T&T’s New Climate Normals – Hotter and… Drier?

What is considered a climate normal? When referring to an average or normal temperature, rainfall, or wind value, climatologists typically refer to the average conditions over the last 30 years. Through 2020, this meant a climate reference period between 1981 to 2010. However, as we shift into a new decade, this reference period has moved to 1991-2020 as today’s reality is much different from 30, 60, or even 100 years ago.

Climatologist Kenneth Kerr, speaking at the Trinidad and Tobago Meteorological Service’s National Climate Outlook Forum on May 12th, said, “Climate change is the single biggest challenge for Trinidad and Tobago as an island, developing state.”

He added that the evidence of changes happening more quickly than previously estimated. “It can no longer be framed as a distant threat. It is an ongoing threat and a disaster risk multiplier.”

Kerr explained, “our planning must be based on climate extremes, being made worse because of climate change.” Using Arouca as an example, the area that rarely saw the level of flooding it did in 2020, with multiple significant flash flooding events, Kerr explained this could have resulted from climate change or our “bad behavior as humans.” He posed the question – will the residents now use these extremes to plan for the future?

Temperatures are climbing

Average annual maximum temperature difference from the 1946-1990 average, showing above average temperatures over the last 3-4 decades (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Average annual maximum temperature difference from the 1946-1990 average, showing above-average temperatures over the last 3-4 decades (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

2020 was the 8th warmest year on record. Trinidad and Tobago’s maximum surface temperatures have become warmer and warmed at a rate of 0.24°C per decade since 1946. Looking at the data, disaggregated by decade, the last two decades have been the warmest decades on record, spanning 2001-2010 and 2011-2020 with the mean maximum temperatures of 32.2°C. Since 1981 each decade has been warmer than the 20th century average of 31.1°C.

Trinidad and Tobago mean maximum temperatures by decade, showing the last two decades at record high mean maximum temperatures (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Trinidad and Tobago mean maximum temperatures by decade, showing the last two decades at record high mean maximum temperatures (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

Trinidad and Tobago’s new average temperature for 1991-2020 compared to 1981-2010 is across the board warmer. May’s average temperature is just as hot as September, coming in at 28.5°C.

Trinidad and Tobago new climate normal for average temperatures recorded during 1991-2020. Across the board, T&T's new normal temperatures are higher than the previous climatological average. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Trinidad and Tobago new climate normal for average temperatures recorded during 1991-2020. Across the board, T&T’s new normal temperatures are higher than the previous climatological average. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

When looking at excessive heat nationwide, according to Kerr, the TTMS is recording unusually hot days in the last several decades, with 2011-2020 having the record highest of 415 days where the maximum recorded temperature was at or above 34°C. Unusually hot nights have also become more common.

Overall drier conditions

Trinidad and Tobago rainfall difference from the 1946-2020 average, showing below average rainfall occurring predominantly in the last decade. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Trinidad and Tobago rainfall difference from the 1946-2020 average, showing below-average rainfall occurring predominantly in the last decade. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

On average, rainfall at Piarco has decreased very slightly over the last 80-odd-years. 2019 was the third driest on record since 1960. Over the last decade, eight of the ten years produced less than average rainfall. Kerr said, “it should be noted that some parts of Trinidad and Tobago have experienced greater decreases than others.”

Trinidad and Tobago new climate normal for average rainfall recorded during 1991-2020. T&T's new average rainfall is drier than the previous climatological average from 1981-2010. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Trinidad and Tobago new climate normal for average rainfall recorded during 1991-2020. T&T’s new average rainfall is drier than the previous climatological average from 1981-2010. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

Trinidad and Tobago’s new climate normal regarding rainfall shows an overall (but slightly) drier average for 1991-2020 compared to 1981-2010. The only month that is slightly wetter is March, which is still the driest month for the year in T&T. Average rainfall for January, February, and December remains unchanged. Notably, all the Wet Season months are drier in the new climate normal.

