4.4 Climate and Rainfall

The varying geographic and physiographic conditions of the State is responsible for the climatic variation in the State from arid to semi-arid in the plateau region, subhumid to humid tropical in the Ghats and humid tropical monsoon type in the west coast plains. For meteorological purposes, the State has been divided into three sub-divisions:-

• Coastal Karnataka consisting of Dakshina Kannada, Udupi and Uttara Kannada districts.

• North interior Karnataka consisting of Belgaum, Bidar, Bagalkote, Bijapur, Dharwad, haveri, Gadag, Gulbarga, Koppal and Raichur districts.

• South interior Karnataka consisting of Bangalore Rural, Bangalore Urban, Bellary, Chikmagalur, Chitradurga, Kodagu, Hassan, Kolar, Mysore, Chamrajnagar, Shimoga and Tumkur districts.

As per Koppen's classification, the State witnesses three climatic types. The tropical monsoon covers the entire coastal belt and the adjoining areas. The southern half of the State, outside the coastal belt experiences hot, seasonally dry tropical savana climate. The remaining regions of the Southern half of the State experiences hot, semi-arid, tropical steppe type of climate. According to the Thronthwaite's classification, the coastal and Malnad regions are per-humid i.e. those having moisture index of 100% and above. The interior regions are semi-arid (moisture index of minus 66.7% to minus 33.3%). Moist sub-humid and dry-humid zones (moisture index of minus 33.3 to plus 20%) are the transition zones covering the region between the malnad and the coast. The arid zone in the State is confined to east of Bellary district, most of Raichur district, east of Chitradurga district and the adjoining Pavagada taluk of Tumkur district with small area in Bijapur and adjoining north-eastern Belgaum district. Very dry areas with moisture indices less than minus 60% occur in Chitradurga, Bellary, Raichur and Bijapur districts, west and south of Gulbarga district and north Tumkur district. Semi- arid regions with moisture indices of less than 50% occur in Bidar district in the north, Bangalore district and adjoining areas of Tumkur and Mysore districts in the south. The sub- humid zone in the State exists as a narrow belt east of Western Ghats from Belgaum in the north to the west of Heggadadevanakote taluk of Mysore district in the south. Adjoining to this in the west is a narrow strip of humid and a wider strip of pre-humid zones. About 77% of the total geographical area of the State, covering interior Karnataka is arid or semi-arid with the State contributing 15% of the total semi-arid or 3% of the total arid areas of the country.

Rainfall Pattern:

Krishnan (1984) has extensively studied the rainfall patterns of the State. The State receives 80% of the annual rainfall in the southwest monsoon period, 12% in the post-monsoon period, 7% in the summer and only 1% in winter. The coastal region, on the windward side of the Ghats, receives 3350 mm of rainfall during the southwest monsoon. On the leeward side of the Ghats the rainfall drops to as low as 600-700 mm. The northeastern monsoon currents affect the eastern part of south interior Karnataka, accounting for 30% of annual rainfall in this region, during October to December. The rainfall increases over and near the Ghats but decreases towards the West Coast. There are two major rainfall deficit areas in the State with annual rainfall of 500-600mm, both lying in north interior Karnataka, one covering Bijapur, east Belgaum, north-east Dharwad and the west Raichur districts and the other east Bellary and Chitradurga district and a small portion of Tumkur district. The region with lowest rainfall of less than 500 mm is around Challekere in Chitradurga district. The humid malnad region has annual rainfall in the range of 1000-3800mm. The convergence of the monsoon westerlies and its vicinity to the Ghats brings good showers to the West Coast of Karnataka. Rainfall intensities are low in the semi-arid regions and less than 140mm in the central Dharwad district, a strip covering Chikmagalur, Kadur, Arsikere, Sira, Hiriyur and Pavagada, northwest of Mysore district and adjoining Mandya district. Daily rainfall intensities range from 180-240 mm in north Bijapur, north Gulbarga and Bidar district. The rainy season is spread over a period of four months (June-September) in the coastal, Ghats, malnad areas and in Bidar district, while over the maidan areas it is spread over a period of five to seven months. The districts, which have a long spell of rainfall, are Hassan, Mysore, Tumkur and Chitradurga. It is advantageous that the rainy season extends over a period of five to seven months in the comparatively low rainfall maidan areas, as it enables agricultural operations to be carried out over longer period. The Coastal region, Ghats, malnad and the adjoining areas, west of Chikkodi, Dharwad, Channagiri, Chikmagalur and Heggadadevanakote receive maximum rainfall during the month of July. In a large part of the northern maidan area, September is the month of maximum rainfall, except for a few taluks in Bidar and Gulbarga districts, which have maximum rainfall in July. In the southern maidan area, the maximum rainfall is the eastern half of Tumkur district and in most of Bangalore and Kolar districts. In the remaining areas of the southern maidan, including the eastern taluks of Hassan district, the maximum rainfall is in October. One of the important aspects of rainfall distribution in the maidan areas, which forms the major part of the State, is the pronounced rainfall in September and October, which are the two most rainy months. Rainfall in these months is important for the maturation of Kharif crops and the sowing and early stages of Rabi crop. Over the major part of the State, September-October rainfall forms one-third of the annual rainfall; it is over 40% of the annual rainfall over the region extending from Bijapur, district to eastern half of Raichur and Bellary districts, the northeastern part of Chitradurga district and the extreme northern parts of Tumkur and Mandya districts.

