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Global food security ensures that all people have access to sufficient, safe, and nutritious food to maintain a hale and hearty life. This requires a stable inclusive food system resilient to crises like climate change, economic instability, and conflict. Presently, world all over is worried about food security for ever increasing population due to escalating threat of climate change and increased frequency of occurrence of extreme weather events beyond the limits known to us until now. Agriculture is indispensable and no government can afford to neutralize its priority for economic well being of its population. In recent years, studies on the effects of inter and intra seasonal variations of weather on agricultural production and development of management practices to marginalize the weather associated risks is considered as an important area of research. Further, there is more focus on generating reliable weather forecasts with best possible spatial resolution and transformation into operational Agrometeorological Advisories based on sound scientific hypothesis and knowledge base. During early 1930s, two distinguished scientists viz., Dr. L.A. Ramdas from India and Dr. Rudolf Geiger from Germany almost simultaneously carried out investigations and established the fact that the performance of crops not only depends upon the ambient weather conditions but also on weather conditions of the lower layers of the atmosphere within which crops complete their life cycle. Their pioneering research laid foundation for emergence of new branch of meteorology which is now referred to as ‘microclimatology’. The famous British scientist Dr. J.L. Monteith carried out studies on microclimatology of field crops and proposed several theories to relate the similarity of physiological processes in plants with several concepts used in physics. His research work formed the basis to quantify the effect of solar radiation and water use on total biomass production and crop yields. The present authors were fortunate to have personal acquaintance with Dr. Monteith and have drawn lot of inspiration from some of his lectures. Microclimatology is a very important subject but did not gain the kind of importance it deserves. There are several reasons for it including lack of infrastructure, inadequate equipments and limited policy support. Most of the students opted for specialization in agricultural meteorology, have limited exposure to physics and mathematics and find it difficult to learn and master it with a very few exceptions .Most of the books on microclimatology available in the market are more theoretical making it more complicated to learn for many of the students of agricultural sciences.

1.1. Meteorology and Climatology Atmospheric science encompasses the main subfields of meteorology and climatology that are similar in the scientific principles and phenomena being examined, but usually differ by approach, time scale, and application. Meteorology is the scientific study of the atmosphere and weather including weather forecasting. It is an interdisciplinary science that involves observing, understanding and predicting weather conditions likely to prevail well in advance (Fig.1.1). The study of meteorology has been around thousands of years, but significant progress did not begin until the 18th century. Climatology is an atmospheric science that focuses on the processes that create weather patterns and variability. Climatology was developed as a science that is based on weather data recorded at multiple locations for comparatively longer periods, usually for 30 years or more. The study of climatology based on the physical processes is influenced by the geographical features, topography and interaction between land and oceans. 1.2. Agricultural Production Life demands food. The production of food depends upon 4 major factors that are soil, genetic material, management practices and weather. Over a period of time, formers have evolved the cropping strategies based on their local knowledge and experience on the changes in weather within a cropping season. With rapid advances in agricultural sciences, several new varieties of crops were developed, appropriate soil and water management practices were evolved and suitable measures for reducing abiotic and biotic stresses on crops were identified. However, the recent threats of climate change due to increased atmospheric

The atmosphere near Earth’s surface, often referred to as the boundary layer, exhibits unique properties influenced by the interaction between the surface and the atmosphere. These properties are crucial for understanding weather patterns, climate, and various environmental processes. Ancient Indians use to worship five natural elements i.e. earth, water, air, energy and the sky. Perhaps they were aware of the interactive effects and processes between these 5 elements that govern life on earth. In a sense, meteorology itself is a science based on interactive effects of these natural elements. Microclimatology is all about the effect of the interactions between these 5 elements on life over the earth. For a beginner of microclimatology, it is important to understand the properties of the atmosphere near the earth’s surface and get familiar with the concept and terminology used to describe/quantify the physical processes taking place between the lower layers of the atmosphere and the earth’s surface. 2.1. Energy The major source of energy in the earth atmosphere system is solar energy (Fig.2.1). The outer surface of the sun is very hot and its temperature is estimated to be around 6000°Kelvin (symbol K). The Kelvin is the base unit of temperature in the international system of units (SI). The Kelvin scale is the absolute temperature scale that begins at the lowest possible temperature that can be attained (absolute zero) taken as 0 degree K. The magnitude or value of each degree of temperature in the Centigrade scale and Kelvin scale is same. The temperature measured in centigrade scale can be converted to Kelvin scale by adding 273.15. The sun emits heat energy in the form of solar radiation. As the solar radiation passes through the atmosphere, it gets partly depleted before reaching the earth’s surface. The processes through which the solar radiation gets depleted in the

