Jul 23, 2014

Perception vs Data: Is This The Rainiest Summer Ever?

Weather report on bTV
"Oh, not again!". This is the thought that flashed through my sleepy head this morning when the weather woman stood in front of a map densely covered by small pictures of rain and lightnings. It has been very rainy summer. The never ending rain and the missing sunshine have been a major topic in the conversations for the last few months. Everyone around is sort of angry for the lost opportunities for good times outdoors. The phrases of the day are "This is the rainiest summer ever!", "There has never been such a summer before" and "I don't remember a summer like this one". It got me thinking if it really is the case or it is our perception playing tricks? I pondered on a similar question in my World Cup post where I tried to find why this tournament is considered to be a fantastic one. In contrast to the emotionally charged football tournaments, the weather perception should be relatively simple to analyze as it has been well recorder for a long time and there is hard data on it as well as there are much less factors to consider.

Weather data
I have decided  to narrow my exploration to the weather in the country and the city I live in - Sofia, Bulgaria as this is where from all the opinions come to me. Then I decided that I should go back to 1973 as period of 40 years covers well the ages of people around me. I found a very good source of data on the US National Climatic Data Center - these guys keep extensive records of the world weather. My data set was ready after some data cleansing and reformatting and I was ready to see what is going on. I assumed that summer includes the full months of June, July and August as this is the popular perception despite it is not astronomically correct.

Rainiest summer?
I shot to the heart of the question - is this the rainiest summer ever? I put together the rainfall in mm and the number of rainy days in Sofia from the beginning of Jun to mid July (July 17 to the precise). As you can see on the chart below, it really is the rainiest summer but it is not the rainiest for the last 41 years. There is much more rainfall this year compared to the last 7 years but it is much less than 2005 and comparably same as in 1976, 1983 and 1995. However, the difference with previous 3 to 4 year is very significant.

Put shortly - it is not the rainiest but among the rainiest summers in our lifetime and it is much rainier than last few years. In terms of number of days with rain things are pretty much the same with one major difference - the difference between last years is not that big. That leads to conclusion that this year when it rains, it pours. 

But is it rainiest simply because it started with lot of rain?
Sometimes people make their opinion by the first moments of encounter and I looked in the monthly data. I was thinking that late start of the summer could be the reason for its label. See below the rainfall over the years for June and July.

The monthly patterns repeat the one I found for the whole summer more or less that makes me think we should not blame June (remember that there is data for half July). Both months have been equally rainy.

Maybe it is the year?
Following the known and unknown patterns of the Nature, some years are rainier, hotter or colder than others. The perception could also be influenced by the shift from cold and rainy winter to hot and dry summer. I looked into the cumulative level of water that came from the sky. The data is irrefutable - this is the rainiest year for the last 41 years in Sofia! 

What about the temperature?
There is nothing surprising in the temperature - it is few degrees colder than last few years but in the trend and in the variation for period of interest. I have not put the charts here for space considerations. 

Okay, enough about Sofia! What about the country?
This year was marked with few flood disasters. However, the reason for them was wrong planning and poor maintenance of sewage and drainage  systems. See the charts bellow for the whole country.

Surprisingly, it seems that the country is not experiencing an extremely rainy year as a whole. But this is of little relevance for the citizens of different regions. After all, it is not very comforting that somewhere it is hot while you are freezing, isn't it? The rain has been focused in few regions and Sofia seems to be one of them. 

Concluding thoughts
I am looking through the window and I don't like the big grumpy clouds coming my way. I had enough rainy days for this summer. Despite the feeling of an ongoing flood this summer is far from being the rainiest one in our lifetime. Far damper summer season happened not so far ago and we should remember. But we don't. The data I pulled out hints that we consider only the recent events to form our opinion. This finding is not very surprising though as there is much of research on the topic. Also we all know that from experience even not verbalized explicitly. We consider different periods back in the different context. It seems that the general case for the weather in Sofia, Bulgaria is only last 4 to 6 years are considered. The perception has another side - the media. News are naturally focused on the drama and coverage of streets turned into running rivers is prevalent these days. However, nothing can take away the joy of the warm days and clouds should not keep us from smiling and having good times!

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