Unseasonal rains: Lessons to be learnt

States should learn lessons from the ab-normal rainfall events and the damage to lives and property.

Many parts of India, and indeed the world, are experiencing abnormal weather events such as extremes of rainfall, winter and summer heat. During March, this year, many states in India endured unseasonal and abnormal rains. This March was reported to be the wettest for the northern and central parts of the country in the past 100 years. The Southern Peninsula received an excess of 221 per cent rainfall, whereas North-western India and Central India received an excess of 270 per cent and 502 per cent respectively.

Crop productivity is highly sensitive to distribution of rainfall during the cropping season.  Intense rainfall during the harvest or post-harvest stage is extremely damaging to crops and livelihoods of farmers. The unseasonal rains in March wrecked havoc for the standing rabi crops such as wheat, mustard, and gram, as well as vegetable and fruit crops over 18 million hectares across 13 states.

Is climate change responsible for the observed abnormal rainfall events or the occurrence of extreme rainfall events is an indication of climate change? Such questions are posed to scientists. Apparently, such events are caused by the Western disturbances. Western disturbances are extra-tropical storms that generally operate between 30° and 60° latitudes from the equator. These storms bring winter rain and snow to north-western parts of India.

Western disturbances are well known to bring mild rains during the winter season (January-February), which is beneficial for the growing Rabi crop. However, in the recent past, western disturbances were increasingly linked to weather disasters in the Himalayan region. 

A study by the Indian Institute of Tropical Meteorology (IITM), Pune, has linked the increased variability in the western disturbances over the Western Himalaya region to the pronounced warming trends over the Tibetan Plateau in recent decades.
Studies pointing to the ‘warming of the Tibetan plateau’ and the ‘weakening of the Arctic vortex’ point to the possibility that these unseasonal and rare events may be linked to climate change and increased human induced greenhouse gas concentration in the atmosphere. However, scientists are not comfortable in attributing a single weather event to climate change.

The World Meteorological Organisation states “while it is impossible to say that this or that weather event was “caused” by climate change, one should anticipate that the magnitude, frequency and duration of extreme events will likely be altered as a result of the earth’s atmosphere warming due to the increased concentrations of greenhouse gases”.

Dr Trenberth of National Centre for Atmospheric Research, USA, provides a much clearer perspective when he argues that "there is a direct influence of global warming on heavy precipitation as the water holding capacity of air increases by about 7 per cent per 1 degree C warming, which leads to increased water vapour in the atmosphere. Hence, storms, whether individual thunderstorms, extra-tropical rain or snow storms, or tropical cyclones, supplied with increased moisture, produce more intense precipitation events."

Extreme rainfall events

Globally, extreme rainfall events are increasing. Studies based on the observed precipitation records of India Meteorological Department have shown that the occurrence of extreme precipitation events and their variability has gone up in many parts of the country.

Some of the notable examples of extreme rainfall related disasters from the recent past include: Uttarakhand cloud burst of 2013, Koshi floods of 2008, Pakistan floods of 2010, Kashmir floods of 2014, Leh cloud burst of 2010 etc. During 2005 and 2006 and again in October 2009, Northern and north-eastern districts of Karnataka were hit by unprecedented floods.

Increased extreme weather events in the last few years are in line with the projections made by the United Nation’s Intergovernmental Panel on Climate Change (IPCC). The IPCC projects that the extreme precipitation events, over most of the mid-latitude and over wet tropical regions to become more intense and more frequent. 

In this context, it is important to mention that a study investigating the links between the record UK floods of October-November, 2000 and climate change concluded that “in nine out of 10 cases, model results indicate that 20th century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales”. Thus, the scientific evidence linking extreme or unseasonal rainfall events to climate change is growing.

There is no escape from unseasonal or abnormal rainfall events. The state administrations need to learn lessons from the recent abnormal rainfall events and the damage caused to not only agriculture but also to lives and property. We need to be better prepared to minimise the damage. We need to improve the modelling and satellite based weather prediction capability.

The state meteorological departments and disaster management institutions should be strengthened. We need to reduce the exposure of agriculture and humans to such events and build resilience among farming and fishing communities.

(The writers are with the Indian Institute of Science, Bengaluru)