Drier than Usual July, Drought Continues

27 08 2021

Dale C. S. Destin |

July was drier than usual like the first five months of the year. The month yielded only 65.5 mm (2.58 in) of rainfall. Although July took over from June as being the wettest month for the current year; it barely made a dent in the ongoing droughts. July has become the only month of the year, thus far, to clock over two-and-half inches of rain. The rainfall for the last seven months ranks among the worst on record and there is not much respite in sight.

Potworks Reservoir, Bethesda, Antigua, on the verge of becoming totally dry – July 7, 2021. Picture courtesy Karen Corbin of the Humane Society

The rainfall for July is the lowest since 2018, when the country had 39.6 mm (1.56 in). The total for the month represents only 67 percent of the normal value of 98.0 mm (3.86 in), a deficit of 33 percent.

The period May-July was also drier than usual. The total of 138.4 mm (5.45 in) was the 13th driest on record starting 1928. The last time this period was drier was 2015 with 74.4 mm (2.96 in).

We continue to witness one of the driest years on record. The last seven months is the fifth driest on record and the driest since 2015. January to July produced only a meagre 270.3 mm (10.64 in), only a little above half of the usual rainfall of 500.1 mm (19.69 in). Again, just four other years have been drier through July: 2015, 2001, 1977 and 1939.

Since the 2020 November’s deluge, the last eight months, December-July, is the seventh driest on record and the lowest since 2015. The period has only yielded 58 percent of normal rainfall. Our starving landscape and parched grounds continue to bear witness to the below normal rainfall.

The upcoming autumn, September to November, is likely to see us continue to suffer from a scarcity of rainfall. The majority of models are forecasting the continuation of lower-than-normal rainfall. Hence, the drought is likely to continue. Our largest catchment, Potworks Reservoir, along with others, are transitioning to dry land, again.

WMO Lead Centre for Long-Range Forecast Multi-Model Ensemble is forecasting 50-60% likelihood of below normal rainfall for Antigua and Barbuda. Also, below normal rainfall is likely for much of the rest of the northeast Caribbean.

Based on models which correlate our sea surface temperatures, across the tropics, with our rainfall, the medium and long term continue to look brown. The year will most likely remain drier than usual with a 61 percent chance of below normal rainfall; this is up 11 percent from last month.

As the meteorological drought goes, so go the other droughts: agricultural, hydrological and ecological. There is also the growing concern that this may precipitate a socio-economic drought, if it has not already done so. Our utilisation of the ocean around us for fresh water has made us resilient; however, this is expensive water, over seven times the cost of that from surface and ground water.  

Potworks Reservoir remain below extraction levels, along with most other surface catchments, according the Antigua Public Utilities Authority (APUA), the country’s water authority. Water rationing has officially started and with the rainfall outlook being gloomy, it is likely to continue for the foreseeable future.

Antigua is not alone in experiencing significant rainfall shortages. The countries around us remain  thirsty for rainfall. Deficit rainfall is occurring across the rest of the Leeward Islands, and it is probable that it will worsen, over the upcoming months.  

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4th Driest May on Record for Antigua

5 06 2020

Dale C. S. Destin|

Potworks Dam, Antigua – June 1, 2020. Currently dry but when full, holds a billion gallons. Pic courtesy Karen Corbin – Humane Society

May 2020 was another very dry month for Antigua. The rainfall total of 20.8 mm (0.82 in) was the lowest since 2001 and the fourth lowest on record dating back to 1928. Only May 2001, 1939 and 1928 have been drier, with May 2001 being the driest with 6.4 mm (0.25 in).

Relative to the normal total for the month of 103.6 mm (4.08 in) only 20% fell; hence, the month had a rainfall deficit of 80%, based on the current base period of 1981-2010.

Such a low rainfall total for May is relatively rare. It happens once every 21 years, on average or has only 4-5% probability of occurring each year.

The rainfall for May is almost “bipolar” – you either get a lot or a little. This makes the rainfall for the month the most unpredictable with the highest variability index of all the months.

The dryness for May was not confined to Antigua. Most of the region from Hispaniola to Trinidad saw, at most, only 25% of the normal rainfall for the month.

The reason for the truant rainfall looks to be due mainly to higher than normal surface pressure and lower than normal relative humidity.  

Rainfall for the year has now fallen to below normal after an excellent start in the first quarter. There are some hopes for the return of seasonal or above seasonal rainfall over the upcoming months. The current forecast is for above normal rainfall for the period June to August.

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Potworks Dam Back Online!

23 12 2019

Dale C. S. Destin|

Potworks Dam, Antigua’s largest water catchment, is back online after being offline from around middle of last month, for the fourth time this year. The billion-gallon catchment water levels rose above extraction levels during the rains of late November and early December allowing for it to be reconnected to country’s water lines, to supply potable water.

