 Welcome to rural water resource management NPTEL course week. So in the first lecture of week two we looked at what the parameters that we are going to look at. We identified six parameters. The parameters would be discussed in detail in this week's lecture, which included precipitation, runoff and discharge and evaporation. So today we would look at precipitation. How is precipitation formed? And as I said, we will focus mostly on rainfall of the types of precipitation. We would look into details of precipitation in the form of rainfall. What are the key methods in which precipitation occurs? It is important to understand how what are the different methods in which precipitation occurs. First method would be frontal, wherein cold air moves and lifts warm air and condensation occurs. Please understand that precipitation would occur, rainfall, cloud formation and then rainfall would occur because of precipitation. So when you have vapor, which is from your evaporation or transpiration or evapotranspiration where water as a liquid is converted to a vapor phase, it is on the land and from the land it has to move up. So it can move up by condensing or cooling. So once it cools down, then it becomes condensed into clouds and then further condensation will lead to your rainfall. So the first precipitation occurs. Now we have the clouds and we have some amount of humidity. Humidity is the amount of water vapor, related to the amount of water vapor. So the first method we will discuss is frontal, where cold air moves, lifts warm air up. So you have your cold air, which is like coming at this space. So for example, both are coming in different directions. This is a cold air front and you have your warm air front. So when cold air moves, it goes down because it's heavier and pushes the warm air up. So it will be like this. So the warm air would move up. By moving up, eventually it will lose its heat or cools down and by cooling down it condenses. So that is how condensation occurs. Why would cold air move down rather than up? Because cold air is more denser and so more heavier. So it will move down. So when both are colliding, the heavier particle or heavier matter would go down and then go up. Same like you have your small toy cars that you play with. You have a very heavy truck and a small car. You hit it. The truck would be still on the ground or it would go down and your toy truck car would go up. So same way, the warm air would move up because of less weight and then your cold air is more denser, heavier. It would push it up. By moving, it pushes it up. So that is your frontal method. The other one is orography. In all these methods, what you would find a consistent pattern is that warm air is lifted up or it is lifted up in elevation and by lifting it up, it cools down. Orography is a process where air moves over elevations and condensation occur. So when you have a mountain, so this is for example, like a mountain and you have your water vapor filled air and current moving. So warm air current, it moves and when it hits your mountain or hill or a higher elevation, it has to go up and by going up, because it's coming with a force, it's coming with a momentum, it has to hit and then it goes up. When it goes up, as I said, it will eventually lose energy and it will cool down. By cooling down, it condenses. So that is orography. Where would you see all this happening in India, mostly on the Western Ghats? So that is why you have a lot of rainfall on the Western Ghats side. So in India as a peninsula, this side where you have Kerala, Maharashtra, etc., Goa, you see that the air current moves and once it hits the Western Ghats, which is an elevation, it moves up. By moving up, it cools and a lot of rainfall happens. So that's why you see a very good lush green color, a land use land cover in the Western Ghats, good for us, thick for us, because a lot of good rainfall has happened. Convection. Convection is when moist air, which means air with a lot of water vapor moves over a hot surface causing sudden rays of air and condensation occurs. So you have a hot, hot surface. The hot surface could be your lake, which is really hot or a road, which is really hot. And then you have your moist air, which is air full of water vapor. It moves. And when it hits that plate, that area where it is very, very hot, suddenly it raises the temperature. So that rays in temperature and the warmth, the air has to compensate. How it compensates is by moving up. It moves up and then cools. So sudden movement, sudden increase in that energy would also leave it to cool down and it condenses. So that is convection. Now you would have an idea where convection would happen. Convection would mostly happen in region-slide deserts where sudden hot surfaces are available or urban areas, urban heat island we call where we have a very hot road surface or covering with higher deflection or warming potential. It suddenly raises the temperature. And then when a water vapor filled air moves up, it just suddenly raises the temperature and by raising it has to do something. It has energy now. So all it can do is just move up vertically. And while moving up, it reduces the temperature, cools down and then condensation happens. Convergence is when two air