Hydrological response of a headwater catchment in Southeast Brazil—Threshold patterns of stormflow response

Abstract

Headwater catchments are essential water sources for sustaining low flow in downstream rivers. The montane region of Serra da Mantiqueira in Southeast Brazil is the largest water supplier for the densely populated area of São Paulo, where we investigated the hydrological response of a subtropical catchment and four of its sub‐catchments. We discussed the relationships between rainfall, streamflow, baseflow, stormflow, soil moisture, and water table depth using high‐frequency field observations over 4 years. Baseflow accounted for most of the streamflow during the dry season and for half of streamflow in the wet season. In contrast, the variations in soil moisture were dampened, with increases in the early wet season preceding the increase in streamflow and decreases in the late wet season following the decrease in streamflow. The mean runoff coefficient and baseflow index varied from 23% to 37% and from 62% to 75% across the catchments, respectively. At the event scale, all catchments had a pronounced threshold behaviour, where stormflow increased sharply when event precipitation reached ≃10 mm, soil moisture reached ≃51% and water table depth decreased to ≃135 cm. The event stormflow coefficient was highly variable, with a maximum of 25%. The temporally integrated stormflow coefficient was low for conditions below a soil moisture threshold (≃3%–10%) and high above a soil moisture threshold (≃8%–15%). Our estimates of flows and threshold behaviours were consistent across the various study catchments, improving our understanding of runoff generation at a catchment scale. This information should help improve the management of water resources focused on water and food security in a context of climate change.

Comparing hydrological responses across catchments using a new soil water content metric

“…The larger range in the relation between SWCm and stream runoff observed in the Weierbach catchment compared to the Ressi and especially to the Can Vila catchments may reflect site‐specific soil characteristics in the three catchments. Although this threshold relation has been observed in many other catchments under different climatic conditions (recent examples are Chittolina et al, 2023; Qazi, 2020; Scaife et al, 2020; Zhao et al, 2020), this is the first time that this behaviour has been associated with different SWC states that underly distinct hydrological processes.…”

“…However, this condition was reached under different moisture states in each site. In Chittolina et al, 2023;Qazi, 2020;Scaife et al, 2020;Zhao et al, 2020), this is the first time that this behaviour has been associated with different SWC states that underly distinct hydrological processes.…”

Preface special issue: “Processes and patterns in tropical hydrology”

“…The authors show that the vegetation type caused notable variations in upper horizon soil hydraulic properties and pore structure, as well as, that the vegetation type exerted a positive control in form of larger soil pores and lower bulk density, resulting in higher water availability and hydraulic conductivities under cushion plants compared to tussock grass. In yet another system of the neotropics, Chittolina et al (2023) investigate the patterns of stormflow response in a subtropical rainforest area in south Brazil. The authors identify a monthly rainfall threshold and show that at the event scale, the stormflow response is controlled by an increase in soil moisture and a rise of the water table.…”