AGRICULTURE CHAPTER METEOROLOGY SUMMARY SHEET For NABARD Grade A/B 2019

1 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

Contents 1 What is Meteorology? ...... 4 2 What is the difference between weather and climate? ...... 4 3 What is Agrometeorology? ...... 5 4 ‘What is atmosphere?’...... 5 4.1 The composition of the atmosphere: ...... 5 4.2 Structure of the atmosphere: ...... 5 4.3 The following are the features of each of these layers: ...... 6 5 The following factors influence the weather and climate of different places around the world: ...... 8 6 : ...... 8 6.1 What are they? ...... 8 6.2 Classification of clouds: ...... 8 6.2.1 Based on shape: ...... 9 6.2.2 Classification of Clouds by The World Meteorological Organization ...... 9 The table given below gives a list of approximate heights of each level and the genera occurring in each: ...... 9 6.3 The table given below gives the detailed classification of clouds: ...... 10 7 : ...... 12 8 Latitude: ...... 12 9 Altitude: ...... 13 10 Classification of Climate: ...... 13 10.1 Various factors based on which classification is done: ...... 13 10.2 Koeppen’s scheme: ...... 14 10.2.1 Climatic Groups based on Koeppen: ...... 14 10.3 Thornthwaite’s Climatic Classification:...... 14 10.3.1 1948 Classification: ...... 14 10.4 Troll Classification: ...... 15 10.5 ICAR Classification: ...... 15 11 Scales of climate and their importance: ...... 16 11.1 The scales of air motion in different climates are given in the Table below: ...... 16 12 Indian Meteorological Department: ...... 16 13 What are Agrometeorological services? ...... 17 14 Integrated Agro-meteorological Advisory Service (IAAS) program of India: ...... 17 14.1 How is the weather forecasting done? ...... 18 15 Crop-Weather modelling: ...... 18 15.1 TYPES OF MODELS: ...... 19 15.2 Some important Crop weather models running in India: ...... 20 15.3 Other crop models reported in recent literature: ...... 20

2 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

16 Weather Forecasting: ...... 20 16.1 Types of weather forecast: ...... 20 16.2 Weather Calender: ...... 21 17 IMD Classification of the rainfall in India: ...... 21 17.1 Criteria to classify the Seasonal Rainfall: ...... 22 17.2 The new categories are: ...... 22 17.3 Certain standardized key terms given by the IMD: ...... 22 18 Drought: ...... 23 18.1 What is Drought? ...... 23 18.2 Different types of drought: ...... 23 18.3 How does the India Meteorological Department monitor the Agricultural Drought?...... 23 18.4 Aridity Anomaly Index (AAI): ...... 24 19 Weather Modification: ...... 24 19.1 Seeding: ...... 24 19.2 There are two basic types of cloud seeding - Cold and Warm: ...... 24 20 Isopleths for different weather parameters: ...... 25

3 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

1 What is Meteorology?

• Meteorology is, by definition, the study of Earth's atmosphere. • It is derived from the Greek word “meteoron” which means "in the sky" or "high in the sky". • Meteorology is an extremely interdisciplinary science, drawing on the laws of physics and chemistry (among others) to aid in our understanding of Earth's atmosphere, its processes, and its structure.

2 What is the difference between weather and climate?

Features Weather Climate

Weather is the state of the Climate is the average conditions atmosphere on a current day at a Definition that are expected at a certain place current time. It changes day to over a number of years. day.

Weather includes sunshine, rain, cloud cover, winds, hail, snow, Climate may include precipitation, sleet, freezing rain, flooding, temperature, humidity, sunshine, blizzards, ice storms, Components and wind velocity, phenomena such thunderstorms, steady rains from as , frost, and hail storms over a a cold front or warm front, long period of time. excessive heat, heat waves and more.

Day to day forecast can be done Climate forecast can only be done depending on the air pressure, Forecast over longer periods of time, such as temperature and other similar 30 years. The average of weather factors. over 30 years helps determine the

4 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

climate of a certain area.

Real-time measurements of atmospheric pressure, Aggregating weather statistics over Determined by temperature, wind speed and periods of 30 years direction, humidity, precipitation, could cover, etc.

Study Meteorology Climatology

3 What is Agrometeorology? • Agrometeorology (abbreviate from Agricultural Meteorology) is the branch of meteorology which investigates the relationship of plants and animals to the physical environment. • It also takes into account the climatic and hydrologic conditions which are significant for agriculture owing to their interaction with the objects and processes of agricultural production.

