Sub-daily rainfall-runoff dynamics in tropical headwater catchments under different forest management: insights from Brazil

Understanding the relationship between forest cover and hydrological processes is challenging due to the high temporal variability of water cycles and their interactions with both land-use and land-change activities. In tropical headwater catchments, rapid responses to intense rainfall events often occur at sub-daily scales, where concentration times are frequently shorter than 24 hours. These event-scale dynamics are particularly sensitive to land cover and forest management, which can strongly modulate runoff generation, storage, and flow timing in headwater catchments. However, hydrological catchments response is commonly analyzed using daily or longer-term aggregated data, potentially obscuring key processes controlling event runoff generation and its timing.

Here we investigate the impact of different forest management strategies on rainfall-runoff event dynamics in five tropical catchments (56–179 ha) located in São Paulo, Brazil. The study area, situated in a transition zone between the Cerrado and Atlantic Forest biomes, comprises catchments with contrasting land uses: actively restored forest (8 years), native vegetation regeneration (more than 13 years), commercial Eucalyptus plantations with short and long cutting cycles (7 and 14 years, respectively), and a mixed forest mosaic with management interventions in small areas (more than 20 years). We use an objective method for identification on discrete rainfall-runoff events based on detrending moving-average cross-correlation analysis (Giani et al., 2022) from continuous hydrometeorological time series of hourly and sub-hourly temporal resolution. A total of three years of monitoring data (2022–2025), covering contrasting wet and dry years, are analyzed, identifying and characterizing each discrete event by its event runoff coefficient, rise time, time scale, and normalized peak discharge. Given their variability dependence on antecedent wetness conditions, events are grouped by season (wet and dry) for each catchment. For each season, median values of event characteristics are calculated over the three-year period and compared across catchments to assess the effects of different forest management strategies on event-scale runoff response.

The results of this study will contribute to the understanding of how land-use changes in tropical regions, whether for commercial or conservation purposes, affect both hydrological processes and functions, and ecosystem services at the headwater scale.

Giani, G., Tarasova, L., Woods, R. A., & Rico-Ramirez, M. A. (2022). An Objective Time-Series-Analysis Method for Rainfall-Runoff Event Identification. Water Resources Research, 58(2), e2021WR031283. https://doi.org/10.1029/2021WR031283