Drought:

Droughts present a serious problem in the State with about two-thirds of the State having 750mm or less annual rainfall. The severity and extent of drought not only depends on low rainfall but also on other hydro-meteorological factors like soil moisture, infiltration and moisture-retention capacity of the soil. Aridity of an area depends on rainfall in relation to potential or actual evapo-transpiration and the moisture holding capacity of the soil. Potential evaporation is a measure of the maximum possible evaporation from the soil and the transpiration from vegetation, if the soil is fully saturated. It is a measure of the consumptive use of water by crops. All arid and semi-arid areas of the State have been determined on the basis of ‘moisture index' calculated according to Thronthwaite's method of climatic classification. An area with moisture index between –33 to –100 percent indicates arid climate while a moisture index between –33 to –60 indicates a semi-arid climate. Considering moderate and severe droughts, the taluks, which have had droughts in 25 percent or more years, are Chitradurga, Hosadurga, Sira, Madhugiri, Shorapur, Athani and Bagepalli. The taluks with the greatest percentage of drought years are Sira, Madhugiri, Korategere, Kadur, Kushtagi, Shorapur, Shahapur, Yadgir, Bangarpet, Mulbagal, Srinivasapur, Gudibanda, Bagepalli, Athani, Raibag, Saundatti and Gokak. The taluks in the northern drought-prone districts have in general, more years of moderate and severe drought than the taluks in the southern districts. There are some taluks in which drought occurred in three or more consecutive years. The largest continuous period of drought was eight years at Gubbi (Tumkur district) from 1920-1927, at Athani (Belgaum district) from 1965-1972, at Chincholi (Gulbarga district) from 1965-1972 and at Nargund (Dharwad district) from 1920-1927.

Temperature:

Temperature is the lowest in the beginning of January and increases thereafter gradually at first, and rapidly after the middle of February or the beginning of March. In the southern maidan region, the highest temperature occurs in April, while in the northern maidan and the coastal areas they occur in May. In January, the mean daily temperature is 31-32 ° C in the coastal areas and slightly above 30 ° C in the northern maidan area except in Bidar district where it is 28-29 ° C. The highest maximum temperature, in May reaches 43 ° C in Gulbarga-Raichur region. In Ghats and Malnad area, it is about 20-24 ° C. It is seen that the mean annual range of temperature (difference between highest mean daily maximum temperature and the lowest mean daily minimum temperature) is smallest in the coastal region (6 ° C) and greatest in the Bellary-Raichur region.

