Comparison of event-specific rainfall-runoff responses and their controls in contrasting geographic areas

Numerous studies have examined the event-specific hydrologic response of hillslopes and catchments to rainfall. Knowledge gaps, however, remain regarding the relative influence of different meteorological factors on hydrologic response, the predictability of hydrologic response from site characteristics, or even the best metrics to use to effectively capture the temporal variability of hydrologic response. This study aimed to address those knowledge gaps by focusing on 21 sites with contrasting climate, topography, geology, soil properties, and land cover. High-frequency rainfall and discharge records were analysed, resulting in the delineation of over 1,600 rainfall-runoff events, which were described using a suite of hydrologic response metrics and meteorological factors. Univariate and multivariate statistical techniques were then applied to synthesize the information conveyed by the computed metrics and factors, notably measures of central tendency and variability, variation partitioning, partial correlations, and principal component analysis. Results showed that some response magnitude metrics generally reported in the literature (e.g., runoff ratio and area-normalized peak discharge) did not vary significantly among sites. The temporal variability in site-specific hydrologic response was often attributable to the joint influence of storage-driven (e.g., total event rainfall and antecedent precipitation) and intensity-driven (e.g., rainfall intensity and antecedent potential evapotranspiration) meteorological factors. Mean annual temperature and potential evapotranspiration at a given site appeared to be good predictors of hydrologic response timing (e.g., response lag and lag to peak). Response timing metrics, particularly those associated with response initiation, were also identified as the metrics most critical for capturing intrasite response variability. This study therefore contributes to the growing knowledge on event-specific hydrologic response by highlighting the importance of response timing metrics and intensity-driven meteorological factors, which are infrequently discussed in the literature. As few correlations were found between physiographic variables and response metrics, more data-driven studies are recommended to further our understanding of landscape-hydrology interactions.