Articles | Volume 18, issue 12
Hydrol. Earth Syst. Sci., 18, 5377–5397, 2014
Hydrol. Earth Syst. Sci., 18, 5377–5397, 2014

Research article 21 Dec 2014

Research article | 21 Dec 2014

The hydrological regime of a forested tropical Andean catchment

K. E. Clark*,1, M. A. Torres2, A. J. West2, R. G. Hilton3, M. New4,1, A. B. Horwath5, J. B. Fisher6, J. M. Rapp7,**, A. Robles Caceres8, and Y. Malhi1 K. E. Clark et al.
  • 1Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK
  • 2Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA
  • 3Department of Geography, Durham, Durham University, Durham, UK
  • 4African Climate and Development Initiative, University of Cape Town, Rondebosch, Cape Town, South Africa
  • 5Department of Plant Sciences, Cambridge, University of Cambridge, Cambridge, UK
  • 6Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 7Department of Biology, Wake Forest University, Winston Salem, NC, USA
  • 8Facultad de Ciencias Biológicas, Universidad Nacional de San Antonio Abad del Cusco, Cusco, Peru
  • *current address: Department of Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA, USA
  • **current address: Department of Evolution and Ecology, University of California, Davis, CA, USA

Abstract. The hydrology of tropical mountain catchments plays a central role in ecological function, geochemical and biogeochemical cycles, erosion and sediment production, and water supply in globally important environments. There have been few studies quantifying the seasonal and annual water budgets in the montane tropics, particularly in cloud forests. We investigated the water balance and hydrologic regime of the Kosñipata catchment (basin area: 164.4 km2) over the period 2010–2011. The catchment spans over 2500 m in elevation in the eastern Peruvian Andes and is dominated by tropical montane cloud forest with some high-elevation puna grasslands. Catchment-wide rainfall was 3112 ± 414 mm yr−1, calculated by calibrating Tropical Rainfall Measuring Mission (TRMM) 3B43 rainfall with rainfall data from nine meteorological stations in the catchment. Cloud water input to streamflow was 316 ± 116 mm yr−1 (9.2% of total inputs), calculated from an isotopic mixing model using deuterium excess (Dxs) and δD of waters. Field streamflow was measured in 2010 by recording height and calibrating to discharge. River run-off was estimated to be 2796 ± 126 mm yr−1. Actual evapotranspiration (AET) was 688 ± 138 mm yr−1, determined using the Priestley and Taylor–Jet Propulsion Laboratory (PT-JPL) model. The overall water budget was balanced within 1.6 ± 13.7%. Relationships between monthly rainfall and river run-off follow an anticlockwise hysteresis through the year, with a persistence of high run-off after the end of the wet season. The size of the soil and shallow groundwater reservoir is most likely insufficient to explain sustained dry-season flow. Thus, the observed hysteresis in rainfall–run-off relationships is best explained by sustained groundwater flow in the dry season, which is consistent with the water isotope results that suggest persistent wet-season sources to streamflow throughout the year. These results demonstrate the importance of transient groundwater storage in stabilising the annual hydrograph in this region of the Andes.

Short summary
This paper presents measurements of the balance of water inputs and outputs over 1 year for a river basin in the Andes of Peru. Our results show that the annual water budget is balanced within a few percent uncertainty; that is to say, the amount of water entering the basin was the same as the amount leaving, providing important information for understanding the water cycle. We also show that seasonal storage of water is important in sustaining the flow of water during the dry season.