Long-term change in precipitation and its variability and consequences in a montane environment

David W. Inouye, billy barr, Rebecca M. Prather

The climate at high altitudes is changing more rapidly than in many other areas, with a variety of consequences for montane flora and fauna. We analyze long-term weather records from Crested Butte (2703m, 1910- 2024) and Gothic (2921m, 1974 – 2024), Colorado, USA, in the West Elk Mountains. In Crested Butte, mean monthly precipitation in the growing season (May – September) can vary by over 2-fold and peak weekly precipitation occurs in late July with the beginning of the summer monsoon. Mean rainfall per storm has been declining significantly since 1910. Many of the variables exhibit a curvilinear relationship with year, with high points at the beginning and end of the instrumental record period. Some of these curves have significant breakpoints, ranging from 1973 (for mean rain per rainy day) to 1985 (number of rainy days/summer, and number of consecutive days without rain). Some measurements are showing increasing variability over time (e.g., coefficient of variation of rainfall amount per rainy day). In Gothic, which typically gets more precipitation than Crested Butte, June is also the driest month, and December the wettest. Warming temperatures are leading to rainfall vs. snow earlier and later in the year, and mean precipitation per rainy day is declining significantly. Although it has snowed every month of the year in Gothic, total winter snowfall has been declining significantly since a peak in 1995. Mean snowfall per snowy day and per storm are both declining. Mean snow density is increasing, and is correlated with rising temperatures. Dates of last snow cover are trending earlier. There is evidence of a 12-14yr cycle of precipitation. Variability of some but not all of the measures we examined is changing. A reconstruction of historic snowfall back to the 1930s (using stream gage data) suggests that it peaked in the 1970s and is now declining. These climate changes have the potential to impact many aspects of the ecology of montane plants and animals, and we give some examples.