4 ‘What is atmosphere?’ Atmosphere is the air surrounding the earth. The atmosphere is a mixture of different gases. It contains life-giving gases like oxygen for humans and animals and carbon dioxide for plants. It also contains water vapour and dust particles. It envelops the earth all round and is held in place by the gravity of the earth.

4.1 The composition of the atmosphere: Constituent By volume (per cent) By weight (per cent) Nitrogen 78.088 75.527 Oxygen 20.949 23.134 Argon 0.930 1.282 Carbon dioxide 0.030 0.045 Total 99.997 99.997

The other gases that are present in smaller quantities are: Neon (Ne), Helium (He), Krypton (Kr) and Hydrogen (H2).

4.2 Structure of the atmosphere: The atmosphere consists of 5 layers:

✓ Troposphere

5 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

✓ Stratosphere ✓ Mesosphere ✓ Thermosphere (Ionosphere) ✓ Exosphere

4.3 The following are the features of each of these layers:

Layer Height of the layer Temperature Remarks increase and decrease within the layer? Troposphere Lowest layer of the Temperature in this This is the most important atmosphere; layer generally layer of the atmosphere The height is about 18 km decreases with because all kinds of on the equator and 8 km on height. weather changes take the poles. It decreases at the place only in this layer. rate of 1 degree It contains dust particles Why a change in thickness? Celsius for every and water vapour. The thickness is greatest at 165 m of height. The air never remains the equator because heat is This is called static in this layer. 6 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

transported to great Normal Lapse Rate. Therefore, this layer is heights by strong called ‘changing sphere’ or convectional currents and troposphere thus the height of the troposphere varies with location, being higher over warmer areas and lower over colder areas. Tropopause • The zone separating troposphere from the stratosphere is known as tropopause. • The air temperature at the tropopause is about – 80 degrees Celsius over the equator and about – 45 degrees Celsius over the poles. • The temperature here is nearly constant, and hence, it is called tropopause. Stratosphere Found just above the In this layer the Weather related incidents troposphere. temperature do not take place in this Extends up to a height of 50 increases with layer. The air blows km. height. horizontally here. (The temperature Therefore, this layer is remains almost the considered ideal for flying same in the lower of aircraft. part of this layer up One important feature of to the height of 20 stratosphere is that it km. After this, the contains a layer of ozone temperature gas. Thus, it is the region increases slowly of the stratosphere that with the increase in absorbs most of the sun’s the height). ultra-violet radiations. This increase in The relative thickness of temperature is due the ozone layer is to the presence of measured in Dobson ozone layer Units. between 17 to 30 km from the earth’s surface. Stratopause The upper limit of the stratosphere is known as stratopause. Mesosphere It is the third layer of the In this layer, the Meteors or falling stars atmosphere spreading over temperature starts occur in this layer. the stratosphere. decreasing with It extends upto a height of increasing altitude 80 km. and reaches up to – 100 degree Celsius

7 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

at the height of 80 km. Mesopause The upper limit of the mesosphere is known as mesopause. Thermosphere It extends upto a height of The temperature It contains electrically 400 km (from 80 to 400 here starts charged particles known km). increasing with as ions, and hence, it is heights. known as the ionosphere. Radio waves transmitted from the earth are reflected back to the earth by this layer and due to this, radio broadcasting has become possible. Exosphere Uppermost layer of the Gases are very sparse in atmosphere. this sphere due to the lack It extends above 400km. of gravitational force. Therefore, the density of air is very less here.

5 The following factors influence the weather and climate of different places around the world:

✓ Ocean currents (the movement of water at different temperatures through the oceans) ✓ Amount of water (clouds) and dust in the atmosphere and the resultant precipitation ✓ Prevailing winds (the direction that winds usually blow from) ✓ Altitude (height above sea-level) ✓ Latitude (angle of sun’s rays and effect on day length) ✓ Distance from the sea ✓ Aspect (the influence of slopes eg. different sides of a valley)

6 Clouds:

6.1 What are they?

A cloud is a mass of water drops or ice crystals suspended in the atmosphere.

