Projecting climate change impacts on stream flow regimes with tracer-aided runoff models - preliminary assessment of heterogeneity at the mesoscale

Abstract

The northern mid-high latitudes form a region that is sensitive to climate change, and many areas already have seen - or are projected to see - marked changes in hydroclimatic drivers on catchment hydrological function. In this paper, we use tracer-aided conceptual runoff models to investigate such impacts in a mesoscale (749km2) catchment in northern Scotland. The catchment encompasses both sub-arctic montane sub-catchments with high precipitation and significant snow influence and drier, warmer lowland sub-catchments. We used downscaled HadCM3 General Circulation Model outputs through the UKCP09 stochastic weather generator to project the future climate. This was based on synthetic precipitation and temperature time series generated from three climate change scenarios under low, medium and high greenhouse gas emissions. Within an uncertainty framework, we examined the impact of climate change at the monthly, seasonal and annual scales and projected impacts on flow regimes in upland and lowland sub-catchments using hydrological models with appropriate process conceptualization for each landscape unit. The results reveal landscape-specific sensitivity to climate change. In the uplands, higher temperatures result in diminishing snow influence which increases winter flows, with a concomitant decline in spring flows as melt reduces. In the lowlands, increases in air temperatures and re-distribution of precipitation towards autumn and winter lead to strongly reduced summer flows despite increasing annual precipitation. The integration at the catchment outlet moderates these seasonal extremes expected in the headwaters. This highlights the intimate connection between hydrological dynamics and catchment characteristics which reflect landscape evolution. It also indicates that spatial variability of changes in climatic forcing combined with differential landscape sensitivity in large heterogeneous catchments can lead to higher resilience of the integrated runoff response. © 2012 John Wiley & Sons, Ltd.