Last year was a relatively quiet year for dengue fever in Singapore, after the rather active years of 2013 and 2014. Ocean cooling may have been one factor, allowing the authorities anti-mosquito campaigns to make a little headway.
Late last year, the numbers began to increase, with a peak being hit early this year.
This year's initial peak is higher than any other in our data series, causing the Singaporean government to forecast in excess of 30,000 cases for 2016.
The general consensus on the cause of the spike in dengue cases has been the recent El Niño event, which normally elevates temperatures in the equatorial Pacific. By some accounts, this event has been one of the strongest on record (at least going by elevated temperatures). By some measures, the 1997-8 event was stronger. Now that the El Niño seems to be weakening, temperatures and the number of dengue cases should fall, at least until the normal seasonal warming period starts.
El Niño usually leads to warming in the Pacific ocean, with increased precipitation in the east, and reduced precipitation in the west. However, individual events have their own characteristics, and this last event differs from previous events in magnitude of warming in the central Pacific, the general lack of enhanced precipitation in western North America. Dengue outbreaks in the Phillipines and in Taiwan in late 2015 were blamed on the current El Niño event (Wendel, 2015).
Clusters of dengue cases are primarily in the eastern part of the island. Data from here, accessed on April 12.
Many of the clusters appear to be at the edges of recently developed land. These lands are those that are expected to be most marginal (i.e., low-lying, wet) and represent good breeding grounds for mosquitos. These lands have been developed recently to accommodate the rapid growth in population over the past sixteen years (according to the Singapore Department of Statistics, population has risen from 4.0 million in 2000 to over 5.5 million in 2016).
Comparison of Google Earth imagery over the past fifteen years in some of the clusters may provide some insight into the relationship between development, land use, and dengue clusters.
First up--Pas Siris. I chose this area as this is where I stayed with my family the last time I was in Singapore (just over three years ago).
Both images cover Pasir Ris and part of Tampines. The upper image was captured on February 8, 2005, and the lower image on February 25, 2015. The three transparent yellow polygons on the lower image represent identified dengue clusters as of April 12, 2016.
There has been some development during the ten years between the two images. But the most important development happened in the area beginning in 1983, before which the area was a low-lying area punctuated by small villages and kampongs.
Unfortunately, the area is so ordinary (cookie cutter buildings), that the only photos I can find of the place were of parakeets hiding in a tree outside my window at night.
One area where dengue clusters seem particularly abundant is Serangoon.
The top image is as the neighbourhood looked in 2008, whereas the lower image is the current imagery over the same area, with dengue clusters (as of April 12, 2016) superimposed on the image. If you were to locate the imagery next week or next month, you will probably find the clusters will have moved, but you will still find plenty in the area.
Very little development has occurred in the interim between the two pictures. The area is another low-lying area (although this is pretty common in Singapore). The name of the neighbourhood is proposed to have come from the name of a bird common to the swamps of the area. There are still a number of green spaces in the area, so perhaps there is a problem with local drainage.
If I were to change anything about my original thesis, that the dengue outbreaks combined natural warming with recent development of marginal (swampy) land in order to settle large numbers of immigrants, it would be to remove the word "recent". Most of Singapore was swampy, and swampy is as swampy does.
References:
Wendel, J., 2015. Dengue fever epidemics linked with El Nino, study says. Eos, 96, doi: 10.1029/2015EO037169. Published October 9, 2015.
Late last year, the numbers began to increase, with a peak being hit early this year.
This year's initial peak is higher than any other in our data series, causing the Singaporean government to forecast in excess of 30,000 cases for 2016.
The general consensus on the cause of the spike in dengue cases has been the recent El Niño event, which normally elevates temperatures in the equatorial Pacific. By some accounts, this event has been one of the strongest on record (at least going by elevated temperatures). By some measures, the 1997-8 event was stronger. Now that the El Niño seems to be weakening, temperatures and the number of dengue cases should fall, at least until the normal seasonal warming period starts.
El Niño usually leads to warming in the Pacific ocean, with increased precipitation in the east, and reduced precipitation in the west. However, individual events have their own characteristics, and this last event differs from previous events in magnitude of warming in the central Pacific, the general lack of enhanced precipitation in western North America. Dengue outbreaks in the Phillipines and in Taiwan in late 2015 were blamed on the current El Niño event (Wendel, 2015).
Clusters of dengue cases are primarily in the eastern part of the island. Data from here, accessed on April 12.
Many of the clusters appear to be at the edges of recently developed land. These lands are those that are expected to be most marginal (i.e., low-lying, wet) and represent good breeding grounds for mosquitos. These lands have been developed recently to accommodate the rapid growth in population over the past sixteen years (according to the Singapore Department of Statistics, population has risen from 4.0 million in 2000 to over 5.5 million in 2016).
Comparison of Google Earth imagery over the past fifteen years in some of the clusters may provide some insight into the relationship between development, land use, and dengue clusters.
First up--Pas Siris. I chose this area as this is where I stayed with my family the last time I was in Singapore (just over three years ago).
Both images cover Pasir Ris and part of Tampines. The upper image was captured on February 8, 2005, and the lower image on February 25, 2015. The three transparent yellow polygons on the lower image represent identified dengue clusters as of April 12, 2016.
There has been some development during the ten years between the two images. But the most important development happened in the area beginning in 1983, before which the area was a low-lying area punctuated by small villages and kampongs.
Unfortunately, the area is so ordinary (cookie cutter buildings), that the only photos I can find of the place were of parakeets hiding in a tree outside my window at night.
One area where dengue clusters seem particularly abundant is Serangoon.
The top image is as the neighbourhood looked in 2008, whereas the lower image is the current imagery over the same area, with dengue clusters (as of April 12, 2016) superimposed on the image. If you were to locate the imagery next week or next month, you will probably find the clusters will have moved, but you will still find plenty in the area.
Very little development has occurred in the interim between the two pictures. The area is another low-lying area (although this is pretty common in Singapore). The name of the neighbourhood is proposed to have come from the name of a bird common to the swamps of the area. There are still a number of green spaces in the area, so perhaps there is a problem with local drainage.
If I were to change anything about my original thesis, that the dengue outbreaks combined natural warming with recent development of marginal (swampy) land in order to settle large numbers of immigrants, it would be to remove the word "recent". Most of Singapore was swampy, and swampy is as swampy does.
References:
Wendel, J., 2015. Dengue fever epidemics linked with El Nino, study says. Eos, 96, doi: 10.1029/2015EO037169. Published October 9, 2015.
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