6.2 Classification of clouds:

Let us have a look at the general classification based on shape:

8 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

6.2.1 Based on shape:

6.2.2 Classification of Clouds by The World Meteorological Organization

The table given below gives a list of approximate heights of each level and the genera occurring in each: Level General Features Genera Polar Temperate Tropical name given region region region to the clouds in this category

High Cirrus Usually thin Cirrus 3 – 8 5 – 13 km 6 –18 km and are Cirrocumulus km (16 500 – (20 000 – made up of Cirrostratus (10 000 45 000 ft) 60 000 ft) ice. – 25 Often 000 ft) indicate fair weather and hence do not produce rain.

Middle Alto Frequently Altocumulus 2 – 2 – 7 km 2 – 8 km indicate an Altostratus 4km (6 500 – 23 (6 500 – approaching Nimbostratus (6 500 000 ft) 25 000 ft) storm. – 13 000 ft)

9 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

Low Stratus They may Stratus From From the From the appear Stratocumulus the Earth’s Earth’s dense, dark Cumulus Earth’s surface to surface to and rainy Cumulonimbus surface 2 km 2 km (or snowy) to 2 km (0 – 6 (0 – 6 and can also (0 – 6 500ft) 500ft) be cottony 500ft) white clumps interspersed with blue sky.

Note: Kindly note some of the exceptions that can exist:

• There is another category which is known as ‘Great Vertical Extent Clouds’. The Genera: Cumulus and Cumulonimbus can be placed under it. • These clouds are most dramatic types of clouds. They are also known as the Storm Clouds. They rise to dramatic heights, and sometimes well above the level of transcontinental jetliner flights.

6.3 The table given below gives the detailed classification of clouds: Genera Species Varieties Supplementa Accessory Mother-clouds and special ry features clouds clouds (most commonly occurring mother-clouds are listed in the same order as genera) (listed by frequency of observation) Genitus Mutatus intortus mamma Cirrocumulus Cirrostratus uncinus radiatus fluctus Altocumulus Homo spissatu vertebrat Cumulonimbus s us Homo castella duplicatus nus floccus Cirrocumulus stratifor undulatus Cirrus mis lacunosus mamma Cirrostratus lenticul cavum Altocumulus aris Homo castella nus floccus

10 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

Cirrostratus fibratus duplicatus Cirrocumulus Cirrus nebulos undulatus Cumulonimbus Cirrocumulus us Altostratus Homo Altocumulus stratifor translucid virga Cumulus Cirrocumulus mis us mamma Cumulonimbus Altostratus lenticul perlucidus cavum Nimbostratus aris opacus fluctus Stratocumulus castella duplicatus asperitas nus undulatus floccus radiatus volutus lacunosus Altostratus translucid virga pannus Altocumulus Cirrostratus us praecipitatio Cumulonimbus Nimbostratus opacus mamma duplicatus undulatus radiatus Nimbostratus praecipitatio pannus Cumulus Altocumulus virga Cumulonimbus Altostratus Stratocumulus Stratocumulu stratifor translucid virga Altostratus Altocumulus s mis us mamma Nimbostratus Nimbostratus lenticul perlucidus praecipitatio Cumulus Stratus aris fluctus Cumulonimbus castella opacus asperitas nus duplicatus cavum floccus volutus undulatus

radiatus lacunosus Stratus nebulos opacus praecipitatio Nimbostratus Stratocumulus us translucid fluctus Cumulus fractus us Cumulonimbus undulatus Homo Silva Cataracta Cumulus humilis radiatus virga Altocumulus Stratocumulus mediocr praecipitatio velum Stratocumulus Stratus is arcus pannus Flamma congest fluctus Homo

11 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

us tuba Cataracta fractus

Cumulonimbu calvus praecipitatio pannus Altocumulus Cumulus s capillat virga pileus Altostratus us incus velum Nimbostratus mamma flumen Stratocumulus arcus Cumulus murus Flamma cauda Homo tuba

Note: In the year 2017, a digitized version of the atlas was brought out. The ones marked in blue colour in the table given above are the new ones that were added.