4.5 Agro climatic Zones (A-Z)

Karnataka is divided in to 10 agro climatic zones taking into consideration the rainfall pattern-quantum and distribution, soil types, texture, depth and physio-chemical properties, elevation, topography major crops and type of vegetation. Agroclimatic zones and their characteristics are shown in Annexure 2. Taluks in these zones are listed in Table 10. Soil, Rainfall and other aspects for each zone in Karnataka are given below:

Table 10: Taluks covered in each of the agro-climatic zones of Karnataka

(Karnataka Agriculture Department)

4.6 Agriculture

Agriculture production in the State is spread over three seasons namely, Kharif (July to October), Rabi (October to March) and summer. These seasons account for nearly 70%, 22% and 8% of annual food grain production respectively. In case of oilseeds, this ratio is in the order of 70%, 15% and 15%. The area coverage under Kharif, Rabi and summer seasons is around 70 lakh hectares, 30 lakh hectares and 6 lakh hectares, respectively. The total cultivable area of the State including net sown area (55.06%), cultivable wasteland (2.28%), current fallows (6.66), and other fallows (2.10%) is 66.09%. The total cropped land includes the net area sown plus the area sown more than once. The agro-climatic conditions of the State permit the cultivation of different types of crops. Some of the important crops grown are Cereals like rice, jowar, bajra, maize, wheat, ragi and minor millets; pulses like tur, Bengal gram, horse gram, black gram, green gram, cowpea etc; oil seeds like groundnut, sesamum, sunflower, soyabean and safflower; commercial crops like sugarcane, cotton and tobacco. The gross and the net cultivated area under agricultural crops had increased from 96.97 lakh hectares to 108.84 lakh hectares and from 100.65 lakh hectares to 106.09 lakh hectares (1955-1956 to 1998-1999).

Agricultural crops like bajra, jowar, minor millets; tur, sesamum, castor and niger are purely Kharif crops. Wheat, Rabi jowar and Safflower are cultivated in the Rabi season. Cereal crops like paddy, jowar, ragi and maize can be grown in all the three seasons. Pulses too are grown in all seasons. Among soil seed crops groundnut and sunflower can be grown during all seasons. In Karnataka, the Kharif crops are cultivated in all the agro climatic zones. The Rabi crops are mostly cultivated in the northeastern dry and the northern dry zones. Water is one of the most important inputs essential for the production of crops. Water besides affecting the performance of the crop directly also influences the availability of other nutrients. Most of the areas in Karnataka lie in the low rainfall region. The total net area sown when distributed according to rainfall patterns reveal that 24.3% of the area is under medium rainfall region, while 66.3% is under low rainfall region. For cultivation in the low rainfall regions, adequate irrigation facilities need to be ensured which depends on several factors like availability of water, soil type, water absorption potential of the plant etc. For most of the crops, except rice, the ideal soil for irrigation is that which is deep, without any water table, has high water-holding capacity, infiltration rate and permeability, and low salt content. Loams and clay loams are generally good soils for irrigation since the run off is fairly low. The efficiency of field irrigation can be determined by measuring the quantity of irrigation water applied and stored in the root-zone. Depending on the soil type, the following broad range of values can be used to compute the irrigation efficiency as given in table 11.

Table 11: Irrigation Efficiency under different soil types in Karnataka

(ICAR, 1980)

The agro-climatic conditions of some of the important crops cultivated in the State are discussed below:

Rice ( Oryza sativa ) is cultivated as purely rain fed crop where the monsoon is precarious. It is grown as both Kharif and Rabi crop. Paddy is cultivated in 11% of the total cropped area in Karnataka (about 1.42 Mha). The major soil groups where rice is grown are riverine alluvium, red loamy, lateritic, coastal alluvium, red sandy, medium and shallow black etc. It is cultivated mostly in all the agro-climatic zones.

Ragi ( Eleusine coracana (L.) Gaertn.) also known as finger millet is an important cereal in Karnataka. It is grown in areas with rainfall ranging from 50-100 cm and in the irrigated areas. This crop flourishes well in red loams, black and sandy loams. Ragi under rain fed conditions or as a mixed crop is grown in rotation with Sorghum and a variety of oilseeds and pulses and occasionally as an off-season crop in rice fallows. The rain fed crop is cultivated both as a Kharif and Rabi crop. The irrigated crop is raised throughout the year in Karnataka. It is rotated with several commercial crops like tobacco, vegetables and turmeric. In the State about 8.37% of cropped area (1.03 Mha) is under ragi cultivation.

