India is undergoing a major transition with changes in rainfall patterns leading to increased frequency of droughts, floods, heat waves amidst fear of a major water crisis in the years to come. Why are these threats increasing? Head of Indian Meteorological Department’s (IMD) Climate Application and User Interface Group, Dr Pulak Guhathakurta, speaks to India Water Portal on what the current research on rainfall shows and what can be done to cope with these changes.
Why do you think it is important to study the rainfall in India?
The south-west (SW) monsoon (June to September), often referred to as the lifeline of India, contributes 75 percent to the annual rainfall in the country with some areas like Gujarat receiving more than 95 percent of its annual rainfall from the SW monsoon. The contribution of the pre-monsoon (March, April and May) and post-monsoon (October, November and December) rainfall is 11 percent. The SW monsoon plays a very important role in agriculture, water resources, power management and consequently the economy of the country but shows considerable variation in terms of onset, withdrawal and amount of rainfall leading to years of excess rainfall or droughts.
The average annual rainfall patterns over different parts of the country show that it ranges from less than 13 cm over Ramgarh in western Rajasthan to 984 cm in Mawsynram in Meghalaya. The rainfall pattern also influences the climate of the country which varies from humid northeast (with 180 days rainfall in a year) to arid Rajasthan (with less than 20 days rainfall in a year). Even the mean rainfall patterns for the country as a whole are variable with the mean monthly rainfall during July (289.2 mm) being highest, contributing about 24.4 percent of annual rainfall (1187.6 mm). The mean rainfall during August contributes about 22 percent of annual rainfall while that during June and September contribute 13.8 percent and 14.6 percent to the annual rainfall, respectively.
Rainfall in India is currently undergoing further changes due to climate change, leading to increasing instances of floods, droughts, making it important to study the trends in rainfall patterns to design better coping strategies for the future. Also, the Indian economy is still dependent on agriculture and the SW monsoon. Droughts and famines can prove to be lethal for the country.
How are rainfall patterns changing? What are the trends seen? Are there any region wise variations?
We, at the IMD, have recently conducted an analysis of long-term (1901–2010) district data to examine the variability and trends in rainfall during the south-west (June–September) and north-east monsoon (October–December) over 36 meteorological subdivisions of India. The analysis shows that there has been an increase in dry days with the decades beginning from 1971–1980 being drier than normal and 2001–2010 being the driest. Rainfall during the month of July is decreasing over many parts of central India while it is increasing during June and August over the west-central and south-western parts of the country.
A decreasing trend in rainfall during the south-west monsoon is seen in 10 subdivisions namely Chhattisgarh, Jharkhand, Uttarakhand, Himachal Pradesh, Arunachal Pradesh, NMMT (Nagaland, Manipur, Mizoram and Tripura), sub-Himalayan West Bengal, Kerala, east Uttar Pradesh and east Madhya Pradesh. Eight subdivisions that include Madhya Maharashtra, Saurashtra and Kutch, south interior Karnataka, coastal Karnataka, Konkan and Goa, coastal Andhra Pradesh, Lakshadweep and Gangetic West Bengal show increasing trends.
Has there been a rise in extreme events?
Analysis of rainfall data for the period 1901–2010 and data on rainstorms over the period 1951– 2015 show that the frequency of very light and light-to-moderate rain events during the monsoon season has decreased over most of the country while frequency of very heavy and extreme rainfall events over shorter time spans has increased over many parts of northern, eastern and southern India.
Heat waves are increasing in the north, northwest, central, east India and northeast peninsula during hot weather season (April-May-June). Similarly, during cold weather season (December–January–February), northern parts of the country including Jammu and Kashmir are experiencing cold waves. Studies also show that there has been a noticeable increase or decrease in frequency of heat or cold wave days during the El Nino or La Nina events.
Analysis of tropical cyclones and monsoon depressions based on data from 1901–2010 shows that the frequency of cyclones is increasing during the post-monsoon season (October–December). Studies also show that there has been a significant decline in cloud cover which is responsible for a good monsoon in most parts of the country leading to a loss of one rainy day during the study period. This decrease in cloud cover is seen in the central and the west coast of the country while an increase in cloud cover is seen over the Indo-Gangetic plains. The high rate of urbanisation and growing particulate pollution in the central and west coast of the country could be one of the reasons for this decline in cloud cover.
What do studies reveal about the frequency of droughts in India, specifically Maharashtra?
Droughts in India: The analysis on meteorological droughts made using monthly rainfall data of the period 1901–2015 finds that the probability of droughts is increasing in all parts of the country except in northeast India. Most affected are east Uttar Pradesh (16 districts), Bihar (15), Assam and Meghalaya (13), east Madhya Pradesh (nine), Kerala (eight), Uttaranchal (seven) and Chhattisgarh (seven) where number of districts (given in the bracket) show a significant increase in drought occurrences.
The intensity of droughts is also increasing. The area affected by drought is showing an alarming increase in states like Uttar Pradesh, Uttarakhand, Jharkhand, Chhattisgarh, Kerala, Assam and Meghalaya and Tripura. Many districts of states like Tamil Nadu, Odisha, east Madhya Pradesh, Himachal Pradesh, Punjab, Haryana, Bihar, Vidarbha, Marathwada in Maharashtra, north interior Karnataka, Tamil Nadu and sub-Himalayan West Bengal are also showing worrying trends with a significant increase in drought-affected areas. Drought occurrences have also been found to be high in most of the southern districts of Tamil Nadu during the northeast monsoon. The ENSO has found to have a signiﬁcant role to play in the meteorological drought occurrences over the Indian region.
Droughts in Maharashtra: Since Maharashtra has been the epicentre of droughts over the last few years, IMD conducted the first in-depth, district-level climatological study on Maharashtra by analysing rainfall data from 1901 to 2006 obtained from 335 rain-gauge stations. The study reveals that rainfall during the pre-monsoon and winter season has decreased considerably while there has been a rise in rainfall in August in most of the districts of the state while eastern and southeastern parts of Maharashtra show decreasing rainfall in July and September. All the districts in the western and central parts of the state receive less than 10 mm of rainfall during the winter season (January and February), while there is a shift during the pre-monsoon season (March to May), with high rainfall area shifting from the eastern to south-western parts of the state.
Rainfall activity is thus getting more and more confined to the monsoon months, which will not fare well for agricultural activities in non-monsoon months and result in less groundwater recharge. This will also impact pre-monsoon temperatures leading to very high summer temperatures and consequent soil-moisture loss. Mean summer temperatures are already rising in most parts of Maharashtra.
Why are these changes happening? Are these inevitable?
Many of these changes are being triggered by climate change. Increasing urbanisation, deforestation, land use changes, pollution due to particulate matter seem to exacerbate these conditions affecting rainfall patterns in major ways. These will continue to influence not only the agriculture and economy but water resources and even the health and survival of populations in the long run.
What do you think needs to be done to cope with these changes?
While rainfall patterns are changing, heavy amounts of rain in shorter spans of time call for the need to have better adaptation strategies to cope with these changes. While there are areas that have less rainfall, it seems that droughts triggered in Maharashtra are more due to poor management and lack of equitable distribution of the available water resources, faulty cropping patterns such as the emphasis on water-guzzling crops like sugarcane etc.
With so much rainfall over short spans of time, we must focus on harvesting and storing as much water as possible and catching the rainwater where it falls besides making efforts at saving our environment by preventing deforestation, focusing on reforestation, identifying and protecting groundwater recharge areas, saving and making judicious use of available water resources.