WEATHER AND CLIMATE EXTREMES
OVER CALIFORNIA TOPOGRAPHY:
PRECIPITATION AND TEMPERATURE
IN OBSERVATIONS AND REGIONAL MODELING
ALEXANDER GERSHUNOV, HIDEKI KANAMARU, NOAH KNOWLES,
MASAO KANAMITSU, DAN CAYAN
Scripps Institution of Oceanography & USGS
WEATHER AND CLIMATE EXTREMES
OVER CALIFORNIA AND THE WEST:
RECENT CHANGES IN HEAT WAVE ACTIVITY
Summer 2006 and the observational record
Tmax
HWI
2006
50
5
10
15
California Heat Waves:
2006 and the climate record
1980
1990
2000
30
1970
20
1960
10
1950
0
0
40
Tmin
HWI
1950
1960
1970
1980
1990
2000
OUTLINE
• Heat Wave Index: intensity, duration
AND spatial extent, all related to impacts
• Trends
• Spatial patterns
• Regional or global?
• Seasonal cycle of trends
Observational Data
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• Western daily Tmax, Tmin and Precipitation @
200 stations: 1901 (1948) – 2004
• California and Nevada daily Precipitation, Tmax
& Tmin @ 286 stations: 1948 – 2005
• California Tmax&Tmin @ 69 stations: May –
July 2006 (thanks to Laura Edwards, DRI)
Working definition of extreme heat
Sacramento Tmax
40
50
8 10 12 14
MJJ
2006
6
14 C
DD*
for
July
2
80
0
4
CDD*
Mean Tmax
40
60
days from May 1 to July 31
30
Bars: 1948-2005 Tmax histogram, Circles: 2006
Tmax histogram, and Vertical line: all-yr 99th %-ile
40
20
20
20
MJJ Tmax
30
Degrees C
0
0.04
10
threshold (t*)
2006 Tmax
May
June
0.02
probability
Time series view
0.0
• Locally extreme temperature
exceeding a high percentile
threshold t* (e.g. 99%-ile)
0.06
MJJ Tmax
1950
1960
1970
1980
1990
2000
Working definition of extreme heat
threshold (t*)
Sacramento
ox
ox
ox
ox
20
17
15
13
12
10
9
9
8
8
7
7
5
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x
o
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ox
ox
ox
Tmax
ox
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ox
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ox
oxx
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ox
ox
ox
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x
x o
xo
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xo
x
oxx
o
ox
ox
ox ox
ox
ox
o
x
ox
ox
0
2
4
6
CDD*
8 10 12 14
• Local heat wave magnitude
and duration reflected in
summing exceedances over
threshold: ∑(ti – t*), for all
days (i) in a season such that
(ti > t*).
99th %-ile of climatological
exceedance sums
1950
1960
1970
1980
1990
2000
Exceedances over threshold are summed up
similar to CDD, but threshold is stationspecific
Exceedance sums are
computed for each year at
each station on the network
that is weighted towards
most populated areas
Working definition of extreme heat
99th %-ile of climatological
exceedance sums
• Spatial extent of locally
extreme conditions
ox
ox
ox
California Heat Wave Index
Tmax
2006
HWI
0
5
10
15
2006 daytime heat was
noteworthy, but not
unprecedented
1950
1960
1970
1980
1990
2000
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20
17
15
13
12
10
9
9
8
8
7
7
5
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o
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ox
ox
ox
Tmax
ox
ox
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For each MJJ on record,
percentage of stations where
exceedance sums (CDD*)
exceed their local 99th %-ile
becomes the regional
heat wave index (HWI)
40
Tmin
HWI
Does this trend reflect
land-use changes or what?
What is the spatial
signature of this trend?
