Hydrological response of a headwater catchment in southeastern Brazil
Part I: Patterns of rainfall-runoff and stormflow
Abstract
Headwater basins are central for meeting water management and, in humid
tropical areas, essential to understand the baseflow, the discharge
component that maintains water availability during the dry season, and
the stormflow generated from recurrent convective clouds that can lead
to flash floods. We measured field data in a typical headwater basin and
four sub-basins, in subtropical climate region of Serra da
Mantiqueira/South-East Brazil, with a multi-instrument
hydrometeorological set (precipitation, streamflow, baseflow, stormflow,
soil moisture SM, water table depth WTD), towards providing regional
data, to our knowledge, hitherto non-existent, on hydrological response
patterns, and variation of stormflow generation with boundary conditions
and scale. Precipitation recovered in September and peaked in January
concurrently with streamflow. Baseflow responded for most of the
streamflow during the dry season and about half in the wettest months,
and peaked ahead in March, highly covariated with WTD. In contrast, SM
described a longer yearly memory, that recovered 3 months earlier than
streamflow, and depleted 2 months latter in March. The monthly scale
stormflow responded significantly to rainfall although with low
predictability. At the event scale, revealling patterns for all basins
showed thresholds of precipitation (≃ 10 mm), SM (≃45% to 57%) and WTD
≃135 cm, below which stormflow was modest. The event stormflow
coeficient (eSC) reached up a maximum of 25%, albeit with large
variance and little seasonality of the median. Estimates of eSC with
double mass and SM thresholds showed pronounced spatial and temporal
differences (3.2 to 9.6% in drier conditions and 7.7 to 15.4% wetter
conditions). Mean streamflow and runoff coefficient were quite lower at
the main basin (21% compared to about ≃32% between sub-basins), where
there possibly exists groundwater flux exportation, that discharge on a
larger spatial scale, by water exiting the basin without passing through
the surface outlet.