‘Brace for hotter days, spells of rain’

THIRUVANANTHAPURAM

Close on the heels of the heatwave declared in Kerala for the rst time in the recorded weather history of the State, P.S. Biju, senior scientist of the India Meteorological Department (IMD), speaks to The Hindu on a range of factors that contribute to very hot days and nights, along with intense rain spells.

For the rst time, the State has been experiencing hotwave conditions. Can you please comment on the circumstances that led to heatwave conditions in Kerala?

The main factor for the heatwave is, of course, global warming. Local factors, such as urban heat island eŸect, aggravate the situation. In fact, the transportation of hot, warm air and its prevalence over a region for a prolonged period, the absence of moisture in the upper atmosphere, a cloudless sky, and large anti-cyclonic “ow provide favourable conditions for heatwave. Further, the regions where mountain gaps exist along the Western Ghats through which the hot air blows into the State from the plains of Tamil Nadu are more prone to heatwave conditions in Kerala.

How did global warming contribute to the rise in hot days and nights in Kerala?

Global warming enhanced the moisture-carrying capacity of air parcels. Since Kerala is a State with a maritime climate, the average humidity level in the atmosphere is higher. So whenever the temperature increases, so does the heat index value (feel-like temperature). This has resulted in an increase in feelings of hotness and discomfort in this millennium. Moreover, the temperature reported by a station is equivalent to the air temperature one feels under a shelter. But a person exposed directly to sunlight experiences more heat.

Can you explain it?

For instance, the maximum temperature reported in Palakkad is 41.6°C. This is the air temperature one experiences when he or she is under a shelter. But when one is directly exposed to sunlight, the effect on his or her body may be more than 50°C. That’s why sunstroke aŸects people who are directly exposed to sunlight more than those who are under a shelter. This is the case in summer.

This temperature “uctuation also leads to intense rainfall during monsoons, as the air parcels carry more moisture than normal during monsoons. As a result, more heatwaves in summer as well as very heavy rainfall in monsoons will become part of the climate of Kerala. In short, severe weather incidents will be more in the future. Severe weather incidences occur often in a shorter time.

Is this the rst time that the State has experienced a heatwave, or has the lack of enough observatories in Kerala

The IMD observatories have not reported or realised heatwaves in the past. Of course, now we have a huge number of observatory networks, including 142 automatic weather stations that may give taluk-wise temperature values.

Should we expect more intense spells in the coming monsoon season?

The long-range rst stage forecast issued by the IMD warns of above normal rainfall in Kerala for the monsoon. Models also suggest El Nino conditions become neutral during the early part of the monsoon season, and La Nina conditions are likely to develop during the second half of the monsoon season. At the same time, the Indian Ocean dipole will also become positive. These are favourable conditions for above normal rainfalls over the State.

When can people expect a respite from the present sweltering weather?

Of course, there may be a change in the second half of May according to the climatology of Kerala.