Abstract
Abstract. Hydrological droughts occur in all climate zones and can have severe impacts on society and the environment. Understanding historical drought occurrence and quantifying severity is crucial for underpinning drought risk assessments and developing drought management plans. However, hydrometric records are often short and capture only a limited range of variability. The UK is no exception: numerous severe droughts over the past 50 years have been well captured by observations from a dense hydrometric network. However, a lack of long-term observations means that our understanding of drought events in the early 20th century and late 19th century is limited. Here we take advantage of new reconstructed flow series for 1891 to 2015 to identify and characterise historic hydrological droughts for 108 near-natural catchments across the UK using the standardised streamflow index (SSI). The identified events are ranked according to four event characteristics (duration, accumulated deficit, mean deficit and maximum intensity), and their severity is reviewed in the context of events of the recent past (i.e. the last 50 years). This study represents the first national-scale assessment and ranking of hydrological droughts. Whilst known major drought events were identified, we also shed light on events which were regionally important, such as those in 1921 and 1984 (which were important in the south-east and north-west of the UK, respectively). Events which have been poorly documented, such as those of the 1940s in the post-war years or the early 1970s (prior to the landmark 1975–1976 event), were found to be important in terms of their spatial coverage and severity. This improved knowledge of historic events can support improved long-term water resource planning approaches. Given the universal importance of historical drought appraisal, our systematic approach to historical drought assessment provides a methodology that could be applied in other settings internationally.
Highlights
In all climate zones, droughts are a major natural hazard and can threaten water supplies and trigger severe societal and environmental consequences (e.g. Bachmair et al, 2016a)
The likelihood of drought occurrence is contingent on an understanding of past hydrometeorological variability, which in itself depends on long historical records of observational data
The period from 1890 to 1910 was a prolonged period of low flows punctuated by periods without flow deficits – e.g. 1903–1905, where above-normal flows were recorded across the country
Summary
Droughts are a major natural hazard and can threaten water supplies and trigger severe societal and environmental consequences (e.g. Bachmair et al, 2016a). Proactive drought risk assessment and planning are essential cornerstones of efforts to manage the impacts of droughts in many countries (Wilhite et al, 2000). Such activities rely on an understanding of the likelihood of droughts of a given severity in addition to information on vulnerability of supply infrastructure, populations, ecosystems etc. The likelihood of drought occurrence is contingent on an understanding of past hydrometeorological variability, which in itself depends on long historical records of observational data (of rainfall, evapotranspiration, river flows, groundwater etc.). While water resource and drought planning efforts have evolved over the last 3 decades to incorporate climate model-based assessments of future climate variability under anthropogenic warming scenarios (Brown et al, 2015), the inherent uncertainties in these simulations mean that historical records are still of fundamental importance in drought planning – as well as in providing the data to corroborate modelling projections and providing a baseline against which future changes can be assessed.
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