Decadal Study of Changing Frequency and Intensity of Rainfall for Selected Locations of Tamil Nadu

Abstract

Understanding the pattern of regional climatic extremes is essential for creating an important adaptation measure to safeguard farmers from monsoon tantrums. This paper focuses on the rainfall variability and intensity for spatially different locations of Tamil Nadu. The daily rainfall data over a period of 30 years (1990-2019) for the study locations were collected from the constituent research centres of TNAU. The results indicated that an increasing trend in SWM rainfall was observed in Coimbatore (209.3 to 300.6mm), Ooty (681.4 to 703.1mm), Aduthurai (227.8 to 320.6mm), Kovilpatti (132.8 to 141.3 mm) while the decreasing trend was observed in rest of the places. A decreasing trend was reported in general for all the places during NEM. The decreasing trend in the number of rainy days was registered in Kovilpatti, Virudhunagar and Killikulam that exhibits an alert in modifying the crop planning programme in those areas. The frequency of rainfall intensity revealed that except Ooty, the number of Heavy Rain (HR) to VHR(VHR) was found to be meagre to absent in most of the study locations.

Full text

Decadal Study of Changing Frequency and Intensity of
Rainfall for Selected Locations of Tamil Nadu
S. KOKILAVANI1*, SP. RAMANATHAN1, GA. DHEEBAKARAN1,
N.K. SATHYAMOORTHY1, B. ARTHIRANI2, T. RAMESH3, K. SATHYABAMA4,
M. JOSEPH5, P. BALASUBRAMANIAN6 and P. ARUNKUMAR7
1Agro Climate Research Centre, TNAU, Coimbatore.
2Agricultural Research Station, TNAU, Kovilpatti.
3ADAC&RI, TNAU, Trichy.
4Tamil Nadu Rice Research Institute, TNAU, Aduthurai.
5Agricultural College and Research Institute,TNAU, Killikulam.
6Horticultural Research Station, TNAU, Ooty.
7Agricultural Research Station, TNAU, Virudhunagar.
Abstract
Understanding the pattern of regional climatic extremes is essential for
creating an important adaptation measure to safeguard farmers from
monsoon tantrums. This paper focusses on the rainfall variability and intensity
for spatially dierent locations of Tamil Nadu. The daily rainfall data over
a period of 30 years (1990-2019) for the study locations were collected
from the constituent research centres of TNAU. The results indicated that
an increasing trend in SWM rainfall was observed in Coimbatore (209.3
to 300.6mm), Ooty (681.4 to 703.1mm), Aduthurai (227.8 to 320.6mm),
Kovilpatti (132.8 to 141.3 mm) while decreasing trend was observed in rest
of the places. A decreasing trend was reported in general for all the places
during NEM. Decreasing trend in number of rainy days was registered in
Kovilpatti, Virudhunagar and Killikulam that exhibits an alert in modifying the
crop planning programme in those areas. The frequency of rainfall intensity
revealed that except Ooty, the number of Heavy Rain (HR) to VHR(VHR)
was found to be meagre to absent in most of the study locations.
CONTACT S. Kokilavani kokilavani.s@tnau.ac.in Agro Climate Research Centre, TNAU, Coimbatore.
© 2021 The Author(s). Published by Enviro Research Publishers.
This is an Open Access article licensed under a Creative Commons license: Attribution 4.0 International (CC-BY).
Doi: http://dx.doi.org/10.12944/CWE.16.3.20
Article History
Received: 02 July 2021
Accepted: 08 November
2021
Keywords
NEM;
Rainfall;
Rainfall Intensity;
Rainy days;
SWM.
Current World Environment
www.cwejournal.org
ISSN: 0973-4929, Vol. 16, No. (3) 2021, Pg. 898-907
Introduction
Water resource managers and hydrologists are
now concerned about the shifting pattern of rainfall
as a result of climate change.4 Due to the extreme
signicant uctuations in rainfall trend, drought and
ood-like dangerous situations might occur often.12
Rainfall intensity aects rainfall segmenting into
inltration and runo, soil movementand the amount

899KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
of water available in plant root zones to promote
crop growth in agriculture.6 The timing and intensity
of rainfall also restrict the transport of nutrients and
plant protection compounds.Agriculture has already
faced a number of challenges as a result of our
environmental changes.14
Greater soil loss may occur as a result of higher
rainfall intensities and many of the management
options for increased climate resilience in agriculture
are those that prevent soil loss and maintain soil
health.On a global scale, the pragmatic intensity
of daily heavy precipitation events, i.e.,the amount
of rain per unit time, increases at a pace similar to
that of vapour pressure. (6–7% K−1). Future climate
change projections also point to increasing rainfall
intensity in some areas.5
Since agriculture is considered to be an important
part of the Indian economy, any changes in rainfall
are taken into considerate account. The inuence
of climate change on agriculture has an impact on
the rising population's food security.For improved
adaptation measures, a thorough understanding of a
region's climate is required.7 Climate extremes have
a signicant impact on crop production, resulting in
food insecurity, which has a negative impact on the
country's economy.
In several places of India, notably the southern
peninsular region, there is a strong increase in
extreme occurrences.11 The evidence of the peak
rainfall intensities at the stations is instrumental
for the planning of disaster management and for
studying the ecological aspects pertaining to water
runo in the locality of the stations. The rainy days
research can provide data on the frequency and
severity of rain events in various meteorological
conditions.When compared to periods of normal and
above-average rainfall, a drought season may have
fewer rain days and less rain per day. As a result,
statistical characteristics of daily rainfall distribution
at several sites across a large area are fascinating
and signicant components of rainfall climatology.9
The most important strategy for sustainable
water resource management is to research on
climate change, specically on changes in rainfall
occurrences and allocation.Most signicantly, a
thorough understanding of precipitation patterns
in a changing environment would aid in better
decision-making and improve communities' ability
to adapt to extreme weather occurrences.The
greatest impediment to successful water resource
management in India is the uneven distribution of
water supplies across the country due to the natural
pattern of rainfall occurrence, which varies greatly in
area and time.2 Climate change further accelerates
this rainfall variability7. In a nutshell, it's important
to assess whether there's a pattern in rainfall and
variability.This research gives an exploratory,
regionally distributed decadal examination of rainfall
variability and intensity across Tamil Nadu's several
agro-climatic zones.
Data and Methodology
The daily rainfall data was acquired from the Agro
Climate Research Centre, Agricultural Colleges
and Research Stations, Tamil Nadu Agricultural
University, Tamil Nadu, over the period 1990 to 2019
and presented in Fig 1.
Fig 1: Data locations for the study area
The data were quality checked and sliced into dierent
time scales on decadal period (1991-2000-I,2001-
2010-II and 2011-2021- III) and converted into
India Meteorological Department (IMD) prescribed

900KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
seasonal period viz., Cold Weather Period (CWP),
Hot Weather Period (HWP), South West Monsoon
(SWM) and North East Monsoon (NEM). The per
cent contribution of seasonal to annual rainfall,
number of rainy days (>2.5mm per day) for the three
decadal period were analysed.
The Co-ecient of Variation(CV)was worked out to
know the dependability of the rainfall for the dierent
seasons. Based on the IMD nomenclature, the
intensity of rainfall was categorized into Very Light
Rain-VLR (0.1-2.4 mm), Light Rain-LR (2.5-7.5 mm),
Moderate Rain-MR (7.6-35.5 mm), Rather Heavy
Rain-RHR(35.6-64.4 mm), Heavy Rain-HR (64.5-
124.4 mm) and Very Heavy Rain-VHR (124.5-244.4
mm) and was worked out for the dierent seasons
on decadal period.
Results and Discussion
Rainfall Variability and Dependability Analysis
for Selected Locations of Tamil Nadu
The decadal rainfall variability, per cent contribution,
number of rainy days and dependability analysis on
seasonal scale for the spatially dierent locations of
Tamil Nadu are represented hereunder.
Fig. 2: Rainfall variability for three decades at Coimbatore
Coimbatore- Western Agro Climatic Zone
At Coimbatore, the annual rainfall received during
the I decade was 700 mm distributed in 50.5
rainy days while it got reduced to 670.4 mm (4.2%
decrease) spread in 45.2 rainy days in the III decade
(Fig 2). Among the dierent seasons, the percent
contribution from SWM to annual rainfall was found
to be higher from the I decade (29.9%) to III decades
(44.8%). The seasonal rainfall during SWM showed
an increasing trend of 30.2 percent from the I to III
decade and NEM recorded a declining trend from the
I decade to III decades (54.3%). The dependability
of seasonal rainfall was found to be higher with
lower Co-ecient of Variation (CV) values in the I
decade in all the seasons except CWP while the CV
in the III decade during NEM was found to be higher
(124.6%) with a lesser number of rainy days (15.9)
from the I decade (21.5). The reduction in NEM
rainfall along with uneven distribution that coincides
during the critical crop growth stages would have a
major impact on the rainfed crop growing areas in
the western zone.
Ooty- High Altitude Zone
At Ooty, the annual rainfall received during the I
decade was 1274.9 mm distributed in 88.4 rainy
days and no signicant reduction in rainfall and
rainy days was recorded in the III decade (Fig 3).
Alike Coimbatore, a higher percent contribution of
SWM to annual rainfall and seasonality trend from
I decade to III decades was observed at Ooty. The
seasonal rainfall was found to be dependable in
all the three decades which recorded less than 50
percent CV. The number of rainy days during SWM
showed an increase from 45.4 during the I decade
to 49.3 in III decade whilst the number of rainy days
during the NEM showed a decrease from 24.8 to
19.2 during I to III decade.

901KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
Cauvery Delta Zone-Trichy and Aduthurai
At Trichy, the annual rainfall received during the
I decade was 883.5 mm distributed in 43 rainy
days while it got reduced to 599.3 mm (32.2%
decrease) spread in 34.2 rainy days in the III decade
(Fig 4). Among the dierent seasons, the percent
contribution from HWP to annual rainfall was found
to be higher from I decade (10.8%) to III decades
(18.3%). Both SWM and NEM showed a declining
trend from I decade to III decade. Only the NEM
rainfall was dependable during I decade with a CV
of 41.2 percent. The CV was found to be more than
50 percent for all the seasons in the III decade which
indicated the lower dependability of rainfall in the
recent years. The number of rainy days was also
found to be decreased from I decade to III decade
in both the monsoon period. Since both monsoonal
rainfalls are not dependable, for the non- delta
blocks, special attention in the selection of crop and
duration needs to be addressed to avert the weather
vagaries during the cropping season.
Aduthurai
At Aduthurai, the annual rainfall received during the I
decade was 1010.8 mm distributed in 45.8 rainy days
while it got increased to 1077.6 mm (6.2% increase)
spread in 48.5 rainy days in the III decade (Fig 5).
The same pattern registered in Coimbatore and
Ooty for the higher percent contribution of SWM to
annual rainfall and seasonality trend from I decade
to III decade was observed at Aduthurai. The NEM
recorded 47 percent of CV value in the I decade and
the dependability of rainfall was higher while in the
III decade, both SWM and NEM recorded less than
50 percent of CV indicated more dependability of
seasonal rainfall. The number of rainy days during
Fig. 3: Rainfall variability for three decades at Ooty
Fig. 4: Rainfall variability for three decades at Trichy

902KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
SWM showed an increase from 13.4 during I decade
to 16 in III decades whilst the number of rainy days
showed a decrease from 27.3 to 26 during I to III
decades.
Fig. 5: Rainfall variability for three decades at Aduthurai
Southern Agro Climatic Zone- Killikulam
Killikulam
At Killikulam, the annual rainfall received during
the I decade was 668.9 mm distributed in 41.2
rainy days while it got reduced to 475.8mm (28.9%
decrease) spread in 31.3 rainy days in the III decade
(Fig 6).Among the dierent seasons, the percent
contribution from NEM to annual rainfall was found
to be higher from I decade (63.6%) to III decade
(72.9%). Both SWM and NEM showed a declining
trend from I decade to III decade. Only the NEM
rainfall was dependable with the CV of 47.1 percent
during I decade and the CV was found to be 36.4
percent in the III decade for the NEM. The number of
rainy days was found to be decreased from I decade
to III decades in both the monsoon period.
Fig. 6: Rainfall variability for three decades at Killikulam
Kovilpatti
At Kovilpatti, the annual rainfall received during
the I decade was 707.0mm distributed in 42 rainy
days while it got reduced to 604.8 mm (14.5%
decrease) spread in 36.5 rainy days in the III
decade (Fig 7). Among the dierent seasons, the
percent contribution from SWM to annual rainfall
was found to be higher from I decade (18.8%) to III
decades (23.4%). The seasonal rainfall during SWM
showed an increasing trend and NEM recorded a
declining trend from I decade to III decade. Only
the NEM rainfall was dependable with CV of 36.4
percent during I decade and in the III decade, each

903KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
monsoonal rainfall was dependable with less than
50 percent CV. The number of rainy days was found
to be decreased from I decade to III decades in both
the monsoon period.
Arupukottai
At Arupukottai, the annual rainfall received during
the I decade was 876.7mm distributed in 47 rainy
days while it got reduced to 683.2 mm (22.1%
decrease) spread in 41.3 rainy days in the III
decade (Fig 8).Among the dierent seasons, the
percent contribution from SWM to annual rainfall
was found to be higher from I decade (29.0%) to III
decades (32.2%). The seasonal rainfall during SWM
Fig. 7: Rainfall variability for three decades at Kovilpatti
showed an increasing trend and NEM recorded a
declining trend from I decade to III decade. Only the
NEM rainfall was dependable with the CV of 41.2
percent during I decade and in the III decade, each
monsoonal rainfall was dependable with less than
50 percent CV. The number of rainy days was found
to be decreased from I decade to III decade in both
the monsoon period.
Fig. 8: Rainfall variability for three decades at Arupukottai
In the Southern Agro Climatic Zone, the reduction
in NEM rainfall during the recent past entrusted
the farmers to switch over to SRI method of rice
cultivation to reduce the water requirement under
irrigated conditions. Under the rainfed condition,
during the purattasipattam, crops like Pulses, Maize,
Chillies, Sorghum and Cotton are grown as in case
of normal rainfall pattern while the declining rainfall
trend was noticed in the recent past which made the
farmers to choose to minor millets (foxtail millet, little
millet) to increase the rainfall use eciency.

904KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
Since more area under rainfed agriculture pertains
to Southern Agro Climatic Zone, the decreasing
number of rainy days in all the seasons along with
decreasing lifeline monsoon exhibits an alert in
modifying the crop planning programme in those
areas. In many parts of Asia, the frequency of heavy
rain has increased, while the amount of rain and the
number of wet days has reduced dramatically.3,5.
Table 1a: Frequency of dierent number of rainy days during dierent seasons at Coimbatore
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 0.7 0.4 0.8 0 0.1 0 0.9 0.5 0.9 0.1 0 0 1.1 0.2 0.1 0.1 0.2 0
HWP 2.6 4.8 3.3 0.5 0.1 0 5.8 3.6 4.5 0.7 0 0 5.2 3.1 4.4 0.9 0.3 0
SWM 14.5 11.7 6.3 0.8 0.2 0 23.1 9 6.1 0.6 0.4 0 21.9 9.8 5.9 0.4 0 0
NEM 7.7 8.8 10.2 1.6 0.9 0 10.1 5.2 8.7 2.5 0.6 0 9.9 5.7 7 1.7 0.2 0
Table 1b: Frequency of dierent number of rainy days during dierent seasons at Ooty
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 1.3 1.3 1.1 0 0 0 1.1 1.0 0.9 0.1 0.1 0.0 1.9 1.0 1.0 0.0 0.0 0.0
HWP 8.2 7.5 9 0.9 1 0.4 7.2 7.2 9.8 1.5 1.0 0.7 10.6 7.4 9.2 1.7 0.8 0.8
SWM 22.7 20.1 19.8 2.9 2.5 5.6 21.4 21.3 22.0 2.9 1.5 2.6 25.2 22.1 22.9 2.3 1.5 2.8
NEM 8.3 9.1 13.4 1.3 1.1 1.7 10.0 9.4 13.0 1.7 1.0 1.2 10.5 7.4 10.2 1.6 0.7 0.9
Table 1c: Frequency of dierent number of rainy days during dierent seasons at Trichy
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 0.4 0.5 0.7 0.5 0 0 2.4 1.6 1.1 0.0 0.2 0.0 0.7 0.4 0.4 0.0 0.0 0.0
HWP 2.7 3.5 3.8 0.6 0.9 0 6.4 4.2 5.8 1.5 0.9 0.0 2.9 3.1 4.4 1.1 0.7 0.0
SWM 4.5 7.8 13.1 4.2 0.9 0 8.7 10.0 12.9 3.6 1.3 0.0 5.6 8.5 10.5 1.8 0.4 0.0
NEM 9.5 14.9 20.7 4.1 1.5 0.7 14.5 14.7 20.5 3.2 1.6 0.5 9.5 9.6 14.5 2.9 1.1 0.4
Table 1d: Frequency of dierent number of rainy days during dierent seasons at Aduthurai
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 2.4 0.9 1.3 0.2 0 0 1.9 1.5 1.2 0.3 0.2 0.2 1.5 0.9 0.9 0.2 0 0
HWP 1.4 0.9 1.7 0.2 0 0 3.2 1.9 3.8 0.6 0.1 0.4 2.1 1.3 2.9 0.1 0.2 0
SWM 7.6 5.1 6.7 1.3 0.5 1 7.6 4.7 8 1.4 0.6 0.3 11.2 4.9 8.5 1.9 0.7 0
NEM 12 9.8 12.8 2.2 1.9 1.2 9.4 6.7 14 2.7 2.5 1.2 6.3 6.4 13.7 4.5 1.3 0.1

905KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
Table 1e: Frequency of dierent number of rainy days during dierent seasons at Killikulam
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 1 0.8 1.3 0.2 0 1 0.9 1.2 2.4 0.4 0 0 0.3 0.8 0.9 0 0 0
HWP 1.6 3.7 3.8 0.3 0 1.6 1.6 3 5.1 0.5 0 0 1.3 3.3 2.4 0.2 0 0
SWM 2.7 2.7 2.9 0.3 0.1 2.7 1.8 1.5 2.3 0.6 0 0 2 1.6 1.4 0.2 0 0
NEM 4.6 9.3 12.5 2.1 0.1 4.6 3.8 6.6 11.9 2.7 0 0 7.4 7.1 10.9 1.8 0 0
Table 1f: Frequency of dierent number of rainy days during dierent seasons at Arupukottai
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 0.8 0.9 0.9 0 0.2 0.1 0.7 1 0.7 0.3 0 0 0.7 0.7 0.4 0 0 0
HWP 2.7 3.3 4.8 0.5 0.1 0 2.5 3.1 5.6 0.8 0.3 0 1.9 3.6 3.4 0.8 0.2 0
SWM 4.9 5.7 6.9 1.7 0.4 0 4 4 7.3 1.3 0.2 0 3.6 5.7 6.7 0.9 0.5 0
NEM 7.4 7.5 11.2 1.9 1.1 0.1 4.1 8.1 10.2 1.9 0.8 0 5.6 6.5 9.7 1.9 0.3 0
Table 1g: Frequency of dierent number of rainy days during dierent seasons at Kovilpatti
Season I II III
VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR VLR LR MR RHR HR VHR
CWP 5.3 2.7 1.3 0.3 0 0 4.2 1.5 2.4 0.0 0.0 0.0 3.0 1.2 1.2 0.0 0.0 0.0
HWP 5.6 6.7 8.9 1.3 0 0 11.3 8.0 10.9 0.9 0.4 0.0 7.8 6.0 7.6 1.2 0.0 0.0
SWM 10.9 9.6 7.6 1.7 0.4 0.0 11.8 6.2 7.8 1.5 0.2 0.0 10.6 4.0 6.6 1.4 0.6 0.0
NEM 17.5 14.4 19.6 4.2 0.9 0.0 20.7 12.2 22.5 3.4 1.8 0.0 21.4 13.0 19.6 2.0 0.6 0.0
Frequency of Rainfall Intensity for Different
Locations of Tamil Nadu
The decadal frequency of rainfall intensity for
dierent locations of Tamil Nadu are portrayed from
Table 1a to 1g.
Total number of RD was found to be 76, 83.3 and
78.1 during I, II and III decadal period for Coimbatore.
More number of VLR (14.5-I, 23.1-II & 21.9-III) was
observed during SWM and no HR incidence was
reported in the recent decade. In NEM, VLR was
found to be increased from 7.7- I to 9.9 in the III
decade and other intensity of rainfall was found to
be decreased in the recent decade.
In Ooty, the rainfall intensity classication from VLR
to VHR was reported during both SWM and NEM
respectively. Light and Moderate Rainfall intensity
has been increased while Heavy and Very Heavy
Rainfall intensity got decreased during SWM from
I to III decade. Light to very heavy rainfall intensity
got reduced during NEM except VLR intensity.Due
to a rise in the frequency of extreme events in the
global warming age, there is a growing trend in the
irregularity of daily rainfall activity.9
Total number of RD was found to be 95.5, 115.7
and 78.5 during I, II and III decadal period for Trichy.
Since, the rainfall intensity categories varying from

