 In the last class, we were discussing about the characteristic future of atmosphere and its related weather and climate. In this class today, we like to discuss some of the important weather elements because these are born from the atmosphere. Let us discuss something on our rainfall. Why I say our rainfall? Without water there is no life. So rainfall is very very important. You know already what is hydrological cycle. Water gets operated from the ocean surface, all water bodies. It also gets transferred through plant system, goes as a evapotranspiration and stays in the atmosphere as water vapour. Normally, they live in the atmosphere up to 10 days for a single water vapour molecule. They stay for 10 days, then gets condensed and falls as precipitation. So one among the precipitation is your rainfall. So one among the precipitation is your rainfall. Other than that you have drizzle, you have snow, you have sleet and you have hail also. These are all some forms of precipitation. In temperate countries you get snow. In tropical situation you get rainfall because of the lapse rate that is being operated at the lower part of the atmosphere. Without rainfall there is no life in the earth. That is already understood. Normally rainfall is being reported for the past 24 hours. For example, today in the rainfall is being recorded by 8.30 am. It is said to be 20mm means in the past 24 hours there was rainfall up to this quantity. This is very very important. Next we move to some theories. I say rainfall. You must understand some basic aspects of rainfall. Rainfall is from both warm clouds as well as your cold clouds. Accordingly it is being defined by two authors. One is rainfall from cold clouds. This theory is proposed by Bergeron. He is from Norway. He has proposed Bergeron ice crystal theory for cold clouds. And another one is collision theory proposed by Brown from Australia. This is for warm clouds. Let me say a symbol about your Bergeron ice crystal theory. There is a cloud. The temperature goes below 0 degree centigrade. All water gets freeze into ice crystals except certain portion. We call it as super cooled water. It stays as super cooled water not as ice crystals. If you examine the saturation vapor pressure between these two ice crystal and this super cooled water. The pressure is more with super cooled water as compared to your ice crystals. What happens? There is a sublimation process, physical process. Sudden change from keeping one stage. The vapor goes as a ice crystal and falls over the existing ice crystals. And because of the weight and the gravitational force it comes as your rainfall. This is for cold clouds. In respect of the warm clouds the process is coelance and collision proposed by Brown of Australia. Where in the temperature does not go below 7 degree centigrade. That is some warmness is there. Here small cloud droplets gets collided and becoming a biggest particle of the cloud. Because of the thickness of the clouds and the presence of abundant moisture in the clouds. There is always vertical agitation. The bottom goes to the top. The top comes to both. It is like a machinery process. By that the rain cloud droplets becomes very bigger and falls as rainfall. At a later stage with your gravitational force as well as your weight. These are all some theories proposed you must understand. Now I am coming to the process. Theory is something different from the process. What are those process? For every season the rain occurs through different process. For example during summer there is convective process. Because of the solar radiation the land gets heated. The air above the land also gets heated. It loses the density and it gets ascent goes to the atmosphere. And through air diabetic cooling process you get rainfall. Another process is orographic rainfall process. This occurs during monsoon season especially during south-east of monsoon season of India. Wherein the trade winds they travels over ocean take enough moisture. And these warm and moist water air they hits on mountain. As a result the air goes up and through air diabetic cooling you get rainfall. There is a warm frontal rainfall also. This occurs during cold weather period. Therein already there is cold air mass exist. Warm air mass comes from somewhere and sits over the cold air mass. And grows like that over addition by addition and you get rainfall. In the case of the cold frontal rainfall what happens is. Already the warm air sits over the cold air mass. Because of natural phenomenon the cold air mass shifts away. Leaving the warm air mass in the agitation mode. In addition the cold air mass pushes the warm air upper side. And through air diabetic cooling you get rainfall. And another one is rain with cycloning. This is very very common during north-east monsoon season of India. There is a dense extensive air mass in the atmosphere. Which has converging effect energy converging. This moves up towards the atmosphere. And through air diabetic cooling again you get rainfall. Cyclone process something different. You get suddenly depression in the your atmospheric pressure. Suppose there is 980 millibar of a portion here. Suddenly there is a drop in the atmospheric pressure 978, 975. Then you get this process of rainfall. This is very very important. So these are all process and it varies with season. Somebody says that is there any rule that same rainfall process occurs throughout the year. It is not so. It gets varied with season. Then coming to the annual rainfall of important countries. This is very very important to understand the spatial and temporal dimension of the rainfall. This is