Difference in rainfall from 1981-2010 compared to 1991-2020 showing Tobago, western and southern Trinidad now drier than the previous average while across eastern Trinidad, conditions have trended wetter. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Difference in rainfall from 1981-2010 compared to 1991-2020 showing Tobago, western and southern Trinidad now drier than the previous average while across eastern Trinidad, conditions have trended wetter. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

While the average rainfall at Piarco has decreased, not all areas are experiencing the same level of drying. Across the entirety of Tobago, Trinidad’s western and southern halves have observed below-average annual rainfall, with rainfall increasing across east-central and northeastern Trinidad.

1951-2020 decadal mean rainfall totals at Piarco, Trinidad showing a decline in rainfall totals in the last three decades (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
1951-2020 decadal mean rainfall totals at Piarco, Trinidad showing a decline in rainfall totals in the last three decades (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

Looking at the total rainfall by decade, the mean rainfall totals have decreased at Piarco, below the 30-year mean rainfall from 1961-1990, at a rate of 10 millimeters per decade, or 50 millimeters per half-century. 2011 to 2020 was the driest decade on record at Piarco since records began at the monitoring site.

Extremes are on the rise

The annual extreme (maximum) one-day rainfall totals at Piarco from 1960 to 2020, showing an increase in extreme rainfall. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
The annual extreme (maximum) one-day rainfall totals at Piarco from 1960 to 2020, showing an increase in extreme rainfall. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

However, the extremes show the opposite. Kerr explained that in recent years, a larger percentage of rainfall at Piarco has come in the form of intense precipitation. There has been a steady increase of rainfall accumulating in the highest annual daily rainfall totals. According to Kerr, six of the highest top ten years for the highest one-day maximum rainfall totals at Piarco have occurred since 1990.

The annual number of extreme one-day rainfall events at Piarco from 1985 to 2020, showing an increase in extreme rainfall with 2020 tied with 2008 and 1993 for the most extreme single-day rainfall events. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
The annual number of extreme one-day rainfall events at Piarco from 1985 to 2020, showing an increase in extreme rainfall with 2020 tied with 2008 and 1993 for the most extreme single-day rainfall events. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

The frequency of the extreme single-day rainfall events remains fairly steady at Piarco, at an average of extreme rainfall, meaning 50 millimeters or more daily. However, from 1985 to present, the average number of extreme single-day rainfall events has trended higher. Based on the records from the TTMS, in the last 35 years, 2020 tied 2008 and 1993 for the highest number of extreme single-day rainfall events in T&T, with seven extreme rainfall days.

The annual number of maximum three-day rainfall events at Piarco from 1960 to 2020, showing an increase in three-day rainfall events. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
The annual number of maximum three-day rainfall events at Piarco from 1960 to 2020, showing an increase in three-day rainfall events. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

Kerr also explained that there had been an increase in the maximum three-day rainfall totals over the last six decades. When there are high three-day rainfall totals, T&T typically experiences high-impact flood events. 2018 had the highest annual maximum three-day total at Piarco at 250 millimeters. The climatologist said, “rainfall upwards of 100 millimeters is of concern.”

Climatologists have observed an increase in extremely wet days contributing to the annual rainfall total. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)
Climatologists have observed an increase in extremely wet days contributing to the annual rainfall total. (Kenneth Kerr, Trinidad and Tobago Meteorological Service)

There has been an increase in extremely wet days, or days in the top 1% of daily rainfall accumulations, contributing to the annual rainfall totals. Notably, 2019 did not produce extremely wet days.

What does this mean for T&T?

There are water implications as 70% of the country’s water supply comes from our reservoirs that depend on rainfall. As parts of eastern Trinidad becomes wetter, one of the most flood-prone areas of the country may have to prepare for an increased number of flooding events.

Warmer than usual temperatures on hot and very hot days can lead to warmer than usual water temperatures, which can cause heat stress such as wilting in aquaponic crops and fisheries. Water temperatures much warmer than 30.0°C can affect warm-water fishes such as tilapia. Further agricultural impacts are possible as hot days and spells can cause heat stress in livestock and wilt in newly transplanted and younger crops.

Periods of excessive heat can increase heat stress for persons with heat-sensitive ailments, amplify existing health conditions in vulnerable persons and worsen chronic health conditions in others.

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