Sorghum ( Sorghum vulgare Pers.), popularly known as jowar, is the most important food and fodder crop of dry land agriculture. They grow well on medium and deep black soils. The Rabi sorghums are wholly confined to black cotton soils and the Kharif sorghums are grown on light soils. A two-year rotation of jowar-cotton is most common during Kharif season in the Deccan plateau. During Rabi, the jowar-cotton, jowar-gram or jowar-jowar rotations are common. About 1.8 Mha (15.02% of the total cropped area) are under jowar cultivation in the State.

Maize ( Zea mays L.) is a short-duration warm weather crop and requires fertile, deep and well-drained soils. However, it can be grown on any type of soil ranging from deep heavy clays to light-sandy ones. A soil pH of 7.5-8.5 is required for its effective growth. At the seedling stage, maize is highly susceptible to salinity and waterlogging. Hence soils ideally suited for maize cultivation should have adequate water-holding capacity and good drainage. Over 85% of the maize acreage is sown under rain-fed conditions during the monsoon when over 80% of the annual rainfall is received. About 0.51 Mha of land is under maize cultivation in the State (4.16% of the total cropped area).

Groundnut ( Arachis hypogaea L.) is an important oilseed crop of the State. It covers an area of 1.23 Mha (9.99% of the total cropped area). The crop can be grown successfully in places receiving a minimum rainfall of 500 mm and a maximum rainfall of 1,250 mm. It is grown on a variety of soil types. It does best on sandy loam and loamy soils and also in black soils with good drainage. Groundnut is raised mostly as a rain fed Kharif crop, being sown from May to June, depending on the monsoon rains. As an irrigated crop it is grown to a limited extent between January and March and between May and July.

Sunflower ( Helianthus annuus L.) is another important oilseed crop grown in Karnataka. The crop requires a cool climate and thrives well in deep, neutral and well-drained light soils as well as in heavy soils. The optimum soil pH for this crop is 6.5-8.5. It performs well in the black cotton soils of Karnataka.

Sugarcane ( Saccharum officinarum L.) constitutes about 2.75% of the total cropped area of Karnataka. The yield obtained is also highest in the State compared to the all India figures. It grows well on medium heavy soils, but can also be raised on lighter soils and heavy clays provided there is adequate irrigation in the former type of soils and drainage is good in the latter type of soils. In peninsular India, it is grown on brown or reddish loams, laterite and black cotton soils. In the canal irrigated tracts of Karnataka, a block system of irrigation is practiced and under it a three-year rotation is compulsory, the sequence of crops being rice, groundnut, jowar, ragi and sugarcane. The maintenance of optimum soil moisture during all stages of growth is one of the prerequisites for obtaining high yields. Therefore, areas well distributed with rainfall or assured irrigation facility is essential. For sustained yields, sugarcane requires adequate manure for 70 tonnes of crop removes from the soil 85-110kg of Nitrogen, 180-330 kg of Phosphorous acid, 60-190 kg of Potash and 70-80 kg of Calcium. About 0.34 Mha of sugarcane is cultivated in the State.

Cotton is an important commercial crop of the State covering 5.17% of the total cropped area (0.64 Mha). It is largely cultivated under rain fed conditions requiring a minimum rainfall of 50cm. Cotton can be grown on a variety of soils. It is grown as a dry crop in the black cotton and medium black soils and as an irrigated crop in the alluvial soils.

Tobacco ( Nicotiana tobacum ) is grown in the State as a Kharif crop in lighter soils and irrigated as and when required. Bidi tobacco is grown as a rain fed crop during Rabi season, mostly in the black soil or loamy soils of Belgaum district.

