Antigua’s Rainfall Intensity – 2013

13 03 2014

By Dale C. S. Destin |

Antigua’s water crisis has intensified as the blame for the crisis shifts to low rainfall intensity as opposed to drought. Late last week, the Antigua Public Utility Authority (APUA), the country’s water authority announced that the water level at Potworks Dam – the country’s largest water catchment, was too low for further extraction. February 21 APUA indicated that there was only one month of surface water remaining with the Potworks Dam only having two weeks supply remaining. Meanwhile, the blame for the water crisis seems to have shifted from insufficient rainfall to insufficient intensity of the rainfall for 2013. Last week, it was shown that the rainfall total for last year was near normal. The rainfall measured was 46.20 inches, the equivalent of 72.2 billion gallons of water falling on the island in 2013. RainfallIntensity2013a

The discussion has now shifted to whether the rainfall intensity was below normal. Already, persons in authority have made emphatic pronouncements that the rainfall intensity was in fact below normal. Hence, there was not enough run off to replenish surface catchments.

However, freely available data from the Antigua and Barbuda Met Service do not corroborate that assertion. Rainfall intensity is defined as the rate of rainfall expressed in a number of ways such as millimetres (mm) or inches per hour or per day. So, a simple way of doing this is to divide the total rainfall for a given month or year by the number of days with rainfall greater than or  equal to one mm (SDII method). The intensity can also be determined by counting the number of heavy rainfall days i.e. days with 10 mm or more (threshold method).

Regardless of how you bisect and trisect the Antigua rainfall numbers for intensity, the picture remains the same – normal to above normal intensity occurred in 2013. Hence, asserting the country had below normal rainfall intensity is just not consistent with the reality. For 2013, using the SDII method the intensity was 8.4 mm per day, the same as the normal of 8.4 mm per day. Using the threshold method, 2013 had 33 heavy rainfall days, which is above normal, compare to the normal of 26.3 days for any given year.

Last week’s blog entitled Antigua’s Water Crisis seems to have unintentionally rubbed some persons the wrong way and misunderstood by some others. For clarity, these are the substantive issues that were raised and should be addressed: a) the lack of a comprehensive drought plan administered by stakeholders; the under optimization of catchments and under utilization of groundwater resources; the non-preparation of the population for the water crisis, and whether 72.2 billion gallons of water were enough to prevent or delay the crisis.



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