10
20
30
2006
0
Percentage of stations
50
Now, if we do the same thing for Tmin,
we get the
California Nighttime Heat Wave Index
1950
1960
1970
1980
1990
2000
HOT DAYS: MJJ 1948 – 2005
Tmax extremes, inland and coastal areas
400
300
200
100
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o
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o
o
1950
o
o
o
o o
o
o
o
1960
o
o
o
o
o
o
o
o
o
o
1980
o
o
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o
o
o
o
o
o
o
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1970
o
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o
o
o
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0
o
x
o
o
o
x
o
o
oxx
o
x
Tmax
o
x
x
o
1990
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
2000
Leading PC of local MJJ heat wave magnitude
ox xx
200
150
o
o
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o
100
o
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o
50
0
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o
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o
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-100
-50
o
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o
o
o
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ox
o
o
1950
1960
1970
1980
1990
o
o
o
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o ox
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0.8
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0.7
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0.6
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0.4
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0.2
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-0.2
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-0.3
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x
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o x xo
-0.5
x
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oxoxox ox x
-0.6
-0.7
-0.8
x
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o
x
ox
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ox o
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xo
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ox xxox ox oxo
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ox
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oxx
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ox
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ox
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ox
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ox xox ox ox
x
xx
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ox
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x
x
x x
x
x
x x x
ox
ox xox
o
2000
PC2 of local MJJ heat wave magnitude
x
x
x
o
x
x
ox
x
x
ox
x
x
xx
x
ox x
ox
x
HOT NIGHTS: MJJ 1948 – 2005
Tmin extremes, inland and coastal areas
300
Tmin shows a broad
pattern of warming
x
o
x
x
200
o
o
o
o
o
o
oo
o
o o oo
o
o
o
o
o
o
o
o
o
o
o
o
o
o
100
o
o
o oo
o o
oo
o
oo
o oo
o
o
o
o
oo
oo
oo
o
0
oo
1950
1960
1970
1980
1990
o
o
o
o
o
o
o
o
o
o
o
o
o
o
ox
x
ox
ox x o
ox ox
oxx ox oxox
o o ox
x
o
x
x
ox ox
xo
xo
ox
ox
oxox ox ox
ox
x
o
ox ox
x
x o
x
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ox
x
o
o
ox xx
ox
oxox
x
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x
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x
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ox
ox
ox ox
ox ox ox ox ox
x
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x xo
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x x
ox
ox xoo
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o oxxx x oox
x
x
x
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o
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x
xo
x o
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oxx x xo
xo
xxo
ox
x x o
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ox ox
ox xox
x
xx
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oxxxxx xox ox xoo
ox
o x
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ox
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x
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ox
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ox x
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oxxox oxx ox ox ox x x o
o ox o x x
o oox
ox
ox x
ox xox o ox
x o
ox
ox
ox
ox ox ox ox oxox ox oox
x
ox
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x
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ox
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oxo ox
ox
oxx x
x
ox o
oxx ox
x
ox
ox ox
ox ox x x x x ox oxx ox
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x
x
xx
x xo
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x
x
oxoxo
x xx
o
xo
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x
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x
xo
ox
ox
ox o
oxxox ox ox oxxx ox oxox ox ox
xo
x
o
x
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ox x oox x ox
x
o
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oxx x
oxoxox ox
x
x
ox
ox
o
o
x
oxx
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
xx
x
2000
Leading PC of local MJJ heat wave magnitude
THESE ARE SUPPOSED TO BE UNCORRELATED. ARE THEY?
