Spatial Analysis of Rainfall Variation in Coimbatore District ...

INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 1, No 2, 2010

© Copyright 2010 All rights reserved Integrated Publishing services Research Article ISSN 0976 – 4380

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Spatial Analysis of Rainfall Variation in Coimbatore District Tamilnadu using GIS

Ishappa Muniyappa Rathod ,Aruchamy.S Department of Geography, School of Geosciences,

Bharathidasan University, Tiruchirappalli24 [email protected]

ABSTRACT

Among the climatic elements the rainfall is the first index, ever thought of by farmers and climatic analyzers as it is the most important single factor which determines the cropping pattern of an area in general and the type of crop to be cultivated and its success or failure in particular. Therefore, the present study deals the rainfall characteristics of the Coimbatore District, which includes the spatial distribution and variability through different seasons, precipitation ratio and frequency occurrences. The study is based on 49 years of the monthly rainfall data for 33 rain gauge stations. While analyzing the long term average of monthly and annual rainfall, the annual rainfall of the district is 1242 mm, of which the winter, summer, southwest and northeast monsoon record 2.07, 14.97, 46.13 and 36.83 mm respectively. The station Upper Niradam receives the highest rainfall of 4655 mm whereas Krishnapuram records the lowest of 414 mm. The annual variability ranges from 21.16 percent to 52.28 percent. The south, southwest and northwestern parts of the district experience the heavy rainfall whereas the least rainfall areas are the east, northeast and southeastern parts of the district. Keywords: Annual and seasonal rainfall, rainfall variability, precipitation ratio and frequency.

1. Introduction

All of the natural conditions, rainfall should be regarded as the fundamentals so for as progress of the society is concerned. Rather it is has always been treated as a fundamental sector for the total development of the society S.K.Sadhukan (1987). Rainfall is a crucial agroclimatological factor in the seasonally arid parts of the world and its analysis an important perquisite for agricultural planning in India, Alak Gadgil (1986). India is a tropical country its agricultural planning and utilization water is depends on monsoon rainfall, more than 75% of rainfall accruing during the monsoon season; monsoon rainfall is uneven both in time and space, so it is important factors to evolving the rainfall analysis.Jagannadhasarma (2005) has analysed the rainfall pattern of the coastal zone of KrishanaGodavary River Basin Andhra Pradesh, India. He has made analysed the annual, monsoon and nonmonsoon rainfall and spatial and frequency distribution of rainfall intensity and G.Vennila (2007) has analysed rainfall variation analysis of Vattamalaikarai subbasin, Tamil Nadu, India. He has interpreted monthly, seasonal variation, intensity and frequency of rainfall. The present study made to understand the rainfall of the region, the highland receives more rainfall than nearby lowlands, especially in their wind ward sides as a result of orographic lifting characters of the region A.AAdebaye (1997). The influence of topography on rainfall distribution. However the study reflecting the more rainfall in the wind ward of western ghat region. Which includes the spatial variation, variability through different seasons, precipitation ratio and frequency.



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2. Study Area

The Coimbatore district is situated in North Western part of the Tamil Nadu, the district covering an area of 4889 sq.km falls between 10°13'4" North to 11° 24'5" North latitude and 76° 39' 25" East to 77° 18' 26" East longitude. Administratively district is divided into six taluks and twelve blocks (Fig.1). The district head quarter is located in the north central part of the region. The temperature ranges between 18.32°C in the month of January and 36.42°C in the month of April. The area is bonded by Western Gates on West, Nilagiri hills in North West and Anaimalai and Palani hill in south. The district gradient of slope gradually decreases towards west to east, the district drain Bhavani, Noyal, Pallar, Amaravathi rivers.

Figure 1: Images showing the study Area

3. Methodology

The base map of Coimbatore district has been prepared from Survey of India Toposheet on 1:250000 scale. Monthly rainfall data for the period of 49 years from 1959 to 2008 has been collected from Indian Meteorological Department Pune, and Economics and Statistical Department Chennai. There are 33 in and around rainfall station have been taken into consideration for analyzing long term mean monthly, seasonal and annual rainfall pattern has



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been calculated. The coefficient of variability where worked out. There are some rain gauge stations have been established during 1980 and 1996. The collected data has been processed and analyzed by preparing various charts maps and diagrams using GIS software.

