Standardized Precipitation Index (SPI)

Learn about the SPI and how it is used to determine drought status in the Commonwealth.

Standardized Precipitation Index (SPI)

The Standardized Precipitation Index (SPI) is one of seven indices used by the Massachusetts Drought Management Task Force to determine the level of drought severity. The SPI reflects precipitation conditions. SPI values are calculated monthly using data from the precipitation database. These values reflect “look-back” periods of three months, six months, and twelve months.

The SPI values for these time periods are equivalent to the number of standard deviations from normal precipitation totals for that time period. This can be understood as:

  • The further a positive number is from 0, the higher precipitation is from normal
  • The further a negative number is from 0, the lower precipitation is from normal

If you would like to access data prior to those dates available below, please email climate.data@state.ma.us

Massachusetts SPI Values for July 2018

REGION 3-Month SPI 6-Month SPI 12-Month SPI
Western Region 0.49 1.11 0.86
Connecticut River Region 0.80 0.94 0.42
Central Region 0.23 0.69 0.50
Northeast Region -0.06 0.82 0.15
Southeast Region -0.71 0.64 0.08
Cape & Islands -0.91 1.20 1.55

2018 SPI Values

2018 07 SPI Table

2018 06 SPI Table

2018 01 SPI Table

2018 02 SPI Table

2018 03 SPI Table

2018 04 SPI Table

2018 05 SPI Table

2017 SPI Values

 

 

 

 

 

 

 

 

 

 

 

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