energy plants need to convert carbon dioxide and water into carbohydrates and oxygen. The carbohydrates produced by photosynthesis are used for vegetative and reproductive growth and to increase crop biomass. The solar energy required for photosynthesis is available during day time. In crop canopies radiation is transmitted through leaves and between leaves resulting in changes of spectral composition rapidly with depth. In the absence of vegetation, solar radiation reaches the earth surface after it gets depleted in the atmosphere due to: • Reflection of incoming radiation by the cloud tops • Absorption of ultraviolet radiation by the ozone present in the atmosphere and infrared radiation by the greenhouse gases and water vapour • Scattering of radiation by the solid particles suspended in the atmosphere The remaining parts of solar radiation called insolation i.e. incoming solar radiation reach the earth surface. After it is incident on the earth surface, a fraction of the solar radiation gets reflected back into the atmosphere. The difference between the incoming solar radiation and outgoing solar radiation is called net radiation. The net radiation can be calculated using radiation balance which takes into consideration both incoming solar radiation and outgoing solar radiation. The equation for radiation balance can be written as:

    Temperature variations in crop canopies can be affected by number of factors including water availability. When soil water is low, canopy temperature can rise rapidly, even upto 10°C warmer than the air temperature. Irrigation can help reduce canopy temperature, but it may not be able to keep below the threshold for heat damage. Canopy management and row orientation can affect the air temperature within a canopy. Potassium fertilization can reduce canopy temperature variation which can increase seed yield. Temperature affects many plant processes including photosynthesis, transpiration, respiration and flowering. The rate of photosynthesis increases with increase in temperature, up to a certain limit. High Photosynthetic rates do not necessarily support high rates of dry matter accumulation may be due to increased respiration. If temperature profiles are measured in crop canopies, normally, it is expected that the temperature may decrease with increase in height and is minimum at the crop canopy in a well irrigated crop during day time. It is mainly due to increase in water vapor content within the crop stand due to soil evaporation. During night time, the temperature decreases with increase in height and temperature of the crop canopy will be more as no transpiration takes place during night time. 4.1. Instability Atmospheric instability occurs when the earth’s atmosphere is unstable, which leads to highly variable weather patterns. In an unstable atmosphere, there will be rapid changes in temperature, pressure and wind with height (Fig.4.1). The instability is caused by the rising of warm air. Atmospheric instability can lead to the development of thunderstorms, tornadoes and convective clouds. The factors that determine the atmospheric instability are as follows: 4.1.1. Temperature Lapse Rate: Lapse rate is the rate at which the air temperature changes with altitude. If the air temperature lapse rate is greater than the adiabatic lapse rate, the atmosphere is unstable. The rate at which temperature of an air parcel changes with increase in height without loosing or gaining heat from the surrounding environment is called adiabatic lapse rate. In case of adiabatic process, there will be no exchange of heat between the air parcel and surrounding environment when the air parcel moves vertically upwards. 4.1.2. Humidity: The humidity in the air parcel determines whether it cools at dry or wet adiabatic lapse rate. Therefore, greater the humidity of the air, unstable conditions will increase. When the dry air mass raises vertically upwards, the rate of decrease in temperature with increase in height is called dry adiabatic lapse rate. The rate at which the moisture air mass gets cooled with increase in height is called wet adiabatic lapse rate.