4. Results and Discussion

4.1 Variation of Monthly Rainfall

The average monthly rainfall of 49 years (1959 to 2008) for 33 rain gauge station of Coimbatore district inferred that the variation of rainfall is found in every month, and the intensity of rainfall gradually increasing from the January to July, and suddenly decreasing trend noticed from July to September. The highly intensity trends noticed in the month of October and November and these month get highest rainfall and it reaches its maximum peak and also its start to decreasing from month of December and lowest of rainfall in the month of January.(Fig.2). However Upper Niradam records 1202.01mm in the month of July, 996.25mm in June, and 924.22 mm in August and it experience lowest rainfall in the month of February which is 14.12mm. The lowest rainfall recorded at Coimbatore town which is 4.1 mm in the month of February and its maximum rainfall is 135mm in the month of October

Figure 2: Monthly variation of rainfall pattern

4.2 Mean Annual Rainfall

The long term mean annual rainfall of the district is 1242.49mm. The district is characterized with unique aerial topography (Fig.4) in quantum of rainfall due to the influence of western Ghat and Anaimalai and Nilgiri hills. The maximum rainfall recorded at Upper Niradam which is 4655.1mm and minimum 414.4mm at Krishnapuram. The southern part of region experiences highest rainfall that is Upper Niradam (4655.1mm),Solaiyar Nagar (3703mm),Anaimalai (3523.3mm), Valparai (2882.7mm), these places influenced by the Western Ghats windward and located at Anaimalai reserve forest part of Western Ghats and gradually decreases toward north, east, north east upland region. Where as Krishnapuram(414.4mm),Annur.(559mm), Coimbatore town (559.3mm),Sultanpet(577.3mm), sulur (577.5mm), these upland region and palaghat gap

Mean Monthly Rainfall

y = 13.267x + 17.305 R 2 = 0.4945

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12 Months

Rainfall (M M)



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are rain shadow regions experiences lowest of rainfall in district. In general south, south west and north western parts noticed the heavy rainfall, the region falls under following zones. 1. High rainfall zone: (above 1000mm): In the southern part Upper Niradam, Soliyar Nagar, Anaimalai, Valaparai, Topslip, Attakatti, in the north western part Anaikatti, coonoor, Ooty, Kodanadu, Kethi, Kotagiri and sudakapalaya in the north eastern part. 2. Moderate rainfall zone (800999mm): Pollachi, P.N.Palayam, Aliyar Nagar, Negamam, 3. Normal rainfall zone :( 700799mm): Mettupalyam Tirumoorthy Nagar, Nallar colony. 4. Low rainfall zones: (600699mm): Vettaikarnpudur, Podanur, Chitrachavadi, and Bhavanisag 5. Very low rainfall zones :( Less than): Annur, Pedamapatti, Coimbatore town, Palladam, Peelamedu, Krrishanpuram, Poolankinar, Sultanpet and Sulur.

Figure 3: Image showing location of rainfall stations



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Figure 4: Image showing mean annual rainfall

4.2.1 Winter Season

During the winter season the region heavily experiences low rainfall and it is driest among the all season which is maximum recorded at adjacent area of the region which Coonoor 86.82 mm in the month of February and lowest recorded at Coimbatore town which is 4.1mm in the month of February. The amount of rainfall decreases north west to north east and central part of region such as Annur, Sulur,Sultanpet, Krishnapurm, and Podanur(Fig.5). Its rainfall average 20mm, this season contributes 2.07% to mean annual rainfall .

4.2.2 Summer Season

This is hot weather season the mount of rainfall gradually increases and however, the amount of rainfall occurrence in this season is largely due to convection effect, this season contributes 14.97% of mean annual rainfall this season average rainfall is 186.01mm and almost 80% area receives more than 186 mm accept north western and southern part of district (Fig.6). The highest amount of rainfall is recorded at the Upper Niradam 224.14mm in the month of May and seasonal average is 370.7 mm and where the lowest rainfall is recorded in Krishnapuram 5.3mm and its seasonal average 69.8 mm.