very important. I can say because of the geographical position of a particular area that I say latitude and longitude. The climate or weather also gets changed. Now you see in the case of your Turkey, Asia and the minimum rainfall 360 millimetre. And the maximum could be seen in the South America or the bottom most layer. It is around 3000 millimetre. Where is 360, where is 3000 millimetre. Similarly if you take our India as a case in Jaisalmer. The annual rainfall is 100 millimetre only. Annual rainfall is 100 millimetre only. So how to express? So rainfall gets varied. The process also gets varied. The theories also get varied. The spatial and temporal dimension also gets varied. Now some facts I want to say about rainfall. What would be the size of the rainfall? The droplet size must be more than 0.5 millimetre. People must understand how to call a day as a rainy day or a dry day. If the rainfall is more than 2.5 millimetre then we call it as rainfall day. Otherwise the rainfall is lesser than 2.5 millimetre means it gets evaporated as a evaporation. Because daily a minimum of 3 millimetre is being goes as a evaporation. So lesser than rainfall 2.5 millimetre does not make a day as a rainfall day. Then coming to the intensity of the rainfall this is also very very important. Here you can see light rain. There are two sub types. Very light rain and one moderate and three heavy rather heavy heavy and very heavy. This is again based on what is the scale. Is it per hour or per day? I can say that you can call it as per day or per day. When rain starts and completes by one hour in a particular day then it can say it is a one hour scale. Or in a day it goes on drizzling drizzling drizzling then it calls a per day. So the rainfall is more than 12.5 centimetre that is 125 millimetre then we call it as a very heavy rainfall. Heavy means the classification is here 6.5 to 12.5 centimetre rather heavy. Then moderate this is always moderation is very very important moderate rainfall. Here I like to say one thing. In the case of European countries the rainfall is 2 mm per day. If you come to country like India the rainfall is 20 mm per day. This is due to some variations. In the temperate conditions the rainfall process is mainly due to cold frontal rain or warm frontal rain. But in respect of our Indian condition you have cyclonic storm, you have orographic rain. That is why the rainfall quantity gets varied. Then why rainfall is very important to crops, not only to crops but also to all human cattle and everything, every life. We call in agriculture crop protection effective rainfall. This is nothing but the amount of moisture or the amount of rainfall that gets infiltrated into the soil profile and stored as soil moisture. This soil moisture is going to used by the crop as a upper transpiration for its growth and multiplication and also giving yield. So effective rainfall is very very important. We say that 60% of the rainfall received to be the effective rainfall in the case of not considering the anti-sildant soil moisture. Suppose today's rainfall is 100 mm the effective rainfall is 60 mm. In the case of the dry land agriculture the entire crop protection depends upon your rainfall. If you take for example India 44% of total annual protection comes from the dry land agriculture. Thus indicating the importance of rainfall for dry land agriculture whether it may be in India or Australia or any other country. The other important aspect of rainfall is irrigated agriculture. Whenever rain falls on a land the water goes inside the soil profile as infiltration and it reaches a deeper layer and getting stored as ground water. That ground water is being used for your irrigated agriculture. So irrigated agriculture is very very important because the risk reduction is very very important as compared to the dry land agriculture. Then crop water requirement, this is very very important. You have your food requirement per day. Colour is 2200, 2500, colour is per day your requirement like that. Plant also, crop also requires water for its growth. That is being discussed in the next slide. Now you can see you have taken the rice crop, its evapotranspiration. The water loss from the soil goes as 1200 to 1400 mm either as evaporation or like your transpiration through the plant process. So we have given different example for this crop, temerate crop is given, tropical crops are given. You kindly see all those things. So here one interesting point is whenever the evapotranspiration is more the yield also would be more. For example you see rice, the evapotranspiration goes up to 1400 mm and the yield is 5 tonnes per hectare. If you come to pulses on the right side its ET is 250 to 300 mm the yield also 200 to 300 kg per hectare. So in the absence of the ET the yield also will be getting reduced indicating that rainfall is mostly required for crop production if you want to sustain or increase the your grain yield from the crops. Now let me say what are the instruments let us use to measure the rainfall. Internationally the rain is to be measured by 3 GMT for India plus 5.30 hours it becomes 8.30 am in the morning. So for having an international comparison we have to record rainfall by 3 GMT in all the countries. There is one honorary rain gauge, it is has to be managed by the manually and one is self recording rain gauge. It is being operated by through a battery or your like a clock then dipping bucket this is automatic systems or equipments being fitted with your automatic weather station. So these are the some things that I like to discuss on the rainfall for today's class. Thank you very much.