One would presume 130 years' time is long enough to master the behaviour pattern of India's lifeline, the southwest monsoon. However, it seems the monsoon code is yet to be cracked, as the India Meteorological Department says, it is still trying to "understand" the phenomenon, let alone predict it.
“First is to understand monsoon better. Prediction is the next stage. We have to understand so many things about the monsoon," Director General Meteorology Ajit Tyagi told NewsWire18 in an interview.
No wonder, India's apex weather bureau, which made its first tentative monsoon forecast in 1882, finds it difficult to get its predictions right.
In 2011, seven out of 10 southwest monsoon forecasts were off the mark.
The overall rainfall in the four-month season ended September was 101per cent of the long period average, compared with the department's prediction of 91-99 per cent.
Tyagi says the sudden re-emergence of La Nina conditions during Aug-Sep are partly to be blamed for the predictions going awry this year.
La Nina, cooling of sea surface temperatures in east central Pacific Ocean, is usually associated with increased rainfall in India. “When we knew La Nina is taking place, we were sure we will be a little bit off (the mark)," Tyagi said.
He also says the models that the department currently uses for long-range forecasts may not be best suited to pick up such unexpected developments.
“This is the problem with statistical forecasts. The dynamical forecasts may update the things (better),” Tyagi said.
The department relies on statistical models for its forecasts, as the skills of dynamical models are yet to be proven. "The spread of dynamical models used to be very wide, they were never able to simulate monsoon rainfall very realistically."
For instance, the monsoon forecasts on the dynamical models in June ranged between sub-normal to above normal rainfall, he said.
“There were (dynamical) models giving sub-normal rainfall. There were models, which were giving 114 per cent also," he said.
In June, the bureau went with the statistical model and lowered its monsoon rainfall forecast to 95 per cent of the long period average from 98% estimated earlier. The actual rainfall in the season turned out to be 101per cent.
“Skill of these (dynamical models) still is not superior to statistical models. When final forecast is given, we still give heavy reliance to statistical models," Tyagi said.
However, in view of the recent experience, the weather department plans to re-look its prediction models, he said.
"...There may be review of this particular incident also. Whether we require some refinement in our statistical model. Also, whether we give over-reliance to statistical model or we should now start giving equal amount of confidence to the dynamical models also," Tyagi said.
EXTREME PREDICTIONS
Even if the weather bureau refines its models, it may still not be able to predict extreme events like drought, Tyagi said.
"Globally, nobody can predict extreme events," Tyagi, who headed the Indian
Air Force's meteorological branch before taking over as head of India Meteorological Department in 2008, said.
Even if the predictions throw up extreme events, the department will be wary of using it because of the uncertainties in the models, he said.
"Even if I have got some indications (about extreme events) with so much of uncertainties in the model I can give (only) a general direction," Tyagi said.
There have been three major droughts in India since 1989, and the weather department has not been able to forecast a single one.
Another big challenge for the weather bureau is to get the forecasts on intra-seasonal and intra-regional variations correctly, he said.
"...(A) problem, which is even more difficult, is intra-season variability within the season. Because of law of averages, I can come close to my forecast that is not a big issue. But whether what I expected within the season... these are bigger challenges than (predicting) total amount of rainfall," Tyagi said.
Most of the southwest monsoon predictions that went wrong this year were the ones on intra-regional and intra-seasonal rains.
CHANGING BEHAVIOUR
Over the years, the behaviour of monsoon, as we know it, is changing. It is getting longer in some places and shorter in others; the quantum of rains is rising in some areas and falling in some others, he said.
However, the overall monsoon rains in the country is the same, he said.
"There has not been any change as far as total rainfall is concerned.
(But) there are some regional changes which are taking place," Tyagi said.
"Pockets in eastern India are getting less rainfall (but) along western
India Gujarat and Madhya Pradesh--these are areas getting little more rainfall," he said.
In the last decade, rainfall in northeast India has been below 90% of the long period average in six years.
The monsoon season is getting longer in northwest India because of late withdrawal and shorter in central due to late onset, he said.
"We did some exercise in the last two years. We found that... central parts of the country, particularly Vidarbha... there is some variation," Tyagi said.
The department is working on new set of 'normals' for monsoon onset, withdrawal and rainfall, which is likely to be introduced next year, he said.
"What we are trying to work out is a new objective fixing of dates based on more data and recent data... Based on this some where monsoon period will be little longer, some where it will (be) little shorter," Tyagi said.
"As far as Kerala is concerned I don't see any major change (in onset date).
The major change may be over northwest India, where there may be some longer period of monsoon," he said.
Over the last five years, southwest monsoon withdrawal from the northwest has started in the last week of September compared with the normal date of Sep 1.
"As I see, (there) may be (changes in monsoon period in) northwest India because of late withdrawal and in central India because of late arrival there may be some adjustment in the total period.".
RISING TEMPERATURES
The climatic changes in India are not limited to the monsoon rainfall, the temperatures are also changing in line with global warming, he said.
The mean temperature in the country has risen by 0.56 degrees Celsius over the last century, most of it during the last decade, he said.
"Last 10 years have shown a marked increase (in temperature), but it is in line with the global rise."
The sharpest rise in the mean temperature is during post-monsoon season (by 0.77 degrees Celsius), followed by winter (0.70 degrees), pre-monsoon season (0.64 degrees) and monsoon (0.33 degrees).
There are changes observed in cyclones hitting the country as well, Tyagi said.
Though the number of post-monsoon cyclones over the Indian Ocean has remained more or less the same, their intensity has increased, he said.
NORTHEAST MONSOON
The weather department expects the current northeast monsoon season to be a little over normal due to La Nina conditions, Tyagi said.
The northeast monsoon, which is primarily active in five subdivisions in southern peninsula--Tamil Nadu and Puducherry, coastal Andhra Pradesh, Rayalseema, south interior Karnataka and Kerala--started earlier this week.
The department, which makes experimental forecasts on northeast monsoon, will start releasing them in a couple of years after evaluating the performance of the predictions, he said.
It may also release forecast of all-India and sub-regional rainfall round the year in a couple of years, he said.
"Every month we will give a... forecast (for the) next three months, and it will be rolling one," Tyagi said. "Our endeavour is that each month by 20th or 25th... we should be able to give you three-month rolling forecast in probabilistic categories."
The department is also working on increasing the timeframe of medium-term forecasts to 7-10 days from the current 5, he said.
"Then it becomes an end-to-end system. We have got short-range forecasts, which we continue to give (for) 2 days, 3 days (and) 5 days. Then medium-range and extended forecasts and monthly and continuous rolling forecasts."
