E-Paper
2020: A year of strange weather events
Floods, cyclones, colder winter, unexpected rains, India has seen them all.
2020 has been strange and difficult in so many ways that it seems almost criminal to add one more to the mix — the weather. Floods, cyclones, colder winter, unexpected rains, India has seen them all.
High rainfall at a time when rainfall is declining
India received a total of 1,286.6mm rainfall until December 27 this year. This is the ninth highest rainfall for the January 1 to December 27 period since 1901. It mostly rains during the monsoon months in India, and with even the north-east monsoon on the way out, it is unlikely that this year’s rainfall will fall too behind other years’ in the remaining days of the year. While ending up among the top 10 rainfall years in 120 years itself is adequate to make 2020 an outlier, there is another reason why this year’s rainfall was unusual: it did not follow prevailing long-term trends. The last time rainfall was this high was in 1990 (1201.1mm).
To be sure, not everything about this year’s rainfall was unusual. The share of extreme rainfall – heavy rain over a smaller area or period of time – was higher than the less intense kinds of rainfall. The share of light rainfall this year (13.4%) was ranked 81st in the 120 years since 1901. The shares of moderate (47.6%), heavy (38.1%), and extreme intensity (0.86%) rainfall were ranked 62nd, 55th, and 20th, respectively. This is in keeping with the long-term trend of an increasing share of heavy and extreme rainfall in total rainfall.
For this analysis, rainfall equal to or under 7.5mm in a grid (a box bound by two latitudes and longitudes) was considered light, between 7.5mm and 35.5mm, moderate, between 35.5mm ad 244.5mm, heavy, and above 244.5mm, extreme.
Low winter temperatures although winters are getting warmer
IMD considers the December to February period as winter. Average maximum temperature from December 1 to December 27 this year in India is 24.17 degrees Celsius, according to IMD’s gridded temperature dataset. For these 27 days of December, this is the second-lowest average maximum temperature since 1951, the earliest year for which IMD’s gridded dataset exists. This is not in line with the long-term trends in average maximum temperatures for this period, although the 2011-2020 decade has seen a lower average maximum temperature than the last decade. Since the 1970s, maximum temperatures in December have, on average, increased.
The average minimum temperature for December 1-December 27 period seems to have followed the long-term patterns, however, and is not low. It is the 33rd highest since 1951. The average for 2011-2020, too, is lower only than that in the 1951-1960 decade. To be sure, these figures reflect the average for India as a whole. This number can get skewed if minimum temperatures in some regions are high even while another is experiencing a cold wave. A place in the plains is said to be experiencing a cold wave if the minimum temperature is 10 degrees Celsius or lower and at least 4.5 degrees below the normal minimum temperature for two consecutive days.
La Niña could be a possible reason for this year’s strange weather
One of the reasons for this year’s rainfall and temperature patterns not following the long-term trends could be the onset of a phenomenon in the tropical Pacific Ocean around September. Changes in sea surface temperatures affect global weather patterns. The La Niña and El Niño phenomena, for example, are measured by anomalies or departure from a long-term average in sea surface temperatures (SST) in the tropical Pacific. This is captured by the Oceanic Niño Index (ONI), which is a three-month running mean of SST anomalies. A positive value of ONI above 0.5 (warmer temperatures) is termed El Niño and often leads to warmer and drier weather, whereas a negative value below 0.5 (colder) is termed La Niña and often leads to colder and wetter weather. The La Niña effect was evident by September, and has only intensified since. The late withdrawal of the south-west monsoon in India is attributed to this. According to the World Meteorological Organisation, La Niña is approaching its peak, but neutral conditions may be as far away as next summer, HT reported on December 25.