masses with similar energy collide. So in the first frontal, we saw cold, which is a higher denser air, here air and cold and warm air moving. But here it is both same. When both are with similar energy collide, convergence happens. The energy has to be converted into some other way. So it raises up. By raising up, you break it into simple physics. Movement is kinetic energy and potential energy is moving up. Vertical movement and higher elevation movement is potential energy, whereas moving is kinetic energy. So kinetic energy is being converted into potential energy by higher elevation. However, when you go to a higher elevation, it cools down. So energy might remain, but you're cooling down. And that is the important process which is needed for condensation to occur. Let's look at some images for better clarity. So in the first part, this is also from the book that I've prescribed for the course. Let's look at orographic and frontal, because these are the two major methods through which precipitation can occur in rural India. So again, focusing on rural India, where we have a frontal surface cold air mass, which is moving. It moves and warm air gets lifted up. So what happens is your frontal surface or cold air mass is moving in and your warm air, which is on this different color or different diagram, it starts to move up. And that moving up would cause it to cool down further and then rain will occur. So that is how precipitation is formed. In the second phase where we are looking at the orographic, what you could see is this is the mountain range. I gave an example of the western guards. It could be any elevation gradient. A gradient means a sudden change in elevation. So what you see here is an elevation gradient. Or here, let's take the example of western guards. So what sea would this be? This would be your ambient sea. So your air mass is coming. So your evaporation is happening on the surface of your sea. Think about the water cycle that we discussed. Evaporation is happening, which means water from the surface is converted into vapor and that vapor is being moved across the land surface. And when it moves across, it is having a lot of moisture, but it is warm because of the temperature and it is moving towards seaward. So while it moves, it goes up because of the mountain, it has to go up. And while it goes up, as I said, the warm air is in a different design. Look at the warm air design. So while the warm air is moving up, it cools down. And because of that, you have a lot of rainfall. So these are the two major, major methods by which precipitation can occur in India. But there is a downfall. What is this? So in the photographic method, what you could see is on one side of the mountain, you have so much rainfall because all of the moisture is being deposited. It picks up from the sea, the moisture, the water vapor goes up and cools down a lot of rainfall. So rainfall occurs in this area. But what happens to this area? So this area becomes as a rain shadow area, where a land without vapor, even though it is very, very close, sometimes even within 1 kilometer, 2 kilometers from your mountain region, you would see that there is less rainfall because all the rainfall occurs on one side of the mountain. So while the mountains help the occurrence of precipitation, it can also take away the rainfall that could have happened on the other side. And that is where we have a rain shadow area. So if you go along the western dots, one side of the western dots is very green, lush, good tropical forest, very good rainfall, 3,000 millimeters even, but per per year. But then when you go to the other side, it's really dry. All the water is already deposited on this side as rainfall, whereas here, it is very, very less rainfall, sometimes even 600 millimeters. So look at the difference, 3,000 on one side, 600 on the other side. The other issue is once the cloud and the air deposits all the moisture, it will pick up the moisture from the other side, which means it will take away whatever moisture is remaining on the other side. So this is very important to understand for rural water management. How do you manage this side of the land to preserve the water, whatever water we have? And how do you manage the other side of the mountain for avoiding floods and droughts? So that is where we will be looking at. So now we've looked at the two major methods by which precipitation can occur. Now let's get into precipitation measure. While there are multiple, multiple methods, we will stick to the method which mostly government agencies use and which you could apply in the rural setting. How is precipitation measured? As I said, it is measured as a unit of thickness to be consistent with your water mass balance equation. Engages. So the device that is used to measure rainfall is called a rain gauge. There are multiple designs, many, many designs and each has its own benefits, pros and why it can be used for a particular reason. So you have to be understanding the pros and cons of using a particular design in your field. If you do not know much, it is always okay to use the simplest one. What you see on the top right corner is the simplest rain gauge which we used in Rajasthan as part of our project. And it is basically a plastic