Figure 5: Images showing rainfall in winter and summer in the study area



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Table 1: Long term (19592008) mean seasonal, annual precipitation ratio and rainfall variability (in %)

S.No Station name Winter Summer SWM NEM Annual

1 Alaiyar nagar 20 155.37 292.72 366.27 834.38 2 Anaikatty 41.26 265.93 261.76 589.64 1158.61 3 Anaimalai 29.4 322.0 2702.8 469.0 3523.3 4 Annur 12.6 115.9 169.9 260.6 559.0 5 Attakatti 30.0 220.7 386.6 570.2 1207.4 6 Bhavani sagar 23.7 153.2 171.2 339.8 687.9 7 Chitrachavadi 15.3 97.7 236.1 308.1 657.1 8 Coimbatore town 9.6 98.2 151.6 299.8 559.3 9 Coonoor 148.2 308.0 369.5 864.3 1690.0 10 Kethi 35.1 401.8 722.5 751.9 1911.3 11 kodanadu 49.4 265.4 389.2 716.9 1421.0 12 kotagiri 45.7 275.7 333.8 599.6 1254.8 13 Krishnapuram 12.7 69.8 60.5 271.4 414.4 14 Metuupalayam 42.8 162.1 147.2 388.6 740.7 15 Nallar colony 21.1 118.0 187.1 385.3 711.5 16 Negamam 14.9 176.4 370.1 341.4 902.8 17 Ooty 15.0 221.6 509.5 363.4 1109.4 18 P.N.Palayam 24.1 171.3 201.1 422.7 819.2 19 Palladam 8.4 111.4 110.8 314.3 544.9 20 Pedamapatti 15.5 120.7 124.2 318.3 578.7 21 Peelamedu 14.0 120.9 147.7 312.9 595.5 22 Podanur 17.1 110.1 148.0 336.7 612.0 23 Pollachi 12.6 132.5 369.1 317.9 832.2 24 Poolakinar 18.1 103.3 99.7 332.9 554.0 25 Solaiyar nagar 28.0 345.7 2846.1 487.2 3707.0 26 Sultanpet 8.9 147.6 136.4 284.4 577.3 27 Sulur 11.8 139.2 113.9 312.7 577.5 28 Sundakapalayam 9.3 110.3 173.1 1713.3 2005.9 29 Thirumurthinagar 22.1 117.5 152.4 408.6 700.6 30 Topslip 24.9 160.3 772.4 369.1 1326.7 31 Upper niradam 29.6 370.7 3655.5 599.3 4655.1 32 Valaparai 28.3 333.9 2098.1 422.5 2882.7 33 Veetaikarnpudur 11.4 115.0 305.3 258.2 690.0 34 Mean 25.78 186.01 573.20 457.49 1242.49



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4.2.3 South West Monsoon Season

Huge amount of rainfall variation noticed in this season, half of northern part of district receives low rain and half of southern part receives heaviest rainfall during season. The average rainfall of this season 573.20 mm and it is 46.13 % of mean annual rainfall. The highest seasonal rainfall recorded in Upper Niradam (3655.5mm), and 1202.1 mm in the month of July, 996.25mm in June, 924.22 mm in August. Soliyar Nagar 2846.1mm, Anaimalais 2702.8mm, Valparai 2098.1mm, Topslip 772.4mm, lowest seasonal rainfall recorded in Krishnapurm 60.5mm, and 7.4 mm rainfall recorded in the month of August Sulur 113.9, Sultanpet 136.4 mm rainfall but southern parts of Districts receives more than 80% rainfall during this season. Most of south and west of Pollchi and Palaghat gap experiences highest rainfall, because of influence by leeward of Western Ghats (Fig.7). Upper Niradam Soliyar Nagar, Anaimalais and Topslip are wettest places of district.

Figure 6: Southwest monsoon rainfall

4.2.4 North East Monsoon Season

The North east monsoon season is important rainy season in the district, total rainfall in this season is low comparatively to the south west monsoon, but the eastern, north western, and



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central Upland region such as Annur, Sulur, Sultanpet, Negamam, Krishnapuram, Podanur Coimbatore town, and Peelamedu experiences maximum quantum of rainfall (Fig.8).this season contributes 36.82% of mean annual rainfall and average rainfall this season is 457.49 mm rainfall. The rainfall is gradually increase east to north west and south western part of the district, the highest rainfall recorded in adjacent area at Sundakapalayam 1713.3 mm, Upper Niradam 599.3, Anaikatty 589.64mm, Attakati 570.2, and where as lowest rainfall is recorded in Vettaikarnpdur 258.2mm, Annur 260.6mm and Krishnapuram 271.4mm, and Sultanpet 284.4mm, 80% of area receives well rain in this season, and most of agricultural activity takes places for showing crops.