x
x
o
150
x
x
x
oxox x
x
x
ox
x
x
100
o
o
50
oo
o
oo
o
o o
o
o
o
o
o
o
o
o
o
o
oooo
o
o
o
o
oo
o
o
o
o
o
o
oo o
o
o
o
o
oo
o
o
o
o
-50
0
oo
o o
o
o
o
o
1950
1960
1970
1980
1990
o
o
o
o
o
o
o
o
o
o
o
o
o
o
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
x x
x
x
x
ox
x
oxx oxo
ox
ox
x
ox
ox
xx
x
ox
ox
ox
oo
x x x
x
x
x
ox
x
x
ox xx
o
x
x
ox
ox
x
x
ox ox
ox ox
x
x
x
ox
x
x
ox x
x
x
x
x
ox
ox ox
ox x
x
xx x
x x x
x
x
x
x
x x
xo
ox
xx
ox
ox
x
x
x
x
x
x
x
o
o
x
x
xo
x o
x
x
x
x
o
o
ox xo
ox oxox ox ox ox x
ox
x
ox
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x
xx
x
x
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oxxxxox oxox ox
xo
o
x
x
x
x
ox x ox
x
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oxoox oxxox x
x
x
x
x
oxx
ox x
x
x
ox ox ox xx
x
x
x
o
x
o x ox
x
x o
x
ox ox x x xx x x
x
x
x
x o
ox x
x
oxoxx
x
x
x
x
oox
x
ox
oxx ox
xx
x
ox ox x x x x
x
x
oo xoox
x xx x
oxoxo
x
xo
x
x o
xxo
ox oxx x
o
ox
oxox
x
ox
ox
x
x
ox
x
PC2 of local MJJ heat wave magnitude
ox
x
ox
x
oxx ox x xx ox x ox x x
ox o ox
x
x
x
ox x oox x ox
x
oxx x
oxoxox ox x
2000
x
ox
x
x x
x
x
xx
oo
x
HOT NIGHTS
Tmin extremes, inland and coastal areas
x
x
ox
ox
x
o
200
o
o
o
o
o
o o oo
o
o
o
o
o
o
o oo
o o
oo
o
o
o
o
o
7yrs
9yrs
11yrs
13yrs
smooth average
1960
1970
1980
1990
2000
0.0
0
oo
1950
150
o
95% confidence
50
o
oo
oo
o
o
o
o
o
o
o
o o
o
oo
o o
o o
o
o
o
o
o o
o
o
o
o
oo
-1.0
100
o
o
0
oo
o oo
oo
oo
oo
o
-0.5
o
oo
o
o
o
o
o
o
o
o
100
o
o
0.5
o
o
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
1.0
o
Tmin shows a broad
pattern of warming
300
o
o
o
o
o
o
o
o
o
o
o
o
o
o
x
ox
ox o
x
x
xo
ox ox
ox ox oxox
x
ox ox ox
ox
x
x
ox ox
xo
xo
ox
ox
oxox ox ox
ox
ox
ox ox
x
x o
x
ox
ox ox ox x ox
x
o
ox
x
o
ox ox ox
ox
x
x
x
o
o
x
ox ox ox ox xxox ox
ox
ox
x
ox ox
ox ox ox ox ox
x
xo
x
o
o
x xo
o
x
o
x
o x o ox
ox
ox xox oxxx
o ox x oox
x
x
x
x
xo
x
x
xo
oxx x xooxx oox oxx
xxo
ox
x x o
o
ox ox
ox xox
o xox x x
oxxxxx xox ox x xooxoxx
ox
x
o
x
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ox
ox
x
x o
x o
ox x
x
x
ox x
ox
oxo o ox ox x x o
ox ox ox x xox
o
o
ox
ox
ox x
ox xox o ox
x
o
o
x
ox ooxx
ox
ox
ox ox ox ox oo
x
x
ox
x
ox
x
ox ox
x
oxoxx
ox
oxo ox
ox
oxx x
ox ox
oxx ox
x
ox
ox ox
ox ox x x x x ox oxx ox
ox
oo xoox
x
xx
ox
oo
xo
x
x
oxoxxoxxxoxoo
x xx
oxxx ox ox oxx ox x o x ox
ox
oox oo
x
oxox
oxox o x x oox o
o
x
x
x
ox x oox o
x
o
x
x
o
x
x
x
oxoo
x
x
ox
x
oxx
x
o
o
o
o
o
o
oo o
o
o
1950
o
o
oo
o
o
1960
1970
1980
central year
1990
x
x
x
x
x
oxox x
x
o
x
x
-50
o
o
o
o
1950
1960
1970
1980
1990
2000
HAVE THEY GONE OUT OF PHASE?
