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Published in: Fowler, H.J. and Kilsby, C.G. 2002. A weather-type approach to analysing water resource drought in the Yorkshire region from 1881 to 1998. J. Hydrol., 262, 177-192. [Abstract] This study used a Drought Severity Index (DSI) developed from the accumulated monthly-precipitation deficit concept of Bryant et al. (1992), the same as that used by Phillips and McGregor (1998), to analyse drought events in Yorkshire from 1881 to 1998. This 'classification' of drought, then allows the processes causing the drought events to be analysed and for different 'types' of drought events to be distinguished. Relating weather type occurrence to the occurrence of drought events in the recent historic past then allows us to extend the drought record back further, and to therefore calculate more accurate return period estimates for recent drought events such as the 1995-96 or the more recent 2003 drought. Table 1 Ranked severity of drought events occurring from 1881-1998 using the directional classification for ‘western’ water resource droughts (all years signify the start of the time-period of drought – i.e. for winter (W) = October, and for summer (S) = April).
Using this categorisation of drought, many drought events can be found at the end of the 19th Century. These have generally not been used in the calculation of return periods for more recent drought events. Anecdotal evidence backs up this work, for example: "The least rainfall [for any calendar year from 1868 to 1924 inclusive] was recorded in 1887 over much of the English Lake District and the Pennines ... the catchment areas for the supply of Halifax, Bradford and Keighley join on the moors overlooking Howarth ... while the water draining to the west of Howarth supplies the towns of Colne, Nelson or Burnley. The capacity of those schemes which were in operation during 1887 was more severely taxed than in those of forty subsequent years ... the level of Lake Derwentwater fell on July 9th to a lower level than ever previously recorded, being 8 inches below low water mark." (Brooks and Glasspoole, 1928; p135-136)
"The drought which prevailed over England and the neighbouring parts of the Continent during the spring and summer of 1893 was so exceptional, both as regards severity and duration, that little apology is needed for submitting the main facts of the case to the notice of the [Royal Meteorological] Society on this, the earliest available opportunity. The drought itself was followed, after a long showery interval in July, by another spell of fine weather in August and September, so that one was at first tempted to extend the limits of the present inquiry up to Michaelmas. On reflection, however, it seemed quite evident that a wide distinction must be drawn between a drought and a mere deficiency of rain; and as the former characteristic ended with the close of June it was decided to confine this investigation to the weather of the four months commencing with March." (Brodie, 1894)
This analysis shows that the severe drought events of the late 1980s and 1990s are not unique within the context of the historic record. Indeed, evidence suggests that the 1880s and 1890s may have had more severe drought events than during recent years.
Using this estimation system, the 18-month drought from April 1995 to September 1996 can be classed as a 40-year event. These return period estimates are much less severe than those generally quoted for the 1995-96 drought. However, since the clustering of dry and wet years is a prominent feature of climate in Europe, as can be seen during the 1880s and 1890s and recently during the 1980s and 1990s, return periods may not be the best way of classifying drought or flood events. References Brodie, F.J., 1894. The Great Drought of 1893. Q. J. Roy. Meteorol. Soc. 20, 1-30. Brooks, C.E.P., and Glasspoole, J., 1928. British Floods and Droughts. Ernest Benn, London, p135-136. Bryant, S.J., Arnell, N.W., and Law, F.M., 1992. The long-term context for the current hydrological drought. In: Proceedings of the IWEM Conference on the Management of Scarce Water Resources. Phillips, I.D., and McGregor, G.R., 1998. The utility of a drought index for assessing the drought hazard in Devon and Cornwall, South West England. Meteorol. Appl. 5, 359-372.
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