The Laramie Basin - Mountains and Plains: The Ecology of Wyoming Landscapes - page 300

Laramie

Annual precipitation (Oct-Sept)
5 year average precipitation
1895-2012 average precipitation

45

17

40

15

35

13

30

11

25

9

20

7

19

Upper Platte River Basin

Annual precipitation (Oct-Sept)
5 year average precipitation
1895-2012 average precipitation

45

17

40

15

35

13

30

11

25

9

20

7

1900 1910 1920 1930 1940 1950 1960

Year (October - September)

1970 1980 1990 2000 2010

Fig. 17.19. the top graph shows annual precipitation from
1895 to 2012 for a 2.5-square-mile tract of land in the vicinity
of Laramie, based on a network of actual data and knowledge
about snow and rainfall events in the area. the bottom
graph shows the same for the Upper Platte River Basin, which
includes the Saratoga Valley and Laramie Basin. A down-
ward trend is suggested. the dashed line in both graphs is ±1
standard deviation from the average for the period of record
(11.8 inches). the red line is a 5-year running average. Average
annual precipitation for the period of record is 12.1 inches.

the average annual precipitation in the early 1900s, when
irrigation systems and Wyoming water law were developed,
was 3-4 inches higher than at present. the top graph is from
the Wyoming Water Resources Data System, prepared with
the PRiSM climate Group data, oregon State University,
http://prism.oregonstate.edu. the bottom graph is from the
Wyoming Water Resources Data System, prepared in col-
laboration with the national climatic Data center (http://
www.ncdc.noaa.gov/oa/ncdc.html), courtesy of christopher
nicholson.