How is Moisture Deficit Calculated?

Question: Can you please explain how the historic average moisture deficit is calculated on http://www.farmwest.com/climate/et For how many years? How is the number calculated? For example, in 2010 to 2014 in the months May 1st and September 30, each year the moisture deficit is around 300 to 400, the difference between evapotranspiration and total precipitation between 40 to 300 but the historical average deficit is always around 60 to 80 mm. With other words, I don't see any correlation of the historic average with one of those two deficit calculations.

Answer: Moisture deficit is evapotranspiration minus effective precipitation. It’s explained in this link: http://www.farmwest.com/node/933 Historical average is calculated within the time period that you’ve selected (e.g., May to Sep) over all the years that a particular station has data (e.g., since 1970). It is just a quick comparison of what it is currently compared to historical average. ~ Stephanie Tam, P.Eng., Water Management Engineer, BC Ministry of Agriculture

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