A total of 12 were added: Seven have been highlighted above, the other clouds added were special clouds:

✓ Flammagenitus ✓ Homogenitus ✓ Homomutatus ✓ Cataractagenitus ✓ Silvagenitus

7 Precipitation: The crop regions are classified on the basis of average rainfall which is as follows.

Rainfall (mm) Name of the climatic region Less than 500 Arid 500-750 Semi-arid 750-1000 Sub arid More than 1000 Humid

8 Latitude: The distance from the equator, either south or north, largely creates variations in the Climate. Based on the latitude, the climate has been classified as ✓ Tropical ✓ Sub-tropical ✓ Temperate ✓ Polar

12 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

9 Altitude: • The height from the MSL (Mean Sea Level) creates variation in climate. • Even in the tropical regions, the high mountains have temperate climate. • The temperature decreases by 6.5 ºC/Km from the sea level.

10 Classification of Climate: We shall have a look at the climate classifications given by:

Note: In bracket, we have mentioned the important points that are relevant for our examination under each category.

✓ Koppen (Only a general idea) ✓ Thornthwaite (Parameters used and climatic classification based on that parameter) ✓ Troll (Parameters used and climatic classification based on that parameter) ✓ ICAR (Indian Council of Agricultural Research) (Parameters used and climatic classification based on that parameter)

10.1 Various factors based on which classification is done: Before having a look at the classifications, we shall see the various factors based on which the classifications have been done:

✓ Evapo-Transpiration (ET) ✓ Potential Evapo-Transpiration (PET) ✓ Precipitation 13 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

10.2 Koeppen’s scheme: • Koeppen has used certain critical values of temperatures of the warmest and the coldest months and of rainfall of the wettest and the driest months along with the seasonal distribution of rainfall to divide the climatic regions. • His climatic divisions generally coincide with vegetational divisions, since Koeppen considered the distribution of vegetation to be the best expression of the totality of climate.

10.2.1 Climatic Groups based on Koeppen:

10.3 Thornthwaite’s Climatic Classification: Thornthwaite gave two classifications—one in 1931 and the other in 1948.

10.3.1 1948 Classification: Thornthwaite’s 1948 classification used two factors: Potential Evapotranspiration and Precipitation.

It was further modified by Mathur (1955) and the following formula was derived to calculate the Moisture Index (Im).

Im = 100 [(P-PE)/PE]

Where P = Precipitation, PE = Potential evapo-transpiration;

Now using the Moisture Index (Im), the following classification was made:

14 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

10.4 Troll Classification: • Troll (1965) proposed a classification called the seasonal climates of the earth utilising monthly rainfall and potential evapotranspiration. • It is based on very sound physical principles and parameters like temperature, radiation, wind speed, vapour pressure, duration of sunshine and albedo which are mainly responsible for loss of water from the / surface have been taken into account. • The importance of Troll's classification lies on the duration of arid and humid months rather than assignment of climatic boundaries based on annual/monthly values of precipitation, temperature and relative humidity. • Thus he came out with a classification of climatic regions based on the humid months in a year. • He defined humid month as the month having precipitation more than PET.

The Troll Classification was modified by ICRISAT for India and the classification was brought out based on the number of humid months:

10.5 ICAR Classification: The ICAR under the All India Coordinated Research Project on Dryland Agriculture adopted classification based on Moisture Deficit Index (MDI).

The Moisture Deficit Index is calculated using the following formula:

The types of climate put forth are as follows:

15 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

11 Scales of climate and their importance: What is it?

• Weather scales group weather phenomena according to their size (the horizontal and vertical distance they span) and how long of a lifespan they have. • In order from largest to smallest, these scales include the planetary, synoptic (both coming under Macro-climate), mesoscale and micro-climate.

11.1 The scales of air motion in different climates are given in the Table below: S.No Types of Climate Horizontal Vertical Scale Time Scale Scale (km) (km) (hrs) 1 Macro-climate A Planetary Scale 2000-5000 & 10 200 to 400 more B Synoptic Scale 500-2000 10 100 2 Meso climate 1 to 100 1-10 1 – 10 3 Micro climate <100m 200 m 6 – 12 minutes

12 Indian Meteorological Department:

• The India Meteorological Department (IMD), also referred to as the Met Department, is an agency of the Ministry of Earth Sciences of the Government of India. It is the principal agency responsible for meteorological observations, weather forecasting and seismology. • It was established in 1875. • IMD is headquartered in Delhi and operates hundreds of observation stations across India and Antarctica. • IMD is also one of the six Regional Specialised Meteorological Centres of the World Meteorological Organization (headquartered in Geneva, Switzerland). • It has the responsibility for forecasting, naming and distribution of warnings for tropical cyclones in the Northern Indian Ocean region, including the Malacca Straits, the Bay of Bengal, the Arabian Sea and the Persian Gulf. 16 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

