The Madden-Julian Oscillation
|Graphic from here.|
|Graphic from here.|
To begin my analysis I needed to get 30 years worth of monthly rainfall data to get an idea of cyclical and long term climatological trends for the valley. This is the basic (but not only) difference between climatology and meteorology; whereas meteorologists focus on day-to-day atmospheric changes, climatologists are more interested in the bigger picture. A climatologists can't tell you if it's likely to rain this afternoon, but he/she can tell you whether it's likely to be dry or wet in July 25 years from now. For climatologists the accepted time period for determining general patterns is 30 years.
Getting the Data
|Automatic rain gauge at the airport. They|
also have a manual gauge.
My first stop was the regional statistics agency (Badan Pusat Statistik, BPS) in Sungai Penuh. The BPS is the government agency responsible for tracking, compiling, and publishing data ranging from demographic and economic indicators to weather information. Every year (theoretically) the BPS publishes a fact-book about its district, and these are generally kept in the library at the BPS office. If you are a foreign researcher you need special permission to access the library; fortunately I had already established a relationship with BPS and I know the guys that work there. Some districts make their data available online, but Kerinci hasn't yet reached this level of sophistication, so you have to personally go to the office.
The records at BPS begin in 1985, and unfortunately there is a significant amount of missing data. Since the rainfall data is collected at Kerinci's "airport", I decided I'd go right to the source. I rode my motorcycle down to
Depati Parbo Airport,
which sits in the middle of a rice field and is reached by following a bumpy
hardened gravel road from Sungai Penuh to the . The Meteorology, Climatology, and Geophysics
agency of the central government maintains a small station there mainly to
collect data for the airport and the farmers of the region. After receiving a tour of the installation, I
asked for the rainfall data over coffee and other refreshments. My new friend, the head of the station, was
happy to oblige. He even invited me over to his house for coffee, an offer I'll take advantage of next time I'm in his neighborhood. village of Hiang
Some Graphs and Stuff
The first thing I looked at was the annual rainfall record, which I've illustrated in the line graph below. The average rainfall over the period for the valley was 1311mm, but as you can see there is a bit of variability. In general it appears that there could be a downward trend, but without further analysis (which I haven't done yet) it is difficult to tell whether this is significant or not. Also, I am reluctant to draw any conclusions based on 27 years (with two missing years), because if you go further back you may find that this apparent trend is part of some longer-term cycle, or is within normal long-term variability. What I did notice, though, is that there doesn't seem to be any clear direct relationship between La Nina/El Nino years and annual rainfall. Some La Nina years have lots of rain, some have below average rain, likewise with El Nino. This doesn't mean that there is no El Nino/La Nina effect here because there could be some sort of combined influence with El Nino/La Nina working in tandem with some other pattern (like the MJO).
I also noticed that this March has indeed been unusually dry, but it's not the driest March on record. In addition, I also noticed that whenever there is an abnormally dry March, April tends to be wet. So although everyone, including the region's farmers, are worried about the lack of rain, I think that the dry spell will end pretty soon. The next step in the project will be to figure out a good, rigorous way to compare my rainfall data with MJO intensity and to see if there is any sort of connection there. In the picture below you can see the intensity of the MJO spanning a period of more than four decades.
|Chart from here.|
We'll see how my little investigation goes. It could prove to be beyond my capabilities. Another possibility is that my wonderful academic adviser sees this post and sends me and angry email admonishing me to get back to work.
(1) Climatology is one of the major strengths of the Department of Geography at the University of Hawai'i.
References and for Further Reading
For an excellent source on the MJO check out the Madden-Julian Conversation blog here.