Driest April for Antigua in Over Two Generations

1 05 2020

Dale C. S. Destin|

Not since 1944 has an April been drier for Antigua than April 2020. It was the third driest April on record – the driest in 76 years or well over two generations. The last time April was drier, V. C. Bird Snr was president of the Antigua Trades and Labour Union and World War II was still raging.

Potworks Dam, May 1, 2020. Picture courtesy Karen Corbin – Humane Society

The island average for the month is 16.1 mm (0.63 in). Only April 1944, with 5.9 mm (0.23 in) and 1939, with 8.4 mm (0.33 in), have been drier in nearly 100 years.

The total for the month represents only 19% of the normal total of 85.6 mm (3.37 in) – a deficit of 81%, based on the current climatological standard period of 1981-2010.

Such a low rainfall total is very rare for April. How rare? It has only around a 4% chance of occurring or once every 25 years on average, based on record: 1928-2019. This would suggest that we were around 50 years overdue for such a parched April.

The reason for us going so many years overdue for such a near record low total is likely due to “positive” climate change. Rainfall for April has been on a steady wetting increase, rising from an average of 53.1 mm (2.09 in) for the period 1928-1957 to 80.8 mm (3.18 in) for the period 1990-2019.

So, if you were to segment the data, there is around an 11% chance of getting 16.1 mm during the years 1928-1957, as compared to just a 0.6% chance for the period 1990-2019. In other words, our current climate for April is over 18 times less likely to produce such a low rainfall total as compared to the past climate of 1928-1957.

Now, based on the segmented data, the return period for April’s rainfall of 16.1 mm is once every 9 years on average for the past climate. However, the return period for the same value in the current climate is once every 167 years on average. Hence, most persons alive along with their grand and great grand children are unlikely to see a similar or drier April in Antigua.

Compared to other months, this April is the driest since June 2018. And of all the 1108 months on record dating back to 1928, it ranks as the 23rd driest. This puts it in the top 2% of all time driest months.

Notwithstanding the miniscule rainfall for April, the rainfall for the year, thus far, is near normal.  However, if not for a wetter than normal first quarter, the situation would be much more dire.

The reason for the absentee rainfall for April looks to be due to a switch from a positive North Atlantic Oscillation (NAO) to a negative NAO. This is manifest in the swing from above normal pressure over the subtropical North Atlantic to below normal pressure. This switch or swing resulted in a reduction of moist unstable air flowing across the area and depositing rainfall.

The pressure over our islands also went from neutral, over the period January-March 2020, to above normal for April. Such a configuration of the pressure would usually also inhibit rainfall, which was evident.

April 2020 was a remarkably dry month. One that most of us have never seen and will likely never see again – happily.

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