Rainfall Changes in the OSC Neighborhood
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.
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.
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