o
o
o
o
o
o
o
o
o
o
o
o
o
o
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
x x
x
x
x
ox
x
ox oxo
ox
ox
x
ox
ox
xx
x
ox
x
ox
2000
ox
ox
oo
x x x
x
x
x
ox
x
x
ox xx
o
x
x
ox
ox
x
x
ox ox
ox ox
x
x
x
ox
x
x
ox x
x
x
x
x
ox
ox ox
x
ox x
x
xx x
x x x
x
x
x
x
x x
xo
ox
xx
ox
ox
x
x
x
x
ox x x
xx
ox oox oxx
ox xooxx oxxxoo
ox
x
ox
ox x
oxx x ox ox x
x
x
x
oxxox oxox ox x xoxx
xo
x
x
x
x
o x ox
ox x
oxoox oxxox x
x
x
x
x
ox ox
o
x
x
x
x
x
ox
x
x
x
ox xox ox ox
x
x o
x
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x
x
x
x o
x
x
o
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x
ox
x
x
ooxx x
x
ox
oxx ox
x x
x
ox ox x x x x
x
x
oo xoox
x
x
xx x
oxoxxoxxox o
oox oxx
xx
o
ox
x
x
oo
x
ox
ox
x
x
ox
x
o
x
x
ox
oo x oxx ox x ox x x
ox o x
x
x
x
ox x oox x ox
x
x
x o
oxx x
oxoo
x
x
x
x
xx
x
ox
x
x x
x
x
xx
oo
x
50
40
Does this trend reflect a
more global forcing?
Are cold extremes becoming
weaker and less frequent?
10
20
30
Tmin
HWI
0
Percentage of stations
California Nighttime Heat Wave Index
1950
1960
1970
1980
1990
2000
MJJ Tmin
HWI.99
-20
-10
0
10
California Heat Wave Index (pre-2006)
CA
1950
1960
1970
1980
1990
o
oo oo
o
o oo o
o o o oooo
oooo oo
ooo o
oooo
o o oooo o
o o
ooo oo
o oooo o ooo o o
o
o
oo o
2000
MJJ Tmin
HWI.99
-10
0
10
+ Cold Wave Index (HWI&CWI)
-20
CWI.01
1950
1960
1970
1980
CA
1990
o
oo oo
o
o oo o
o o o oooo
oooo oo
ooo o
oooo
o o oooo o
o o
ooo oo
o oooo o ooo o o
o
o
oo o
2000
MJJ Tmin
HWI.99
-10
0
10
California and Nevada (HWI&CWI)
CA
Cal&Nev
-20
CWI.01
1950
1960
1970
1980
1990
oooo oo oooooooo o oooooo
oo
o
o
oo oooo ooooooooo oooo o
o oo o o o o
o oooooo o oooo
o
o
o oooo oooooooo
ooo o
oooooo oo
oo
oooooooooo oo o
o
ooo
oo
o
o
o
o
o
oooooo oooo o ooo
oooooo
oo o
oo
o
o o ooo
o
ooo
ooooo ooo
oo oo
oo
o oo
ooo
oo o
oo
ooooooo o o
o
o
o
o
o
o
o
o
o
ooooo oooooo o o
oo
oooooo oo
o o
o
oo
oo
ooooo
oo
oooo
oo
o oo oo o
oooo o
ooo
oo
oooooooo oooo o
2000
MJJ Tmin
HWI.99
-10
0
10
+ the Western US (HWI&CWI)
CA
Cal&Nev
WUS
-20
CWI.01
o
oo
1950
1960
1970
1980
o
oo o
oo
o
oo
o
1990
o o
o
o o
oo
oo
o
o
o
o o
o
o
o
o
o
o
ooo
o
o
o
o
o
o
o o
o
o oo
o
o
o
o
o
o
o o oo oo
oooo oo oooo
oo
o
o
oo oooo oooooooooooo ooooooo
o oooo o o o o
oo
o o
o
o
o
o
o
o
o
o
o
o
o
o
o
o ooo oooo o ooooooooooooooo ooo
oo
o o oo
oooo
ooo
ooo
ooo
oo
ooo o
oo
oooo
oooo ooo ooo
ooooooo
oo
ooo ooo o
ooo
o oo
oooo o
o
o
ooo
o
o
o
oooo oo o o o
oo
o ooooooooooooo oooo o ooo
o
o
o
o
ooooo oooooo o o
oo
ooooooo oo
o o
o
oo
oo
oooooo
oo
oooo
oo
o oo oo o
oooo o
ooo
oo
oooooooo oooo o
2000
+ 2006, California Data
HWI.99
0
20
40
MJJ Tmin
2006 o
-20
CWI.01
CA
Cal&Nev
WUS
o
oo
1950
1960
1970
1980
o
oo o
oo
o
oo
o
1990
o o
o
o o
oo
oo
o
o
