Climate change in Montana

Records from climatological stations having approximately 100 years of record and snow courses with approximately 75 years of record were analyzed to determine how temperatures, precipitation, and snowpack have changed over the past 100 years. There were 24 snow courses in Montana with about 70 years of record that were analyzed. Trend analysis indicates an average of about 15 percent decrease in April 1 snow water equivalent. However, three snow courses in Glacier National Park that have been measured for over 80 years show an upward trend of about 4 percent over the 70 year period and a 13 percent increase for the 83 year record. Part of the explanation of decreasing snow packs might be related to increasing tree canopy cover. Those that are located in more open areas show less of a decrease than those located in more timbered stands. Trend analysis for these 17 stations showed the average annual temperature has increased about 1.40 C over the past 100 years. None of the stations show any acceleration of temperature increases in the more recent years suggesting that increases may be more natural than man caused. The trend of annual precipitation at 20 stations (four in Northwest Wyoming) showed an increase of about two percent over the last 100 years. However, some stations showed increases while others showed decreases. Again, there does not appear to be different rates of change in recent years compared to earlier years.