\f
TEXTBOOK OF AGRICULTURAL METEOROLOGY
TechnicalEditors
Prof. M.C. Varshneya Head Department of Meteorology Centre of Advanced Studies in Agricultural Meteorology Mahatma Phule Krishi Vidyapeeth, Pune, Maharashtra
Dr P. Balakrishna Pillai Former Dean Faculty of Agriculture Kerala Agricultural University, Trichur, Kerala
Mi
Higs3Hjr
ICAR
]
T
Published by Indian Council of Agricultural Research New Delhi
Printed First Reprint Second Reprint Third Reprint Fourth Reprint
May 2003 June 2004 March 2006 February 2012 November 2013
Project Director (DKMA) : Dr Rameshwar Singh
lncharge (English Editorial Unit) : Dr Aruna T Kumar
Chief Production Officer : Dr V K Bharti Technical Officer (Production) : Kul Bhushan Gupta
All rights reserved Š 2013, Indian Council of Agricultural Research, New Delhi
ISBN : 81-7164-019-2
Price : ? 250
Published by Dr Rameshwar Singh, Project Director, Directorate of Knowledge Management in Agriculture, Indian Council of Agricultural Research, Krishi Anusandhan Bhavan-I, Pusa, New Delhi 110 012 and printed at M/s Chandu Press, D-97, Shakarpur, Delhi 110 092.
Contents Page No. 1
1. Introduction
M.C. Varshneya P. Balakrishna Pillai
2. Atmosphere
A.S.R.A.S. Sastri B. Ajithkumar
4
3. Radiation
M.C. Varshneya B.I. Karande
8
4. Air Temperature
T.R.V. Naidu N.J. Thakore
19
5. Soil Temperature
A.M. Shekh H.R. Patel
28
6. Air Pressure
S.S. Salunke M.C. Varshneya
44
7. Atmospheric Moisture
S.S. Salunke
69
8. Clouds, their Types and Classification V.H. Deosthali
82
9. Rainfall
M.C. Varshneya V.B. Vaidya
93
10. Soil Moisture
N.L. Bote
115
11. Evapotranspiration
T.N. Balasubramanian V. Geethalakshmi
130
12. Climate and Crop Production
P. Balakrishna Pillai V.M. Nair
145
13. Weather in the Incidence of Pests and Diseases
P. Balakrishna Pillai B. Ajithkumar
154
14. Drought
Jayant Sarkar M.P. Shewale
160
15. Climatic Classification
N.L. Bote P. Balakrishna Pillai
168
16. Weather Forecasting
G.S.L.H.V. Prasada Rao P. Balakrishna Pillai
180
17. Remote Sensing
N.L. Bote
191
18. Crop Modelling and its Applications Annexures (I to XV) Abbreviations Index
M.C. Varshneya
197 201 215 217
1. Introduction M. C. VARSHNEYA and P. BALAKRISHNA PILLAI Climate has played decisive role in the evolution of the Earth and its ecosystem. Climate determines our habits and habitat, human progress and civilization. Successful crop production requires a suitable combinations of several factors like soil, water, crop variety etc. Climate of a place has a crucial role
in growth and production of crop plants. Studies of all the agricultural systems, viz. crops, cropping systems and farming systems are incomplete without the study of effect of weather on them. The potential productivity of these systems depends not only upon the irrigation, fertilizer and seed but also upon the optimum weather conditions. The agricultural production of the country in 1999’s has touched 204 million tonnes. The production was achieved by applying irrigations, using chemical fertilizers and hybrid seeds. These practices have attained its limits, which can hardly be further
stretched. Each and every growth phase of a plant is influenced by the prevailmg weather conditions. Each crop has its own weather optimum for the expression of its full yield potential. It is an established fact that the occurrence of pests and diseases in crop plants is very well related to weather conditions. Changes in weather parameters like rainfall, relative humidity etc. have influence on the occurrence of several devastating pest and disease problems in crop production. So knowledge of the influence of weather parameters on growth and yield of crops is essential in successful crop production. Definition Meteorology is the science dealing with the physics of atmosphere, while, Agricultural Meteorology is the science which deals with the interactions of atmosphere with crops, grasses, trees, animals, pests and diseases. Agricultural Meteorology is the study of those aspects of meteorology, which have direct relevance to agriculture. Its main objective is to know and define the effects of meteorological and hydrological factors on agriculture and to apply knowledge of the atmosphere to practical agricultural use.
