The Laramie Basin - Mountains and Plains: The Ecology of Wyoming Landscapes - page 299

6.5

43

6.0

42

5.5

5.0

41

4.5

40

4.0

39

3.5

38

3.0

1890 1910 1930 1950 1970 1990 2010

Year

Fig. 17.18. Mean annual temperature for Laramie from 1895
to 2011. An increasing trend since about 1982 is suggested,
though the highs and lows are still within the range of historic
variability. the solid horizontal line is the average tempera-
ture for the period of record (40.3°F); the dashed lines are ±1

standard deviation. See also fig. 3.9. From the Wyoming Water
Resources Data System, prepared with PRiSM climate Group
data, oregon State University (http://www.prism.oregonstate
.edu/terms.phtml), courtesy of christopher nicholson.

has displaced many other meadow species. the hay,
though abundant, is generally considered to be inferior
to that existing previously. 31 Restoration to more desir-
able species will be difficult, should that be considered
a practical and worthwhile goal.
climate change is likely to influence basin eco-
systems even more than other human activities. chap-
ter 3 includes a discussion of climate change in general,
and the potential effects are considered throughout
this topic. For the Laramie Basin speciically, even
though mean annual temperatures during the past 10
years are still within the range of historical variabil-
ity, the record suggests a gradual warming trend since
the mid-1980s fig. 17.18; see also fig. 3.9). With regard
to precipitation, the trends are more difficult to ascer-
tain. However, unless annual precipitation increases
along with temperature, a warmer climate will lead to
more rapid drying and more frequent water stress dur-
ing the growing season.
though inconclusive, a closer look at precipitation
records is warranted. the most intuitive approach is to
look at records from a single weather station. However,
there is great variation from year to year. Also, precipi-
tation events tend to be patchy across the landscape;
downpours occur in one area but not nearby. For a better

estimate of trends, meteorologists now combine infor-
mation about typical storm patterns with data from a
network of weather stations to calculate annual precip-
itation for tracts of ground roughly 2.5 miles square.
When this is done for Laramie, a slight downward trend
is apparent (fig. 17.19). the mean annual precipitation
in the past 10 years is 9 percent less than in the previous
decade (11.1 inches instead of 12.2 inches).
Similarly, climatologists have integrated precipita-
tion data for large drainage basins. Specifically, scien-
tists with the national climate Data center divided
the state into ten basins and produced historical mean
annual precipitation for each year going back to 1895. 32
A cursory examination of the ten graphs suggests that
six of the basins have had no obvious trend upward or
downward during a period of 116 years. Four, includ-
ing the Upper Platte River Basin—of which the Lara-
mie Basin is a part—have had slight downward trends
(see fig. 17.19). Significantly, none of the basins had an
upward trend over the entire period of record. With
warming, climate scientists predict that there will
be less snowfall and more rainfall during the winter
months, and that snow cover will disappear earlier
in the spring. As described in chapter 3, this trend is
already happening. even if annual precipitation stays