Trinidad and Tobago Dryness Monitor and Outlook By End of September 2021



ISSUED AT: 11:44 AM

Date: Friday 23rd of July 2021

Dryness Indicator for April to June 2021 & 3-month Dryness Outlook for July to September 2021

Key Message

No observed or forecast dryness level concerns up to September 2021 as  rainfall  amounts in  May and June have resulted in increases in soil moisture and river levels across most areas.


Trinidad and Tobago Dry/Wet Spell Monitor and Outlook by End of September 2021



ISSUED AT: 11:44 AM

Date: Friday 23rd of July 2021

Dryness Indicator for April to June 2021 & 3-month Dryness Outlook for July to September 2021

Key Message

No observed or forecast dryness level concerns up to September 2021 as  rainfall  amounts in  May and June have resulted in increases in soil moisture and river levels across most areas.

Dryness Indicator for April to June 2021

Over April to June 2021 there were no concerns of dryness impacts as the country observed accumulated rainfall totals that exceeded the average, leading to increased soil moisture and river levels. This guidance tool can be used for decision making or for heightening awareness on dryness. The colour-coded map shows threshold values indicating the observed level of dryness over the period. The dryness indicator for the three months February to April 2021 is based solely on rainfall.

Figure 1. The colours on this map show observed dryness levels based on the rainfall differences from average, which have been standardized and expressed as the number of standard deviations less than average. The period used to compute the dryness is  the  3-month period April  to June  2021 compared to the historical average for the same 3-month period. The yellow to red colours on the map are used to indicate areas with borderline-dry to extremely-dry levels of dryness. The grey colour indicates areas where there is no significant dryness concerns.

Dryness Outlook for July to September 2021:

The Dryness Outlook for the 3-month period, July to September 2021 indicates that there are no concerns for short-term impactful dry conditions over the next three months for both islands, as the expected rainfall amounts are likely to maintain or increase current soil moisture and river levels. Dryness indicator values for the period range between -0.1 to -0.4 on the Standardized Precipitation Index (SPI) scale, which are below the levels for dryness concerns. The outlook is based solely on rainfall and should be used only for guidance.

Figure 2. The colours on this map show the predicted levels of dryness for the period July to September 2021.  It is based on the standardized rainfall difference between observed and predicted rainfall from April to September 2021 and the historical average rainfall for the same period. The yellow to red colours indicate borderline dry to extremely dry levels of dryness. The grey colour indicates areas where there is no significant dryness concerns.

 

Dryness Indicator Guide: The Dryness Indicator is a tool for keeping track of the level of dry conditions, rainfall deficit and length of the dry period across Trinidad and Tobago. It is based on the TTMS’s Dry Spell and Meteorological Drought Policy which uses the Standardized Precipitation Index (SPI) to indicate levels of dryness. The SPI is a simple measure of dryness based solely on the total rainfall for a given time period (e.g. over the last 60 days) compared with the long-term average rainfall for that period. In short, it indicates how extreme a recent period of rainfall has been compared to the historical data for that location.

The colours on the map indicate observed or predicted levels of dryness based on the difference between observed or predicted rainfall and the average rainfall, which is then standardized and expressed as the number of standard deviations less than average. The colours moving from yellows to reds show increased levels of dryness. The grey areas indicate areas where the dryness is either very close to the average, average or on the wet-side. Negative SPIs indicate less than average rainfall and dryness. In general, dryness concerns and negative impacts are expected when the value of the dryness indicator lies near -1.0. Concerns for dryness impacts increase, as the size of the negative value increases.