The Worst Drought on Record for Antigua

25 03 2016

Dale C. S. Destin |

Antigua is witnessing the worst drought in recent history, dating back to, at least, 1928. The current drought is now over 32 months in length, similar to the drought of 1964-67. However, to date, the record rainfall deficit of 1143 mm (45 in) caused by the current drought, exceeds that of 1964-67 by 254 mm (10 in) or around 29%.

RainfallDeficitGraphic

While we don’t have observed monthly rainfall totals beyond 1928, we do have annual totals going back to 1871. Based on this record, 2015 is now the driest year in the series. This translates to 2015 rainfall total occurring once per 500 years, on average. Thus, it’s perhaps the most intense drought since the arrival of Christopher Columbus.

Not only the last year has been the driest on record, but so to have the last two years (24 months). Further, the last 32 months – July 2013 to February 2016, is the driest such period on record. We are missing about a year’s worth of rainfall.

Surface water contributes to around 30% of our potable water mix. However, since the drought started, the country has been completely out of surface water twice with an aggregate duration of around 14 months. We were out of surface water April to September 2014 and again from August 2015 to present.

The drought was caused by a number of climate actors not necessarily all acting at the same time. These include mainly an abundance of the dry and dusty Saharan air layer (SAL) from Africa, positive North Atlantic Oscillation (NAO), negative Tropical North Atlantic (TNA) Index and El Nino. It is fairly well established that these phenomena, in the mentioned phases, cause less than normal rainfall across our area with the converse being true.

The drought got kicked off by the SAL along with unpredictably strong vertical wind shear, sinking air and the weakening of the Atlantic Ocean overturning circulation. Happily, this resulted in a failed hurricane season in 2013, but unfortunately it also plunged us into what has become our worst rainfall deficit on record.

Contributing to the persistent drought, the NAO has been predominantly positive over the duration of the drought with only nine of the last 32 months having negative (rain-favoured) values. Meanwhile, the TNA was negative (unfavourable rainfall values) for most of January 2014 to June 2015. In 2015, El Nino developed and reach super (record) strength during the latter half of the year.

Droughts are expensive, and severe droughts are severely expensive. It’s believed that the drought has cost the country hundreds of millions of dollars, directly and indirectly. I will address this matter more in a subsequent blog.

The current drought is anticipated to become the longest on record – a further very unwelcome new record. Initial predictions had the drought easing significantly or ending around mid-year. However, our last set of forecasts has it continuing into the second half of the year.

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Once in a Generation Dry March for Antigua!*

30 03 2015

Dale C. S. Destin |

We are about to exit a severely dry March for most of Antigua. So far for the month, the Met Office, located at the V. C. Bird International Airport, has measured only 8.4 mm of rainfall. This severe dryness only happens once in a generation, on average. This total is not expected to change much between now tomorrow, when the month ends. Hence, this is likely to be among the top five driest Marches and the top 10 driest month of all times.

Top 4 Driest Marches for Coolidge, Antigua
March 2015 in perspective

Barring unexpected appreciable rainfall over the next 24 hours, this will be the fourth driest March on record dating back to 1928. Only March 1999, 1944 and 1930 have been drier.

Relative to other months, this March ranks 10th of all 1047 months of recorded rainfall, at the Airport, for the period.

The probability of March having such little rainfall is quite low; it’s around 3%. This means that this severe dryness we have experienced only happens once in every 33 Marches or once in a generation, on average.

Looking at the year on a whole, this is a 17 year event. The probability of a (any) month of a year, at the Airport, yielding 8.4 mm or less is around 6%. This means that this happens once every 17 years, on average.

March is the second driest month at the Airport with an average rainfall of 46 mm (1.81 in). The minimum and maximum rainfall totals on record are zero and 179.1 mm (7.05 in) respectively.

Drought

Currently, we are in our worse drought, in terms of intensity, since 2002/2003 and it is likely to get worse. We have been in a drought since September 2013.

It reached serious levels in 2014 but was reduced to slight levels in October 2014. At the end of January 2015 it had reintensified to moderate levels and with this month being brutally dry, it is set to drop to severe levels.

Projections

However, seasonal forecasters are not optimistic about rainfall for much of the rest of 2015. Indications are that El Nino, which tends to restrict our rainfall, mainly in the rainy season, is expected to continue deep into the year.

Additionally, the tropical North Atlantic sea surface temperatures are projected to remain near normal for much of the rest of the year. This is generally not helpful for rainfall in our nook of the world.

If El Nino strengthens to moderate levels or worse, our rainfall deficits are likely to be worse that those of last year’s. Recall that last year that we had a water crisis which are yet to get over.

Further, strategies and tools are required to sustainably deal with our water insecurity issues. Two such required tools are an integrated water resource management programme and an integrated drought management programme. Meanwhile, be conservative and efficient with your water usage.

[*It turned out that unexpected heavy downpours stopped March from having “once in a generation” dryness. The heavy downpours that stopped this March from being the fourth driest occurred after midnight on March 31. However, In meteorology, the last day of a month ends at 8 am on the first day of the next month. .

So, instead, the eventual total rainfall for March, at the Airport, was 11.9 mm, the driest since 2001, the seventh driest March and the 18th driest month on record. This kind of dryness, instead, happens once in every 16 years, on average]





How dry has this September been?

19 09 2012

By Dale C. S. Destin

Antigua is currently experiencing a meteorological drought, which started in February of this year. Notwithstanding the active hurricane season, so far, September has been especially dry. The first half of the month only yielded 1.3 mm / 0.05 inch of rainfall at the V. C. Bird International Airport. This tied with September of 1986 for the lowest total at the Airport on record (1971-2012). Below normal rainfall was anticipated for the month so this does not come as a surprise. This sort of rainfall is consistent with a warm Pacific Ocean (El Nino) and a lukewarm/cold tropical north Atlantic (TNA) Ocean. The lowest total rainfall for the month of September on record at the Airport is 27.2 mm or 1.07 inches (1978, at the start of a strong El Nino and cold TNA), while the highest is 410.2mm or 16.15 inches (1995, during a moderate La Nina Episode and warm TNA). Thus, based on record, there has never been a sub-inch total for the month; only two other month has never experienced sub-inch rainfall – August and December. However, at the current rate, and based of the outlook, sub-inch rainfall is quite possible and would obviously make it a record dry September. Further, it would make the drought become severe.








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