Exploring Controls on Rainfall-Runoff Events: 1. Time Series- Based Event Separation and Temporal Dynamics of Event Runoff Response in Germany

摘要

Analyzing a response of catchments to rainfall inputs allows for deeper insights on the mechanisms of runoff generation at catchment scale. In this study an automated time series-based event separation procedure consisting of available base flow separation, runoff event identification, and rainfall attribution methods and of a novel iterative procedure for the adjustment of thresholds used to identify single-peak components of multiple-peak events is proposed. Event runoff coefficient, time scale, rise time, and peak discharge of more than 220,000 identified rainfall-runoff events are then used to analyze dynamics of event runoff response in 185 catchments at multiple temporal scales. In mountainous catchments with poor storage event runoff response is strongly controlled by the characteristics of rainfall and is generated by event-fed saturation or infiltration excess. A distinct switch between saturated and unsaturated states occurs in these catchments. A weak relation between rainfall and runoff event properties is instead observed in lowland and hilly catchments with substantial storage, where a gradual transformation between functioning states occurs and the response is driven by preevent saturation. The seasonality of their event characteristics is governed by the contribution of snowmelt and the seasonality of the aridity index rather than of rainfall properties. Long-term changes of total precipitation amount alone do not explain season-specific long-term changes of event characteristics that are rather consistent with changes of seasonal indicators of the wetness state. The effects of land use changes are detectable only in a few cases and display themselves mostly in the characteristic response time of catchments.