Bangalore is a rapidly changing city, both for the better and for worse. If somebody from the Bangalore of the ’80s or the ’90s were to visit the city today, it would be very difficult for them to recognize the city – and so it is to those who return from elsewhere after decades. The same is said of Bangalore’s weather, of how ‘it isn’t what it used to be‘. Cold winters, warm but never-too-hot summers and an extended season of rains populate the Bangalore weather of our dreams – dreams that appear to be increasingly disconnected from reality.
Many blame global climate change as at least part of the reason for a hotter Bangalore, along with local urbanization and related heat island effects, while others focus only on the latter. What does data from weather stations tell us? This post seeks to find out.
The question of whether Bangalore is heating up can be broken down into four parts. First, is the climate of Bangalore getting hotter in the long run? Second, is the change in temperatures consistent with global climate change? Third, is this warming related to the changes that we might be feeling? And fourth, could there be changes in temperature in the city above and beyond what gets recorded at a weather station?
The long term temperature trends of Bangalore tell an astonishing story.
It turns out that over the last century, between 1901 and 2000, minimum temperatures have been consistently rising in Bangalore at a rapid rate. However, maximum temperatures don’t quite follow the same trend. Instead, it appears that maximum temperatures peaked in the 1920s and 1930s! Since then, they fell sharply by 1940 by about 1.5°C and have been rising steadily ever since.
Why was Bangalore facing such high maximum temperatures in the 1920s and ’30s? The answer is that we simply don’t know. It is important to note while there are prominent global trends at play like anthropogenic climate change, there are often distinct but important local trends in climate that need to be understood and dealt with locally. These trends may be anthropogenic or natural, but their impacts are often quite real. The wind systems around Bangalore could have been different then, or cloud cover was unusually low for a couple of decades, or it could have been entirely something else.
Apart from the mysterious hump in maximum temperatures, it is also pertinent to note that temperatures are rising faster in Bangalore than the global average! Minimum temperatures in the city have increased by about 1.32 degrees Celsius over the last hundred years (± 0.11°C). This is about double the global average. It is equally interesting to note that maximum temperatures are rising even faster since 1940.
Trends in minimum temperatures of individual months also indicate that December, February and March are warming faster than the other months. All months display the same peculiarities in maximum temperatures as seen in the graph above. It is also unfortunate that comparable data is not currently available to examine how temperatures in Bangalore have been in the last decade.
Do these changes confirm our perceptions of the changing climate of Bangalore? The answer to that is both yes and no. Climate data strongly supports the notion that winter nights are getting significantly warmer in the city – with summer nights joining in. Day time temperatures are not increasing (despite what people think!), at least at the century timescale. The difficulty when it comes to understanding perceptions of weather and climate is that people are experiencing weather in the present, and employing memory to remember weather from the past. Both of these are quite flawed, and that is not a slur on anyone’s judgement. Also, it is quite difficult to perceive a 1° change over a century (or even 2 decades!) when temperatures change by about 10°C every day, and an even larger number over the year.
Finally, the faster rise in minimum temperatures in Bangalore could indeed be because of urbanisation, land use change, and heat island effects. But one cannot conclude for certain by looking at this data alone. Also, the built up area near somebody’s home could have increased, with a corresponding loss of trees. Data from a weather station in the central business district of Bangalore can never be able to tell us the effect of that.
How has urbanisation affected ambient climate in Bangalore? Are there other factors that determine whether you feel that a summer is particularly hot? More on these questions in the second part of this article.
Written by Pavan Srinath.
The data used in this article is available here from IMD. You can also download the CSV file here. This article is the first in a series being written in the run-up to the Open Data Camp Bangalore 2013 that is happening over the weekend of March 2-3.