| Sumario: |
Pristine tropical forests play a critical role in regional and global climate systems. For a
better understanding of the eco-hydrology of tropical “evergreen” vegetation, it is
essential to know the partitioning of water into transpiration and evaporation, runoff
and associated water ages. For this purpose, we evaluated how topography and vegetation influence water flux and age dynamics at high temporal (hourly) and spatial
(10 m) resolution using the Spatially Distributed Tracer-Aided Rainfall-Runoff model
for the tropics (STARRtropics). The model was applied in a tropical rainforest catchment
(3.2 km2
) where data were collected biweekly to monthly and during intensive monitoring campaigns from January 2013 to July 2018. The STARRtropics model was further developed, incorporating an isotope mass balance for evapotranspiration
partitioning into transpiration and evaporation. Results exhibited a rapid streamflow
response to rainfall inputs (water and isotopes) with limited mixing and a largely timeinvariant baseflow isotope composition. Simulated soil water storage showed a transient response to rainfall inputs with a seasonal component directly resembling the
streamflow dynamics which was independently evaluated using soil water content
measurements. High transpiration fluxes (max 7 mm/day) were linked to lower slope
gradients, deeper soils and greater leaf area index. Overall water partitioning resulted
in 65% of the actual evapotranspiration being driven by vegetation with high transpiration rates over the drier months compared to the wet season. Time scales of water age
were highly variable, ranging from hours to a few years. Stream water ages were conceptualized as a mixture of younger soil water and slightly older, deeper soil water and
shallow groundwater with a maximum age of roughly 2 years during drought conditions (722 days). The simulated soil water ages ranged from hours to 162 days and for
shallow groundwater up to 1,200 days. Despite the model assumptions, experimental
challenges and data limitation, this preliminary spatially distributed model study
enhances knowledge about the water ages and overall young water dominance in a
tropical rainforest with little influence of deeper and older groundwater.
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