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Maryland State Government Maryland Department of the Environment

Assessing Drought

Maryland will implement a staged process for defining drought conditions. Drought indicators will be monitored on an ongoing, year-round basis, and drought status will be determined on a variable timeframe according to drought stage (See Tables 1 and 2 below). The frequency of evaluation will increase if the drought intensifies as indicated below:

  • Stage 1 Monthly
  • Stage 2 Bi-weekly
  • Stage 3 Weekly
  • Stage 4 Weekly or as needed

Stage 1 – Normal (Green)

No more than one indicator outside of the normal range.

  • Precipitation exceeds the percent of normal precipitation for the time period in Table 2
  • Streamflows are above the 25th percentile
  • Ground water levels are above the 25th percentile
  • Reservoirs exceed 120 days of storage

Stage 2 – Watch (Yellow)

At least 2 indicators meet the following conditions:

  • Precipitation levels are at or below the percent of normal precipitation for the time period in Table 2
  • Streamflows fall between the 10th and 25th percentile
  • Ground water levels fall between the 10th and 25th percentile
  • Reservoirs contain between 90 and 120 days of storage

Stage 3 – Warning (Orange)

At least 2 indicators meet the following conditions:

  • Precipitation levels are at or below the percent of normal precipitation for the time period in Table 2
  • Streamflows fall between the 5th and 10th percentile
  • Ground water levels fall between the 5th and 10th percentile
  • Reservoirs contain between 60 and 90 days of storage

Stage 4 – Emergency (Red)

At least 2 indicators meet the following conditions:

  • Precipitation levels are at or below the percent of normal precipitation for the time period in Table 2
  • Streamflows are at or below the 5th percentile
  • Ground water levels are at or below the 5th percentile
  • Reservoirs contain 60 days or less of storage

 

 

Precipitation As Percent of Normal for Evaluation
Period 1

Streamflow As Percentile of Normal2

Ground Water
Levels As
Percentile
of Normal2

Reservoir Storage in days

Stage 1
Normal

See Table 2

>25

>25

>120

Stage 2
Watch

25

25

120

Stage 3 Warning

10

10

90

Stage 4
Emergency

5

5

60

1 These values vary depending of length of review period. For more detail see Precipitation discussion and Table 2.

2 At the 25th percentile, it means that historical streamflows or ground water levels are lower than this value only 25% of the time for the evaluation period. 10th and 5th percentiles represent increasingly lower streamflows or ground water levels and more severe drought events.

TABLE 2.  Precipitation Triggers  

Number of Months
Analyzed

Normal
(% of 
Normal
Precipitation)

Watch
(% of
Normal
Precipitation)

Warning
(% of
Normal
Precipitation)

Emergency
(% of
Normal
Precipitation)

3

>75.0

75.0

65.0

55.0

4

>80.0

80.0

70.0

60.0

5

>80.0

80.0

70.0

60.0

6

>80.0

80.0

70.0

60.0

7

>81.5

81.5

71.5

61.5

8

>82.5

82.5

72.5

62.5

9

>83.5

83.5

73.5

63.5

10

>85.0

85.0

75.0

65.0

11

>85.0

85.0

75.0

65.0

12

>85.0

85.0

75.0

65.0

   

Related Topics

What Can You Do?

For More Information
For more information, contact the Water Supply Program at 410-537-3702 or water.supply@maryland.gov


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