13 What are Agrometeorological services? • All agrometeorological and agroclimatological information that can be directly applied to try to improve and/or protect the livelihood of farmers in agricultural production may be considered to belong to agrometeorological services. • This improvement/protection applies to yield quantity, quality and income while safeguarding the agricultural resource base from degradation • The Agromet Advisory Services provide a very special kind of inputs to the farmers as advisories that can make a tremendous difference to the agriculture production by taking the advantage of benevolent weather and minimize the adverse impact of malevolent weather. • This has a potential to change the face of any country in terms of food security and poverty alleviation. • Agrometeorological services rendered by India Meteorological Department (IMD), Ministry of Earth Sciences is a step to contribute to weather information-based crop/livestock management strategies and operations dedicated to enhancing crop production and food security.

14 Integrated Agro-meteorological Advisory Service (IAAS) program of India: • India’s Integrated Agro-meteorological Advisory Service (AAS) program is one of the largest agrometeorological information programs in the world. • The Indian Meteorological Department (IMD) started broadcasting weather services for farmers by radio in 1945. • Agrometeorological advisories were first initiated in 1976 to provide state level forecast- based advisories to farmers based on short-range weather forecasts issued by the India Meteorological Department (IMD). • Made available to farmers one day in advance, these advisories were inadequate for planning weather-based agricultural practices and/or undertaking precautionary measures, which required a much longer lead time. • In agriculture, location-specific weather forecasts in the medium range (3-10 days in advance) hold greater salience for farmers. • In addition, forecasts issued need to be finetuned to the specific requirements of farmers, particularly in recommending activities and modifications to specific farm-level practices. • Keeping these needs in mind, the NCMRWF (National Center for Medium-Range Weather Forecasting) was established in 1988 by the Government of India as a scientific mission to develop operational Numerical Weather Prediction (NWP) models for forecasting weather in the medium range. • To disseminate these forecasts and build forecast-based agricultural advisories, Agro Meteorological Field Units (AMFUs) were created across the country, in all 127 agroclimatic zones. • IMD took over leadership of the AAS in 2007 (IAAS was launched in collaboration with different organizations/institutes/stakeholders on 1st April 2007 for weather-wise farm management) and launched a District-level Agrometeorological Advisory Service (DAAS) in

17 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

2008, with the aim of providing relevant weather information and management advisories at a district scale across the country.

14.1 How is the weather forecasting done? • Today, IMD issues quantitative district level 5-day weather forecasts twice a week using a Multi-Model Ensemble technique based on forecast products from models available in India and other countries. • Weather forecasts for seven parameters (rainfall, maximum and minimum temperatures, wind speed and direction, relative humidity and cloudiness) as well as weekly cumulative rainfall forecasts are generated. • These products are disseminated to Regional Meteorological Centres and Meteorological Centres of IMD located in different states. • Experts in these centres add value to IMD forecast products, which are then communicated to 130 AMFUs located within SAUs, ICAR Institutes, and Indian Institutes of Technology.

• Weather forecast collected over 5 days is sent to all regional met centres of IMD for value addition keeping local synoptic condition and climatology in consideration. • The value-added forecast is provided to concerned agro-met field units for advisory preparation on every Tuesday and Friday of the week and prepared advisories disseminated to farmers through multi-channel dissemination network.

15 Crop-Weather modelling: • It is a representation of a crop through mathematical equations explaining the crops interaction with both above ground and below ground environment. • Crop-weather modelling, firstly used by BAIER in 1979, refers to the techniques that can be used to determine the likely effects of weather on crop, its growth and production. • It is not wrong to say that they are computer programs that mimic the growth and development of crops.

18 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

15.1 TYPES OF MODELS: Depending upon the purpose for which it is designed the models are classified into different groups or types, they are:

✓ Statistical models ✓ Mechanistic models ✓ Deterministic models ✓ Stochastic models ✓ Dynamic models ✓ Static models ✓ Phenological models

Statistical models: These models express the relationship between yield or yield components and weather parameters. In these models relationships are measured in a system using statistical techniques.

Example: Step down regressions, correlation, etc.

Mechanistic models: These models explain not only the relationship between weather parameters and yield, but also the mechanism of these models (explains the relationship of influencing dependent variables). These models are based on physical selection.

