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.





Record Low Rainfall for the Past 24 Months

15 07 2015

Dale C. S. Destin|

Very few Antiguans, if any, have witnessed a drier 24-month period ending June. July 2013-June 2015, is now the driest such 24 months on record, dating back to 1928. The cumulative rainfall of the past two years is the lowest in, at least, 87 years.

For the past two dozen months, the country, on average, only received 1666.2 mm (65.6 in) as compared to the long-term average or normal total of 2392.7 mm (94.2 in), an unprecedented deficit of 726.4 mm (28.6 in) or 30%.

Since June 2013, there has only been three months (December 2013, August 2014 and November 2014) with above average rainfall or positive rainfall anomalies (anomaly = departure from the long-term average) and none since the start of 2015.

Rainfall_Anomaly_for_Antigua-2013-Present

Clearly, such low rainfall for the given period is quite rear; it has a 2% chance of happening, which translates to it happening once every 50 years, on average. The previous record for a similar 24 months was 1701.8 mm (67.0 in) observed July 1964-June 1966.

Within the period July 2013-June 2015, we saw a number of notable low rainfall periods: The just ended official dry season, January-June 2015, is now the 3rd driest on record and the driest since 2001. The year 2014, became the 13th driest on record and the driest since 2003. The wet season, July-December 2013, is the 15th driest.

MonthlyRainfallAccumulationsforAntigua1

With no end to the drought yet in sight, more records are expected to fall or come very close to falling. Recent analyses give 2015 a fifty-fifty chance of becoming the driest year on record. This means that the combined rainfall total for 2014 and 2015 could become the record lowest of any two successive calendar years.

The driest of any consecutive 24 months on record is April 1967 to March 1969 with 1701.8 mm (67.0 in), while 1929-1930 is the driest of any two calendar years in a row with 1691.6 mm (66.6 in). October 2000 to September 2001 holds the record for the lowest rainfall for any 12 straight months with 604.5 mm (23.8 in) and 1983 holds the record for a calendar year with 680.7 mm (26.8 in).

We will continue to monitor what is shaping up to be an unprecedented situation. Visit Antigua and Barbuda Meteorological Service Climate Section for more. Also follow us also @anumetservice, facebook and tumblr to keep updated with weather & climate info for the protection of life, property, livelihood & the enhancement of the economy.





Near Record Dryness for the First Half of May

17 05 2015

Dale C. S. Destin |

The first half of May 2015 is over and the Met Office, located at the V. C. Bird International Airport, Coolidge, Antigua, has measured only 1.7 mm (0.07 in) of rainfall. This represents the second driest such period on record. The only time May 1-15 was drier was back in 2001.

May 1-15 Rainfall at the V. C. Bird Int'l Airport

We are clearly not having a normal May or year but normally we would have received around 37.8 mm (1.49 in) by now. Instead, we have had near record dryness.

The rest of the country has not fared better. In fact, there are a few areas that are yet to see measurable rainfall for the month. Neighbouring islands are also experiencing similar rainfall deficits.

This severe dryness for the first half of May is very rare. On average, this happens once every 250 years, which translates to a 0.4% probability of May 1-15 being this dry.

The near record low rainfall seems largely connected with the anomalous cooling of the tropical North Atlantic which is associated with a positive North Atlantic Oscillation (NAO). Another significant driver of the dryness is the above normal flow of very dry, dusty air from the Sahara Desert to the region.

A dry start to the month does not always imply a dry month; however, of the six other times we have had 10 mm (0.40 in) or less for the first half of May, the eventual month’s total has never exceeded 56 mm (2.20 in). Only once such a dry start did not signal a dry month.

Overall, the second half of May has produced as little as 3.9 mm (0.15 in) and as much as 434.7 mm (17.1 in). Hoping to be wrong, but it would not be “tempting fate” to say that we absolutely will not get anywhere remotely close to 434.7 mm over the next two weeks.

Climatologically, the past 30 years show that rainfall on a whole for May is not changing. However, May 1-15 is trending positively (wet) while May 16-31 is trending negatively (dry). These trends are not considered significant, at the moment, but May 1-15 is not far away from being so.

The driest May on record at the Airport, dating back to 1928, is May 2001 with 7.6 mm (0.30 in). This record appears to be in jeopardy.

Follow us also on @anumetservice, facebook and tumblr for the latest on the current drought and other weather & climate news.








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