CHAPTER-9

WEATHER HAZARDS

Drought, Floods, Frost, Tropical cyclones, Extreme weather conditions such as heat –

wave and cold –wave.

DROUGHT

The term drought can be defined by several ways.

1. The condition under which crops fail to mature because of insufficient supply of water

through rains.

2. The situation in which the amount of water required for transpiration and evaporation by

crop plants in a defined area exceeds the amount of available moisture in the soil.

3. A situation of no precipitation in a rainy season for more than 15 days continuously. Such

length of non-rainy days can also be called as dry spells.

FLOOD

Years in which actual rainfall is ‘above’ the normal by twice the mean deviation or more is

defined as years of floods or excessive rainfall. Like droughts, the definition of floods also varies

one situation to another and forms one region to other.

FROST

Frost is water vapor, or water in gas form, that becomes solid. Frost usually forms on objects like

cars, windows, and plants that are outside in air that is saturated, or filled, with moisture. Areas

that have a lot of fog often have heavy frosts.

TROPICAL CYCLONE

Tropical cyclone, also called typhoon or hurricane, an intense circular storm that originates over

warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy

rain. Drawing energy from the sea surface and maintaining its strength as long as it remains over

warm water, a tropical cyclone generates winds that exceed 119 km (74 miles) per hour. In

extreme cases winds may exceed 240 km (150 miles) per hour, and gusts may surpass 320 km

(200 miles) per hour.

EXTREME WETHER CONDITIONS

HEAT WAVE

A heat wave is a period of excessively hot weather, which may be accompanied by high

humidity, especially in oceanic climate countries. While definitions vary, a heat wave is

measured relative to the usual weather in the area and relative to normal temperatures for the

season. Temperatures that people from a hotter climate consider normal can be termed a heat

wave in a cooler area if they are outside the normal climate pattern for that area.

COLD WAVE

A cold wave is a rapid fall in temperature within a 24-hour period requiring substantially

increased protection to agriculture, industry, commerce, and social activities. The precise

criterion for a cold wave is determined by the rate at which the temperature falls, and the

minimum to which it falls. This minimum temperature is dependent on the geographical region

and time of year.

CHAPTER –10

Modifications of crop microclimate, Climatic normals for crop and livestock production

Relation of weather with agriculture

Solar Radiation: It includes light intensity, light quality and duration of sunlight. Out of total

radiation received, only 50% in photosynthetically active radiation (PAR) which lies in 400-

700nm range. Rest is UV or IR. Now there is an exponential relation between amount of light

intercepted by canopy and Leaf Area Index (Leaf Area/ground area). The sum of these values for

individual days is directly proportional to crop yield.

Temperature: A term growing degree days is used which is given for a crop from time of

flowering to harvest date. Every crop has a temperature range below or above which GDD for

that particular day is zero. GDD is the sum of difference of daily temperature and base

temperature. So the harvest date is predicted depending on the when the GDD is achieved.

Precipitation, Evaporation and Transpiration: There is a relation to calculate the length of

growing period which includes Evapotranspiration. We need to know amount of precipitation

and crop water requirement. Also transpiration causes cooling so maintains temperature. This

prevents crop from damaging.

These factors are responsible for proper crop growth and development. If anyone of the factors is

affected, the crop will be affected accordingly as in case of heavy rains, high temperatures etc.

AGRICULTURE AND WEATHER RELATION

Higher CO2 levels can affect crop yields. Some laboratory experiments suggest that elevated

CO2 levels can increase plant growth. However, other factors, such as changing temperatures,

ozone, and water and nutrient constraints, may counteract these potential increases in yield. For

example, if temperature exceeds a crop's optimal level, if sufficient water and nutrients are not

available, yield increases may be reduced or reversed. Elevated CO2 has been associated with

reduced protein and nitrogen content in alfalfa and soybean plants, resulting in a loss of quality.

Reduced grain and forage quality can reduce the ability of pasture and rangeland to support

grazing livestock.

More extreme temperature and precipitation can prevent crops from growing. Extreme events,

especially floods and droughts, can harm crops and reduce yields.