Deterministic models: These models estimate the exact value of the yield or dependent variable. These models also have defined coefficients.

Stochastic models: A probability element is attached to each output. For each set of inputs different outputs are given along with probabilities. These models define yield or state of dependent variable at a given rate.

Dynamic models: Time is included as a variable. Both dependent and independent variables are having values which remain constant over a given period of time.

Static models: Time is not included as a variable. Dependent and independent variables having values remain constant over a given period of time.

Phenological models: These models predict crop development from one growth stage to another. These predictions are based on accumulated heat limits.

Two important terms in the process of development of model are:

Model calibration: Calibration is adjustment of the system parameters so that simulation results reach a predetermined level, usually that of an observation.

Model validation:

19 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

The model validation stage involves the confirmation that the calibrated model closely represents the real situation. The procedure consists of a comparison of simulated output and observed data that have not been previously used in the calibration stage.

15.2 Some important Crop weather models running in India: • CERES • DSSAT • PRECIS • InfoCrop-RICE • CROPGRO-Groundnut

15.3 Other crop models reported in recent literature: Models Details REALSOY Soyabean IRRIGATE Irrigation scheduling model COTTOM Cotton GWM General weed model in row crops CropSyst Wheat and other crops LUPINMODE Lupine SIMPOTATO Potato WOFOST Wheat and maize, water and nutrient WAVE Water and Agrochemicals ORYZA1 Rice, Water EPIC Erosion productivity impact calculator SIMCOY Corn QCANE Sugarcane, potential conditions AUSCANE Sugarcane, potential & water stress conditions, erosion

16 Weather Forecasting: It means any advance information about the probable weather in future, which is obtained by evaluating the present and past meteorological conditions of the atmosphere.

16.1 Types of weather forecast: Types of forecast Validity period Main users Predictions Short range Upto 72 hours Farmers marine Rainfall distribution, heavy agencies, general rainfall, heat and cold wave public conditions, thunder storms etc. a) Now casting 0 to 2 hours b) Very short range 0-12 hours

20 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

Medium range Beyond 3 days and Farmers Occurrence of rainfall, upto 10 days temperature Long range Beyond 10 days upto Planners This forecasting is provided for a month and a Indian monsoon rainfall. The season outlooks are usually expressed in the form of expected deviation from normal condition.

16.2 Weather Calender: • In order to provide the farmers with an efficient weather service, it is essential that the weather forecaster should be familiar with the crops that are grown in a particular agroclimatic zone. • The type of forewarnings to be given depend on the stages of the crop. • In case of farmers, they should become familiar with weather bulletins and learn how to interpret. • To meet the above requirement, the detailed information collected from the agricultural departments has been condensed by the IMD and presented in a pictorial form known as crop weather calendar.

This calendar has three parts as follows: a) Bottom part b) Middle c) Top part

✓ Bottom part provides the activities related to crop or information related to phenological stages of the crop and the months. ✓ Middle part gives information regarding normal weather condition required for active crop growth. It is divided into different sections according to rainfall, rainy days, minimum temperature, maximum temperature, pan evaporation and sunshine hours. ✓ Top part gives information related to the weather abnormalities or to take precautionary measures.

17 IMD Classification of the rainfall in India: In the year 2016, the IMD had come up with the revised terminologies used in weather forecasting.

Below, we shall have a look at the earlier terminologies and the new ones:

Classification of all India rainfall:

21 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

Long Period Average (LPA): Averages of rainfall received between 1951 and 2001 (50 years) are termed as the Long Period Average or LPA and are considered as normal. This is computed to be 89cm.

17.1 Criteria to classify the Seasonal Rainfall: The rules have been changed to classify seasonal rainfall. IMD has introduced 6 new categories replacing old four rainfall categories (excess, normal, deficient and scanty).

17.2 The new categories are: ✓ Large Excess: 60 percent and above ✓ Excess: between 20 percent and 59 percent ✓ Normal: minus 19 percent to plus 19 percent ✓ Deficient: minus 20 percent to minus 59 percent ✓ Large deficient: below 60 percent ✓ No Rain: 0 percent

17.3 Certain standardized key terms given by the IMD: Heat wave: When the temperature is greater than 4.5-degree C above usual temperatures for the particular region.

Severe heat wave: When the temperature greater than or equal to 47-degree C.

Cold wave: When the temperature is less than 4.5-degree C above usual temperatures for the region.