Scope and Applications of Agricultural Meteorology The field of interest of agrometeorology extends from the soil surface layer to the depth up to which tree roots penetrate. In the atmosphere, it is interested in the air layer near the ground in which crops and higher organisms grow and animals live, to the highest levels in the atmosphere through which the transport of seeds, spores, pollen and insects may take place. This science strives to optimize food production by the maximum exploitation of the atmospheric environment at a minimum cost without disturbing the agro-ecosystem and also tries to minimize the impact of adverse weather on crops and to make use of crop weather relationship to boost agricultural production.
2
Agricultural Meteorology
While, genetic potential of various cultivars has been utilized optimally, soil and irrigation resources have also been tapped to the hilt. However, potential of weather has not been tapped as yet. It is essential that agricultural scientists should understand the role of microclimate in formation of yield in a plant and outbreak of pests and diseases. Pests and diseases damage 40% of our total agricultural production. Thus, timely forecast of incidence of pest or disease can result in saving the losses. Microclimatic modifications, viz shade management, use of reflectants, antitranspirants, wind breaks and mulches help in increasing the production. Similarly, production of smoke, heating of grape orchards by artificial heating, irrigating crops by sprinkler and flooding the plots during frost are some of the practices recommended by agrometeorologists to save the crop from inclement weather. However, intercropping and multiple cropping are some of the well-known practices that help farmers economically and in facing the contingencies. Agromereorological methods can be used in efficient land use planning, determining suitable crops for a region, risk analysis of climatic hazards and profit calculations in farming, production or harvest forecast and in adoption of farming methods and choice of farm machinery. Different Aspects of Agricultural Meteorology Agricultural meteorology is having different important aspects of study such as crop modeling and remote sensing in yield forecasting, weather forecasting in disaster management, sustainability of agricultural production under environmental pollution and depletion of ozone layer of the atmosphere and climate change. These aspects have been discussed below in brief.
Yieldforecasting: Forecast of yield can be done with the help of dynamic crop growth models. They can help to predict yield 1-2 months in advance. This leaves sufficient margin to planners and Governments to manage the shortages. Thus, study of crop weather modeling is a new emerging field in agricultural meteorology. Disaster management: Natural calamities such as cyclones, floods, drought and earthquakes are common in India. Cyclone in Andhra Pradesh, Gujarat and Orissa, floods in several parts of the country including Rajasthan, drought in Gujarat, Rajasthan, Maharashtra, Karnataka, Andhra Pradesh and Orissa and earth quake in Uttar Pradesh, Gujarat and Maharashtra are of recent occurrences. Losses due to these calamities are in millions of rupees and loss of life is innumerable. Agricultural Meteorologists have to understand these phenomenon and devise the ways to save the crop under such odd conditions. Environmental pollutions: Industries are spewing venom in the form of smoke, trace gasses and discharges which pollute both air and water. Air pollution has increased due to vehicles. It has reached the alarming proportions. Water streams have been polluted by the industrial waste but ground water has been polluted by excessive fertilization. Out of 27 states of India, 24 states are facing the problem of ground water pollution. Thus, agricultural meteorologist has to develop technology to sustain agricultural production under polluted environmental conditions.
3
Introduction
M **| -
•
f.
(Source : Model WS01. Delta - T Devices Ltd. Cambridge) Fig 1.1 Automated weather station
Ozone holes: The Carboflurocarbons added into the atmosphere has punctured the ozone layers. The ultra-violet radiations may pass through the depleted ozone layer and can incident over the earth surface. These ultra-violet radiations may cause skin diseases in human beings and may damage the crops. Therefore, agricultural meteorologist has to devise technology to save crops and sustain agricultural production under higher ozone levels. Climate change: Increasing carbondi-oxide concentration in the atmosphere is resulting in increase of temperatures and thereby melting of snow of mountains. This has led to climate change in several parts of the world. The climate change has to be studied and its effect on agriculture needs to be analysed by the agroÂŹ meteorologists.
Emerging fields: Remote sensing is an emerging technique giving enough room to forecast the yield and to exploit the yield potential of an area. Similarly,
production under controlled climatic conditions in greenhouses and polyhouses has dawned a new era in agricultural meteorology. Data collection and acquisition: Meteorological data are collected in surface observatories with the help of manual and self recording analog instruments. Therefore, time lag and manual errors remain in data set. It will be advisable to replace them with automated weather station networks with interconnectivity through satellite. An automated weather station with standard sensors is shown inFig 1.1 Agrometeorology has thus developed into a full-fledged discipline and researcher in the subject will require thorough knowledge of both meteorology and agriculture.Thus, studies in the field of agricultural meteorology can help in increasing the production, better management of shortages, meeting the challenges and in improving the quality of life in general, and agricultural production in particular.
