01 Jun 2022
01 Jun 2022
Status: this preprint is currently under review for the journal HESS.

Hydroclimate and bedrock permeability determine young water fractions in streamflow across the tropical Andes mountains and Amazon floodplain

Emily Burt1, Daxs Herson Coayla Rimachi2,3, Adan Julian Ccahuana Quispe2, and A. Joshua West1 Emily Burt et al.
  • 1Zumberge Hall of Science 325C, 3651 Trousdale Pkwy, Los Angeles, California, USA 90089
  • 2Universidad Nacional San Antonio Abad del Cusco (UNSAAC), Cusco, Peru
  • 3Universidad Científica del Sur, Lima, Peru

Abstract. The role of topography on water transit times and pathways through catchments is unclear, especially in mountainous environments – yet these environments play central roles in global water, sediment, and biogeochemical fluxes. Moreover, the vast majority of intensively monitored catchments are located in northern latitudes. As a result, the interplay between water transit, topography and other landscape characteristics is particularly underexplored in tropical environments. Here we present the results of a multi-year hydrologic sampling campaign (twice-monthly and storm sampling) to quantify water transit in seven small catchments (< 3 km2) across the transition from the Andes mountains to Amazon floodplain in southern Peru. We use the stable isotope composition of water (δ18OH2O) to calculate the fraction of streamflow comprised of recent precipitation (“young water fraction”) for each of the seven small catchments. Mean unweighted young water fractions (Fyw) are 3–10 % in the Andes, 15–23 % at mid-elevation and 3–4 % in the foreland floodplain. Weighting the Fyw calculation by volume of streamflow and precipitation yield Fyw of 7–47 %. Across these catchments, topography does not exert a clear control on water transit; instead stream Fyw is controlled by a combination of hydroclimate and bedrock permeability. Mid-elevation sites are posited to have the highest Fyw due to less permeable bedrock, poorly developed soils and more frequent and intense rainfall. The data presented here allow us to explore relationships between topography, bedrock permeability, hydroclimate and stream baseflow Fyw – particularly highlighting the role of bedrock permeability and hydroclimate in determining water transit times in a tropical mountain setting.

Emily Burt et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-188', Francesc Gallart, 14 Jun 2022
  • RC2: 'Comment on hess-2022-188', Anonymous Referee #2, 24 Oct 2022

Emily Burt et al.

Emily Burt et al.


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Short summary
Mountains store and release water, serving as water towers for downstream regions and affecting global sediment and carbon fluxes. We use stream and rain chemistry to calculate how much streamflow comes from recent rainfall across seven sites in the Andes mountains and nearby Amazon lowlands. We find that the type of rock and the intensity of rainfall control water retention and release, challenging assumptions that mountain topography exerts the primary effect on watershed hydrology.