State Climate Update for Arizona

Conditions through March 2006

 

The primary climate variables of temperature and precipitation are monitored for the state of Arizona by climatically homogeneous areas termed ‘climate divisions’. There are 7 climate divisions for Arizona (see map). From the stations within each climate division, mean values of temperature and precipitation for the division as a whole are computed. Calculated from the divisional temperature and precipitation data is the Palmer Drought Severity Index (PDSI), a type of wetness/dryness index based on budgeting input (precipitation) against demand (evapotranspiration) in simulating soil moisture through time.

 

Here, values for the most recent month along with 3-, 6-, 12-, 24-, 36-, and 48-month mean temperature and total precipitation values are ranked within a historical context (1895-present) and the rankings are divided by the number of years of data and multiplied by 100% to create percentiles. Low percentile values indicate cool or dry conditions while high values indicate warm or wet conditions. For example, a temperature that falls at the 100th percentile means that it is the highest temperature for the period of record. As the PDSI is a cumulative index that describes conditions as they have evolved up to the present, only the value of the current month is translated to a percentile.

 

Based upon analysis by the Monitoring Group of the Governor’s Drought Task Force, precipitation data are stratified into the following drought categories:

           

Numerical Category

Description

Precipitation Percentile

0

no drought

40.01 – 100

1

abnormally dry

25.01 – 40.00

2

moderate drought

15.01 – 25.00

3

severe drought

5.01 – 15.00

4

extreme drought

0.00 – 5.00

 

 

SHORT TERM CONDITIONS: 1-6 MONTHS

A change from the recent warm and very dry conditions continued during March across Arizona. The month was characterized by air temperatures below average and precipitation at or above average across the entire state. Air temperatures for the past 3- and 6-month periods were above average for all regions of the state. Precipitation totals for the past 3- and 6-month periods are very low. The entire state is characterized by precipitation amounts indicative of “abnormally dry” to “severe drought” conditions over the past 3 months, with conditions even more dramatic over the past 6 months with many areas of the state receiving precipitation of an amount indicative of “extreme drought”. The Palmer Drought Severity Index (PDSI) has fallen dramatically since the wet winter of 2004-05. The PDSI indicates moist conditions only along the western edge of the state (CDs 1 and 5), but the recent dryness in these two areas is very likely to significantly drop the PDSI values in the coming months. Elsewhere, the PDSI signals very dry conditions.

 

 

Temperature

Precipitation

PDSI

CD1

41.1

61.6 (0)

62.5

CD2

30.4

65.2 (0)

9.8

CD3

44.6

48.2 (0)

10.7

CD4

33.9

58.0 (0)

5.4

CD5

25.0

66.1 (0)

81.3

CD6

48.2

73.2 (0)

5.4

CD7

42.9

64.2 (0)

9.8

 

MARCH 2006: percentiles of temperature, precipitation (with drought category), and Palmer Drought Severity Index for the 7 Arizona climate divisions


 

Temperature

Precipitation

CD1

80.4

26.3 (1)

CD2

58.5

10.3 (3)

CD3

81.3

9.8 (3)

CD4

70.5

8.0 (3)

CD5

68.6

18.8 (2)

CD6

88.4

17.9 (2)

CD7

78.6

10.7 (3)

 

JANUARY 2006 - MARCH 2006: percentiles of temperature, and precipitation (with drought category) for the 7 Arizona climate divisions


 

 

Temperature

Precipitation

CD1

85.6

21.6 (2)

CD2

72.5

3.6 (4)

CD3

86.5

4.5 (4)

CD4

82.9

1.8 (4)

CD5

87.4

28.8 (1)

CD6

96.4

3.6 (4)

CD7

87.4

2.7 (4)

 

OCTOBER 2005 – MARCH 2006: percentiles of temperature, and precipitation (with drought category) for the 7 Arizona climate divisions


 

 

INTERMEDIATE TERM CONDITIONS: 12-24 MONTHS

The intermediate time periods of 1 and 2 years define the break point in the more recent drought conditions. The past 12 months have been marked by dryness characteristic of “extreme drought” across 3 of the 7 Arizona climate divisions, and “severe drought” across another 2 divisions. The period represents the conditions generally since the end of the wet period of winter 2004-05. The two areas of exception are again along the western edge of the state, where northwestern (CD 1) and southwestern Arizona (CD 5) received precipitation of an amount indicative of “abnormally dry” conditions.

