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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.
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