tube with markings to tell the thickness of rainfall. So I put it on a spool and when it rains, water is collected in the plastic tube. And since the tube has markings centimeters in centimeters, we call it graduated. What happens is you get a thickness of rainfall. So every day I would ask the students to go collect the rainfall in the gauge and then empty it and then put it back because if you don't empty it, the second day's rainfall also will be recorded. So it is kind of manually intensive, but it is the most simplest design. So now you can understand there is both manual and automatic rain gauges. It depends on your budget and how much technical capacities you have to install, monitor, manage these resources. So it takes time. So both manual and automatic gauges exist in the market. If you want a simplest one, you can go for manual. If you have the manpower, you can go for manual. If someone is there to collect the data, otherwise automatic is good. Usually measured as a rainfall level in a known container. So as I said, the plastic container I know, I know the centimeters where the centimeters are drawn and if rainfall occurs, I can measure. What is the downside of it? If you do not collect the rainfall quickly, it will overflow. Once the tube fills up, it will overflow. So that's what I'm saying. There's frozen ponds. I cannot use that rain gauge in, for example, the western regards where it can fill up within an hour and every hour I cannot ask someone to take a measure. So it depends. If you can use it in a other side of the western regards, where I said it is dry, yes, you can use it. So not more than 20 centimeters you are expected on a particular day. 20 centimeters is like a flood. So what I'm saying is 200 millimeters, even easily you could measure. So here, this gauge would go around 30 centimeters. So need to convert rainfall level one dimension to a volume. So what you get through these weight gauges is a thickness which is one dimension. So the top one is a manual. The bottom one is a IMD automatic station where you could see that water can come in and record on a graph sheet. I'll also show you the inside diagram from the book on how a rain gauge would look at. But for you to understand, this is how data looks like. Rainfall would come in, rain will occur and you'll take it as a measure. Multiple methods available for conversion. Simplest equation is multiplication with contributing area. So if you know that for a school area or for that particular local village, one rain gauge is there. I just multiply the area of the village by your rain gauge depth, the rainfall depth, I will get the volume. So that is the total volume I can expect in the village because of rainfall. Okay. There are multiple protocols that you should follow while installing a rain gauge. All those protocols are given in the booklet by a rain gauge. You can also refer to IMD's guidelines, SOPs, we call them, or USGS SOPs on how to set up a rainfall gauge. Since this course is going to talk about how you can use this data, it is very important to understand how the data is collected. So that is where we're discussing these in this lecture. Let's take one, just one rain gauge type as an example. We call it the dipping bucket. So this is the receiver, which is a funnel, a funnel which collects rainfall in a 30 centimeter diameter. So rainfall occurs, you will collect rainfall through this. Rainfall will be collected and drips into the container part of your instrument. It's the same as your green instrument here, but just a different diagram. What you have here is a dipping bucket. So it is a small bucket divided into two. So you can see two compartments of the bucket. So once rainfall comes in, it fills one side of the bucket. Once the bucket is full because of the weight, it will tilt. So when it tilts, a recording device will record as one. So one tilt will be recorded as one in your chart. So then this part of the compartment will get the rainfall. Then it will tip this side. So then two, so like that three, four, five, six. So it will oscillate between the two compartments depending on the rainfall received and the number of tips, the number of tipping of the bucket would be measured. We know the volume of each bucket. We know the volume of each compartment because when we put it in, we measure it. And if you have the number of tippings, then we can just multiply the volume of one bucket times the number of tips that is recorded in the device to give the total volume. So this is a automatic range where you do not have to collect daily, but it gets recorded and sent to the servers if it is remotely connected or it be recorded inside the machine itself in a digital or analog fashion. The water doesn't stay, which means the water would come, tip, and then come out. You can also put a measuring tube here and collect the water and measure, but it's not needed because water can flow out. What is the benefit? You don't have to change or go after a big, big event like the gauge I showed in the school. You have to empty it and then put it back here. There's no empty. You just measure the rainfall. So IMD is the key agency for monitoring rainfall across India, Indian Meteorological Department, IMD. So I've told you about rainfall