Hydropedological units are of critical importance in modulating catchment response in terms of storage and flux dynamics under changing hydrological conditions. We examined the short-term impacts of an extreme drought on the storage dynamics and runoff response in hydropedological units in a headwater catchment in the Scottish Highlands. These included poorly drained histosols in riparian zones and freely draining podzols on steeper hillslopes. To characterise the storage and runoff dynamics prior to, during, and after the drought period, precipitation, soil moisture, shallow ground water levels, and consequent runoff were monitored and stable water isotopes samples collected. Storage changes in the histosols were remarkably small (<40 mm), compared to those in moorland (~100 mm) and forest (~200mm) covered podzols. Although storage in all soils recovered soon after the drought, this took longest (3-4 months) for the forested podzols. During events, there was consistent threshold behaviour in most hydropedological units and the integrated response at the catchment scale, which was not affected by drying or wetting. The results suggest that during dry periods, large parts of the catchment were disconnected from the river network and runoff was generated mainly from the wet histosols. However, during events, there was an intermittent connection of the hillslopes that recharged the wetland and stream. This contributed to strong recovery and resilience of the catchment in its runoff response. Nevertheless, as future climate projections for northern environments suggest that prolonged dry periods are likely to become more frequent, further work is needed on the potential cumulative or carry over effects of consecutive drier periods.
The authors would like to thank Jonathan Dick, Maria Blumstock, Claire Tunaley and Jason Lessels for assistance with the field work and Audrey Innes for lab sample preparation. Climatic data were provided by Iain Malcolm and Marine Scotland Fisheries at the Freshwater Lab, Pitlochry. Additional precipitation and temperature data were provided by the UK Meteorological Office and the British Atmospheric Data Centre (BADC). We are grateful for the careful and constructive comments of two anonymous reviewers that helped to improve an earlier version of this manuscript. The European Research Council ERC (project GA 335910) is thanked for funding.
- water storage
- run-off response