Figure 7: Northeast monsoon rainfall

4.3 Variability of Rainfall

“Variability defined as the deviation from mean” or “ratio of the standard deviation to the mean rainfall” and in other words variability of coefficient of variation.

4.3.1 Annual Variability of Rainfall

Annual rainfall variability of region stretches between 19.69% to 387.91% at adjacent area of the region which is Coonoor and Sundakapalyam respectively, and 21.16% at Topslip and highest variability recorded in the central part of region that is Padanur (52.28%) and P.N.Palayam(51.81%) at northern part of region(Fig.9). Sultanpet experiences very low



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variability in eastern part district and in south western part Topslip and Vettaikarnpudur experiences low variability and Anaikatti, Coonoor experiences low variability in north western part of the region where as rest of district experiences homogenous variability in the region.

Figure 8: Image showing annual rainfall variability

4.4 Winter Season Rainfall Variability

The variability rainfall is higher in this season while comparatively to other season, because low rainfall areas experiences greater fluctuation of variability (Fig.10). The lowest variability recorded adjacent area of region which is Coonoor 77.29% maximum at Palladam 232.2% and lowest variability recorded north western part which is Anaiktti 115.34% and southern part such as Upper Niradam, Solaiyar Nagar, Valaparia, Anaimalai experiences the low variability and central part eastern part gradually increase variability of rainfall, this fluctuations indicates the region experiences heavy low rainfall.



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Table2: Long term (19592008) mean seasonal, annual precipitation ratio and rainfall variability (in %)

4.5 Summer season variability The variability during this hot weather season maximum recorded at (Fig.11) P.N. Palayam (86.36%), Attaikatti (79.93%), Negamam (78.34%), Sulur (77.86%), and Krishnapuram (76.07%) Coimbatore town (67.35%) Podanur (63.36%), Peelamedu (56.6%), and variability generally decreases from north to south and lowest variability experience adajecent area at Tthirumrthy Nagar 44.32%, and Solaiyar Nagar (49.07%), Sultanpet (52.03%), Vettaikarnpudur

Rainfall Variability

S.No Station Name

Annual

Precipitation

ratio

Winter

Summer

SWM

NEM

Annual

1 Alaiyar nagar 99.41 149.95 63.71 41.91 51.13 27.6 2 Anaikatty 119.02 115.34 65.19 74.07 46.51 29.23 3 Anaimalai 151.9 130 62.82 31.99 43.56 26.13 4 Annur 240.0 174.36 65.08 58.25 76.63 48.47 5 Attakatti 146.1 143.5 79.93 68.69 47.24 32.33 6 Bhavanisagar 89.05 128.54 62.93 71.96 43.5 27.65 7 Chitrachavadi 160.2 190.65 63.78 42.69 52.87 32.63 8 Coimbatore town 180.3 209.68 67.35 49.06 53.61 33.69 9 Coonoor 89.13 77.29 48.88 38.71 34.08 19.69 10 Kethi 88.31 124.9 65.01 43.38 24.37 28.43 11 kodanadu 136.72 119.78 71.72 41.46 31.23 23.57 12 kotagiri 96.38 120.94 74.77 34.99 35.89 28.03 13 Krishnapuram 195.5 231.65 76.07 73.71 52.77 42.2 14 Mettupalyam 140.7 139.06 56.6 62.99 46.77 31.63 15 Nallar colony 176.26 201.89 64.01 60.05 55.68 42.52 16 Negamam 120.94 227.51 78.34 42.11 54.25 31.81 17 Ooty 97.42 128.97 53.77 33.58 36.73 24.77 18 P.N.Palayam 210.77 187.17 86.36 73.94 60.14 51.81 19 Palladam 132.5 232.2 80.25 67.52 42.2 31.51 20 Pedamapatti 171.85 182.94 63.53 67.45 50.32 32.25 21 Peelamedu 171.5 183.14 56.6 65.01 50.49 33.99 22 Podanur 332.0 201.11 63.36 82.72 68.02 52.28 23 Pollachi 166.6 181.42 58.06 31.62 54.9 29.26 24 Poolankinar 151.62 214.77 71.73 89.99 44.1 35.02 25 Solaiyar nagar 160.82 131.29 49.07 39.31 38.65 32.9 26 Sultanpet 118.09 165.95 52.03 69.86 41.35 28.24 27 Sulur 223.0 180.5 77.86 75.98 57.01 42.71 28 Sundakapalayam 2115.36 214.34 55.85 51.17 453.74 387.91

