Investigating rainfall trend over India using the wavelet
technique
Ranjit Kumar Paul and P. S. Birthal
ABSTRACT
In this paper, using the wavelet technique we analysed rainfall behaviour in the country across
different agro-climatic zones over a century. Findings indicate that at the national level there is no
significant trend in rainfall in the long run, but there are pockets of change in the rainfall pattern.
There was a significant increase in the rainfall in the arid zone, whereas in the humid, semi-arid
tropics and semi-arid temperate zones the trend was downward but insignificant. The behaviour of
rainfall was different during this period. Except in the arid zone, we find a similar trend in other zones
– increasing initially, tapering off in the middle and then declining but with some difference in time
intervals. In the arid zone, the behaviour of rainfall had been erratic. In the short run, the direction of
change in trend remains the same as in the long run but the change is statistically significant.
Ranjit Kumar Paul (corresponding author)
ICAR – Indian Agricultural Statistics Research
Institute,
New Delhi 110012,
India
E-mail: ranjitstat@gmail.com
P. S. Birthal
ICAR – National Institute of Agricultural Economics
and Policy Research,
New Delhi 110012,
India
Key words | agro-climate, India, rainfall trend, wavelets
INTRODUCTION
Indian agriculture is rain-dependent, with almost two-thirds
of the net cropped area being rain-fed. Therefore, a regular
rainfall pattern is crucial for agricultural growth; too much
or too little rain can have a devastating effect on agriculture.
A regular pattern in rainfall may not be observed all the
time. The series may behave erratically, with highs and
lows. Recent evidence shows monsoon rainfall in India is
becoming more erratic (Manton et al. ; Kumar et al.
; Goswami et al. ; Mall et al. ; Ghosh et al.
; Paul et al. ). Auffhammer et al. () have shown
that the Indian climate has become drier and warmer,
adversely affecting the crop yields.
India is a large country, and regional patterns in rainfall
and temperature are more important for agriculture. A few
studies have analysed behaviour of rainfall at disaggregated
spatial units, at the level of meteorological sub-division, state
and district. Guhathakurta & Rajeevan () found a sharp
decrease in the number of rainy days and amount of rainfall
in many sub-divisions of India. They reported a decline in
rainfall in the months of June, July and September and an
increase in August in a few sub-divisions. Goswami et al.
() studied rainfall behaviour over central India for the
period 1951–2000 and observed a significant increase in
heavy rainfall events and a decrease in moderate rainfall
events. They also reported a rise in the frequency of extreme
rainfall events such as droughts and floods. Krishnakumar
et al. () studied variations in monthly, seasonal and
annual rainfall in the state of Kerala for the period 1871–
2005, and found a significant decline in the south west mon-
soon (June–September) rains, especially in the months of
June and July; and an upward trend in winter rainfall in
the months of January, February and April. Soltani et al.
() computed rainfall and rainy day trends in Iran.
Some studies have also attempted to predict rainfall be-
haviour and estimation of trends using recently developed
nonparametric techniques like wavelets. Kallache et al.
() applied discrete wavelet transform (DWT) analysis
to river run-off data from gauges in Southern Germany to
separate the variability of small and large time-scales, assum-
ing that the trend component is part of the latter.
Adamowski et al. () proposed a method for trend detec-
tion and estimation based on continuous wavelet transform
353 © IWA Publishing 2016 Journal of Water and Climate Change | 07.2 | 2016
doi: 10.2166/wcc.2015.079