Ian Lewis, Manager – Antigua Public Utilities Authority (APUA) Water Business Unit

For the year, the Dam first fell below extraction levels back in April but was topped up in late May. It again went below extraction levels in September but was topped up later that month. And again, it fell below extraction levels around mid-November but was partially recharged late November/early December; hence the reason why it is back online.

There is now a slight meteorological drought, which started in October. Based on the latest forecasts, over the upcoming months, it is expected to persist or worsen. Prior to this drought, there was a severe drought from October 2017 to April 2019 – 19 month long.

For the month of November, the catchment area – Bethesda Village, received a little over 100 mm (over 4 in) of rainfall. This is below normal but twice the total for October – 54.9 mm (2.16 in), which is well below normal 150-175 mm (6-7 in). Already, for December, the area has had over 100 mm (over 4 in), which is more than usual.

With Potworks back above extraction levels along with other smaller catchments, water rationing has been terminated, according to the Antigua Public Utility Authority (APUA), the water authority. However, there remains a hydrological drought of, at least, moderate intensity, with no end in sight.

Potworks Dam is less than a quarter full (over three-quarters empty). It has around 200,000 million gallons compared to a capacity of a billion gallons. It has been over five years since it reached capacity; being close to empty or empty has been the norm since 2014.

Potworks Dam – December 4, 2019. Pic courtesy Karen Corbin – Antigua Humane Society

According to APUA, at the usual rate of extraction, the Dam has two to three months of water supply. This means that it will be a part of the country’s water mix until March – the heart of the dry season. Thus, there is not enough surface water to last through the dry season – January to June 2020.

Recharge of catchments is very unlikely during the dry season. This is especially so for this coming dry season, as the outlook is for below normal rainfall being most likely. Hence, Potworks is expected to come offline again by March and will likely remain offline from then until the wetter portion of the wet season – August to November.

Precipitation forecast for January-March 2020, based on 12 global models – 40 to 50% chance of below normal rainfall for Antigua and the rest of the Eastern Caribbean
The outlook shows 45% chance of below normal rainfall for Antigua and the northeast Caribbean for March to May 2020

Given the season and the forecast, a return to water rationing is almost inevitable in about three months, when Potworks Dam is expected to be offline again. Water conservation and efficiency cannot be over encouraged. Let us treat water like the scarce but precious commodity that it is and make every drop count. Think rain!

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Driest June in Over a Generation for Antigua, Droughts Continue

23 07 2018

Dale C. S. Destin |

June 2018 was the driest for Antigua in 33 years – over a generation. With the median age of the Antiguan population being around 31, most Antiguans have never seen a drier June. Not since 1985 has Antigua experienced a drier start to summer.

Potworks_Dam_Jul6_2018

The total rainfall for the month of 12.7 mm (0.50 in) was a parched 18% of what normally falls – 69.3 mm (2.73 in). Thus, there was an excruciating 82% rainfall deficit for the month.

This was the third driest June on record dating back to 1928. Only 1985 and 1974 Junes were drier with 12.4 mm (0.49 in) and 8.1 mm (0.32 in) respectively. The 12.7 mm for this June has a return period of 34 years i.e. such severe dryness for the month only occurs once in every 34 years, on average.

ModerateMetDroughtUnchangedThe last three-month period – April to June, upon which the assessment of the current intensity of the drought is based, had 128.3 mm (5.05 in), only around half of the normal total of 258.6 mm (10.18 in). This puts the meteorological drought current intensity at moderate, unchanged the previous assessment.

Overall, we are in a serious meteorological drought, but currently it is at moderate intensity. The overall description of the drought is based on the worst intensity achieved since it started; however, over time, the intensity will fluctuate.

Potworks Dam, with a billion-gallon capacity, has been totally dry for a couple of months now. The vegetation of the Island is struggling – grass has virtually ceased growing in some locations. Many fields are bare, with some having large cracks. These are indicative of the fact that the droughts not just meteorological, are at moderate levels or worse.

Happily, the full impacts of the droughts continue to be masked by the presence of the desalination plants; however, impacts are starting to break through. Potable water is being rationed, some places have been left without water for many hours to weeks, at a time. There will be a big press conference this morning by APUA – the water authority, to provide answers to the water problem.

The dry season – January to June, had well below normal rainfall. On a scale of 1 to 100, with 100 being best rainfall situation and 1 being the worst, the rainfall was less than a 10. Only 254.3 mm (10.01 in) or 59% of the normal total of 434.6 mm (17.11 in) fell. It was the 10th driest dry season on record dating back to 1928. Only dry season 2015 was drier since 2004.

RainfallForPast24Months_June2018

Rainfall (in) for the past 2 yrs. All periods showing well below or below normal rainfall.

