Water budgets of three small catchments under montane forest in Ecuador: experimental and modelling approach

Abstract

AbstractThe water budget of forested catchments controls the local water supply and influences the regional climate. To assess the anthropogenic impact on the water cycle, we constructed a water budget for three ∼10 ha catchments under lower montane forest on the east‐facing slope of the Andes in south Ecuador at 1900–2150 m elevation. We used field hydrological measurements and modelled surface flows with TOPMODEL, a semi‐distributed catchment model. We measured incident precipitation, throughfall, stemflow, and surface flow between May 1998 and April 2002 in hourly to weekly resolution, and determined all variables needed to parameterise TOPMODEL. On average, of the four monitored years and three catchments, incident precipitation was 2504 ± SD 123 mm, throughfall 1473 ± 197 mm, and stemflow 25 ± 2 mm yr−1. Fog water input was negligible. Mean annual interception loss in the forest was 1006 ± 270 mm, and mean annual surface flow, calculated with TOPMODEL in an hourly resolution was 1039 ± 48 mm. The resulting mean annual evapotranspiration was 1466 ± 161 mm of which 32% ( =471 ± 162 mm) was transpiration if evaporation from the soil was neglected. Our study catchments show a high evapotranspiration attributable to the strong solar insolation near the equator, the small impact of fog, the generally low intensity of incident precipitation and additional wind‐driven advective energy input. Copyright © 2006 John Wiley & Sons, Ltd.