Modelling non-stationary water ages in a tropical rainforest: A preliminary spatially distributed assessment

Alicia Correa*, Christian Birkel, Jason Gutierrez, Joni Dehaspe, Ana María Durán-Quesada, Chris Soulsby, Ricardo Sánchez-Murillo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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 time-invariant 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.

Original languageEnglish
Pages (from-to)4776-4793
Number of pages18
JournalHydrological Processes
Volume34
Issue number25
Early online date1 Oct 2020
DOIs
Publication statusPublished - 15 Dec 2020

Keywords

  • Costa Rica
  • humid tropics
  • ReBAMB
  • tracer-aided modelling
  • transpiration
  • water ages
  • water partitioning
  • FLUX TRACKING
  • CATCHMENT TRANSIT-TIME
  • TRANSPIRATION
  • STABLE-ISOTOPES
  • HYDROLOGICAL MODEL
  • PRECIPITATION
  • CONNECTIVITY
  • INTERCEPTION
  • STORAGE DYNAMICS
  • SOIL-WATER

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