Dealing with drought could become a challenge in areas where rising summer temperatures

cause soils to become drier. Although increased irrigation might be possible in some places, in

other places water supplies may also be reduced, leaving less water available for irrigation when

more is needed.

Many weeds, pests, and fungi thrive under warmer temperatures, wetter climates, and increased

CO2 levels. Though rising CO2 can stimulate plant growth, it also reduces the nutritional value of

most food crops. Rising levels of atmospheric carbon dioxide reduce the concentrations of

protein and essential minerals in most plant species, including wheat, soybeans, and rice. This

direct effect of rising CO2 on the nutritional value of crops represents a potential threat to human

health. Human health is also threatened by increased pesticide use due to increased pest

pressures and reductions in the efficacy of pesticides.

MODIFICATION OF CROP MICROCLIMATE

Many vegetable crops do not perform to their full potential in unfavorable condition of

environment. Producers can, however, modify the environment a small scale,

creating microclimates more suitable for growing high value, warm-season crops.

Artificial control of field environment to keep the optimum condition of plant growth and crop

production - A practice of environmental control requires a complete knowledge of physiology

of plants and physical environment.

It is be done through:

1. Controlling wind velocity

2. Controlling heat load

3. Controlling water balance.

CLIMATIC NORMALS FOR CROP AND LIVESTOCK PRODUCTION

CLIMATIC NORMALS FOR CROP PRODUCTION

Rice

Temperature and solar radiation influence rice yield by directly affecting the physiological

processes involved in grain production and indirectly through the incidence of pest and diseases.

The difference in yield is mainly due to temperature and solar radiation received during its

growing season. It requires high temperature, ample water supply and high atmospheric humidity

during growth period. Rice tolerates up to 40°C provided water is not limiting. A mean

temperature of 22°C is required for entire growing period. If high temperature drops lower than

15°C during the growth phase, the rice yield is greatly reduced by formation of sterile spikelets.

The period during which low temperature is most critical, is about 10–14 days before heading.

Solar radiation - Low sunshine hours during the vegetative stage have slight ill effect on grain

production, whereas the same situation during reproductive stage reduce the number and

development of spikelets and thereby the yield. For getting grain yield of 5 t/ha, a solar radiation

of 300cal cm2/day is required. A combination of low daily mean temperature and high solar

radiation during reproductive phase is good for getting higher yield. Rainfall - Rice requires high

moisture and hence classified as hydrophytes. Rice requires a submerged condition from

sprouting to milky stage. The water requirement is 125 cm. An average monthly rainfall of 200

mm is required to grow low land rice and 100 mm to grow upland rice successfully.

Wheat

Optimum temperature for sowing is 15–20°C. At maturity, it requires 25°C. At harvest time,

wheat requires high temperature of 30–35°C and bright sunny period of 9–10 hours. Moisture -

One ha of wheat consumes about 2500–3000 tones of water. Water deficiency at the heading

stage results in shriveled grains and low yield.

Maize

This crop is best suited for intermediate climates of the earth to which the bulk of its acreage is

confined. Temperature - Maize requires a mean temperature of 24°C and a night temperature

above 15°C. No maize cultivation is possible in areas where the mean summer temperature is

below 19°C or where the average night temperature during the summer falls below 21°C.

However, high night temperature also results in low yield. Moisture - Maize is adapted to humid

climates and has high water requirements. It needs 75 cm of rainfall during its growth period.

The average consumptive use of water by maize is estimated to range between 41 and 64 cm.

From germination up to the earing stage, maize requires less water. However, at flowering, it

requires more water and the requirement reduces towards maturity.

CLIMATIC NORMALS FOR LIVESTOCK PRODUCTION

Direct effects of climate change on livestock

The most significant direct impact of climate change on livestock production comes from the

heat stress. Heat stress results in a significant financial burden to livestock producers through

decrease in milk component and milk production, meat production, reproductive efficiency and

animal health. Thus, an increase in air temperature, such as that predicted by various climate

change models, could directly affect animal performance.

