India’s rainfall patterns changing drastically, say Stanford scientists

Longer dry spells and wetter wet spells could spell doom for the Indian agriculture, they warn

 
By Anushka Kaushik
Last Updated: Monday 17 August 2015

 

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Tough times are ahead for the Indian agriculture which is highly dependent on the summer monsoon. According to a study by scientists from Stanford University in the United States, there has been a consistent drop in the average seasonal rainfall India receives during the summer monsoon months of July-August. The study also warns of extreme weather patterns in future.

The scientists analysed temperature and precipitation data from 1951 to 2011 and found a significant decreasing trend in the mean rainfall during the summer monsoon months. In contrast, there has been an increase in the daily rainfall variability during July-August by a 5 per cent level.

Changes in atmospheric conditions have led to such higher frequency of dry spells and increasing intensity of wet spells, notes the study, which defines wet and dry spells as three or more consecutive days of extremely high or low rainfall. Such extreme weather events are increasing the risk of drought and flood in central India.   

Stronger convective activity over southern and eastern India leads to increased intensity of wet spells. Similarly, the decreased intensity of dry spells occurs due to reduced extent of horizontal cold air transfer (which occurs after reduction in upper-level cyclonic anomaly). 

Additionally, the frequency of occurrence of dry and wet spells is influenced by high vertical wind shears. The study posits that between 1981 and 2011, reduced levels of upper and lower-level winds weakened wind shears, increasing the frequency of dry spells and reducing the intensity of wet spells. 

The study observed atmospheric conditions from 1951 to 2011. They measured precipitation during the period by using a new statistical method that accounts for spatial and temporal relationships between rainfall levels, temperature, and other geophysical phenomena. These parameters have been ignored in previous statistical tools. Such statistical tools are crucial while investigating factors, such as temperature and rainfall that can change overnight. 

With 60 per cent of employment in the agriculture industry in India and more than 56 per cent of agricultural area being rain-fed, studying the modifying patterns of the monsoon is crucial. It’s vital for the stability of Indian agriculture to study monsoon levels, particularly in the summer months as it accounts for 85 per cent of the annual rainfall received in the country. The study was published in the June issue of Nature Climate Change. The findings improve the understanding of impact of climate change on rainfall extremes and would help manage risks associated with irrigation and agriculture.  

 


Research: Observed changes in extreme wet and dry spells during the South Asian summer monsoon season

Research: Analysis of variability and trends of extreme rainfall events over India using 104 years of gridded daily rainfall data

Research: The basic causes of the large-scale deficiency in the South-West Monsoon rainfall over India in 1965 and 1966

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