2. Atmosphere A.S.R.A.S. SASTRI and B. AJITHKUMAR The earth's atmosphere is different from any other body in the solar system. Scientists believe that earth's earliest atmosphere was swept away by solar winds, vast streams of particles emitted by the sun. As the earth cooled, solid crust formed and the gases that had been dissolved in the molten rock were gradually released, a process called degassing. Thus an atmosphere believed to be made up of gases similar to those released during volcanic eruptions came into being. Scientists have proposed two probable sources of the free oxygen in the atmosphere. Water vapour that are carried into the upper atmosphere is dissociated into hydrogen and oxygen by the action of the sun's ultra-violet radiation. Hydrogen, being a very light gas, escapes the atmosphere, whereas the heavier oxygen atoms remain and combine to form molecular oxygen. This process is very slow and not adequate to account for the present percentage of oxygen in our atmosphere. Another source of oxygen is green plants. Oxygen is generated during photosynthesis. Composition of the Atmosphere Atmosphere may be defined as a gaseous envelope surrounding the earth. It is found to be complex system, not a simple chemical element nor even a compound, but a relatively stable mixture of a number of gases. Four gases, viz nitrogen, oxygen, argon, and carbondioxide account for 99.98% of the air by volume. In addition to these gases atmosphere also contains, water vapour. Another constituent of the atmosphere is the aerosol which come from natural and man-made sources. These include suspended particles of sea salt, dust, organic matter and smoke. Permanent gases: Nitrogen forms about 78% of the total volume of dry air, and oxygen about 21%, of the remaining per cent the greater part is argon followed by carbondioxide. Other gases present are neon, helium, krypton, hydrogen, xenon, ozone, radon etc. (Table 2.1)
The carbondioxide released by the animals during respiration is utilized by the plants for photosynthesis which in turn release oxygen. This reciprocal use by animals and plants helps to maintain the ratio of these gases in the atmosphere. Sea water also plays dominant role in controlling carbondioxide concentration of the atmosphere. When carbondioxide concentration increases, more is absorbed by sea water and when the concentration drops it releases carbondioxide. Nitrogen in the atmosphere is utilized by bacteria for fixation. Water vapour: Water vapour contributed by evaporation from water bodies and soils and transpiration from plants constitutes an important component of the atmosphere. The content of water vapour is highly varying. It may range from a minute proportion to a maximum of 4 per cent by volume. Dust: Apart from visible dust, air also contains small particles of organic matter
5
Atmosphere
such as seeds, spores and bacteria. It also carries inorganic particles such as fine particles of soil or of smoke or salts from ocean spray. Besides the solid impurities in the atmosphere, formation of NH4 takes place frequently by N2 and H2 of the atmosphere at the time of lightening. The NH, thus formed is carried down by rains to soil. Table 2.1 Principal gases of dry air
Constituent Nitrogen (N2) Oxygen (02) Argon (Ar)
Carbondioxide (C02) Neon (Ne) Helium (He) Methane (CH,) Krypton (Kr) Hydrogen (H2)
Per cent by volume
78.08 20.94 0.93 0.03 0.00182 0.000524 0.00015 0.000114 0.00005
Properties of atmosphere 1. It exerts pressure 2. It has weight 3. It supports combustion 4. It diffuses heat and gases 5. It conducts sound 6. It is denser to the surface of the earth and becomes thinner as it goes up to a height of 314 miles. 7. The temperature of the atmosphere decreases by about 1째C for every 100 m in altitude. But this fall in temperature does not take place beyond a certain limit. Stratification of Atmosphere The atmosphere is divided vertically into four layers on the basis of temperature (Fig 2.1).
Troposphere: The lowermost layer of the atmosphere is called troposphere. It is the zone where weather phenomena and atmospheric turbulence are most marked and contains 75% of the total gaseous mass of the atmosphere and virtually all the water vapour and aerosols. Throughout this layer there is a general decrease in temperature with height at a mean rate of about 6.5째 C/km and the whole layer is capped in most places by temperature inversion layer (layer of relatively warm air above a colder one). This inversion layer is called tropopause. Variations ir. the altitude of troposphere exist between different latitudes. Its elevation is 16 km at the equator and 8 km at the poles. Stratosphere: A second major atmospheric layer is the stratosphere which extends upwards from the tropopause to about 50 km. In the stratosphere the temperature at first remains nearly constant to the height of 20 km thtn it begins
6
700
400
107
600
10-u
io*
500
300
10*
THERMOSPHERE
400
300
VI
’O'7
v
|Kf" "
.5
200
a.
r
<
-1 s
100
"
IO5c —
90
10“ 3
80
io-2
70
-1 10
110'9 JO'4 10'7
io"6
40 30
20 10
0
100 1000
10“ 10" io;f I0'J
!03
1014
11
./ I
.
