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S.E. Rainfall? 2007 was normal – thanks to December

INTERESTING TREND NOTED

At the BEE rain gauge in Westmoreland, the year 2007 ended with a calendar-year total of 42.29 inches of rain. That's a bit more than officially recorded for Portland at the airport; the airport is not a typical location for rainfall in the Rose City, being right at the Columbia River, and the totals downtown and in other parts of the city frequently vary.

In this case, the major part of the disparity seems to date from the rainfall of December 2 and 3.

The second and third days of December combined for the largest two-day rain total we have recorded - by far - since we installed our own rain gauge in early 1997: 1.56 inches on December 2nd was followed by 3.43 inches on the 3rd (which, itself, was easily the heaviest single day or rain we've recorded during the same period).

Together, that added up to 4.99 inches of rain in two days - astonishing, but far less than the 11 inches recorded during the same period at Vernonia, an hour northwest of Portland, which caused an appalling flood disaster in that community, from which residents are still recovering.

That means that 11.8% of our entire 2007 rainfall here in Inner Southeast Portland fell in just two days! And, adding in the rain that fell in the rest of that month, the 10.70-inch total for December more than doubled the next highest month in 2007 (November), and represented 25.3% of all the rainfall of the year.

Over the years in which we've been recording rainfall, the dry years have lined up at about 30 inches per year, and the normal ones in the low 40-inch range. The two wettest years in this period were 1998 and 2006. Here are the Inner Southeast annual totals since 1998:

1998 -- 47.63'

1999 -- 41.75'

2000 -- 30.01'

2001 -- 29.67'

2002 -- 30.04'

2003 -- 42.20'

2004 -- 32.11'

2005 -- 40.99'

2006 -- 46.38'

2007 -- 42.29'

No pattern, there, to suggest we're heading into another drought year - but of course, it could happen again anytime, as it last did in 2004.

What we have noticed, though, is that in recent years we've had more days of rainfall in excess of one inch than we used to get, so there may be a new trend developing in which we regularly experience dry years, but are sometimes rescued by occasional days of heavy rain.

There were three such days in 1998; two in 1999; none in 2000; one in 2001; three in 2002; eight in 2003; three in 2004; seven in 2005; seven in 2006; and five in 2007.

Since 2000, the number of more-than-an-inch rainy days per year has correlated strongly with each total annual rainfall total in Inner Southeast. Such a steady eight-year trend does seem significant.

So be sure to take along an umbrella!