Abstract
Abstract. We present a new modeling approach analyzing and predicting the Transit Time Distribution (TTD) and the Response Time Distribution (RTD) from hourly to annual time scales as two distinct hydrological processes. The model integrates Isotope Hydrograph Separation (IHS) and the Instantaneous Unit Hydrograph (IUH) approach as a tool to provide a more realistic description of transit and response time of water in catchments. Individual event simulations and parameterizations were combined with long-term baseflow simulation and parameterizations; this provides a comprehensive picture of the catchment response for a long time span for the hydraulic and isotopic processes. The proposed method was tested in three Andean headwater catchments to compare the effects of land use on hydrological response and solute transport. Results show that the characteristics of events and antecedent conditions have a significant influence on TTD and RTD, but in general the RTD of the grassland dominated catchment is concentrated in the shorter time spans and has a higher cumulative TTD, while the forest dominated catchment has a relatively higher response distribution and lower cumulative TTD. The catchment where wetlands concentrate shows a flashier response, but wetlands also appear to prolong transit time.
Highlights
Water management with the aim to sustain catchment ecological services requires an understanding of the hydrologic cycle
We argue in this paper that both responses are essential to understand catchment behavior, since one response represents actual conservative solute travel time and the other represents hydraulic dynamics
Three adjacent small headwater catchments draining to the same river system were selected for a comparative study of land use and stream flow to quantify the impact that different land use types have on stream flow
Summary
Water management with the aim to sustain catchment ecological services requires an understanding of the hydrologic cycle. Stable water isotopes have been used in hydrology for two purposes: (1) to identify the temporal variations of water sources for baseflow and for individual storms; and (2) to identify the source of runoff during an event, e.g. whether it comes from rain or snowmelt (event water) or from water stored in the watershed prior to the event (groundwater, soil water, lakes etc.) (Vitvar et al, 2005) This knowledge has been used to understand the interactions between precipitation, runoff pathways and runoff generation processes, and as a proxy for the capacity of a catchment to store water and chemicals and regulate its flow (Soulsby et al, 2009).
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