Snowy Range Mountains, Wyoming |
| Snowy Range Mountains, Wyoming |
There is growing statistical evidence that solar activity and the occurrence of El Niño are highly correlated (see Landscheidt, 2001). Similar findings resulted when the relationship between various atmospheric indices and the Palmer Severe Drought Index for the 10 climate divisions in Wyoming were examined, as discussed below.
The NCEP has examined the relationship of ENSO and I have summarized their findings for Wyoming in a series of 3-monthly average precipitation charts for the state. The figure shows generally drier autumns and winters and wetter springs. When looking at La Niña, generally the reverse scenario prevails even when recent precipitation trends are factored in.
The General Circulation Model (GCM) predicts that with an increase in average temperatures due to an increase in CO2, an increase in total precipitation is expected. However, it is interesting to note that from August to January this is not being observed over Wyoming. Thus in order to determine if atmospheric indices can or need to be adjusted to climate trends to determine potential droughts, a straightforward statistical methodology was employed.
Looking at the relationship of total monthly precipitation across the 10 climate divisions in Wyoming, it was found that from 1958-99, only the North Pacific Index showed the highest correlation (greater than at a 95 percent significance level); mostly positive. Even on a month to month bases, high correlations were obtained. It should be noted with some caution that reporting station density varies widely between climate divisions and precipitation is a more variable parameter than temperature. The other indices studied were:
The 10.7 cm solar, sunspot number, NINO 3.4 (mid Pacific), Southern Oscillation, Quasi-Biennial, Western Pacific, Pacific Decadal, Pacific North Atlantic, North Atlantic, and Arctic Oscillations.
Comparing the Palmer Severe Drought Index by climate division with the above indices revealed the best correlation for 10.7 cm, Sunspot Number and NINO 3.4. The best months for the 10.7 cm index are January, June, September, and December. For NINO 3.4, the best months are April, June, August, and December. However, unlike the Total Precipitation-Indices correlations, the 10.7 cm and NINO 3.4 shows a mix of significant positive AND negative correlations. See a comparison of Sunspot vs Average Palmer Severe Drought Index across Wyoming's 10 Climate Divisions
One final comment. When looking at the top-5 severest monthly Palmer Drought Index values (most negative) by climate division from 1958-2001, in all but one division (#2), did the occurrence fall within a year of solar maximum.
The importance of water in the western states cannot be overstated. Snow pack from winter's mountain snows help fill reservoirs. This water is then used to irrigate farmlands. Summer rains are equally important to ranchers. Heavy thunderstorms and seasonal monsoon rains help prairie grasslands grow by fighting the drying effects from the intense sun and associated heat.
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Last Updated 18 October, 2001
