Factors controlling the temporal variability of streamflow transit times in tropical alpine catchments

Abstract

The mean transit time (MTT) of water is an essential descriptor of streamflow generation and catchment water storage. Research on how MTTs fluctuate over time and the variables influencing such variation is limited. In this study bi-weekly stable isotopic data in precipitation and streamflow are presented, together with daily records of precipitation amount, streamflow, and climatological information. The data were collected over an 8- year period in a nested system of 8 tropical alpine catchments in the Zhurucay Ecohydrological Observatory in southern Ecuador, situated at an elevation of 3400 to 3900 m a.s.l. Isotopic data were used to investigate the temporal variability of streamflow MTTs estimated using yearly periods and a 1-month moving window (i.e., 81 yearly calculated MTTs per catchment). The factors controlling the temporal variability of MTTs were identified using simple and multiple linear regression models between estimated MTTs and hydrometeorological variables. Results reveal that streamflow MTTs at all catchments were short (<1 year) and varied little among catchments (191.30±47.10 days), suggesting that a yearly time span for estimating the temporal variability of MTTs is appropriate. A combination of hydrometeorological variables (i.e., precipitation, streamflow, and runoff coefficient) over antecedent periods up to 1 year was found to control MTT temporal variability among catchments. Overall, these findings point to the prevalence of steady-state conditions in the investigated hydrological system. Our study is key to provide insights into the factors controlling the temporal variability of streamflow MTT in tropical catchments, overcoming data limitations of past investigations. It also provides an increase in the process-based knowledge of the hydrology of high Andean Páramo catchments, with significant implications for improved water supply management