Colorado Climatology 7 
be no progressive change. These fluctuations are large and often 
in the same direction for several successive years. 
In the meteorological data for the last one hundred years, the 
record of some places extending still further back, there is nothing 
to support the idea of any permanent change in the climate having 
taken place, or about to take place, and the mean temperature shows 
no indication of any permanent change either warmer or colder. 
The small modifications claimed by cultivation, the planting of trees, 
and the erection of buildings, even of a large city, are too small to 
alter the mean temperature of any section of the country. 
Colorado being an arid state, the amount of precipitation is at 
all times a vital question. Liability to a marked deficiency in rain¬ 
fall in any region is a matter of grave concern to those engaged in 
agriculture and other interests. We often hear it stated that the 
rainfall is changing, that the settling up of the country and the 
planting of trees and building of reservoirs, forming lakes and wet 
places throughout the country, is causing an increase in the amount 
of our precipitation, but long series of observations taken at differ¬ 
ent places over the world, do not bear out that claim. 
That the forests that cover the sides of the mountains exert a 
retarding influence in the melting snow and the drainage of the 
water, thus prolonging the period in which the same may be made 
available in irrigation, is true. Complaints are heard that the snows 
do not lie as long in summer as they used to before so much of the 
forest cover was removed, but there is no reason to believe that the 
amount of snow falling on the high mountains or plains either for 
that matter, is different from that of ages ago. In general, the pre¬ 
cipitation seems to decrease with increase of altitude, as from the 
Missouri river west to near the base of the Rocky mountains, then 
there seems to be an increase in the amount to the tops of the higher 
mountains and on the crest of the range, especially on the windward 
side. There also seem to exist what have been termed islands of 
greater rainfall, where the precipitation, especially in winter, seems 
to be a great deal more than on the lower levels. In our case the 
line of lowest rainfall seems to be some 30 or 40 miles east of the 
v foothills, and to increase to the eastward as well as westward to the 
summit of the mountains. The existence of islands of greater rain¬ 
fall has long been noticed, several of which are found in this State. 
The rainfall in some of the more favored localities is at least twice 
as much as it is only a short distance away. These islands often 
occur at the sources of our larger streams, and. since it is from the 
slowly melting snow on the high mountains that a fairly constant 
stream of water is available for the irrigation of the valley lands, 
the snowfall is very important to the well being of the people of the 
State, particularly those engaged in agriculture. 
