Regional Climate Change Detection

What is a climate? How does one define a climate in terms of

measured variables? After defining it, how does one measure

actual change in a statically defensible manner. Most of local climate change is simply assumed to be occurring because global change is occurring

Anecdotal Evidence Often Used

More frequent extreme-heat days A longer growing season An increase in heavy rainfall events Earlier breakup of winter ice on lakes and

rivers Earlier spring snowmelt resulting in earlier

high spring river flows Less precipitation falling as snow and more

as rain Reduced snowpack and increased snow

density

Use an Indexing Method

Climate is largely a monthly/seasonal phenomena – not annual

Take a weather site and say it has 100 years of data for all 12 months and pick a variable like max temperature. Use all 100 months of January to compose the average max.

For each month then in each year, compute the Z-score for that month/year

Z-Score = (x - µ) /

Now Generate a Composite Index

NEIyr = (Zmxyr + Zmnyr + Zrnyr + Zswyr) / 4 Can then weight each of the 4Z’s The result is a wave form some given site for

one of the Z parameters

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106-0.8-0.6-0.4-0.2

00.20.40.60.8

Vermont SiteMinTemp

'432769'

IND

EX

This form of Indexing

Is identical to the approach used for the Stock Market; what matters is the behavior over time of the relative amplitude of the Index.

Weighting the Indicators:

WMAX 0.25 0.25 0.25 0.25 (equal) WGD1 0.4 0.4 0.1 0.1 (emphasize temp) WGD2 0.2 0.1 0.6 0.7 (emphasize rain) Just try all kinds of combinations: Dick with

the data! There is no “right” way to do this just a

consistent way.

Sum up all the good stations1 4 7

10

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

58

61

64

67

70

73

76

79

82

85

88

91

94

97

10

0

10

3

10

6

10

9

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Annual Northeast Climate Index Comparisons for All Variables Combined

NEI

Linear (NEI)

IND

EX

Warm and Wet

Cool and Dry

Deconvolve the parameters

Define the Index Seasonally:

Each Arrow Is separated by Exactly 40 years

Experiment with Weights:

The Pacific Northwest Index

Predict the Future

Cool Wet To Return in 2000

The RPNI (Pacific Northwest)

1900190519101915192019251930193519401945195019551960196519701975198019851990199520002005

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

RPNI 20 Sites

Annual RPNI