906KOKILAVANI et al., Curr. World Environ., Vol. 16(3) 898-907 (2021)
LR to VHR reduced in both SWM and NEM from I
decade to III decade, the total number of rainy days
decreased in the III decade.Total number of RD was
found to be 71.1, 74.4 and 69.6 during I, II and III
decadal period for Aduthurai. The total number of
rainfall intensity values were found to be more or
less equal during SWM and NEM season, minimal
variation was found at Aduthurai location.
Total number of RD was found to be 50, 46.3 and
41.6 during I, II and III decadal period for Killikulam.
Heavy and Very High Rainfall intensity was absent
in the II and III decade. Total number of RD was
found to be 63.1, 56.9 and 53.1 during I, II and III
decadal period for Arupukottai. During NEM, LR and
MR was found to be lower when compared with I
and III decade.Total number of RD was found to be
118.9, 127.5 and 107.8 during I, II and III decadal
period for Kovilpatti. Since, total number of rainfall
intensity values were found to be more or less equal
during SWM and NEM season, minimal variation was
found at Kovilpatti. The frequency of rainfall intensity
revealed that except Ooty, the number of Heavy
Rain (HR) to VHR(VHR) was found to be meagre to
absent in most of the studied locations. The rainfall
intensity frequency for Coimbatore inferred similar
ndings.1
Conclusion
It's worth looking at the frequency and intensity
trends separately since it's feasible that the
number of extreme occurrences will rise without a
commensurate rise in the intensity of each event.
The results of the study indicated that an increasing
trend in SWM rainfall was observed in Coimbatore
(209.3 to 300.6mm), Ooty (681.4 to 703.1mm),
Aduthurai (227.8 to 320.6mm), Kovilpatti (132.8 to
141.3 mm) while decreasing trend was observed in
rest of the places. A decreasing trend was reported
in general for all the places during NEM. Decreasing
trend in number of rainy days was registered in
Kovilpatti, Virudhunagar and Killikulam that exhibits
an alert in modifying the crop planning programme
in those areas. The frequency of rainfall intensity
revealed that except Ooty, the number of Heavy
Rain (HR) to VHR(VHR) was found to be meagre
to absent in most of the study locations. The daily
rainfall analysis would also pave a way to x the
reasonable premium and relatedpayout structure
for the rainfall-based crop insurance products in the
specic location.
Acknowledgement
The authors would like to thank Agro Climate
Research Centre, Tamil Nadu Agricultural
Universityfor the support to carry out the research
in a successful way. The author also profoundly
grateful for other research stations for sparing the
valuable meteorological data.
Funding
There is no funding or nancial support for this
research work.
Conict of interest
There is no conict of interest in the manuscript.
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