Drought In Western North America Worst For 800 Years?
By Paul Homewood
I have just come across a paper that came out last month, titled “Chronic 2000-04 Drought, Worst in 800 Years, May Be the ‘New Normal’. The authors claim :-
- The chronic drought that hit western North America from 2000 to 2004 left dying forests and depleted river basins in its wake and was the strongest in 800 years, scientists have concluded, but they say those conditions will become the "new normal" for most of the coming century.
- Climate models and precipitation projections indicate this period will actually be closer to the "wet end" of a drier hydroclimate during the last half of the 21st century.
- The situation will continue to worsen, and that 80 of the 95 years from 2006 to 2100 will have precipitation levels as low as, or lower than, this "turn of the century" drought from 2000-04.
These are very extreme claims, but what do the facts tell us?
Let’s start by looking at the precipitation figures for the West Region (California/Nevada).
Climate At A Glance
Annual 1912 – 2011 Average = 16.50 Inches
Annual 1912 – 2011 Trend = -0.02 Inches / Decade
Over the last 100 years the trend is virtually non existent, a meaningless 0.02 inch/decade decline, and, as Figure 2 shows, the average precipitation in the last decade is pretty much in line with most other decades in the 20thC, except for the period 1901-1920.
So clearly there is nothing unusual happening at the moment, but let’s take a look at the specific period that the paper spoke about , 2000-2004.
Rainfall for 2000-2004 amounted to an average of 15.32 inches/year. (In fact the driest point was 1999-2003, which came in at 14.56 inches). This point can clearly be seen in Figure 3, along with several other drier interludes, for instance, 1928-32 and 1987-91 when rainfall averaged 13.07 inches and 13.15 inches respectively. So there is certainly nothing “unprecedented” about the latest drought.
As noted above, the authors claim :-
The situation will continue to worsen, and that 80 of the 95 years from 2006 to 2100 will have precipitation levels as low as, or lower than, this "turn of the century" drought from 2000-04.
So do the precipitation numbers since 2004 bear this out? Three years have been wetter and four drier, whilst the average is 15.87 inches, close to the long term average of 16.5 inches. The one thing that is really missing is the odd year of really heavy rain, such as 1983 which had 31.47 inches.( No doubt if we had another year like that, it would be viewed as yet another instance of “extreme weather caused by global warming”!)
To be fair, the authors do mention areas such as New Mexico and Colorado, which are included in the Southwest region, rather than the West. So is there any evidence of a worsening drought there, or for that matter in the Northwest? Well, actually, no. On the contrary rainfall is steady or increasing.
Climate At A Glance
Annual 1912 – 2011 Average = 13.53 Inches
Annual 1912 – 2011 Trend = 0.00 Inches / Decade
Climate At A Glance
Annual 1912 – 2011 Average = 26.90 Inches
Annual 1912 – 2011 Trend = 0.19 Inches / Decade
Finally, let us have a look at the official Palmer Drought Severity Indexes, which factors in temperatures as well as rainfall, as a proxy for evapotranspiration.
The 2000-2004 drought is clearly visible, (minus numbers denote drought), but the severity has been exceeded several times before, while drought lasted for longer during the 1920’s and 30’s. This is well shown up in Figure 6, which gives a five year running average.
So yet again we see a climate study that makes alarmist claims, which simply are not borne out by the facts. How do these ridiculous papers ever see the light of day? Perhaps the authors give us a clue when they say :-
“The effects are driven by human-caused increases in temperature”
How much grant money would have been thrown at them, if they had found nothing alarming to report?