JOINT PSL -- NCEI SEMINAR: Systematic Assessment of Drought Termination in the UK in Reconstructed River Flow Data

Simon Parry

Center for Ecology & Hydrology, Wallingford, UK and Loughborough University, Loughborough, UK Image

Friday, Dec 08, 2017, 2:00 pm
DSRC Room 1D403

Abstract

Drought termination has often been characterised as an abrupt return to 'normal' conditions, although this may reflect a reporting bias towards extreme transitions that were more memorable and newsworthy. Assessments of the variability of drought termination in the historical record have been hindered by the lack of an objective definition and by relatively short observed streamflow time series. An objective approach to identify and characterise drought termination has been applied to 108 reconstructed river flow records in the UK from 1891-2015. The chronologies that result provide a much improved perspective on the historical variability of drought termination as well as how this varies in space and time. For many catchments, the use of reconstructed data increases by three-fold the amount of data available, with a corresponding three- or four-fold increase in the number of identified events. In addition, many new maxima for drought severity, duration and termination rate occurred in years in the reconstructed records which pre-date observed data, highlighting the value of the reconstructions. Well-known notable recent events such as the abrupt drought termination in 2012 were found to be less rare in the reconstructed historical record than previously concluded from available observed data. The broader distribution of drought termination characteristics in reconstructed records implies the need to re-assess our understanding of the responsiveness of catchments and the likelihood of abrupt or gradual transitions at the end of drought. In turn, this may assist water managers to be more resilient to the broad spectrum of possible scenarios for drought termination, at a time towards the end of a drought when answers are frequently sought by a wide range of stakeholders to questions on how long deficits will continue and what is required for recovery.