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 weathersource.com, | |||
analyzed and summarized by Rycke Brown | |||
Gardening
is easy, if you do it naturally.
|
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