Understanding CDI Phases

Seasonal variability is tracked through five phases based on percentile thresholds calculated from historic rainfall, soil moisture and plant growth information, as well as the trend in rainfall conditions.

Primary producers can use this information to prepare for changing conditions, and to operate effectively in current conditions.

Primary producers can use this information to prepare for changing conditions, and to operate effectively in current conditions.

The movement of seasonal conditions through the five phases is based on the following thresholds:

  • Non drought phase: At-least one indicator is above the 50th percentile.
  • Recovering phase: All indicators are below the 50th percentile but above the 30th percentile.
  • Drought Affected (weakening) phase: At least one indicator is below the 30th percentile and the rainfall trend is positive over the past 90 days.
  • Drought Affected (intensifying) phase: At least one indicator is below the 30th percentile and the rainfall trend is negative over the past 90 days.
  • Drought phase: At least one indicator is below the 5th percentile.
  • Intense Drought phase: All three indicators (rainfall, soil water, plant growth) are below the 5th percentile

The five phases are defined as below. During these phases the following responses could be considered by primary producers:

CDI Phase

Technical definition

Description - typical field conditions

Intense Drought

All three indicators (rainfall, soil water, plant growth) are below the 5th percentile

Ground cover is very low, soil moisture stores are exhausted and rainfall has been minimal over the past 6-12 months.

Drought

At least one indicator is below the 5th percentile

Conditions may be very dry, or agronomic production is tight (low soil moisture or plant growth). It is possible to be in Drought when there has been some modest growth, or a few falls of rain.

Drought Affected (intensifying)

At least one indicator is below the 30th percentile and the rainfall trend is negative over the past 90 days.

Conditions are deteriorating; production is beginning to get tighter. Ground cover may be modest, but growth is moderate to low for the time of year. When indicators are close to the Drought threshold drought conditions are severe.

Drought Affected (weakening)

At least one indicator is below the 30th percentile and the rainfall trend is positive over the past 90 days.

Production conditions are getting tighter, but there have been some falls of rain over the past month. It is rare to enter the Recovering phase from the Non-Drought category; Usually there is a quick (1-2 week) transition into Drought Affected or Drought. When indicators are close to the Drought threshold drought conditions are severe.

Recovering

All indicators are below the 50th percentile but above the 30th percentile

Production is occurring but would be considered ‘below average’. Full production recovery may not have occurred if this area has experienced drought conditions over the past six months.

Non-drought

At least one indicator is above the 50th percentile.

Production is not limited by climatic conditions.