Abstract
Abstract. Drought termination can be associated with dramatic transitions from drought to flooding. Greater attention may be given to these newsworthy and memorable events, but drought terminations that proceed gradually also pose challenges for water resource managers. This paper defines drought termination as a distinctive phase of the event. Using observed river flow records for 52 UK catchments, a more systematic and objective approach for detecting drought terminations is demonstrated. The parameters of the approach are informed by a sensitivity analysis that ensures a focus on terminations of multi-season to multi-year droughts. The resulting inventory of 467 drought terminations provides an unprecedented historical perspective on this phenomenon in the UK. Nationally and regionally coherent drought termination events are identifiable, although their characteristics vary both between and within major episodes. Contrasting drought termination events in 1995–1998 and 2009–2012 are examined in greater depth. The data are also used to assess potential linkages between metrics of drought termination and catchment properties. The duration of drought termination is moderately negatively correlated with elevation (rs = −0.47) and catchment average rainfall (rs = −0.42), suggesting that wetter catchments in upland areas of the UK tend to experience shorter drought terminations. More urbanized catchments tend to have gradual drought terminations (contrary to expectations of flashy hydrological response in such areas), although this may also reflect the type of catchments typical of lowland England. Significant correlations are found between the duration of the drought development phase and both the duration (rs = −0.29) and rate (rs = 0.28) of drought termination. This suggests that prolonged drought development phases tend to be followed by shorter and more abrupt drought terminations. The inventory helps to place individual events within a long-term context. The drought termination phase in 2009–2012 was, at the time, regarded as exceptional in terms of magnitude and spatial footprint, but the Thames river flow record identifies several comparable events before 1930. The chronology could, in due course, provide a basis for exploring the complex drivers, long-term variability, and impacts of drought termination events.
Highlights
Drought termination, generally defined as the end point of a drought, has been neglected in research literature relative to drought onset
Whilst abrupt drought terminations may result in more destructive and newsworthy impacts (e.g. Webster et al, 2011; Lavers and Villarini, 2013; Parry et al, 2013), gradual drought terminations are problematic for water resource managers who must reconcile public relations with continued water restrictions during wet weather
Monthly mean flow data were converted into a percentage anomaly of the monthly long-term average (LTA), calculated from a 1971–2000 reference period (Eq 1)
Summary
Generally defined as the end point of a drought, has been neglected in research literature relative to drought onset. Studies which address this phenomenon have focused on extreme transitions at the end of a drought Hisdal et al, 2001; Pfister et al, 2006; Marsh et al, 2007; Fleig et al, 2011; Li et al, 2013), but these have generally not considered the drought termination phase. A limited historical perspective can be gained from studies of drought termination on an event basis, including those based on hydrometeorological
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