Near Record Driest November for Antigua

7 12 2021

Dale C. S. Destin|

Most Antiguans alive have never endured a November like the just ended one. The month was second driest on record, dating back to 1928. It registered a near record breaking 29.2 mm (1.15 in) of rainfall, the lowest since 25.1 mm (0.99 in) in 1947, almost 75 years ago. This very rare November rainfall event has around a 0.7 percent chance annually or once every 143 years, on average.

November usually logs 152.1 mm (5.99 in) of rainfall annually (1991-2020); this means that only a little over 19 percent of the usual total fell this year. The deficit of 81 percent is the second worst for the year, behind May with 83 percent. November is usually the wettest month of the year.

The absentee rainfall for November has virtually ensured that 2021 will be among the top eight driest, on record. Although unlikely, this year could even break the record for the driest year set by 2015, when just 574.5 mm (22.62 in) rainfall was accumulated.

Thus far, the total for 2021, through November, stood at 537.2 mm (21.15 in). Normally, this period yields 1059.2 mm (41.7 in); hence, there is close to a 50 percent shortfall of rainfall. Less than 37.3 mm (1.47 in) of rainfall for December would see the record fall. Such low annual rainfall is extremely rare. The chance of this meagre annual total is less than 0.2 percent. This translates to a 500-year event or worse, an event with a return period of once every 500 years or more, on average.

November has also virtually sealed the fate of the wet season (July-December). It is certain to be among the driest, if not the driest, on record. The current record is 405.6 mm (15.97 in) for the 1983 wet season. Thus far, July-November, the total for the 2021 wet season is 332.5 mm (13.09 in).

While it is possible that the rainfall for the wet season will be at a record low, the rainfall for the last seven months ending November was in fact record breaking. No other May-November has been drier, on record going back to, at least, 1928. The total of 405.4 mm (15.96 in), for this year, eclipsed that of 406.4 mm (16.00 in) observed in 2015.

It goes without saying that serious meteorological drought continues, and it is highly likely to get worse, in the short-term. Also evident are agriculturalhydrologicalecological and socio-economic droughts, at varying intensities. Potworks Reservoir now has ZERO drop of water. All other surface catchments are in a similar state or below extraction levels.

Potworks Reservoir with zero drop of water – December 2, 2021. Picture courtesy Karen Corbin, Humane Society

Antigua Public Utilities Authority (APUA), the countries water resource manager, informed the public yesterday that 95 percent of all potable water, being produced by the organization, is desalinated water from the sea. We were also informed that the total water production of six million gallons per day is, at least,  a million gallons below the country’s daily requirement; hence, water is being rationed.

With such lean rainfall figures and with the recent conclusion of COP26, the obvious question would be: Was this caused by anthropogenic (human induced) climate change? From my reading of the latest IPCC report and other papers, the answer is no. According to the report, there is a low confidence in the change in agricultural and ecological droughts in the Caribbean, thus far. However, the long-term projection is for an increase in the intensity and frequency of droughts, but this will not be for all regions. Unfortunately ,the Caribbean is likely to be among the regions to bear the negative changes.

Whereas climate change is unlikely to have been a factor in November’s rainfall, or lack thereof; it was noted that suppressing rainfall conditions prevailed across the area for much of the month. Strong positive velocity potential anomalies caused sinking air, which is prohibitive to cloud growth and hence rainfall. The velocity potential is associated with the Madden-Julian Oscillation (MJO) with positive values being indicative of the dry portion of it.

Three-day centred average animation of daily IR and 200-hPa velocity potential anomalies (base period 1991-2020). Velocity potential anomalies are proportional to divergence with green (brown) contours corresponding to regions in which convection tends to be enhanced (suppressed).

This extreme dryness for November was not endured by Antigua only. The unusually low or near record breaking rainfall was observed across much of the Eastern Caribbean. For example, reports out of Trinidad and Tobago indicate that much of the country had its second driest November, on record.

November was the last hope for the replenishment of national surface catchments, this year. With the very disappointing rainfall, the next possible time for replenishing precipitation is May. The issue with insufficient potable water is likely to get worse before getting better.

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