Severe cold wave: When minimum temperature is 2-degree C or lower.

22 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

18 Drought:

18.1 What is Drought?

Drought is the consequence of a natural reduction in the amount of precipitation over an extended period of time, usually a season or more in length, often associated with other climatic factors (viz. high temperatures, high winds and low relative humidity) that can aggravate the severity of the drought event.

18.2 Different types of drought: ✓ Meteorological Drought ✓ Hydrological Drought ✓ Agricultural Drought ✓ Socio-Economic Drought

Meteorological Drought:

• In India, according to India Meteorological Department, meteorological drought over an area is defined as a situation when the seasonal rainfall received over the area is less than 75% of its long-term average value. • It is further classified as "moderate drought" if the rainfall deficit is between 26-50% and "severe drought" when the deficit exceeds 50% of the normal.

Hydrological Drought:

Meteorological drought, if prolonged, results in hydrological drought with marked depletion of surface water and consequent drying up of inland water bodies such as lakes, reservoirs, streams and rivers and fall in level of water table.

Agricultural Drought:

It occurs when soil moisture and rainfall are inadequate to support crop growth to maturity and cause extreme crop stress leading to the loss of yield, leading to extreme stress and wilting in the plants.

18.3 How does the India Meteorological Department monitor the Agricultural Drought? • India Meteorological Department (IMD) monitors the incidence, spread, intensification and cessation of drought (near real-time basis) on a weekly time scale over the country based on Aridity Anomaly Index. • It also issues Weekly Drought Outlook, based on this index, which indicates the impending drought scenario in the country in the subsequent week. • Based on aridity anomaly index, weekly Aridity Anomaly Reports and maps for the Southwest Monsoon Season for the whole country and for the Northeast Monsoon Season for the five meteorological sub-divisions are prepared.

23 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

• These Aridity Anomaly maps/reports help to assess the moisture stress experienced by growing plants and to monitor agricultural drought situation in the country.

18.4 Aridity Anomaly Index (AAI): Aridity is the Thornthwaite’s concept to describe water deficiency experienced by plants.

Thornthwaite gave the following formula for computing aridity index (AI):

✓ PE denotes the water need of the plants (which is called potential evapotranspiration). ✓ AE denotes the actual evapotranspiration and (PE-AE) denotes the water deficit.

The positive values of the anomalies have been classified into three different classes as follows:

Note: There is another index known as SPI (Standardized Precipitation Index), computation of which is done at a monthly time scale. Kindly note the full form of it.

19 Weather Modification: Weather modification refers to willful manipulation of the climate or local weather.

19.1 Cloud Seeding: • Exploding demand of water resources and continued population growth has given rise to the problem of water scarcity in many regions of our planet. • To meet the demand of water resources scientist have started using weather modification commonly called as cloud seeding. • Cloud seeding is a weather modification technique which involves the introduction of material into a cloud (using aircraft or ground-based generators) with a view to encouraging the formation and growth of ice crystals or raindrops and, in turn, enhancing the precipitation (snow and/or rain) falling from the cloud.

19.2 There are two basic types of cloud seeding - Cold and Warm:

• Cold cloud seeding (glaciogenic seeding) involves adding particles such as silver iodide crystals or dry ice pellets to the super-cooled (below freezing point) water already present in

24 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1

clouds to promote the formation of ice crystals. The ice crystals grow, fall and melt to below the freezing level to become raindrops. • Warm cloud seeding (hygroscopic seeding) involves adding salt particles (sodium, magnesium and calcium chlorides), which attract water into or just below the base of suitable clouds to enhance the growth of cloud droplets by coalescence.

20 Isopleths for different weather parameters:

Isopleth: A line on a map connecting points having equal incidence of a specified meteorological feature.

Isotherm Lines of equal temperature Isobar Lines of equal pressure Isohyets Lines of equal rainfall Isotach Lines of wind speed Isopleths Lines of equal rainfall depth Isohels Lines of equal sunshine duration Isonephs Lines of equal cloud cover Isonomals Lines of equal thermal anomalies Issallobars Lines of equal pressure distribution Thermoisopleths Lines of equal soil temperature Isochrones The line joining all points of same key time elements, such as time of start of precipitation

25 | P a g e www.edutap.co.in Q u e r y ? [email protected] 8 1 4 6 2 0 7 2 4 1