If the earth’s surface is perfectly smooth, the wind flows parallel to the earth’s surface without any friction and the wind velocity will be uniform at different heights above the earth’s surface. As the earth’s surface is not smooth, it offers friction, slows down the movement of the wind near the surface. Therefore, the wind velocity increases very slowly with increase in height up to a certain level, and there after the wind velocity increases with increase in height more rapidly (Fig.5.1). When the wind speeds are measured at different heights above the ground and plotted on a graph with height Z in logarithmic scale on y-axis and wind velocity on x-axis, the wind velocity will be zero at certain height above the ground and thereafter the wind velocity uniformly increases with increase in height. The height at which the mean wind velocity is zero due to roughness is called roughness parameter (d). Therefore, the roughness parameter is defined as the height at which mean wind velocity is zero due to roughness of the earth’s surface. In a cropped soil, the crop also obstructs free movement of air. If wind profile measurements are taken in a cropped soil and are plotted on a graph with height on y-axis in logarithmic scale and mean wind velocity on the x-axis, the mean wind velocity will be zero at a height above the roughness parameter. The difference in height (Z-d) at which the wind velocity is zero when the height is plotted on logarithmic scale is called zero plane displacement (Z0). Therefore, the zero plane displacement can be defined as the height by which the roughness parameter increases due to presence of the crop (Fig.5.2).

In cropped soils, evaporation refers to evaporation of water from the soil and transpiration refers to evaporation of water from plant canopies (Fig.6.1). Evaporation and transpiration play very significant role in mass and energy transfer. The latent heat of vaporization is defined as amount of heat required to evaporate 1 gm of water at a temperature of 100°C; i.e. the boiling point of water is 540 cal/gm. The amount of heat required for evaporation of water at ordinary temperature of about say 30°C is 610 cal/gm. Fig. 6.1: Process of evapotranspiration The evapotranspiration from crop depends upon several factors as indicated below: • The evapotranspiration increases with increase in air temperature. • The evapotranspiration increases with increase in wind speed up to a certain limit. • The evapotranspiration decreases with increase in relative humidity • The evapotranspiration increases with increase in Saturation Vapor Pressure Deficit (SVPD). SVPD = es – ea

Microclimate under irrigated conditions and dryland conditions can differ significantly due to variations in water availability, which influences several environmental parameters such as temperature, humidity, soil moisture, and vegetation cover. The crops are grown both under irrigated and dryland / rainfed situations. The major difference between irrigated and dryland conditions is availability of water. In irrigated areas, the crops are regularly provided with water through irrigation at regular intervals. Under dryland situations, the water availability to the crops depends upon the rainfall and/or stored soil moisture. Under irrigated situations, there are two different possibilities as indicated below: • vast stretch of irrigated areas • isolated pockets of irrigated areas in predominantly dry areas. In dryland areas the following possibilities exist: • humid and moist sub-humid areas where predominantly rice based cropping systems are adopted during rainy season • per-humid areas where plantation crops and rice grown during rainy season. • dry sub-humid areas with rice based cropping systems in low lands and finger millet, maize based cropping systems in upland areas • semi-arid regions where kharif crops are grown during rainy season. • rabi-crops grown under conserved moisture conditions during post rainy season. • arid regions where pearl millet based cropping system are practiced during rainy season. • hill agriculture The microclimatic conditions are likely to vary between irrigated and rainfed conditions due to different agro-ecological settings. The comparative analyses of microclimatic variation under both conditions are given below:

Forest microclimate is the climate within a forest in contrast to a nearby open area created by a clearing or pasture. A robust observation is that less sunlight reaches the ground in a forest than in open areas, but this depends on the size of the clearing, the height of trees surrounding the clearing, and the location in the clearing (relative to the edge) where measurements are obtained. Daytime temperature is generally lower in forest than in open areas, with greatest differences during the growing season; but this, too, is subject to edge effects and whether the canopy is sparse or dense. Wind near the ground is less than in exposed areas or above the canopy. Another point is that there are various microclimates within a forest canopy. The environment of the forest overstory differs from that of the understory, and this has important consequences for species conservation and protection from climate change. The forest microclimate has important implications for habitat and biodiversity conservation and may act to buffer forest understory organisms from the severity of climate change. Forest microclimates differ not only in contrast with open land, but also vertically with position in the canopy (Fig. 8.1).