 

There is very little evidence of drought within the state when examining precipitation totals for the past 2 years. Only one region registered precipitation totals suggestive of drought; precipitation for southeastern Arizona (CD 7) ranked only in the 19th percentile, which is indicative of “moderate drought”.

 

Temperatures across the state were well above normal for the past 2 years, and most significantly so across southern Arizona.

 

 

Temperature

Precipitation

CD1

77.5

28.4 (1)

CD2

75.7

7.2 (3)

CD3

86.5

4.5 (4)

CD4

77.5

2.7 (4)

CD5

89.2

36.9 (1)

CD6

98.2

11.7 (3)

CD7

94.6

1.8 (4)

 

APRIL 2005 – MARCH 2006: percentiles of temperature, and precipitation (with drought category) for the 7 Arizona climate divisions


 

 

 

Temperature

Precipitation

CD1

77.3

91.8 (0)

CD2

85.5

71.8 (0)

CD3

85.5

76.4 (0)

CD4

92.7

46.4 (0)

CD5

83.6

95.5 (0)

CD6

92.7

68.2 (0)

CD7

81.8

19.6 (2)

 

APRIL 2004 – MARCH 2006: percentiles of temperature, and precipitation (with drought category) for the 7 Arizona climate divisions


 

LONG TERM CONDITIONS: 36-48 MONTHS

The pattern of precipitation rankings for the longer-term 3-year period across the state closely matches that for the past 2-year period. The 36-month precipitation totals were above average for 5 of the 7 climate divisions in Arizona. Only across the southeastern (CD 7) and east-central (CD 4) portions of the state did the precipitation fall far below average. Across southeastern Arizona the 3-year precipitation total is suggestive of “severe drought”, while that across east-central Arizona is indicative of “moderate drought” conditions.

 

Dryness is more evident for the longer 4-year period. Only two regions of the state (northwestern (CD 1) and southwestern (CD 5)) are characterized by 4-year precipitation totals that are above average, while three regions of the state (northeastern (CD 2), west-central (CD 3), south-central (CD 6)) can be characterized as “abnormally dry” over the past 4 years. The long-term problematic areas within the state are the east-central (CD 4) and southeastern (CD 7) regions, where 4-year precipitation totals are suggestive of “severe drought” conditions.

 

Temperatures for the period were well above the historical median; however, to some extent the longer time periods likely reflect the general climatic changes of the past several decades in addition to the recent warmth that typically accompanies dryness in Arizona.

 

 

Temperature

Precipitation

CD1

84.4

78.9 (0)

CD2

90.4

51.4 (0)

CD3

92.7

53.2 (0)

CD4

97.3

23.9 (2)

CD5

89.9

88.1 (0)

CD6

97.3

52.3 (0)

CD7

94.5

12.8 (3)

 

APRIL 2003 – MARCH 2006: percentiles of temperature, and precipitation (with drought category) for the 7 Arizona climate divisions


 

 

 

Temperature

Precipitation

CD1

84.3

57.4 (0)

CD2

91.7

38.0 (1)

CD3

97.2

35.2 (1)

CD4

98.2

11.1 (3)

CD5

91.7

79.6 (0)

CD6

98.2

37.0 (1)

CD7

97.2

9.3 (3)

 

APRIL 2002 – MARCH 2006: percentiles of temperature, and precipitation (with drought category) for the 7 Arizona climate divisions


 

 

SUMMARY

● The recent warm and extremely dry conditions abated in March across the entire state of Arizona, as the month was cooler and wetter than average statewide.

 

● Precipitation totals for the past 3- and 6-month periods are very low, with much of the state characterized by amounts indicative of “severe” to “extreme” short-term drought over the past 3 to 6 months.

 

● The Palmer Drought Severity Index (PDSI) has fallen dramatically since the wet winter of 2004-05. The PDSI indicates moist conditions only along the western edge of the state (CDs 1 and 5); elsewhere, the PDSI signals very dry conditions.

 

● The past 12 months have been marked by dryness characteristic of “extreme” or “severe” drought across 5 of the 7 Arizona climate divisions, and dryness or drought elsewhere.

 

● There is very little evidence of drought within the state when examining precipitation totals for the past 2 years; drought is evident only across southeastern Arizona (“moderate drought”) during the period.

 

● The 36-month precipitation totals are above average for 5 of the 7 climate divisions in Arizona; however, across southeastern Arizona the 3-year precipitation total is suggestive of “severe drought”, while that across east-central Arizona is indicative of “moderate drought” conditions.

 

● The long-term problematic areas within the state are the east-central and southeastern regions, where 4-year precipitation totals are suggestive of “severe drought” conditions.