The nine-month period – October 2017 to June 2018, the duration of the drought thus far, is deemed severely dry. This means that the total is in the bottom 5% of the historical data. Such dryness happens around once every 20 years, on average.

The total for the last nine months of 464.6 mm (18.29 in) is the lowest since 2001 and the third lowest on record dating back to 1928. The period normally gets 845.1 mm (33.27 in).

Based on the last set of rainfall outlooks from regional and especially international sources, the news remains bad for rainfall. Below normal rainfall is most likely for the next six months – August 2018 to January 2019. Thus, there is every reason to believe that the droughts will continue and likely worsen. The chance of the droughts ending is at most 20% or slight.

Prob Multi-Model Ensemble Forecast For ASO_Jul2018

Probabilistic Multi-Model Ensemble Forecast of Rainfall For Aug-Oct 2018

Recall that the current drought started in October 2017 with the intensity at serious levels. On average, serious meteorological droughts last for close to a year, but not continuously at serious intensity. Will it go for another three months? Yes, it is now almost certain that this drought will last for a year or more.

Our confidence of 2018 being a drier than normal year is growing. It has increased from 60% to 75% confidence. The best forecast for the amount of rain for the year is around 855 mm (33.7 in) with a 70% chance of the amount ranging between 625 mm (24.6 in) and 1139 mm (44.8 in). Normally, we get 1206.5 mm (47.5 in) annually.

Accumulations_June2018
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Very Dry March; Droughts Reintensify

26 04 2018

Dale C. S. Destin |

March 2018 was the driest since 2014 and the 12th driest March on record dating back to 1928. The island-average total for the month was 17.8 mm (0.70 in). This represents only 34% of the usual amount of 51.8 mm (2.04 in).

D&P_RainfallGraphic_Mar2018

Rainfall in inches for the past 24 months. Multiply by 25.4 to get mm.

The last three-month period – January to March, upon which the assessment of the current intensity of the drought is based, had 116.1 mm (4.57 in), only 66% of the normal total of 176.0 mm (6.93 in). This puts the meteorological droughts current intensity at moderate, down from slight.

DroughtGraphic: Slight_to_Moderate

With Potworks Dam about to go totally dry and the vegetation of the Island struggling, there is little doubt that other droughts are at moderate levels or worse. Thankfully, the full impacts of the droughts are being masked by the presence of the desalination plants.

Rainfall_Accu_Anu

Interestingly, in a negative way, the rainfall accumulation for the year, thus far, is not very dissimilar to that of 2015 and 1983 – the driest and second driest years on record, respectively. We make no conclusions here but it may be an ominous sign.

The six-month period – October 2017 to March 2018, the duration of the drought thus far, was seriously dry. The total for the period of 326.4 mm (12.85 in) is the fifth lowest on record dating back to 1928. It is also the lowest total for the given period since 2001. The rainfall deficit since the drought started is at 260.1 mm (10.24 in).

Based on the last set of rainfall outlooks, the news is not good for rainfall. Overall, below normal rainfall is most likely for the six-month period April to September. Thus, there is every reason to believe that the droughts will continue and likely worsen.

Even if the rainfall total turns out to be near average, it will not be enough, especially with respect to the hydrological drought, as the monthly evaporation rates significantly exceeds rainfall totals for most of the upcoming months. The chance of the droughts ending is slight – less than 30%.

Recall that the current drought started in October 2017 with the intensity at serious levels. On average, serious meteorological droughts, for Antigua, last for close to a year, but not continuously at serious intensity. We have just passed the six-month mark. Will it go another six months? The answer looks more likely to be yes rather than no.

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Antigua and Barbuda Battered by Torrential Rains

16 09 2016

Last week Monday, Antigua and Barbuda was battered by torrential rains from a tropical disturbance. This resulted in major flooding in many parts of the country, especially in low-lying and flood-prone areas. We had not seen such downpours in nearly a decade.

Satellte loop of the tropical disturbance

Satellite loop of the tropical disturbance

Many parts of Antigua got more than the average total rainfall for September in less than 24 hours. On average, Antigua got around 139.7 mm (5.5 in) in less than 24 hours, with many areas getting over 180 mm (over 7 in), which is much more than the island-average of 144.0 mm (5.67 in) for September.

RadarRainfallAccumulation-24hrs ending 2amSep62016

Radar rainfall accumulations for the 24 hrs ending 2 a.m. Sep 6, 2016

With the average rainfall total of 139.7 falling on 108 square miles (the size of Antigua), it means that about 8.6 billion imperial gallons (IG) of water fell on Antigua between 2 am, September 5 and 2 am September 6. As a reference, this amount of water could serve the country for three years. It’s also close to 100 times the 90 million IG collected by Potworks Dam.

