Landscape structure and rainstorms swing the response of recession nonlinearity

Abstract. Streamflow recession discloses hydrological functioning, runoff dynamics, and storage status within catchments. Understanding recession response to landscape structure and rainstorms can be a guidance for assessing streamflow change under climate change. Yet, the documented response direction of recession is inconsistent and diverse. This study tested how landscape structure and rainstorms regulate the response direction. We derived recession rate, a, and nonlinearity, b, from power-law recession (-dQ/dt = aQ^b) in 19 subtropical catchments with a broad spectrum of 260 rainstorms. Results showed that the recession rate increases with the drainage density and L / G ratio (flow-path length over gradient), indicating that the catchments with the dense network or more short-and-gentle hillslopes would result in high rates. Apart from landscape structure, the rate surprisingly decreases with rainstorm amount. Probably because rainstorm facilitates connectivity in the saturated zones, which might conjoin more water from slow reservoirs and thus water drains slowly. Additionally, the recession nonlinearity increases with spatial heterogeneity (drainage area) but decreases with hillslope hydraulics (drainage density). The swing of response direction, which lies in the predominance between spatial heterogeneity and hillslope hydraulics, needs further clarification, particularly for regional recession assessment under climate changes. Incorrect response direction from landscape structure would lead to considerable bias inference.