Articles | Volume 19, issue 10
Hydrol. Earth Syst. Sci., 19, 4201–4213, 2015
Hydrol. Earth Syst. Sci., 19, 4201–4213, 2015

Research article 20 Oct 2015

Research article | 20 Oct 2015

Multidecadal change in streamflow associated with anthropogenic disturbances in the tropical Andes

A. Molina2,3,1, V. Vanacker4,5, E. Brisson6,1, D. Mora2, and V. Balthazar4 A. Molina et al.
  • 1Department of Earth and Environmental Sciences, KU Leuven, Celestijnenlaan 200E, 3001 Heverlee, Belgium
  • 2Programa para el Manejo del Agua y del Suelo (PROMAS), Universidad de Cuenca, Av. 12 de abril s/n, Cuenca, Ecuador
  • 3Department of Geology, Escuela Politécnica Nacional, Ladrón de Guevara, 11-253, Quito, Ecuador
  • 4Earth and Life Institute, Georges Lemaitre Centre for Earth and Climate Research, University of Louvain, Place Louis Pasteur 3, 1348 Louvain-la-Neuve, Belgium
  • 5Secretaria de Educación Superior, Ciencia, Tecnología e Innovación, Whymper E7-37 y Alpallana, Quito, Ecuador
  • 6Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany

Abstract. Andean headwater catchments are an important source of freshwater for downstream water users. However, few long-term studies exist on the relative importance of climate change and direct anthropogenic perturbations on flow regimes in these catchments. In this paper, we assess change in streamflow based on long time series of hydrometeorological data (1974–2008) and land cover reconstructions (1963–2009) in the Pangor catchment (282 km2) located in the tropical Andes. Three main land cover change trajectories can be distinguished during the period 1963–2009: (1) expansion of agricultural land by an area equal to 14 % of the catchment area (or 39 km2) in 46 years' time, (2) deforestation of native forests by 11 % (or −31 km2) corresponding to a mean rate of 67 ha yr−1, and (3) afforestation with exotic species in recent years by about 5 % (or 15 km2). Over the time period 1963–2009, about 50 % of the 64 km2 of native forests was cleared and converted to agricultural land. Given the strong temporal variability of precipitation and streamflow data related to El Niño–Southern Oscillation, we use empirical mode decomposition techniques to detrend the time series. The long-term increasing trend in rainfall is remarkably different from the observed changes in streamflow, which exhibit a decreasing trend. Hence, observed changes in streamflow are not the result of long-term change in precipitation but very likely result from anthropogenic disturbances associated with land cover change.

Short summary
Andean catchments play a key role in the provision of freshwater resources. The development of megacities in the inter-Andean valleys raises severe concerns about growing water scarcity. This study is one of the first long-term (1970s-now) analyses of the role of land cover and climate change on provision and regulation of streamflow in the tropical Andes. Forest conversion had the largest impact on streamflow, leading to a 10 % net decrease in streamflow over the last 40 years.