Re-construction of historic drought in the Anglian Region (UK) over the period 1798–2010 and the implications for water resources and drought management

Abstract

Summary This study reconstructs droughts during the period 1798–2010 and assesses the consequences for water resource planning, drought management and resilience across the Anglian region (UK). Rain gauge series were extended to cover the period 1798–2010 and used to produce a 213-year daily dataset on a 5 km × 5 km grid matching recent data produced by the UK Met Office. Potential evapotranspiration data was extended using the Thornthwaite equation, based on data from the Central England Temperature series and potential evapotranspiration from the Met Office Rainfall and Evapotranspiration Calculation System. Rainfall and potential evapotranspiration series were input to rainfall-runoff models and flows simulated from 1800–2010. Reservoir simulation using these flows indicates that inclusion of pre-1920 droughts does not reduce yields and actually increases yields at five reservoirs, ranging from 1% to 16.6%, compared with the post-1920 period, the period normally used in reservoir yield calculation and the preparation of Water Resources Management and Drought Plans. Post-1920 droughts define drought intensity at all 5 reservoirs and, with some exceptions, comprise the three worst droughts in the period 1800–2010. Droughts during 1933–36 and 1943–46 are the most severe in the west of the Anglian region, 1989–92 in the north and 1996–98 in the east. 1854–1860 emerges as the period of regionally highest ranked drought severity in the period 1800–1919, but 1893–1907 also features strongly in the west. Contiguous dry winters and summers are a feature of the more severe droughts. Drought periods are consistent with previously reported major drought episodes in England and Wales, with the notable exception of 1801–1816, which emerges as much less severe from this study. The worst hydrological droughts from runoff deficiency analysis do not generally appear critical for reservoirs, emphasising the importance of simulating reservoir response over a long time span and suggesting that individual reservoir storage and infrastructure provide resilience. Despite spatial variability, the more severe droughts are widespread (e.g. 1854–60, 1933–36) and may influence resilience of the larger integrated water resource system that includes river and groundwater sources. Extended sensitivity analysis should be carried out to quantify uncertainty arising from data reconstruction and hydrological modelling, including the choice of model, before inclusion of reservoir yields in Water Resource Management Plans. The ‘library’ of drought information from this study, paralleled by sensitivity analysis, will be useful during drought for reservoir scenario projection and quantification of the risk of restrictions to supply, such as the effect of a ban on the use of hosepipes; in ‘planning mode’ for testing the robustness of Drought Plans; and for application to other catchments across the region. Long rainfall and temperature series and recorded river flows are available for extending the approach used here to elsewhere in the UK, Europe and other parts of the world.