29 Thirumurty nagar 94.06 190.55 44.32 43.59 44.8 24.94 30 Topslip 64.93 161.04 63.24 28.02 50.48 21.16 31 Upper niradam 195.74 130.42 72.86 41.33 56.66 39.69 32 Valaparai 132.64 128.05 62.3 31.02 46.51 26.87 33 Veetaikarnpudur 119.58 177.18 54.93 38.15 61.17 26.93



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(54.93%), Mettupalayam (56.6%), and Pollchi (58.06%),.The variability of region highest experience in north and eastern part of region. This season will be low because west of influences by the pre monsoon winds.

4.6 South west monsoon variability of rainfall The south west monsoon rainfall variability experiences very less variability, comparatively to the other season, that is the 28.02% lowest at Topslip, Anaimalai, Valparai, Solaiyar Nagar and west of Pollachi and south of Chitrachavdi experiences very less variability due to heavy rainfall during this season(Fig.12). Where as very high variability experiences at adjacent area of region Poolankinar 89.99%, Sultanpet, Sulur, Krishnapurm, Podanur, and P.N.Palayam.

Figure 9: Image showing rainfall variation in winter and in southwest monsoon season

4.7 North East Monsoon Variability

The north east monsoon rainfall variability experiences higher than the south west monsoon due to lesser rain, the maximum variability recorded at adjacent area of such as Sundakaplayam 453.74% and lowest at Kethi 24.37% and north of Pollachi indicated higher variability and Anaimalai, Topslip, and Sultanpet experiences low rainfall variability. However rest of area experiences uniformity of variability (Fig.13). 4.8 Precipitation ratio

Precipitation ratio= PxPn x 100

Where Px and Pn, represent the maximum and minimum of rainfall over the series of year and Pm is the mean annual rainfall.The abnormalities of rainfall at any location may be brought by a simple ratio of precipitation. It is the difference between maximum and minimum rainfall of over the series of expressed in terms of mean. This ratio may give the stability of rainfall with special relationship. Higher the ratio, higher in abnormality in rainfall and vice versa.The lowest abnormality found at Topslip, which is 64.93% and increasing the abnormality in the north



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eastern region of adjoining area that is Sundakpalayam 2115.36 % and this (Table.2) extreme abnormality found in the north east region and it not good relationship to the rainfall pattern in the north east region.

Figure 10: Image showing rainfall variability on Northeast monsoon

The higher abnormality of rainfall shows in the central part of the region and north east and eastern part of region showing the higher the abnormality of rainfall. Where as southern and north western part of the region gradually decreasing the abnormality of rainfall, and this results shows good relationship to rainfall pattern.

5. Conclusion

Coimbatore district bounded by Western Ghats, in the west and north of Nilagiri hills, in the south Anaimalai and Palani hills, and this district stretches in rain shadow region of Western Ghats. Normal rainfall of region during 19592008 is 1242.49 mm and this district receives above normal rainfall of Tamil Nadu state. The maximum rainfall recorded at Upper Niradam 1202.01mm in the month of July, and lowest of region recorded at Coimbatore town 4.1mm in the month of February. The Coimabtore districs experiences driest in the month of January. The analysis of region heavy rainfall experiences towards the south and south western part and north western part in summer, south west monsoon and north east monsoon season, and huge amount of deficit in the east, north east and gradually in south east part and central part of district. The south west monsoon contributes the highest percentage of rainfall, which is 46.13% (573.2048



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MM), north east monsoon 36.82% (457.4909 MM),summer 14.97% (186.0131 MM) and winter season contribute lowest of which is 2.07 %( 25.7851MM),

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