The recent dry spell at Hazelrigg began during March 1995 and has continued throughout the winter of 1995/1996. See the 1995 and 1996 monthly rainfall plots, and the corresponding 1995 and 1996 daily rainfall plots for Hazelrigg Field Station. In the last twelve months, only May 1995 and February 1996 have received above average rainfall. November 1995 was the driest November on record, with August 1995, January 1996 and March 1996 being the second driest August, January and March respectively on record at Hazelrigg since October 1966. This twelve-month dry period has been studied in detail using daily rainfall depth measurements from Hazelrigg field station beginning in October 1966.
The driest period of any given length can be found within the hazelrigg daily rainfall data by searching for the lowest rainfall total over a period of that length. This exercise has been automated, so that the six driest (non-overlapping) droughts for a period of any given length are extracted and stored. This has been performed for a range of drought lengths from one week to 46 weeks (more than ten months). The exercise has been carried out using Hazelrigg daily rainfall data from the 1st October 1966 to the 1st March 1995.
Against these 30-year record droughts is compared the 1995/1996 drought. The driest periods of length one week to 46 weeks have been calculated from the Hazelrigg daily rainfall data between 1st March 1995 and 16th April 1996.
The results are presented below.
The 'red through to violet' lines represent the 'driest through to sixth driest' droughts of each length. i.e. during the driest twenty week period only 136.5 mm were measured, and the sixth driest twenty week period received 214.5 mm. These droughts were extracted from the October 1966 to March 1995 daily rainfall data.
The broad black line represents the driest spell of each given length during the 1995/1996 drought.
NOTE: The annual (52 weeks) average rainfall depth at Lancaster University is 1054.5 mm.
Thus the 1995/1996 drought does not contain any unusually dry periods of length less than 30 weeks. However, for all periods of length 36 weeks and longer, the 1995/1996 drought is the driest within our 30 year record.
The total rainfall depth recorded at Lancaster University between the 1st April 1995 and 31st March 1996 (366 days) was 596.6 mm. This represents only 57% of the average rainfall over the same twelve month period of 1054.5 mm.
An alternative method of presenting the data in the figure above is to plot the average rainfall depth per day for the drought period rather than the total rainfall depth (simply the total rainfall depth recorded divided by the number of days in the period). Again, the 'red through to violet' lines represent the 'driest through to sixth driest' droughts of each length, and the broad black line represents the 1995/1996 drought.
Martin Lord, 16th April 1996.