Ian Lockwood

MUSINGS, TRIP ACCOUNTS AND IMAGES FROM SOUTH ASIA

Rainfall Changes in the OSC Neighborhood

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OSC's Weather Bug weather station located on the auditorium roof. A lightening strike in September pulverized the anemometer (wind gauge) and fried the main box of electronics. There is now a new anemometer mounted and we hope to get it up and running shortly.

OSC’s Weather Bug weather station located on the auditorium roof. A lightening strike in September pulverized the anemometer (wind gauge) and fried the main box of electronics. There is now a new anemometer mounted and we hope to get it up and running shortly.

Rainfall patterns in southern India and Sri Lanka have been unusual in the last twelve months with the recent floods in Chennai illustrating extreme events with devastating effects on human populations. Here in the suburbs of Sri Lanka’s capital city we have been monitoring weather patterns to see to what extent this year’s rainfall is different from past years. We have our own weather station courtesy of WeatherBug but it has been down for several months after a lightening strike damaged key components. In order to get a better sense of rainfall I visited the Sri Lanka Meteorological Department to learn more about what they do. After an informal tour of their forecasting center I was able to purchase uncertified rainfall and solar radiance data for all of their 23 main stations in the last 12 months. Certified data requires official requests that take time to organize-hence the use of uncertified data. To better understand this year’s trend with past patterns I compared the 2015 data to a data set of 1960-81 averages available at the Sri Lanka Department of Statistics. In this post I highlight the data from Colombo station over the last 12 months.

OSC’s DP 2 students are currently working on a short data analysis exercise of other stations around the country to further test the guising question: to what extent is the 2015 station monthly rainfall data different than the 1960-81 averages? In the initial assessment we can make is that the pattern is different than past years with relatively dry months receiving usually high levels of rain and months where monsoon rain expected being relatively deficient. We will review the data once the November and December data is available early in 2016.

What is significant about the 2015 data, as recorded by the Colombo station, is the relatively low rainfall levels at the beginning of the South Western monsoon (May-June) and the high readings in September. In fact, September has a value (631 mm) –more than twice the long term 1961-90 average (245 mm). I also accessed freely available Accuweather rainfall data online to check how it compares to the Meteorological Department data. As is evident in the graph below, there is a slight difference in the two readings over all months of the year, perhaps the result of the measurement stations being in two different locations. There is a significant degree of variability in rainfall even in the Colombo area (as is evident when you compare the Colombo station data to Ratmalana and Katunayaka stations). However, all stations show 2015 September reading to be abnormally high.

A year's worth of rainfall data derived from raw daily (un-verified) data purchased from the Sri Lanka Meteorology Department.

A year’s worth of rainfall data derived from raw, daily (un-certified) data purchased from the Sri Lanka Meteorology Department in November 2015.

Rainfall in Colombo. The 2015 data from the Meteorological Department and Acuweather is graphed against the 1961-90 data (sourced from the SL Department of Statistics). The yellow line is data for 2015 taken from Accuweather's Colombo station/source in 2015.

Rainfall in Colombo. The 2015 data from the Meteorological Department and Acuweather is graphed against the 1961-90 data (sourced from the SL Department of Statistics). The yellow line is data for 2015 taken from Accuweather’s Colombo station/source in 2015.

iPhone snapshots from the Sri Lanka Meteorological Department's head office in Colombo.

iPhone snapshots from the Sri Lanka Meteorological Department’s head office in Colombo.

Dramatic changes in rainfall patterns obviously encourage soul searching about potential causes. However, weather and climate patterns are notoriously complex with a variety of variables impacting the spatial and temporal weather conditions that different parts of the planet experience. El Niño, for example, is a major climatic issue at play in the South Asian monsoon this year. Several models that consider human-induced climate predict changes in monsoon and rainfall patterns in South and South East Asia (see links below). At the time of writing the world had focused it attention on the Paris United Nations Conference on Climate Conference. It will likely be some time before we fully understand the connections between Colombo’s 2015 rainfall patterns and broader global climate trends. Examining the raw data from the source has nevertheless given my students and me a unique perspective on the data and the bigger ideas that it might be connected to.

REFERENCES

Burt, T.P and K. D. N. Weerasinghe. “Rainfall Distributions in Sri Lanka in Time and Space: An Analysis Based on Daily Rainfall Data.” Climate. 2014. Web. 9 December 2015.

“Chilly weather at night for two weeks more: Former Met. Chief.” the Sunday Times. 15 February 2015. Web.

“Devastating monsoon flooding from Sri Lanka to northwest Australia.” NOAA. 23 January 2015. Web.

“Historical Rainfall Chennai Floods Southeast India. ” Earth Observatory. 9 December 2015. Web. 9 December 2015

“How El Niño plans to hijack monsoon 2015.” Resources Research Blog. 26 May 2015. Web. 18 November 2015.

Loo, Yen Yi. “Effect of climate change on seasonal monsoon in Asia and its impact on the variability of monsoon rainfall in Southeast Asia.” Geosciences Frontiers. Volume 6, Issue 6, November 2015. Web. 12 December 2015.

“More rains and hotter days ahead.” the Sunday Times. 24 May 2015. Web.

Piratheeparajah, N. “Spatial and Temporal Variations of Rainfall in the Northern Province of Sri Lanka.” Journal of Environment and Earth Science. Vol.5, No.15, 2015. Web. 12 December 2015.

Sathisraja, Anushiya. “Weather patterns have turned chaotic: Met. Dept. Chief.” the Sunday Times. 1 November 2015. Web.

Sri Lanka Department of Statistics. “Annual and Monthly rainfall observations 1961-90.” 2013. Web. 8 December 2015.

Wipulasena, Aanya and Anushiya Sathisraja.  “Climate change has come to stay, Earth getting warmer.” Sunday Times. 29 November 2015. Web & Print. 9 December 2015.

World Meteorological Organization. Web.

 

 

Written by ianlockwood

2015-12-13 at 1:03 pm

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