Driest 6 years since 1903

The six-year rainfall total of 3142 mm to January 2019 was the lowest in a century. The only lower totals ended in the months January, February, and March 1903.

Rainfall shortages at Dec 2018 and Jan 2019

Graph of Rainfall Shortages

This graph shows all the present rainfall shortages at Manilla, short term and long term, as percentile values. The latest values, as at the end of January, are shown by a black line with large circles. Those from one month earlier, at the end of December, are shown by a thinner line with smaller circles.

Changes this month

The pattern

At this date, rainfall totals for short periods, one month to six months, are below normal but they are not serious shortages (below the 10th percentile). Now, nearly all rainfall totals for nine months up to twenty years are serious shortages or worse. Extreme shortages (below the first percentile) occur at durations from 12 months to 24 months, and at 6 and 7 years. Severe shortages (below the 5th percentile) have now developed at 30 months, 36 months and 48 months.

Short-term shortages

At durations less than nine months, rainfall shortages hover around the 20th percentile. While not classed as “serious”, such values cause the drought to extend to ever longer durations.

Extreme shortages

There are now extreme shortages (1st percentile) at durations of 12 months (331 mm), 15 months (444 mm) 18 months (548 mm), and 24 months (821 mm). The extreme 7-year shortage has now worsened, to become the 7th driest on record. However, the 6-year shortage is even worse, the 4th driest.

Long-term shortages

In the longer term, serious shortages at 8 years, 10 years and 20 years persist from the December graph, and a new one appears at 15 years.
Such long-term rainfall shortages were common early in the 20th century. They have hardly occurred since the Keepit Dam was built in 1960.


Further Explanation

Drought 2018 contour chartMuch more detail was given in the post: “Contours of Manilla’s 2018 Drought” (with data up to October only). Notes include: “Long-term shortages”, “Classes of rainfall shortage”, and “Manilla rainfall records”.

Driest 18 months in 50 years

In December 2018, droughts of long duration got worse.

Rainfall shortage November-December 2018

Graph of Rainfall Shortages

This graph shows all the present rainfall shortages at Manilla, short term and long term, as percentile values. The latest values, as at the end of December, are shown by a black line with black circles. Those from one month earlier, at the end of November, are shown by a thinner line with smaller white circles.

Changes this month

Short-term shortages

Although December rainfall (34.5 mm) was below normal, it was enough to keep the totals for 2, 3, 4, and 5 months above the level of “serious shortage”. Because the 6-month total rose to 186 mm, it too did not count as a serious shortage.

Extreme shortages

There were extreme shortages (1st percentile) at durations of 9 months (210 mm), 12 months (327 mm), 18 months (536 mm) and 7 years (3891 mm). The 18-month shortage was the most extreme, being the fifth lowest in history, after four lower values in 1966 (the lowest: 514 mm). The extreme 7-year shortage that has now appeared is lower than any since 1942.

Worsening long-term shortages

This drought brings worsening long-term rainfall shortages. Among the 14 selected durations longer than 2 years that are shown here, 10 of them are now serious shortages (10th percentile) or worse.
As well as the extreme 7-year shortage, two serious shortages that appeared in November are now worse: the 10 year total fell from 5964 mm to 5944 mm, and the 20-year total fell from 12209 mm to 12200 mm. The 10-year shortfall amounts to nearly one year of rain.
Such long-term rainfall shortages were common early in the 20th century. They have hardly occurred since the Keepit Dam was built in 1960.


Further Explanation

Drought 2018 contour chartMuch more detail was given in the post: “Contours of Manilla’s 2018 Drought” (with data up to October only). Notes include: “Long-term shortages”, “Classes of rainfall shortage”, and “Manilla rainfall records”.

November Drought Gets Longer

In November 2018, the drought faded in the short term, but became worse in the long term.

Rainfall Oct Nov 2018 Manilla

Graph of Rainfall Shortages

This graph shows all the present rainfall shortages at Manilla, short term and long term, in terms of percentile values. The latest values, as at the end of October, are shown by a black line with black circles. Those from one month earlier, at the end of October, are shown by a thinner line with smaller white circles.

Changes this month

November rainfall was almost normal at 50.2 mm, further raising the totals for 2, 3, 4, and 5 months, so they did not qualify as serious shortages. The 6-month total of 156 mm qualified as a serious shortage.
The remaining extreme shortages were at 9 months (201 mm) and 18 months (564 mm).

Worsening long-term shortages

Rainfall totals for periods from 72 months to 360 months (6 years to 30 years) are now all below normal. In decades before September 2017 those totals had been normal. (See the September 2017 plot on the graph in this earlier post.)

Three of the current data points are far below normal. The 7-year total (3935 mm) is a severe (almost extreme) shortage, not seen since 1946. The 120-month (10-year) total (5986 mm) is a serious shortage, not seen since 1967. Similarly, the 240-month (20-year) total is a serious shortage, not seen since 1949.
Such long-term rainfall shortages were common early in the 20th century. They have hardly occurred since the Keepit Dam was built in 1960.


Further Explanation

Drought 2018 contour chartMuch more detail was given in the post: “Contours of Manilla’s 2018 Drought” (with data up to October only). Notes include: “Long-term shortages”, “Classes of rainfall shortage”, and “Manilla rainfall records”.