Indirect effects of climate change on livestock

Most of the production losses are incurred via indirect impacts of climate change largely through

reductions or non-availability of feed and water resources. Climate change has the potential to

impact the quantity and reliability of forage production, quality of forage, water demand for

cultivation of forage crops, as well as large-scale rangeland vegetation patterns. In the coming

decades, crops and forage plants will continue to be subjected to warmer temperatures, elevated

carbon dioxide, as well as wildly fluctuating water availability due to changing precipitation

patterns. Climate change can adversely affect productivity, species composition, and quality,

with potential impacts not only on forage production but also on other ecological roles of

grasslands. Due to the wide fluctuations in distribution of rainfall in growing season in several

regions of the world, the forage production will be greatly impacted. With the likely emerging

scenarios that are already evident from impact of the climate change effects, the livestock

production systems are likely to face more of negative than the positive impact. Also climate

change influences the water demand, availability and quality. Changes in temperature and

weather may affect the quality, quantity and distribution of rainfall, snowmelt, river flow and

groundwater. Climate change can result in a higher intensity precipitation that leads to greater

peak run-offs and less groundwater recharge. Longer dry periods may reduce groundwater

recharge, reduce river flow and ultimately affect water availability, agriculture and drinking

water supply. The deprivation of water affects animal physiological homeostasis leading to loss

of body weight, low reproductive rates and a decreased resistance to diseases. More research is

needed into water resources’ vulnerability to climate change in order to support the development

of adaptive strategies for agriculture. In addition, emerging diseases including vector borne

diseases that may arise as a result of climate change will result in severe economic losses.

CHAPTER- 11

Weather forecasting, Types of weather forecast, Uses of weather forecasting, Climate

change, Climatic variability, Global warming, Causes of climate change and its impact

on regional and national Agriculture

Weather forecasting

Weather forecasting is the prediction of what the atmosphere will be like in a particular place by

using technology and scientific knowledge to make weather observations. In other words, it's a

way of predicting things like cloud cover, rain, snow, wind speed, and temperature before they

happen.

TYPES OF WEATHER FORECAST

Types of forecast Validity period Main users Predictions

1 Short range

a) Now casting

Up to 72 hours

0-2 hours

Farmers marine

agencies,

general public

Rainfall distribution, heavy

rainfall, heat and cold wave

conditions, thunder storms etc. b) Very short range 0-12 hours

2 Medium range Beyond 3 days

and up to 10

Farmers

Occurrence of rainfall,

Temperature.

Weather

forecasting

services

Agriculture including

forestry and Animal

husbandry

General Public

Fishing

Mountaineering

Cyclones, floods and

drought

Government and Post

officials

Off shore drilling

Aviation

Civil & Military

Defence services

Shipping

Mercantile & Naval

days.

3 Long range Beyond 10 days

up to a month

and a season.

Planners This forecasting is provided for

Indian monsoon rainfall. The out

looks are usually expressed in the

form of expected deviation from

normal condition.

USES OF WEATHER FORECASTING

1. The forecast of the weather events helps for suitable planning of farm.

2. It helps in to undertake or withheld the sowing operation

3. It helps in following farm operation:

I) To irrigate the crop or not

II) When to apply fertilizer or not.

III) Whether to start complete harvesting or to withhold it.

4. It also helps in to take measures to fight frost.

5. It helps in transportation and storage of food grains.

6. Helps in management of cultural operations like plugging harrowing hoeing etc.

7. It helps in measures to protect livestock.

CLIMATE CHANGE

Alterations to the earth’s atmosphere that occur over much longer periods—decades to

millennia—are characterized as “climate change.” While climate change can be caused by

natural processes—such as volcanic activity, solar variability, plate tectonics, or shifts in the

Earth’s orbit—we are usually referring to changes attributable to human activity when talking

about climate change, such as increased greenhouse gas emissions. The Fifth Assessment Report

from the Intergovernmental Panel on Climate Change (IPCC 2013), for example, found that on

average global temperatures increased about 0.85°C from 1880 to 2012, and concluded that more

than half of the observed increase in global average temperatures was caused by elevated

emissions of carbon dioxide and other greenhouse gases.

