Using stable isotopes and tracer-aided modelling to assess hydrological impacts of urbanisation

Urbanisation is known as a fundamental driver of actual land use change. A good understanding of how catchments are affected by urbanisation (particularly in terms of water quantity and quality) is necessary to be able to propose more sustainable approaches of urban planning. Northern catchments are of particular interest since they are more sensitive to changes. It has been shown that isotopes are helpful to assess the hydrological impacts of urbanisation. Using precipitation and stream isotopes data, a lumped convolution model (with a gamma distribution) has been calibrated on a 7.9 km² Scottish catchment. This catchment is characterised by one urban tributary and one rural tributary. The 4.5-year period of study has been marked by hydroclimatic variability. The model highlighted the differences between the two types of catchments. Urban zones generally had a faster response than rural areas. And more particularly, cumulative urban impacts have been observed at the catchment’s outlet. Additionally, a moving window approach has been used to gain insight into the non-stationary behaviour of transit times. Most urbanised sites obtained low MTTs over all sub-periods (more time-invariant), whereas rural site responded with more variability to events (both during drier and wetter periods).