o
o o
o
o
o
o
o
o
ooo
o
o
o
o
o
o
o o
o
o oo
o
o
o
o
o
o
o o oo oo
oooo oo oooo
oo
o
o
oo oooo oooooooooooo ooooooo
o oooo o o o o
oo
o o
o
o
o
o
o
o
o
o
o
o
o
o
o
o ooo oooo o ooooooooooooooo ooo
oo
o o oo
oooo
ooo
ooo
ooo
oo
ooo o
oo
oooo
oooo ooo ooo
ooooooo
oo
ooo ooo o
ooo
o oo
oooo o
o
o
ooo
o
o
o
oooo oo o o o
oo
o ooooooooooooo oooo o ooo
o
o
o
o
ooooo oooooo o o
oo
ooooooo oo
o o
o
oo
oo
oooooo
oo
oooo
oo
o oo oo o
oooo o
ooo
oo
oooooooo oooo o
2000
Global Context?
European Hot and Cold Summer Indices
100
HSI AND CSI
CRU2
2003 event warmest in 500 years?
(Luterbacher et al. 2004)
0
50
HSI: Percent of area experiencing
Summer temperatures above the
90th percentile
relative to 1950:1999 climatology
-50
CSI: Percent of area experiencing
Summer temperatures below the
10th percentile
relative to 1950:1999 climatology
1900
1950
2000
2050
2100
Gershunov and Douville 2006
European Hot and Cold summer indices
100
HSI AND CSI
0
50
CRU2
CNRM hist
commit
-50
The scale of recent observed warming
is on the high side of that
projected by the model
for current levels of
anthropogenic forcing
1900
1950
2000
2050
2100
Gershunov and Douville 2006
European Hot and Cold summer indices
100
HSI AND CSI
-50
0
50
CRU2
CNRM hist
commit
a2
1900
1950
2000
2050
2100
Gershunov and Douville 2006
European Hot and Cold summer indices
100
HSI AND CSI
-50
0
50
CRU2
CNRM hist
commit
b1
a2
1900
1950
2000
2050
2100
Gershunov and Douville 2006
North American Hot and Cold summer indices
100
HSI AND CSI
50
CRU2
CNRM hist
commit
b1
a2
-50
0
The scale of recent observed warming
is on the low side of that
projected by the model
for current levels of
anthropogenic forcing
1900
1950
2000
2050
2100
Gershunov and Douville 2006
Seasonal Cycle of
Observed California and Nevada Tmin HWI95
0
20
40
60
80
100
AVE
Dec
Nov
Oct
Sep
Sig @ 95%
Aug
Jul
Jun
Sig @ 99%
May
Apr
Mar
Feb
Jan
1950
1960
1970
1980
1990
+1%/decade
trend
reference
2000
California Heat Waves Summary
Seasonal/monthly view of daily extremes in time and space:
individual seasons vs. multi-year climatology
• State-wide temperature extremes are on the rise, especially in
Spring and Summertime and at Night
• Nighttime heat wave trend is large-scale, independent of
topography, except for inland – coastal differences
• Summer 2006 heat-wave activity was noteworthy during the day,
unprecedented (in 59 years of quality observations) at night
• July 2006 nighttime heat cannot be explained by trend alone
• Trend is consistent with larger scale, global changes, due to
anthropogenic causes
• Regional California and Nevada trends are strongest in the spring
and summer at night
WHAT DOES IT ALL MEAN?
To be continued…