Number Theory: Is an early start to summer likely this year?

On February 10, Delhi’s Safdarjung weather station recorded a maximum of 29

On February 10, Delhi’s Safdarjung weather station recorded a maximum of 29.7°C, seven degrees above normal. Day temperatures at the capital’s base station were at least 5°C above normal from February 9 to February 11. This early warmth is not just limited to Delhi and is not likely to be temporary. The India Meteorological Department does not expect a significant drop in temperatures in the coming days, HT reported on February 10. Does this mean we are going to see an early start to summer like last year? While the weather forecast for the next two weeks does say that the rest of February will be warmer than normal in most parts of India, an early summer could still be held off by a colder than normal March. However, historical trends suggest we should prepare for an early summer, irrespective of current temperatures, at least to protect the spring harvest, which was badly affected last year due to unseasonal heatwaves. Here are five charts that explain this argument.

HT Image

February has been consistently warmer than normal so far

It might be relevant to check maximum temperature for look for an early arrival of summer. The maximum temperature is also relevant to agriculture. While the February maximum was colder than normal last year, the March maximum was the ninth highest since 1951. This affected the yield of wheat, the main cereal grown in the winter season, increasing inflation. This year, temperatures appear to be rising in February itself. The average maximum for India up to February 11 was 26.84°C, 0.62 degrees above normal, and 26th highest since 1951, the earliest year for which the weather office’s gridded dataset is available. While this in itself is not record-breaking, daily data suggest a trend has set in. In January, the maximum was regularly below normal. The February maximum, on the other hand, has been above normal continuously for the nine days to February 11. It means that the overall deviation in February is not the result of a few unusual days of high maximum temperatures.

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States important for wheat output are experiencing a warmer February than India average

To be sure, the India average may not necessarily be relevant in terms of agriculture. This is because the average can be pulled up or down due to a few states that do not contribute much to farm output. However, states important for farm output are experiencing a warmer February than the India average would suggest. It is the third warmest February since 1951 so far in Odisha, Jharkhand and Chhattisgarh; among the top 10 warmest for Gujarat, Punjab, West Bengal, Andhra Pradesh, Telangana and Karnataka; and among the top 15 for Haryana, Uttar Pradesh, Madhya Pradesh and Maharashtra.

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Even at the state level, the overall deviation from normal is not just a result of a temporary warming. All the states listed above have experienced warmer than normal daily maximum continuously in the past week. In Uttar Pradesh, Punjab, Haryana and Madhya Pradesh, the highest producers usually in that order and accounting for three-fourths of India’s wheat output, the maximum temperature has been consistently above normal in the past nine, 12, 10, and nine days, respectively.

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This is because rainfall has been missing this year, especially in wheat-growing states

The high maximum temperatures this February have a simple explanation: lack of rainfall. India has received 3.1mm rain up to 8:30am on February 12, which was 52% less than the 1961-2010 average, or the long-period average (LPA), and 35th lowest since 1901. As is expected from temperature deviations seen above, the February deficit is more acute at the state level. Most states have received no rainfall at all in February. This includes states like Madhya Pradesh and Gujarat, both important for wheat output. While it has rained in Uttar Pradesh, Punjab, Haryana and Bihar, all significant wheat producers, the deficit is still more than 99% in these states. In fact, in all these states except Gujarat, there is a rain deficit of more than 33% even if seen in the context of total rain since January. The Met department classifies a deficit of more than 20% compared to 1961-2010 average as deficient at the state-level.

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Past trends show we should prepare for early arrival of summer

The weather bureau’s forecast for the two weeks starting February 10 shows that the maximum temperature will be above normal over northwestern India, Uttar Pradesh and the east coast in the first week, and almost all of India in the second week. It is possible that the maximum would drop after that, but it is wishful thinking without a forecast. Past trends suggest the government should make long-term plans for an early end to winter. Almost all states were warmer than normal in both halves of February in the 2011-20 decade compared to the 1981-2010 average. To be sure, given limited resources for quick adaption, it might be wiser to first study regional trends in the future. It is not necessary that places that warmed less in the past decade will also warm less in the next.

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