There is an increased use of Glass houses and poly houses in commercial agriculture. The glass houses and poly houses provide a controlled environment for plants throughout the year. Some of the aspects of related to the advantages of Glass houses and poly houses are highlighted in the following text: 9.1. Glass houses Glass houses are also referred as greenhouses. The glass prevents harmful ultraviolet radiations. The glass is transparent to solar radiations of wavelengths up to 300 nm and does not allow long-wave radiations to pass through it (Fig.9.1). Therefore, the Glass houses maintain higher temperature and high relative humidity during daytime as well as nighttime and offer the following advantages: 9.1.1. Controlled Environment: Glass houses facilitate regulation of temperature, humidity, and light intensity, creating optimum environment for growing various plant species. This is especially beneficial for tropical and sub-tropical plants that require specific conditions to grow and survive. 9.1.2. Protection from Pests and Diseases: The enclosed glass house protects plants from pests and diseases. The glass house also protects the plants from harsh weather conditions thereby minimizing risk of infestations and environmental stresses. Fig. 9.1: Microclimate management in Glass house 9.1.3. Extended Growing Season: By maintaining stable climate, glass houses enable cultivation of plants that may not survive outdoors in certain climates thereby extending the growing season for sensitive species. 9.1.4. Research and Conservation: Botanical gardens often use glass houses for research purposes, studying plant growth, genetics and breeding. The glass houses will also serve as a means for conserving rare or endangered plant species by providing stable environment for propagation. The advantage of glass houses is that the structure has long life span. 9.2. Poly houses The poly houses are constructed using polythene material. The poly houses protect the plants from wind, cold weather, hail storms, extreme temperatures, insects and pests. The polythene house farming is a popular greenhouse technology due to its low cost of construction and maintenance. Generally, heat accumulation (70 to 75 per cent of solar energy) takes place inside the polyhouse. Solar radiation is allowed to pass through the polythene material and the long wave radiation cannot escape through polythene. The benefits of poly houses are:

A farm microclimate refers to the specific climatic conditions of a small, localized area within a farm. These conditions can differ significantly from the broader regional climate due to various natural and man-made factors. Understanding and managing microclimates is crucial for optimizing crop growth, animal welfare, and overall farm productivity. Modern commercial dairy production requires a special approach to the microclimate on the farm. High quality milk and animal health depend on the conditions of their keeping. At the same time, farm for dairy production for the most part do not have the means to control and manage the microclimate, in contrast to poultry farm. When organizing the correct process of controlling the microclimate, a prerequisite is the presence of an automated system for collecting data. Generally animals adapt to a wide range of weather conditions although their growth and productivity varies with weather conditions. Buffaloes and cows form the main component in dairy industry. The extent to which these animals can adapt to different weather conditions is given below: Successful management of buffalo rearing will be incomplete without wellplanned and adequate housing facilities (Fig.10.1). Improper planning in the arrangement of animal housing may result in management problems, increase in disease incidence, additional labour charges and hence decrease in the profit of the farmer. During erection of a house for dairy buffaloes, care should be taken to provide comfortable accommodation for individual animals. It is important to ensure: • Proper sanitation • Durability • Abundant supply of clean water • Arrangements for the production of clean milk under convenient and economic conditions. Buffaloes may be successfully housed under a wide variety of conditions, ranging from close confinement to little restrictions except at milking time. However, two types of farms are in general use.

The fate of smoke from a wild land fire depends in large part on the airflow carrying it away from the fire which can involve a complex interaction of eddies that may occur near the ground or expand beyond the atmospheric mixed layer (Fig.11.1). The buoyancy of smoke and ambient atmospheric conditions determines how high and how quickly the smoke rises, and thus where it travels. The smoke plume distribution is affected by number of factors as indicated below: • Elevation: The smoke plumes at higher elevations disperse the smoke particles more vertically while plumes from lover elevations disperse more horizontally. • Temperature: The large difference between the smoke and surrounding air affects the Plume dynamics. The buoyancy force increases the vertical velocity of the particles, while heat diffusion increases surrounding air temperature. • Moisture: The presence of moisture can modify the distribution of smoke and chemistry of smoke particles. • Topography: Topography can influence emissions that remain within the mixing zone. • Atmospheric stability: Atmospheric stability can affect the distribution of smoke.