I
-206 0 200 400ÿ0 800 loop lionr 50 - -100ÿ0 -(So <0 -k) 6 20 40 *c Mcsopausc
MESOSPHERE
IO2 10'
100
j
10"
1
10
I <
-4
10
1
E
.= _W
a
i-5 10
60 50
200
v
J10*
.£
6
M
o»
so
40
SlratopnftBS'
30
10”
Id’*IO’2
STR/TOSPHERE ,Trop«>p* u*«.
20 10
TROP&QTHERE -100-80-60-40-20 0 20 40 Temperature
(Source : Model WS01. Delta - T Devices Ltd. Cambridge) Fig. 2.1 Vertical distribution of atmosphere with different zones
increase until the height of about 50 km above the earth's surface. The top of the layer, where maximum temperatures are attained is called as stratopause. Higher temperature occurs in the stratosphere because of absorption of ultraviolet radiations by ozone. to
Mesosphere: Above the stratopause average temperature decreases to minimum of about -90°C around 80 km. This layer is commonly referred to as the mesosphere. Above 80 km, temperatures again begin rising with height and this inversion is referred to as mesopause.
7
Atmosphere
Thermosphere: Above the mesopause atmospheric densities are extremely low. The lower portion of the thermosphere is composed mainly of nitrogen and oxygen in molecular (02) and atomic (O) forms whereas above 200 km atomic oxygen predominates over nitrogen (N2 and N). Temperatures rise with height owing to the absoiption of ultraviolet radiation by atomic oxygen. Above 100 km the atmosphere is increasingly affected by solar X-rays and ultraviolet radiation which cause ionization. The term ionosphere is commonly applied to the layers above 80 km, although sometimes it is used only for the region of high electron density between about 100 and 300 km. Exosphere is the layer above ionosphere. BOOKS TO BE REFERRED
Critchfield, H. J. 1987. General Climatology, edn 4, 453 pp. Prentice-Hall of India Pvt. Ltd. New Delhi. Gates, E.S. 1984. Meteorology and Climatology. Thomas Nelson and Sons Ltd.
UK. Miller, A.A. 1971. Meteorology, 154 pp. Charles E. Merrill Publishing Co., Columbus, Ohio.
QUESTIONS 1. Give the composition of the atmosphere 2. Give a diagrammatic representation of vertical distribution of atmosphere.
3. Radiation M.C. VARSHNEYA and B.l. KARANDE The prime source of energy injected into our atmosphere is the sun, which is continually shedding part of its mass by radiating waves of electromagnetic energy and high-energy particles into space. Radiation is a form of energy that is emitted by all objects having a temperature above absolute zero. It is the only form of energy that can travel through the vacuum of outer space. Thus, energy receipt and disposal from earth must be in the form of radiation. Radiation is propagated in the form of electromagnetic waves from its source of emittance. Electromagnetic wave corresponds to oscillations of the electric and magnetic vectors perpendicular to each other represent magnetic fields (Fig 3.1). A wavelength of electromagnetic wave is the distance between two successive points of the same phase along the wave. Electromagnetic spectrum consists of wide range of wavelength (Fig 3.2) extending from cosmic, gamma rays (wavelength < 10'9 nm) to electric waves (wavelength > 1015 nm). The wavelengths of major interest in agriculture are the ultra-violet (UV), visible (PAR) and infrared (IR). Wavelengths below 400 nm is referred to as ultra-violet (UV). The visible region also called photosynthetically active radiation ( PAR) extends from approximately 400 to 700 nm and is sub-divided into various wave bands ~1
Range for electric vectors
Individual electric vector
i /
y
Direction of
/
y
propagation
I
y
\
A
Magnetic field
Range for magnetic vectors
Fig. 3.1 Electromagnetic wave Wavelength (gm)
10"6
10‘3
X raysGamma rays
r.
1012
!
