Floods or weak monsoon: Effects of sharp swings in rainfall patterns may become stronger in future

What caused the Jammu and Kashmir ( J&K) floods over the past two weeks? Even as monsoon over the whole of India was still in deficit to the extent of 11% from what is considered ‘normal’ by meteorologists as of September 10, the rainfall in J&K was 16% above the normal since the beginning of the monsoon season.

Comparisons are already being made with the heavy flooding in Uttarakhand in June last year, which also resulted in major loss of life, as well as episodes of flash flooding in Leh in 2010.

And even as flooding occurs in J&K, just a little further south, in Punjab, Haryana and western Uttar Pradesh, rainfall is as little as half of what would be considered normal in a number of districts. Recent research on different aspects of the monsoon has raised the prospect that the rainfall patterns could be increasingly uncertain in coming years.

Western Disturbance

Meteorologists feel that broadly similar processes lie behind the extreme weather in J&K and the devastating floods in Uttarakhand last year. In both cases, the monsoon rainfall system moving from east to west essentially interacted with a quite different rainfall system, unrelated to the monsoon, which meteorologists call a ‘western disturbance’.

Such disturbances are usually prevalent over north India during the winter and the pre-monsoon season and originate in the Mediterranean or the Atlantic Ocean. In the case of the Uttarakhand disaster, a western disturbance bearing rain and moving from west to east essentially locked or collided over the Uttarakhand region with a monsoon rainfall system moving in the opposite direction. The combined effect of the two was to produce a massive burst of rain within a very short time. A similar event happened a few days ago and this time the point of ‘collision’ was over J&K.

“Neither system was enough to produce such large amounts of rainfall on its own,” says GP Sharma, a meteorologist with Skymet, a private sector weather forecasting service. “But when the two interacted, each essentially accentuated the effect of the other.”

The rainfall over the course of the current season has been highly variable. It started off on a weak note with June recording an all-India deficit of 43%. During July, the rainfall picked up, only to weaken again during the second week of August. It then picked up again.

While this zigzag pattern in the monsoon alternating between ‘dry’ and ‘wet’ spells has been widely pointed to, recent research by scientists Deepti Singh and others at Stanford, and published in the journal Nature Climate Change in April this year, has confirmed, and added to, what meteorologists knew earlier:

that while, on the one hand, average rainfall during the July-August season over the ‘core monsoon’ region (essentially a belt stretching across central India from west to east) has decreased since the ’50s, rainfall on a daily scale has become much more volatile than earlier. The number of dry and wet spells, when the monsoon is below and above average, has essentially increased in the past few decades.

Further, the wet spells are getting wetter, and dry spells, such as the ones we have seen this season, have been getting longer. “During this season we have also seen big breaks in the rainfall pattern,” says Sulochana Gadgil, a meteorologist with the Indian Institute of Science. “The cloud banks which typically move beyond the core monsoon zone during the monsoon season have not moved too much beyond peninsular India.”

Making it Worse

But even as the monsoon has become more uncertain, the effects of sharp swings in the rainfall patterns on human habitation and the environment could well become stronger in the future.

In both J&K and Uttarakhand, deforestation and the destruction of natural tree cover could well have played their part in worsening the situation. Forests and natural grasslands act as a kind of sponge absorbing rain and then release it slowly over time. Remove forest cover and the rain simply runs off the surface of the land without being absorbed by it.

Further, since the soil has not absorbed the moisture it actually becomes dryer during the non-monsoon months. “What we are seeing is consistent with the expectation that the effects of rainfall and flooding have been worsened by environmental destruction,” says TR Shankar Raman, an ecologist with the Nature Conservation Foundation, Mysore.

So even as rainfall patterns have become more uncertain, environmental destruction has made the effect of those patterns on the landscape and human settlements more destructive as well.