Explore the vast range of titles available.

Our study proposes a data‐driven framework that identifies the level of functional simplicity of catchment's stormflow generation during dormant/growing seasons, using daily scale observations of streamflow and precipitation. We classify 619 rain‐dominated catchments across Canada, the United States, Great Britain, and Australia into three behavioral classes—simple, intermediate, and complex—based on the validity of (segmented) linear models in explaining the inter‐event relationship between precipitation volume and stormflow volume. Results reveal that simple stormflow generation behavior occurs at 108 catchments during dormant seasons with the linear model explaining most variability of inter‐event relationship between precipitation and stormflow volumes (median R2 of 0.81). These simple catchments are typically steep with wet/out‐of‐phase climate and strong precipitation persistence. The functional simplicity of simple catchments is further explored using spectral (coherency) analysis, which indicates the level of synchronicity between daily scale precipitation and streamflow time‐series. Simple catchments exhibit a strong coherency value at high frequencies, resembling the dynamic of a nearly Linear Time‐Invariant system. Indeed, the portion of precipitation volume that becomes stormflow tends to remain constant during dormant seasons, since the transfer function translating precipitation pulses to the streamflow hydrograph is nearly linear and time‐invariant. Complex catchments, in contrast, exhibit nonlinear relationships and time‐variant transfer functions, with weak coherency between precipitation and streamflow time‐series. Our results guide modeling frameworks to adjust the simplicity/complexity level with the catchment's “observation‐based” functional behavior. By synthesizing the causes/drivers and empirical equations relevant to simple stormflow behavior, our study contributes to the development of a unified hydrologic theory of stormflow generation. Plain Language Summary Catchments are often assumed to behave complexly during stormflow generation with time‐dependent and hysteretic functional behavior. This complexity challenges the synthesis of the “heap of facts” observed in diverse experimental catchments, hindering the development of a consistent body of hydrologic theory. Such synthesis is essential to develop (and regionalize) reliable models to predict and forecast hydrologic response, identify vulnerabilities to flood/drought, and conduct land‐use and climate‐change scenario analyses. Our results show that despite all within‐catchment complexities, many landscapes' wet climates, out‐of‐phase seasonality (with large time difference between precipitation and temperature peaks), and steep topographies could override small‐scale heterogeneities, resulting in a “simple” catchment‐scale functional behavior. Such functional simplicity is relatively more prevalent during dormant seasons than growing seasons. Simplicity is governed by linearity and stationarity of catchment functional dynamics. Identifying and synthesizing simple functional dynamics is a crucial first step in understanding non‐simple functional dynamics and, ultimately, in developing a generalizable theory of catchment hydrologic function applicable to catchments of different levels of simplicity/complexity worldwide. Key Points Dormant seasons' simple stormflow functionality is prevalent, occurring mostly along steep catchments with wet/out‐of‐phase climate Simple catchments transfer precipitation pulses into the streamflow hydrograph using a (nearly) time‐invariant transfer function during dormant seasons A flashier simple catchment with a faster decay rate transfers a larger portion of precipitation volume to stormflow volume