Infrared —
Ultraviolet
1018
10-12
102
0.7
0.4
-Radio waves-» «-
•*
- Visible ,
1016
,1012
109
103
Electric waves
101
Frequency (Hz)
Fig. 3.2 Electromagnetic spectrum on logarithmic wavelength and frequency scales
Radiation
9
(Table. 3.1). The divisions are based on subjective colours experienced by humans. The infrared (IR) region has wavelength longer than those of the red end of the visible spectrum, up to 40,000 nm. Table 3.1 Spectrum of ultra-violet (UV), visible (PAR) and infrared (IR) radiations
Approximate wavelength range (nm)
Color
below 400 Ultra violet Photosynthetically active radiation 400 to 425 Violet 425 to 490 Blue 490 to 560 560 to 585 585 to 640 640 to 740 above 740
Green Yellow Orange Red
Infrared
Frequency (cycles s'1 or hertz)
Representative wavelength (nm) 254
x
io14
471
7.31 x 6.52 x 5.77 x 5.26 x 4.86 x 4.41x 2.14 x
10'4 1014 1014 1014 1014 1014
292 260 230 210 193 176 85
11.30
410 460 520 570 620 680 1400
Energy (kJ mol-1)
IQ14
(Source : Nobel, P. S. 1983. Biological Plant Physiology and Ecology)
The per cent of solar radiation received on earth in different region, i.e. UV, PAR and IR is presented in Table 3.2. Table 3.2 Percentage of solar radiation received on earth
Wave Band (nm)
Radiation X &
y Rays
Energy (%)
0-300
1.2
UV
300 - 400
7. 8
PAR(Visible)
400 - 700
39. 8
700 - 1500
38. 8
1500 -oo
12.4
IR (Near) IR (Far)
(Source: Montieth and Unsworth 1990. Principles of Environmental Physics)
Basic Concepts
The wavelength of electromagnetic radiation is given by:
X =-
...(3.1)
V
where,
X , wavelength (the shortest distance between two consecutive points of
same phase on a wave pattern); v, frequency (number of vibrations per second); c, speed of light (a universal constant approximately equal to 3 x 108 m sâ&#x20AC;&#x2122;1) The time period T (time of one vibration) is equal to 1/v, and the wave number
10
Agricultural Meteorology
is equal to
\l\.
Radiant flux density: It is defined as the energy received on a unit surface in unit time (previously it was referred to as 'intensity'). Its unit in SI system is watt per meter square (W nr2) or joule per meter square per second (J nr2 s'1) while in CGS system is calorie per centimeter square per minute (cal cm-2 min'1), where 1 cal cm'2 min'1 = 697.93 Wnv2. Blackbody Radiation: A body that emits radiation at the maximum possible intensity in every wavelength is a 'blackbody'. Such a body will also absorb all radiation's incident upon it completely. The blackbody is a physical ideal, a perfect radiator and the perfect absorber.
Emissivity (z): It is defined as the ratio of the emittance of a given surface at a specified wavelength and temperature to the emittance of an ideal blackbody at the same wavelength and temperature. Thus, the emissivity s of a blackbody is unity. Absorptivity (a): It is defined as the ratio of the amount of radiant energy absorbed to the total energy incident upon the surface. Thus, the absorptivity (a) of a blackbody is also unity. Hence, for a blackbody, 8 = a = 1, in contrast, for a 'white body', s = a = 0. Naturalbodies are having absorpitivity or emissivity less than one. Earth behaves, in total, as a 'grey body'. Reflectivity (r): It is defined as the ratio of the radiant energy reflected from the surface to the total energy incident upon the surface. Transmissivity (t): It is defined as the ratio of transmitted radiation to the total radiation incident upon the surface. The sum of absorptivity, reflectivity and transmissivity of a surface, at a specific wavelength, is equal to or less than unity. Thus cxa)+ra) + tm = i
... (3.2)
Laws of Radiation The radiation laws of wave and particle concept are given below,
Kirchoffs law: The law states that a good absorber of radiation is also a good emitter under similar conditions. E(Ji)=aa)
... (3.3)
Planck's law: Planck introduced the 'particle concept' suggesting that the electromagnetic radiation consists of a stream or flow of particles or quanta. Each quantum has an energy content E given by, E
=hv
...
(3.4)
where h is Planck's constant with a value of 6.626 x lO'34 Js. The greater the frequency (shorter wavelength), the greater is the energy content of the quantum.
Stefan-Boltzman Law (or Stefan's Law): The energy flux density E of radiation from a blackbody is a function of fourth power of its absolute temperature. E = cjT4
...(3.5)
Fi r s tf e wpa ge soft hi sbooka r epubl i s he d onki s a n. c ombyi t spubl i s he r . I fyouwi s ht opur c ha s eaha r dc opy oft hi sbook,pl e a s ec ont a c tt hepubl i s he r .
Publ i sher
Dr .Ra me s hwa rSi ngh Di r e c t or a t eofKnowl e dgeMgt .i nAgr i . I ndi a nCounc i lofAgr i c ul t ur eRe s e a r c h Kr i s hi Anus a ndha nBha va n-1, Pus a-Ne wDe l hi1 10012. Pr i c e-Rs .250/ -