Wednesday, October 9, 2013

Statistics Show Our County is Drying

This writer has asserted, relying on memory, that we used to have more summer rainfall in this area in the mid-eighties than we have now, and concluded that our tiered water rates are the reason, as we have been feeding the water cycle less as we save water to save money.  Grants Pass city staff have told us that we are using less every year, which has caused the city to raise rates to cover overhead, which is most of the cost of cleaning and delivering water.
An analysis of three decades of monthly summer rainfall totals for the 97526 zip code, from June 1983 to September 2012, shows that precipitation in July and August, our driest and hottest months, has fallen 0.09 inch per decade, from 0.41 inch to 0.32 inch to 0.23 inch. 
Average high rainfall for the two months, a measure of storm strength, has also fallen from 0.25 inch the first decade to 0.17 inch in the second, and 0.12 inch the third.   In the first decade, there were bigger storms on average in July and August, the middle of the irrigation season, than in June-August or July-September: 0.25 inch as opposed to 0.23 and 0.24 inches.  This reverses in the second decade: 0.17 inch in July-August as opposed to 0.22 inch with June or September included.  It proportionately drops more in the third decade, with 0.12 inch compared to 0.17 inch with June or September averaged in.
This fits well with the idea that irrigation feeds the water cycle and increases rainfall in the general area, particularly thunderstorms.  But some would blame this drop in rainfall on global warming caused by higher CO2 levels.  More heat doesn’t necessarily mean less rain, as monsoons and summer thunderstorms in particular are caused by heat sending moisture high in the air, but less rain almost certainly means more heat from lack of evaporative cooling.
Temperature records for the same three decades in July and August alone, show that the average mean mid-summer temperatures fell from the first decade to the second, from 71.4° Fahrenheit to 69.2°, a drop of 0.6 °; and it rose to 73.2°, a gain of 4°, in the third.  It looks like temperatures rose from lack of rain, but the lack was not sufficient to stop a general cooling trend in the second decade.
Since we started metering water and charging higher rates for higher use, both our water use and our mid-summer rainfall in Josephine County have fallen steadily.  Average temperatures during the same period have gone up and down over the decades, so the lack of rain is not temperature-driven, and is probably due to less irrigation in the City of Grants Pass and its surrounding areas, where many farms are no longer being irrigated because they are no longer being actively farmed.

Grants Pass Precipitation for June-September, 1983-2012

Summer Rainfall by the month, 

averaged by season and decade June-Aug July-Sept July-Aug
1983-1992 0.45 0.46 0.41
1993-2002 0.38 0.43 0.32
2003-2012 0.47 0.29 0.23

Monthly High Daily Rainfall

averaged by season and decade June-Aug July-Sept July-Aug
1983-1992 0.23 0.24 0.25
1993-2002 0.22 0.22 0.17
2003-2012 0.17 0.17 0.12

Average Temps in July, August          high         mean          low
1983-1992 102.1 71.4 43.3
1993-2002 101.5 69.2 41.3
2003-2012 102.5 73.2 48.8

Data from, 

analyzed and summarized by Rycke Brown

Gardening is easy, if you do it naturally.