Climate

Project Lead: Carl Waite Staff Writer: Carl Waite

The VMC Meteorological Monitoring Network

The VMC takes meteorological measurements at 0.5, 7.5, 17, and 24 meters above the forest floor at 1300' at the canopy research tower at the Proctor Maple Research Center in Underhill, VT.
The VMC takes meteorological measurements at 0.5, 7.5, 17, and 24 meters above the forest floor at 1300' at the canopy research tower at the Proctor Maple Research Center in Underhill, VT.

The Vermont Monitoring Cooperative (VMC) has been monitoring weather conditions in Vermont for over 20 years. VMC currently operates seven meteorological stations across a range of elevations and cover types, maintaining real-time data streams and archiving of long-term data. Weather and climate are related but very different phenomena, weather being the condition of the atmosphere (precipitation, temperature, cloud cover or humidity for example) over the short term, while climate refers to longer-term averages and expected seasonal patterns. Without long-term weather records it would be impossible to tease out yearly fluctuations from bigger climate trends, which makes this information critical to scientists and planners of all kinds. One of the complexities of climate analyses is the high degree of spatial variability. Multiple VMC stations allow for the assessment of climate trends and patterns across a broader region of VT than any single station could provide.

The Data

Table 7. Monthly average deviations from long-term normal for mean, min and maximum temperatures at Mt. Mansfield West. Red indicates warmer than normal months and blue indicates colder than normal months. Note that data for March and April are absent due to station maintenance.
Monthly average deviations from long-term normal for mean, min and maximum temperatures at Mt. Mansfield West. Red indicates warmer than normal months and blue indicates colder than normal months. Note that data for March and April are absent due to station maintenance.

Meteorological observations are taken at seven VMC sites from Lake Champlain to Mt. Mansfield. Although the stations are not identical, variables collected include wind speed and direction, air temperature, relative humidity, barometric pressure, solar irradiance, precipitation, and at Lake Champlain stations, water temperature. These variables are logged as 15 minute data at most stations. The longest record comes from the Mt. Mansfield summit station operated by the WCAX transmitter crew and supervised by the National Weather Service, going back to 1954, predating the VMC! Other stations operated by the VMC began operation in the early to mid- 1990s, with the newest station added in 2010.

 

2014 in Summary

Daily maximum 2014 wind speeds compared to the long-term averages highlights the increased frequency of wind events in fall and winter.
Figure 19. Daily maximum 2014 wind speeds compared to the long-term averages highlights the increased frequency of wind events in fall and winter.

While the Mt. Mansfield West meteorological station was not operational during March and April, overall the remaining months in 2014 were only slightly above the average for temperature, compared to the long-term trends. This was primarily driven by warmer than normal temperatures in May, June, October and December, coupled with cooler than normal temperatures in February, August and November (Table 7). January temperatures were unusually dynamic with the largest daily deviations in both above and below average temperatures (Figure 19).

Perhaps more interesting was the increased variability in maximum wind speed over the winter and fall months of 2014. While the long-term average of maximum wind speeds is muted because not all high wind events occur on the same day each year, the increased variability and frequency of high wind events in 2014 is apparent (Figure 20).

While June was a relatively wet month in 2014, it was followed by consecutive months of below average precipitation (Table 8). However, none of these deviations are significant enough for widespread forest health impacts.

A two-week moving window smooth of daily temperature data for 2014 in comparison to the long-term mean.
Figure 20. A two-week moving window smooth of daily temperature data for 2014 in comparison to the long-term mean.

Long-term Trends

Table 8. Precipitation totals recorded at the Mt. Mansfield West met station for 2013 in comparison with the 1997-2014 long-term mean (normal).
Precipitation totals recorded at the Mt. Mansfield West met station for 2013 in comparison with the 1997-2014 long-term mean (normal).
Long-term trends in mean monthly climate metrics show a steady but insignificant increase in mean, min and maximum temperatures on Mt. Mansfield.
Figure 21. Long-term trends in mean monthly climate metrics show a steady but insignificant increase in mean, min and maximum temperatures on Mt. Mansfield.

Based on the daily data between 1997 and 2014, we have seen a consistent (although not significant) rise in mean, max and min daily temperatures (Figure 21). Despite the caveat that short term datasets may not reflect long term trends, this rise is congruent with regional and national trends (IPCC, 2014; EPA 2014). The most extreme change is in daily minimum temperatures, up 3 degrees on average over this data record. Most of this increase occurs in the spring and summer on Mansfield, with July reporting the strongest (and only significant monthly) long-term increase in mean temperature (p = 0.03). The addition of 2014 data did not alter these trends, although temperatures were closer to the long term average than in 2013.

Implications

In 2012 the USDA released a new map of plant-hardiness zones to reflect more accurately the growing conditions on the ground. The USDA release was accompanied with a caveat that not all the changes in the map were due to climate change; new methods accounted for some of the difference.
Figure 22. In 2012 the USDA released a new map of plant-hardiness zones to reflect more accurately the growing conditions on the ground. The USDA release was accompanied with a caveat that not all the changes in the map were due to climate change; new methods accounted for some of the difference.

Because climate variability is high, both temporally and spatially, conditions witnessed in 2014 and the longer term trend are not necessarily indicative of a new climate regime. However, the widespread warming witnessed across the VMC meteorological network are in agreement with regional and national assessments indicating that temperatures have increased over the past several decades (Betts, 2011; EPA, 2014; IPCC, 2014). Further, the dramatic variability in winter temperatures witnessed in 2014 could represent an additional stress for species adapted to cold weather dormancy. The variable spring temperatures may eventually affect phenological adaptations, potentially increasing vulnerability to insects, diseases and spring frost injury, and may have an adverse impact on major agricultural crops in Vermont such as apples and sugar maples (Figure 22; Grubinger, 2011; Rustad, 2012).

If this trend continues, for species at either the far northern or southernmost portion of their range, climate instability could make survival challenging. Even when climate conditions remain within a species' natural tolerance, differences in competitive advantages among species due to phenological changes or erratic and unseasonable temperature fluctuations could alter ecosystem structure and function (Pucko, 2014).

Sunrise on Lake Champlain

While warming trends continue it is perhaps the increase in variability that may stress forested ecosystems the most.

References

Additional Resources

VMC Project Database Link