When we heard that our allotment site was to have a metered water supply connected, I had to investigate what the likely cost of water would be and how this would affect annual rents paid by plotholders.
The annual rainfall data has enabled me to determine the average rainfall between 1988 and 2008 for this area is 753mm, although it has varied between 555mm and 997mm. Statistically, the rainfall within standard deviation of normal gives a most likely range of values 624mm to 882mm per year.
It seems likely that there will be a correlation between rainfall and our water usage, since we will need to use more water in dry seasons than in wet ones.
Also our usage will vary seasonally, since we would expect to have more crops needing watering, say, from May to October than in February!
The aim of this project, therefore, is to record our monthly water usage, then correlate this with monthly rainfall, to try to identify how our usage relates to months of the year and to annual rainfall for that year.
This chart shows our actual water usage from May 2010 to May 2012. The dark blue dotted line shows the average usage by month, and totals around 66 cubic metres for our 15 plots, each around 200 sq metres in area.
Annual Rainfall here was 741mm during 2010 (just below normal), while only 535mm fell in 2011 (the driest on record here).
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