CLIMATE VARIABILITY

While the climate tends to change quite slowly, that doesn’t mean we don’t experience shorter-

term fluctuations on seasonal or multi-seasonal time scales. There are many things that can cause

temperature, for example, to fluctuate around the average without causing the long-term average

itself to change. This phenomenon is climate variability, and when scientists talk about it they

are usually referring to time periods ranging from months to as many as 30 years.

For the most part, when discussing climate variability, we’re describing natural (that is, non-

man-made) processes that affect the atmosphere. For example, the North Atlantic Oscillation

(NAO) refers to anomalous changes in atmospheric pressure at sea level that occur near Iceland

and the Azores High. NAO-positive phases are often associated with above-average storm counts

over parts of Europe and the U.S. You’re also likely familiar with the El Niño Southern

Oscillation (ENSO) phenomenon near the equatorial Pacific Ocean, where fluctuations of sea

surface temperatures typically alternate every few years between a warming phase (El Niño) and

cooling periods (La Niña), with a neutral phase in between. Many researchers have found that

negative ENSO years are correlated with a higher probability of Atlantic hurricane formation, as

well as warmer, dryer weather in northern states.

GLOBAL WARMING

Since CO2 is confined exclusively to the troposphere its higher concentration may act a serious

pollutant. Under normal conditions with normal CO2 Concentration the temperature at the

surface of the earth is maintained by the energy balance of the sun rays that strike the planet the

planet and heat that is radiated back into space. However when there is an increase in CO2

concentration the thick layer of this gas prevents the heat from being re-radiated out. This thick

CO2 layer thus functions like the glass panels of a greenhouse or the glass windows of a motor

car, allowing the sunlight to filter through but preventing the heat from being re-radiated in outer

space. This is the so-called greenhouse effect.

Nitrogen and oxygen the main constituents of the atmosphere play no part in the green house

effect. But there are approximately 35 trace gases that scientists believe contribute to global

warming. Carbon dioxide (CO2) is considered to be one of the most important of these

greenhouse gases absorbing most of the heat trapped by the atmosphere. Other gases of special

importance in global warming are chlorofluorocarbons (CFCs), methane, nitrous oxide and

ozone. Although the average concentrations of these gases are much lower than that of carbon

dioxide, they are much more efficient than carbon dioxide at soaking up long – wave radiation.

Overall carbon dioxide is estimated to cause almost 60 per cent of the warming effect and CFCs

about 25 per cent and the remainder is caused by methane, nitrous oxide, ozone and other trace

gases.

The Greenhouse effect

1.Nearly all the incoming solar energy arrives extra terrestrially with wavelength less than 4 μm

(short wavelength radiation) while the outgoing energy radiated by the earth has essentially all of

its energy in wavelength greater than 4 μm (long wavelength or thermal radiation)

2. Essentially all the incoming solar radiation with wavelengths less than 0.3 μm (ultraviolet) is

absorbed by oxygen and ozone in the stratosphere.

3. Most of the long wave-length energy radiated by the earth is affected by a combination of

radioactively active gases most importantly water vapour (H2O), CO2, N2O and CH4.

4. Radioactively active gases that absorb wavelengths longer than 4 μm are called greenhouse

gases.

5. These gases trap most of the outgoing thermal radiation attempting to leave the earth's surface.

This absorption heats the atmosphere which in turn radiates energy back to the earth as well as

out to space.

6. The greenhouse effect adds 33°C of warming to the surface of the earth i.e. if there was no

greenhouse effect the earth would have an average temperature of –18°C or about 0°C.

Global Warming and Climate Change

Carbon dioxide is a green house gas that is confined to the troposphere and its higher

concentration may act as a serious pollutant. Under normal conditions the temperature at the

surface of the earth is maintained by energy balance of the sun rays that strike the planet and heat

that is reradiated back into space. However when there is an increase in CO2 concentration the

thick layer of the gas prevents the heat from being reradiated out. This thick CO2 layer functions

like the glass panel of a green house allowing the sun light to filter through but preventing the

heat from being reradiated into outer space. Therefore, it is warmer inside the green house than

outside. Similar condition is resulted in the troposphere of the earth and termed as Green house

effect.

