Kerala once again is in the throes of flooding and landslips triggered by extreme rainfall events which often lead to loss of lives and damage to property. As the resurgent rain has brought back memories of the worst floods in Kerala, P.S. Biju, a climate scientist of India Meteorological Department (IMD), Thiruvananthapuram, who won the best scientist award in atmospheric science in 2022 instituted by the Ministry of Earth Sciences, speaks about the challenges faced by the State. Excerpts:
Kerala was talking about rain deficit in the past two months, which was around 50% in June and 26% on July 31. Now, hardly within three-four days, the State is talking about a situation of flash floods and landslips. Does it sound strange?
Climatology will not speak reality, but climate change is a reality. As Mark Twain said, “Climate is what we expect and weather is what we get”. Obviously, the number of severe weather incidences is on a steady increase in Kerala. The monsoon data of the last 120 years (1901-2020) clearly indicate that there has been a rise in temperature in this millennium (2000-2020) by more than 0.5 degree Celsius in all observatories in Kerala. However, the monsoon was deficient in the last 120 years in the State for only 17 years.
There is always an 85% chance of Kerala getting a normal monsoon every year. But severe weather incidences such heavy rainfall days and thunderstorm activity have increased as a result of climate change. The fact is that if we analyse the data between 1991 to 2020 (30 years) and 1901-2010 (110 years), it can be seen that many places in Wayanad, Kasaragod, Idukki, Thrissur, Kozhikode, Ernakulam, and Kannur, the frequency of heavy rainfall has been increasing.
Since 2018, August has become a crucial month in the monsoon calendar of the State. Any reason?
It is true that the extreme rainfall events have increased significantly in August of late. But four years are a shorter period in climate science to reach a conclusion. But the change I noticed during the past few years is that there was a rising trend in heat influx during the months of June and July. This is expected to draw more moisture to the atmosphere, leading to the formation of convective clouds which ultimately leads to severe weather incidents.
Thunderstorms normally happen during the pre- and north-east monsoon periods in Kerala. But has it become a regular feature during the southwest monsoon period?
Thunderstorm activities are reported during the monsoon as well, but not with severe lightning as in summer or Thulavarsham. In the coming years as well, thunderstorm days during the southwest monsoon may increase. Usually, during the active spell of monsoon, stratus clouds dominate over cumulonimbus clouds. That is why thunderstorm days are fewer in monsoon. But, nowadays, the presence of frequent convective clouds (cumulonimbus or thunderclouds) is also reported in the monsoon season, which is also one of the main reasons for extreme rainfall events.
You were instrumental in setting up 100 automatic weather stations in Kerala after the floods of 2018. Is there any pattern in the spatial distribution of extreme rainfall events over the State?
Now we have more than 100 automatic weather stations (AWS) in Kerala, the first State to achieve this in India. As I said earlier, we need the data from a relatively longer period to make such an assessment. However, stations such as Vythiri, Hosdurg, Kudulu, Peermade, Kunnamkulam, Kodungallur, Koyilandy, Kuttiyadi, Neryamangalam, Piravom, Aluva, Irikkur, Ayyankunnu and so on are the heavy rainfall belts. But more studies need to be done in the coming years to make a real assessment.
Is the monsoon witnessing any major change in terms of its spatial distribution, intensity, quantity and so on?
No major change in spatial distribution or quantity of rain. In fact, the speciality of rain in Kerala is that most of the cloud condensation happens in three-four hours. Hence, 60% of the rainwater goes into the ocean without any use due to the topography of Kerala, slanting from east to west. This is not a cause for concern. But due to the increase in heavy rainfall incidences, flood situations have become frequent in the State.
Is the IMD fully equipped to foresee the changes in the weather in advance?
Of course. In a tropical country, weather prediction is more challenging than in other regions due to the fast development of weather events. The IMD is rated first in the world in weather prediction, especially in cyclone monitoring. But preparedness from all government bodies is essential to act on time on the basis of predictions by the IMD. Now we have technologies to forecast up to subdivision level, and more than 80% accuracy is reached at district-level forecast.
Should Kerala be ready to witness more similar weather aberrations and extreme climatic conditions in the near future?
Yes. The coming years will see similar types of extreme weather events. We have to prepare to face those events and suitable mitigation methods should be developed by all associated government bodies.
A lot of agencies outside the IMD are trying to forecast the weather just using models and a lot of other agencies are installing AWS. Is that data useful in predictions?
There are many models available globally. Most of them are simply based on satellite data. IMD scientists take models only as a reference. The real forecast is based on the synoptic systems and mesoscale systems. Being the nodal agency with experience of 147 years and the presence of experts, IMD can only make the correct forecast. But any weather station periodically calibrated by IMD experts is also valid.