Agricultural residues

Agriculture residues like rice husk, bagasse, groundnut shells, maize cobs etc have immense potential to be used as fuel substitutes. The importance and contribution of crop residues as a source of fuel for domestic use has been recognized in several studies (NCAER 1985;Leach 1987; Barnard 1990). The green revolution has not only increased the productivity of the grains, but also the generation of residues. Potentially, organic residues can be utilized for a variety of purposes like fuel, fertilizer, feed etc. Perhaps the most important criticism of the use of agriculture residues to produce fuel is the conflict with food production (Brown, 1980; Hall, 1984). However, in the long term, the use of agricultural feedstock for energy production may actually help to increase the supply of conventional agricultural products (Trindade, 1981). Crop residues that have high lignin content can be used as fuel, while the others as fodder. An exception to the latter are rice husks that contain silica and maize cobs, which are difficult for the cattle to consume. Plasket (1981) predicts that 30 tonnes/ha/year of matter for energy production could remain after mechanical extraction of the protein –rich juices for feed from grasses, Lucerne and other perennial species. Agricultural residues can be used more efficiently as substrates for anaerobic digestion to produce both energy and fertilizers.

In Karnataka, the agriculture residues are used as fodder, fuel, thatch and manure. Ninety two percent of the stalk from cereal crops is used as fodder, 4% as thatch, 2% as manure and 2% have other use. Major portion of the cotton stalk, groundnut shells, coconut shells and leaves are used as fuel (Madhulika Sinha and Malati Hegde, 1987). A brief account of some of these residues is given below.

Rice husk: During the milling of rice, husk and bran are obtained as by products. The quality of husk produced depends upon the type of rice mill from where the husk is obtained. In the single huller and the battery of hullers, the husk is obtained in a fine broken State and is always mixed with bran and broken rice. This husk-bran mix is used as a boiler feed. The average higher value of rice husk ranges from 2937.29 to 3461.31 kcal (Vimal & Tyagi, 1984). Proximate analysis gives the percentage of volatile organic matter, fixed carbon and ash content. Ultimate analysis is needed for the computation of air requirement for complete combustion, weights and percentages of products of combustion and various heat losses on furnace tests. The proximate and ultimate analysis of paddy husk is given in table 12.

Table 12: Proximate and Ultimate Analysis of Paddy Husk

(Biswas and Goswami, 1996)

Paddy husk is mainly used as fuel in most parts of Karnataka. In some places, it is left in the fields for decomposition, so as to enrich the soil (Madhulika Sinha and Malati Hegde, 1987).

Maize cobs: These comprise of about 30% of maize grain. The cobs are used as fuel or as a supplementary feed for cattle. These are rich in pentosans and are a great potential source of furfural-which is used widely in petroleum, nylon, and vegetable oil manufacturing.

Bagasse: Sugarcane is the fibrous residue left after the extraction of juice from sugarcane. The quantity of bagasse depends upon the fiber content-33-36% in the Northern India and 26-30% in Southern India. Bagasse usually comprises 25-30% of weight of the sugarcane (Isaias, 1980). In India, bagasse is used mainly in sugar factories for generating steam in the boilers and concentrating sugarcane juice. The average gross calorific value of bagasse with 48% moisture is about 2223 kcal/kg. One tonne of bagasse generates 2.5 tonnes of steam.

Groundnut shells: Depending upon the season, variety and soil conditions, about 1/3 weight of groundnut pod consists of shell. Due to their large percentage of crude fiber, groundnut shells are not used as cattle feed. The calorific value and proximate ultimate Analysis of groundnut shells is given in table 13.

Table 13: Proximate/Ultimate Analysis of Groundnut Shells

(Vimal and Tyagi, 1984)

Groundnut shells are reported to be good raw materials for the manufacture of activated carbon for bleaching purposes. The carbon can also be employed to decolorize oils, sugars, pharmaceuticals and as an adsorbent in gas masks.

Cotton sticks: It is estimated that on an average, the rain fed crop gives about 2.5 tonnes per hectare of cotton stalk and the irrigated crop gives about 5 tonnes per hectare. Cotton sticks are also quite suitable for the manufacture of hardboards, paper and other industrial products.