A hydrograph showing the short-term response of streamflow to a single precipitation event, including the rising limb, peak, and recession. It reveals how a watershed transforms rainfall into runoff.
A storm hydrograph is a plot of discharge versus time at a watershed outlet in response to a specific rainfall event. It displays several characteristic features: the initial rise beginning when the first direct runoff reaches the measurement point, the rising limb showing increasing discharge as more of the watershed contributes runoff, the peak or crest representing the maximum discharge, and the recession limb as runoff gradually diminishes after the rainfall ends. The shape and timing of the storm hydrograph depend on storm characteristics (intensity, duration, spatial distribution), catchment properties (area, slope, shape, soil, land use, drainage density), and antecedent conditions (soil moisture, groundwater levels). Important parameters derived from storm hydrographs include peak discharge, time to peak, lag time, time of concentration, and total runoff volume (the area under the direct runoff hydrograph). Storm hydrograph analysis is fundamental to flood forecasting, design of flood control structures, and development of rainfall-runoff models. Comparison of storm hydrographs for similar storms over time can reveal the effects of land use change, urbanization, or watershed management practices on the hydrological response.