Climate change in Western Montana: local needles in the global haystack
Abstract
Global and national climate-change statistics do not inform individuals and communities about specific challenges they face at home. Often local climate-scale data is available but not in a form that elucidates change through time. To investigate site-specific climate trends, the Western Regional Climate Data Center provides free on-line monthly temperature and precipitation data. We investigated 20 sites in Montana (10 SW and 10 NW), selected for spatial distribution and length and continuity of records. Sixteen had more than 100 yrs of record (mean 105, range 75 to 118). All had some missing years, and we eliminated others from analysis, based arbitrarily on missing five or more days/month or one month/year. Mean annual temperature, total annual precipitation, and seasonal temperature and precipitation were graphed for the 20 sites over the period of record. The slopes of regression lines were used to describe change per century. Standard deviations and r2 values provided numerical descriptions of annual variability and the predictive values of the slopes. In NW Montana, average temperature for the 10 sites was 44.1°F/6.7°C (range 39.8 to 46.1°F/4.3 to 7.8°C) and average annual precipitation was 16.3 in/41.4 cm (range 12.6 to 20.9 in/32.0 to 53.1 cm). Changes averaged for all 10 sites were about +2°F/3.6°C and about +0.2 in/0.5 cm/100 yrs. Eight of the 10 sites experienced temperature increases, ranging from about 0.5 to about 4.5°F/0.9 to 8.1°C, with two sites unchanged. Four sites had precipitation losses (up to almost 3.5 in/8.9 cm) and four had precipitation gains (up to about 3.5 in/8.9 cm), with two unchanged. In one community, a 100-yr temperature rise of more than 4°F/7°C accompanied a loss of more than 3 in/7.6 cm of precipitation! In SW Montana, the 10-site average for the period of record was 42.41°F/5.78°C (range 36.37 to 46.86°F/2.43 to 8.26°C) and 15.53 in/39.45 cm (range 11.86 to 18.57 in/30.12 to 47.17 cm), with changes averaging about +1.5°F/2.7°C and +1.2 in/3.0 cm/100 yrs. Nine of the 10 sites experienced temperature increases, ranging from about 0.3 to 4°F/ 0.5 to 7°C, with one site seeing a temperature decrease over the whole record, which reversed to an increase over the past 50 years. Three sites lost precipitation (up to over 7 in/18 cm) and six sites gained (up to about 7.5 in/19 cm), with one unchanged. There may be a trend toward increasing precipitation in already wetter areas and decreasing precipitation in already drier areas. Seasonal changes in precipitation and temperature trends were often well defined at particular sites, but were highly variable within the region. There were no conclusive correlations between temperature and precipitation trends. Plotting just the past 50 years indicate many steepening slopes, especially for temperature change. Our results capture some of the variability of local climate change experienced within a relatively small geographic area and emphasize that different communities will require specific local data to customize their response to climate change appropriately. This analysis is also compelling graphic illustration of why long-term trends do not closely predict conditions in specific years and that change is happening in everyone's back yard.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMGC11E..06R
- Keywords:
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- 1600 GLOBAL CHANGE;
- 1616 GLOBAL CHANGE / Climate variability;
- 1637 GLOBAL CHANGE / Regional climate change