Assessing the long-term hydrologic responses of river catchments in Taiwan using a multiple-component hydrograph approach

Taiwan is facing increasingly severe disasters, such as droughts and floods, which are affected by extreme weather. The assessment of hydrologic response characteristics provides helpful information for understanding catchment behavior and evaluating the ability of rivers to maintain streamflow during extended dry periods. Many studies have used the baseflow index to investigate the hydrologic response characteristics; however, the division of streamflow into two components, quickflow and baseflow, is oversimplified for real scenarios. The spectrum range of response timescales is wide, and the concept of a two-component hydrograph results in different hydrological processes becoming allocated to the baseflow component. To this end, this study selected 23 catchments in Taiwan with data covering the period 1953–2019 and separated streamflow into four components: fast runoff, intermediate interflow, slow runoff, and dry weather flow. The ratio of each component to streamflow was used an indicator of the hydrologic response characteristics of each catchment, and the rainfall–runoff process was presented more realistically. The results showed that baseflow was composed of intermediate interflow, slow runoff, and dry weather flow. According to correlation and regression analyses, rainfall intensity was the most important factor affecting the composition of streamflow, followed by the mean catchment elevation. In terms of regional characteristics, the proportion of dry weather flow in southern Taiwan was low (5%) compared with other regions. During the study period, the streamflow in southern Taiwan was mainly composed of fast runoff because this region had the highest rainfall intensity. The largest variability in the streamflow composition was observed in central Taiwan owing to the large variability in the mean catchment elevation. The results of this study are helpful for establishing rainfall–runoff models and provide a reference for sustainable water resource management.