THE CLIMATE ADJUSTMENT PROCESS - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 161

(a) 8.0

17

7.5

16

7.0

15

6.5

14

6.0

13

5.5

12

5. 1880

1900 1920 1940 1960 1980 2000 2020

Year

Maximum: 7.4 m/s (16.6 mph), 1923 10-Year mean 30-Year mean

Minimum:
Record mean:

5.6 m/s (12.6 mph), 2008 and 2009
6.7 m/s (14.9 mph)

(b)

Figure 12-4. (a) Annual average wind speeds and their 10-year and 30-year rolling averages
recorded at the Blue Hill Observatory outside Boston from 1885 - 2010. (b) Photographs of the
Blue Hill Observatory taken in 1886 (left) and present day (right). Source: Blue Hill Observatory
(www.bluehill.org).

present, the magnitude of the potential bias increases with the length of the reference
period. The problem is compounded if the trend is caused by a real and persistent
change in climate; in other words, if the assumption of climate stability is violated.
Then, the bias resulting from the ordinary MCP process may be even larger if the
trend continues in the future.
Thus, MCP, while still a mainstay of wind resource assessment, cannot remove
all uncertainty in the long-term wind climate and must be applied with considerable
caution. The following practical guidelines are offered.