Estimating Curve Number under changing catchment’s land cover structure

The Curve Number method, developed in the 1950s in the United States, is commonly used to estimate runoff depth resulting from heavy rainfall. Over many years, it has been tested in various regions and for different purposes beyond its original use. Despite numerous studies on this method, some issues still require consideration, i.e., a universally accepted procedure for CN determination from rainfall-runoff data. In this work, the authors attempt to estimate the CN parameter for a small, lowland catchment in central Poland. Historical data on catchment land cover and original rainfall-runoff measurements are used to determine the CN for three periods of different catchment land cover structures. Approaches for CN estimation are compared and discussed. The study states that a) over the period 1974-2018, a gradual increase in forest areas is observed, while the average CN parameter dropped from 59.6 to 55.9; b) among considered approaches, the least-squares calibration is a straightforward concept, allowing for reliable estimation of CN from rainfall-runoff data; c) further research is still needed to focus on the influence of actual initial losses on Curve Number value.