Certain gases in the atmosphere known as green house gases like CO, CO2 and CH4 are able to

absorb and emit heat. When sunlight strikes the earth’s surface it warms up emits heat which

radiates upwards into space. This heat warms up the green house gases so that they also emit heat

some into space and some back down to earth which results in heating up of the earth

atmosphere also known as global warming.

CAUSES OF CLIMATE CHANGE

1. Carbon dioxide emissions from fossil fuel burning power plants

Our ever increasing addiction to electricity from coal burning power plants releases enormous

amounts of carbon dioxide into the atmosphere. CO2 emissions come from electricity

production, and burning coal accounts for 93% of emissions from the electric utility industry.

Every day, more electric gadgets flood the market, and without widespread alternative energy

sources, we are highly dependent on burning coal for our personal and commercial electrical

supply.

2. Carbon dioxide emissions from burning gasoline for transportation

Our modern car culture and appetite for globally sourced goods is responsible for about 33% of

emissions. With our population growing at an alarming rate, the demand for more cars and

consumer goods means that we are increasing the use of fossil fuels for transportation and

manufacturing. Our consumption is outpacing our discoveries of ways to mitigate the effects,

with no end in sight to our massive consumer culture.

3. Methane emissions from animals, agriculture such as rice paddies, and from Arctic

seabeds

Methane is another extremely potent greenhouse gas, ranking right behind CO2. When organic

matter is broken down by bacteria under oxygen-starved conditions (anaerobic decomposition)

as in rice paddies, methane is produced. The process also takes place in the intestines of

herbivorous animals, and with the increase in the amount of concentrated livestock production,

the levels of methane released into the atmosphere is increasing.

4. Deforestation, especially tropical forests for wood, pulp, and farmland

The use of forests for fuel (both wood and for charcoal) is one cause of deforestation, but in the

first world, our appetite for wood and paper products, our consumption of livestock grazed on

former forest land, and the use of tropical forest lands for commodities like palm oil plantations

contributes to the mass deforestation of our world. Forests remove and store carbon dioxide from

the atmosphere, and this deforestation releases large amounts of carbon, as well as reducing the

amount of carbon capture on the planet.

5. Increase in usage of chemical fertilizers on croplands

In the last half of the 20th century, the use of chemical fertilizers (as opposed to the historical use

of animal manure) has risen dramatically. The high rate of application of nitrogen-rich fertilizers

has effects on the heat storage of cropland (nitrogen oxides have 300 times more heat-trapping

capacity per unit of volume than carbon dioxide) and the run-off of excess fertilizers creates

‘dead-zones’ in our oceans. In addition to these effects, high nitrate levels in groundwater due to

over-fertilization are cause for concern for human health.

IMPACT OF CLIMATE CHANGE ON REGIONAL AND NATIONAL AGRICULTURE

Climate change and agriculture are interrelated processes, both of which take place on a global

scale. Climate change affects agriculture in a number of ways, including through changes

in average temperatures, rainfall, and climate extremes(e.g., heat waves); changes in pests and

diseases; changes in atmospheric carbon dioxide and ground-level ozone concentrations; changes

in the nutritional quality of some foods; and changes in sea level.

Climate change is already affecting agriculture, with effects unevenly distributed across the

world. Future climate change will likely negatively affect crop production in low

latitude countries, while effects in northern latitudes may be positive or negative. Climate change

will probably increase the risk of food insecurity for some vulnerable groups, such as the poor.

Animal agriculture is also responsible for greenhouse gas production of CO2 and a percentage of

the world's methane, and future land infertility, and the displacement of local species.

Agriculture contributes to climate change by (1) anthropogenic emissions of greenhouse

gases (GHGs), and (2) by the conversion of non-agricultural land (e.g., forests) into agricultural

land. Agriculture, forestry and land-use change contributed around 20 to 25% to global annual

emissions in 2010.