The
monsoon, which provides 80 per cent of the total rainfall in the
subcontinent and on which India is completely dependent for its
agriculture, is witnessing disturbing changes.
There has been a decline in the average total seasonal rain during the period 1980-2011, according to a new study.
The
study was carried out by Stanford Woods Institute for the Environment,
the Stanford University's hub of environment research, and published in
the latest issue of Nature Climate Change. It also found changes in the
atmosphere like winds and moisture which are likely to be responsible
for changes in wet and dry spells.
After studying trends of monsoon rains over 60 years, the researchers have warned of extreme weather conditions in future.
They have
also found that there is substantial variability within the monsoon
season, including fluctuations between periods of heavy rainfall (wet
spells) and low rainfall (dry spells).
"These
fluctuations can cause extreme wet and dry regional conditions that
adversely impact agricultural yields, water resources, infrastructure
and human systems," the study said.
According
to the study, the mean rainfall during July-August shows a significant
(10 per cent significance level) decreasing trend since 1951 over the
monsoon "core" in the data set of the India Meteorological Department
(IMD) which is consistent with reported decrease in all-India rainfall.
This
decrease in mean rainfall occurs despite an increase in seasonal mean
low-level moisture convergence and convective available potential energy
expected from increased moisture availability in response to
atmospheric warming.
In
contrast, the daily rainfall variability during July-August shows a
statistically significant (5 per cent significance level) increasing
trend.
The study revealed that the intensity of rainfall in wet spells during
1981-2011 was significantly higher than during 1950-1980.
At
the same time, dry spells became 27 per cent more frequent during
1981-2011, which had twice as many years with three or more dry spells.
Studying
the pattern of monsoons in South Asia since 1980, researchers observed
an increase in the intensity of wet spells and in the frequency of dry
spells.
"Through a comprehensive statistical analysis of precipitation
observations (1951–2011), we show that statistically significant
decreases in peak-season precipitation over the core monsoon region have
cooccurred with statistically significant increases in daily-scale
precipitation variability," the researchers said.
The
study said the changes in extreme wet and dry spell characteristics are
supported by increases in convective available potential energy and
low-level moisture convergence.