Clearly, with all this water, it should come as no surprise the we had areas with major flooding. Notwithstanding the negative impacts of the flooding, it was rainfall to make most Antiguans and Barbudans, particularly water resources managers and farmers, smile from ear to ear. It resulted in significant recharging of catchments, many of which were dry or below extraction levels since early last year.

Potworks Dam: left – Aug 24, 2016, right – Sep 6, 2016

Potworks Dam, which was dry for over a year, was filled to around one-eighth, according to the Antigua Public Utilities Authority – APUA (the water authority) . It collected around 90 million IG of water, enough to augment water supplies for the next three to four months. APUA has since indicated an easing of water rationing, at least, for the short-term.

Monday September 5, 2016 was the wettest day for quite a while for many areas of Antigua. At the Airport it was the wettest day since Hurricane Earl’s unwelcome visit in 2010. It was also one of the wettest days since Hurricane Lenny in 1999. Only three other days have been wetter since Lenny – the “father” of all flooding for Antigua.

Although this type of rainfall has been rare for the past 15 years, it does occur fairly frequently at a rate of around once every four to five years, based on rainfall measured at the V. C. Bird International Airport – the home of the Antigua and Barbuda Meteorological Service. In other words, it has about a 20-25% chance of happening each year.

The rains caused major flooding of low-lying and flood-prone areas. This resulted in an unknown number of cars being stalled in flood waters and a number of homes came very close to being flooded. There were minor rock slides reported but damage, if any, is unknown. In the wake of the event, many roads were damage due to erosion.

Flooded road

Flooded road

Flooded road

Flooded yard

The event proved very challenging to forecast. Several days before the event, most models forecast up to five inches of rainfall to occur. However, as we got closer to September 5, the models shifted the rainfall to the south of Antigua. Up to the morning of the event, none of the models surveyed came remotely close to forecast the rainfall that eventually occurred.  

Can we get a repeat of last week Monday?  It is probable but highly unlikely. The chance of getting two such days in a given year is around seven percent. So whereas getting dowsed by such drenching rainfall is not unusual, especially at this time of the year, it is highly unusual for it to happen twice in a year.

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Antigua is out of Surface Water Again

17 08 2015

Dale C. S. Destin |

Drought stricken Antigua is currently out of surface water once again, according to the Antigua Public Utilities Authority (APUA), our water authority. All surface catchments have fallen below extraction levels or have dried up as of the end of July for the second time in a year.

Potworks Dam, Aug 1, 2015 | Courtesy Karen Corbin, Humane Society

Potworks Dam, Aug 1, 2015 | Courtesy Karen Corbin, Humane Society

The country is now relying enormously on desalinated potable water. Our current daily potable water mix is around 83% desalinated water and 17% groundwater. Under normal conditions, 57% of our potable water comes from the sea, 28% from surface catchments and 15% from the ground.

According to APUA, around 5.5 million imperial gallons (MIG) of potable water are being produced per day, based on recent figures. However, the country requires around 8 MIG per day to satisfy demand. This means that there is a hefty daily deficit of around 2.5 MIG or 31%.

APUA plans to install a new desalination plant later this year; this will reduce the deficit but fall well short of eliminating it. In the interim, the water deficit could increase further as the drought continues.

The country was last out of surface water around this same time last year, 2014, after nearly a year into the current severe and prolonged drought. Unfortunately, we have found ourselves in this position many times in the past, when our surface catchments, which amount to a total capacity of around 1346 MIG, go dry.

Other years of depleted catchments include 2009/2010, 2000-2003, 1991, 1983 and 1973/1974 with perhaps 1983 being one of the most memorable as water had to be barged from Dominica.

A paper by A. J. Berland et al., published in 2013, shows that Antigua’s water woes and insecurities date back to colonial times.

Bethesda Dam, July 31, 2015 | Courtesy Karen Corbin, Humane Society

Bethesda Dam, July 31, 2015 | Courtesy Karen Corbin, Humane Society

Antigua has been in drought for around two years to date. Over the past three months, it has been at severe levels with rainfall in the bottom 1% of the historical records or amounting to less than 28% of the average. Further, year to date, we have had record low rainfall; the driest ever January-July dating back to at least 1928.

During the later part of 2014, we saw a significant recharge of catchments, due mainly to above normal rainfall in November, the only wet month for that year. The rainfall reduced the drought to slight levels but was not enough to end it. Since then, it has been all downhill.

The outlooks for rainfall remain depressing. Lower than normal rainfall is likely for August and August-October, and below to near normal rainfall is likely for November-January. Meanwhile, above normal temperature over much of August-January could exacerbate things.

We rely heavily on the wet season (July-December) rainfall to recharge catchments to take us through the dry season (January-June). If the drought persists, as we expect it to, catchments could remain below extractable levels or dry until the next wet season.

The need for water conservation and efficiency, at this time, cannot be over emphasized.

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