1606 or 1607?

The main accounts the flood, written at the time, give the year as 1607. However, the plaques on church walls, and other sources say 1606. Also, sometimes the date is 20th January, and sometimes the 30th. Was there one flood or two - or even more? The answer lies in the change from the Julian calendar system (created by Julius Ceasar in Roman times), to the Gregorian one, which we use now.

There are two complications. The easier one to explain is that the start of the year has not always been on the first of January. We are so used to the idea that January is the first month of the year that it may seem odd to celebrate New Year’s Day in March. However, since Roman times, the new year started on the Ides (22nd) of March, not in January. The Christian church followed the Roman (Julian) system until about four hundred years ago (the tax year still starts in April). Catholic countries generally adopted the Pope's new system faster than others. So to the local folk of the area, January was nearing the end of the year 1606. To the more up-to-date people of London, on the new system it was reckoned as the first month of the year 1607.
Julian:16061607
 JulyAugSeptOctNovDec JanFebMarAprMayJune
Gregorian:16061607


There is another complication. Because a year is 365¼ days long, every fourth year is a leap year - it has an extra day on February 29th, so that the calendar stays in step with the sun and the seasons. Unfortunately, it is not precisely 365.25 days, and after 1500-plus years, festivals such as Christmas and Easter had drifted about ten days from their proper place. Pope Gregory decided to sort this out by declaring that in future three of every four century years would not be a leap year, so 1600 was, but 1700, 1800 and 1900 would not. Also, to make up for the ten-day drift, he decreed that 10 days would disappear, so that October 4th was followed by October 15th. The new calendar is called the Gregorian calendar, after Pope Gregory. It took immediate effect in Italy, but was not adopted in England until 1752. (At the same time, new year’s day was officially moved from March to January). Strangely, in Scotland it was adopted in 1600, where James VI was the king, but in England the old calendar continued to be used, even though James became James I of England in 1603. Roman Catholic countries were quicker to take up the Pope’s new system than Protestant ones. So the date was the 20th January on the system used at the time, but to us it would be the 30th.

Julian Gregorian
SunMonTueWedThurFriSat  SunMonTueWedThurFriSat
          123456
    123  78910111213
45678910  14151617181920
11121314151617  21222324252627
18192021222324  28293031   
25262728293031         
The same month, in the old and new calendars. Date of flood is shown in blue.

Confirmation of this explanation is given by the fact that several sources note that the flood happened on a Tuesday.