research will determine if these differences can be explained by functional catchment properties.