A short post today to break the hiatus, where we take a look at the year’s rainfall so far.
A major limitation with the weather and climate discussions in popular media is that rainfall is discussed in terms of deficits and excess in terms of percentage points – which really conveys a lot lesser information than you might think. This gets condoned by the Met department as they rarely put out other kinds of information. Deficits and excesses should always be examined in the historical context – so that one can figure out how unusual or infrequent a certain event is. Monsoonal rainfall in India varies so much that few numbers actually end up breaking or making records – it’s a different and depressing story that even as a country we are not yet fully equipped to deal with even the likes of ‘normal variation’
With this in mind, given below is a graph of 57 years Bangalore’s rainfall data and calculated cumulative numbers – to examine the progress of the monsoon. The median line shows well, the median (50th percentile) progress of the monsoon – this means that at any point, 50% of the years got more rainfall than the black line, and 50% got lesser. Similarly, I’ve drawn lines for select percentiles and the maxima and minima. Overlaid on this is the current monsoon in red.
As you can see, the city was doing alright in terms of rainfall received, up until the monsoon started. Rainfall in June quite literally flatlined, taking Bangalore from an above-median rainfall regime to a below median one, quickly dropping below the 25th percentile line – what this means is that the city had received more rains in over 45 of the last 60 odd years. Things could have picked up if we had received good rains in July – but mediocre quantities of rain in July has kept us in the same low-rainfall regime.
A caveat here is that the historical data-set underestimates rainfall by a small amount – which means that the 2012 numbers may actually be worse in comparison, although not by much. As one can see, there is plenty of rainfall yet to be received in the year, on average. How much Bangalore will actually get in 2012, only time will tell.
Written by Pavan Srinath. Views are personal.