West Coast Atmospheric Precipitation Trends

There is thence much beak virtually heavy atmospheric precipitation together with drought along the United States of America West Coast these days, every bit good every bit claims virtually long-term trends, that I idea it would survive useful to expect at the actual data.

In the figures below, I demo the wintertime atmospheric precipitation (November through March) for the states of Washington, Oregon, together with California for 1918 to 2018 using the NOAA Climate Division information available from the NOAA ESRL website.  The West Coast has a Mediterranean climate,  which agency the twelvemonth is divided into moisture together with dry out seasons, together with Nov through March includes the overwhelming bulk of atmospheric precipitation everywhere along the coast.

First, California.   Quite a chip of upwards together with down, amongst 1977 existence the lowest (about vii inches) together with 1982 the highest (about 33 inches).  Little overall trend.   With an average of alone xx inches during the wintertime season, lots of variability, a huge population, together with an enormous agricultural institution based on irrigation, yous tin run into why California has invested inwards a  massive multi-year reservoir capacity.

Oregon every bit good shows trivial long-term tendency inwards precipitation, amongst 1977 (a twelvemonth of a huge persistent ridge) existence the driest of the terminal century.  Mean atmospheric precipitation is higher than California (about 27 inches compared to California's xx inches), the population inwards much less, together with in that place is far less irrigated agriculture.  Thus, they tin larn away amongst less reservoir capacity than California.

And thence in that place is Washington State.   Winter average atmospheric precipitation is virtually 42 inches together with the lowest it has fallen to is virtually 22 inches, far inwards a higher house the minima of California together with Oregon.  Plenty of variability twelvemonth to year.  There appears to survive a slight upward tendency inwards wintertime atmospheric precipitation over the past times century.

 So what should yous conclude from all this?   

(1)  With all the beak of droughts together with floods inwards the media, in that place is actually real trivial long-term tendency inwards wintertime atmospheric precipitation over the United States of America West Coast.

(2)  The West Coast has a lot of year-to-year variability, thence having dry out together with moisture years is non unusual.

Why thence much wintertime variability inwards atmospheric precipitation along the West Coast?

Several reasons.  The West Coast is greatly influenced past times atmospheric rivers, which select periods of real heavy precipitation.  These features are intermittent together with merely getting 1 or 2 to a greater extent than or less tin brand a huge departure inwards seasonal precipitation.

Another argue is El Nino together with La Nina.  The oscillation betwixt them, a style of natural variability, tin hit moisture together with dry out years inwards diverse portions of the coast. 

The bottom line:  West Coast atmospheric precipitation is characterized past times moisture together with dry out years, atmospheric precipitation increases northward, together with trivial overall tendency has occurred over the past times century.  Not sexy, but the truth, nevertheless.