During most of the years, there will be loss of agricultural production by at least 15 to 20 per cent per annum due to unfavourable weather situations. The farmers practicing agriculture expect uniform returns every year as the investment costs are much higher and cannot afford loss in production. Of late, the inter-seasonal and intra seasonal variations in weather are very frequent. The weather conditions observed were found to exceed even beyond known limits. Exceptional deviation from any one single weather parameter like air temperature, rainfall and wind can trigger considerable loss in production or sometimes even crop failure (Fig.12.1). Fig. 12.1: Components of a microclimate and its interlinkages Large scale weather modification is not practicable to a greater extent as uniform results cannot be expected under these conditions. There is need to explore cost effective management options that may significantly alter some weather parameter that is detrimental to crop production at field level by the farmers themselves. Therefore, microclimatic modification is an emerging technology to alter or change the unfavourable weather conditions detrimental to crop growth using cost effective and easily manageable techniques for minimizing the loss in crop production. The options for microclimatic modification have to be decided based on whether and the nature of weather aberrations. For example, dry spells are most common during rainy season in most of the arid and semi-arid regions. The farmers growing crops under rainfed conditions suffer considerable loss in production due to occurrence of dry spells as the crop experiences moisture stress. These dry spells may occur any time during the growing season. In such situations, the farmer needs to adopt a management option even before sowing a crop. Sometimes, the occurrence of weather aberration cannot be anticipated and the farmer has to prepare for adopting a management option based on weather forecast. Such measures are temporary and needs to be adopted to ward off the unfavourable weather conditions to a certain extent. Microclimatic modification can be a permanent, seasonal or temporary option depending upon the climate of the region. The crop microclimate refers to the climate just above and within the crop canopy and in the soil root zone that can be influenced by the day-today management practices. Microclimate modification is a measure to change or regulate the weather parameter at farm level. The microclimate management option also depends upon the nature and type of the soil as well.

The weather plays a very significant role in crop production. The agricultural production depends upon four factors i.e., soil, genetic material, management practices and weather. Of these four factors, the farmers have least control on weather and have to evolve management strategies to cope up with the weather conditions. The crops can be grown only when the seasonal weather conditions are conducive to crop production. The different weather factors on crop growth and development are as follows: 13.1. Temperature For each species of plants, there are upper and lower limits of temperature beyond which the growth is negligible. The optimum temperatures at which growth is maximum may vary from crop to crop but will be within the range of 15 to 30°C. Temperatures beyond 45°C cause wilting of plants. There are also optimum temperature requirements during different stages of crop growth. 13.1.1. Warm Season Crops: The Warm season crops are rice, sorghum, maize, pearl millet, groundnut, pigeon pea, cowpea etc. These crops are also called tropical crops. These crops can be grown during monsoon season and in early summer season. The optimum temperatures for these crops fall in the range of 15°C to 38°C. 13.1.2. Cool Season Crops: The crops which grow best under cool weather conditions are called cool season crops and are generally grown during winter season. The important cool season crops are wheat, mustard, Chickpea, barley, potato, Safflower. These crops are also called temperate crops. The optimum temperature for better growth of these plants range from 10°C to 30°C. 13.2. Effect of Temperature on Growth and Development The crop development is described in terms of its various stages of growth including germination of seeds, emergence of seedlings, tillering, flower initiation, grain formation, physiological maturity and harvest maturity etc., before it completes its life cycle. The various stages of growth, the crop passes through are called phenophases. Phenology is the study of timing of the phenophases. The temperature and day length (photo period) will have considerable influence on phenology of the crops. The temperature from which crop development begins is called base temperature. The base temperature is considered as 8°C for the crops grown during kharif season and 5°C for the crops grown during winter

