A longer?term perspective on soil moisture, groundwater and stream flow response to the 2018 drought in an experimental catchment in the Scottish Highlands

The drought of summer 2018, which affected much Northern Europe, resulted in low river flows, biodiversity loss and threats to water supplies. In some regions, like the Scottish Highlands, followed two consecutive, anomalously dry, winter periods. Here, we examine how drought, its antecedent conditions, soil moisture, groundwater storage, flows Bruntland Burn; a sub-catchment Girnock Burn long-term observatory Cairngorm Mountains. Fifty years rainfall-runoff observations modelling studies provided unique contextualisation this extreme event relation more usual storage dynamics. Whilst precipitation 2018 was only 63% mean, moisture across catchment were less than half their average seasonal levels 0.5 m lower normal. Hydrometric isotopic showed that ~100 mm during (May-Sept) sustained almost entirely by drainage, representing ~30% evapotranspiration occurred over same period. A key reason so severe because preceding winters also dry failed adequately replenish stores. As result, had biggest deficits for decade, likely since 1975–1976. Despite this, recovery rapid autumn/winter with stores returning normal values, along stream flows. study emphasizes data from experimental sites are understanding non-linear flux-storage interactions catchments “memory effects” govern evolution of, from, droughts. This is invaluable both terms (a) giving insights into hydrological behaviours will become common resource management problems future under climate change (b) providing challenge models.