14.1. Slope It is a crucial topographic factor that affects water drainage, erosion and accessibility of agricultural machinery. Steep slopes increase the risk of soil erosion, and water run-off requiring erosion control measures such as contour ploughing or terracing. Slope also affects the availability of sunlight, as steeper slopes may cast shadows and influence microclimates within a field. 14.2. Altitude / Elevation Elevation is the vertical distance of a point or location above a reference point, often mean sea level. It influences temperature, atmospheric pressure, and the types of crops that can be grown in an area. Higher altitudes generally experience cooler temperatures, which may limit the choice of crops that can thrive. Elevation affects the length of the growing season and influences the choice of appropriate crop varieties. In summary, elevation is an absolute measure of the vertical distance above a reference point (such as MSL), while it is a relative measure that describes the variation in elevation within a specific area or region. Elevation provides information about the height of a point, whereas it provides insights into the topographic features and slopes of a given agricultural landscape. Both elevation and relief are important considerations in agriculture as they influence factors such as water drainage, temperature gradients, and suitability for specific crops. 14.3. Aspect Aspect refers to orientation of the slope (north, south, east or west). It affects the distribution of sun light; wind patterns and temperature gradients in a field. In the northern hemisphere, the north side of slope is often shaded while the southern side receives more solar radiation and heat, creating warmer microclimates and potentially influencing the choice of crops or planting strategies. Aspect can also impact the risk of frost or cold air drainage in certain regions. Whereas, in the southern hemisphere, the south side slopes get shaded and north facing slopes receive more solar radiation. 14.4. Relief Relief refers to the variation in altitude between different points. It is a relative measure on changes in altitude across a particular landscape or agricultural area. The valley slopes are preferred sites for agriculture in mountain regions due to several reasons: • The valley slopes offer relatively flatter terrain, making it easier for farming activities such as cultivation, irrigation and mechanization. • The valleys tend to have better access to water resources such as rivers or streams which can be used for irrigation water. • The valley slopes provide good sun exposure and protection from strong winds creating favourable microclimates for crop growth • The natural drainage patterns of valleys help preventing water logging and ensure better water management.

There is growing demand for increasing fruit production as fruits are considered to be healthy, nutritious and easy to digest. Fruits are natural foods and have export potential as well as provide opportunities for increasing employment by establishing fruit processing industries. Some of the fruits can be grown around the year where as some fruits are of seasonal in nature. Usually, the fruit cultivation is undertaken by establishing orchards. In case of orchards, wrong decisions in planting may result in huge loss and therefore right method of planting is the key factor for establishing orchards. The fruit crops are of three types depending on the adoptability to the climate of the region and are grouped as • tropical fruits • sub-tropical fruits • temperate fruits The microclimate of the orchards depends upon • height of the plants/trees • horizontal spread • canopy architecture • spacing/plant density • age of plantation • seasonal weather 15.1. Tropical Fruits The tropical fruits require higher temperature throughout the year. The crops do not require low temperature for breaking dormancy and for flowering. The plants are ever green and grow throughout the year. There plants are well adopted to regions where the minimum temperatures are more than 10°C and very sensitive to frost. There are grown in tropical regions between 23°N to 23°S latitudes. The optimum maximum temperature for growth and development ranges from 30 to 37°C. 15.2. Sub-Tropical Fruits The sub-tropical fruits perform better between temperate and tropical climates as the plant requires both high and low temperatures. Some of the fruit crops are green and some of those are deciduous. The temperate fruit crops are very sensitive to frost. The sub-tropical fruit plants break dormancy of flower buds

16.1. Global Warming The industrial revolution from mid 18th century is recognized as the primary cause of atmospheric pollution. Some of the gases like CO2, Chlorofluorocarbons, methane, nitrous oxide etc. are getting released into the atmosphere in greater volumes by combustion of fossil fuels. These gases can absorb the heat radiation leading to increase in air temperature and are called as greenhouse gases. When there is no vertical movement of air, these gases can accumulate near the ground and causes serious health hazards (Fig.16.2). Fig. 16.2: Global warming Under unstable conditions, there will be more convection and vertical movement of air that can prevent pollution near ground level. These air pollutants can be transmitted and carried away to long distance by strong winds. So, the air pollution which defies local, regional or even continental boundaries can cause atmospheric pollution and global warming. Therefore, air pollution control is not an issue for just one location or region and is now a matter of global concern. 16.2. Climate Change As the greenhouse gases are spreading into the atmosphere, there is gradual increase in the air temperature and if no control measures are uniformly adopted

Urban climatology deals with changes in climatic conditions that prevail in large cities and towns that differ from the surroundings. Urban climates are influenced by large built-up areas, increased human activities and dense population and are found to experience differences in temperature, humidity, wind speed and direction and rainfall compared to adjoining areas. Tall buildings, paved streets and parking lots affect radiation balance, wind flow and run-off. The atmosphere in urban areas will have higher concentration of pollutants like carbon monoxide, oxides of sulphur and nitrogen, hydrocarbons, oxidants and particulate matters. Heavy concentration of air pollutants will have considerable impact on temperature, humidity, wind, and precipitation in and around urban areas. Heavy concentrations of air pollutants for longer periods or several days may lead to temperature inversions. The temperature inversions prevent convection and vertical movement of air. The centre of urban area will be warmer by even 5 to 6°C compared to adjoining areas. During summer months, the concrete structures absorb, store and reradiate more solar energy per unit area compared to vegetation. During nights, radiative losses from urban buildings and roads keep city warmer than the rural areas. The average relative humidity in cities is usually lower due to lack of evapotranspiration from vegetation. The mean wind speed will be 20 to 30 percent due to increased frictional drag induced by built up urban terrain (Fig.17.1). The urban areas influence precipitation patterns in its vicinity as turbulence and convection get modified by city environment. 17.1. Urban Heat Islands An urban heat island is a type of microclimate that is created when an urban area becomes warmer than the surrounding area. It is common in large cities (Fig.17.2). The characteristic features of urban heat islands are as follows: • Increased temperature • Large temperature difference by even 5 to 6°C • The south facing buildings receive more sunlight in the northern hemisphere • The tall buildings in urban areas create streets that act like deep valley • The albedo will be very less. The darker areas lead to more absorption of incoming solar radiation and emit more of long wave radiation • The concrete structures are built with materials having low specific heat. Therefore, concrete structures warm up faster and lead to quick rise in temperature • The higher density of buildings reduces wind speeds.

Remote sensing is a technology that enables us to acquire information about one object or phenomenon without making physical contact with the object. Generally, we are used to take observations in site or at the site. Development of remote sensing technology is now making it possible to quickly and almost simultaneously to collect information from the earth surface and other planets as well. Remote sensing is used to measure the thermal complexity and structural complexity of microclimates and how organisms respond to environmental changes. The thermal complexity is a result of the response and behaviour of different characteristics of the earth surface including vegetation, soils, structures, water bodies etc. Optical remote sensing makes use of visible, near infrared and short-wave infrared sensors to form images of the earth’s surface by detecting the solar radiation refl ected from targets on the ground. Different materials refl ect and absorb differently at different wavelengths. Thus, the targets can be differentiated by their spectral refl ectance signatures in the remotely sensed images (Fig.18.1). Satellite Refelcted Solar Radiation Forest Water Grass Bare Soil Paved Road Built-up Area Atmosphere Incident Solar Radiation Sun Structural complexity is defi ned as minimum number of numerical specifi cations required to describe an object in physical space. Structural complexity is a key ecological factor that describes the three-dimensional physical structure of the ecosystem. It is often linked with biodiversity.

Agriculture is number one priority in economic planning and for the welfare of the people. It is most indispensable sector. Severe food shortages due to short comings and mismanagement of agriculture will have long lasting effect. In recent years, the uncertainties in agriculture are increasing due to climate change and farmers are required to be very vigilant and cautions right from planning of field operations till they recover their investment and end up with better returns. The governments all over the world are very much cautious of the problems of the farmers. There is greater realization that strengthening meteorological services to generate accurate and timely weather forecasts is the starting point to help farmers in carrying out appropriate management practices to ensure better crop production and minimise the risks associated with unfavourable weather situations. The farmers can manage to take their own decisions with regard to choice of crops, land preparation, fertilizer applications, weed control, irrigation scheduling etc which are of routine nature (Fig.19.1). But there are several issues for which farmers do not have adequate knowledge just based on weather forecast. It is now very much realised all over the world that there is need to transform the weather forecasts into an actionable operational agrometeorological advisories based on sound scientific hypothesis and authentic database. Though it appears to be very simple and easy solution, the agencies that