presentation methods and how to measure the data. And now we could see how IMD has put up their rain gauges, automatic or manual across India. You could see there's a good representation on the western grass side because there's a lot of rainfall. But in central India, there's very less according to this diagram. And also in some parts of your Kashmir, you do have less rainfall measuring devices in Rajasthan, Gujarat, Manjipuradesh. So all this is very important to understand where we could have more better input from IMD. So we can get need for higher spatial coverage. Looking at this, we can ask, we can get for more data, we can get higher temporal coverage. Spatial coverage means across the area of India, we can propose to have more stations. Higher temporal coverage means if it's given daily, in some regions, can you do some daily or hourly so that I can understand how rainfall can be converted into floods or I can understand how I could capture the rainfall for my rainwater harvesting. For example, across the western grass. Also, there is a need for better instrumentation and maintenance because when there is a extreme event like flood, some of the rain gauges can be washed away or damaged. So there is need for better instrument maintenance. This can be visible if you go to the websites and download the data. We will be looking at some websites in this class to download this data and you'll see some gaps. Some gaps in your data could be because of an instrumentation error. Debris. So if you have a rain gauge, debris is the unwanted material that can fall inside your rain gauge. For example, a leaf. A leaf can fall inside the rain gauge and prevent the rainfall from going inside the rain gauge. This would affect your quality of data. The third thing is power. Some of these automatic ones would need a solar panel or battery power for operations. Sometimes there might be a short circuit. The power is lost. So it is always necessary to have a backup power supply or good power supply. The other thing is easier access to data. Sometimes it gets tricky to get all the data, the formats, etc. So it will be good to have easier access to the data or more information on how to access all these data together. However, all these require more funding. There is an interest to take this data and use it for public good. So if we show that, okay, I'm going to use this data, then the government would be ready to find more so that we could do better water. For example, in a village, if there is no rain gauge, the village people can ask for a rain gauge. For these, for example, I want to do rainwater harvesting, for which I need to understand how much rainfall is occurring. So for this funding exercise, you could say that I'm having such deliverables like, for example, rainwater harvesting. I'm going to increase the storage capacity in the village. Next. This is a physical measurement. Is there another measurement, other options? Yes. Remote sensing. So remote sensing products, just a quick definition what a remote sensing is. In our lectures, remote sensing is the process of satellites collecting data for your hydrological parameters. Okay, so satellites are known to estimate rainfall or collect data on rainfall at a global scale. See here, the entire globe is mapped. For example, you could see western guards here and the rainfall is around. It's in the blue and green colors. I could see around 20 millimeters for that particular day. Okay, it is a day on 2005 year. And then you have the month and then you have the daily. So normally remote sensing products, the data file name like .nc4 is a type would give you the details about the data. 3b42 is the level of processing of the data. It is a daily time scale. As I said, spatial and temporal spatial, it is global. So we don't have to worry about it. Temporal is daily, daily coverage 2005 08 28. So this is a remote sensing product, which is a satellite sense product of the rainfall. So you can also have this, which is free of cost. Just go to the website I've given in the bottom. Or you can also look at other sources for rainfall to remote sensing. And it is a big program. There's a lot of international collaborations for mapping rainfall. Let's see an example. So this is a picture of the globe and tremendous amount of funding and energy has been put at that info. Because while occurring in one region can impact another international boundary. As I said, Ganges is cross boundary. So it's not, it is very important for us to understand what is the rainfall in Nepal to understand the Ganges flow in India and how we manage it in India and Bangladesh. So for this, there's a lot of these collaborative programs. And this is one collaborative program GPM consideration where India is a part along with United States, Japan, France, and the European Union. You can see the satellites that they have put up across the globe to monitor these rainfall events and how much precipitation occurs. The data is free of cost, which is, which means it is open source. Anyone can access it. All you have to do is just set up an account in the NASA download the page and then download the data. How to use this data is a part is not the scope of this lecture. It may be covered in the GIS lecture. But what I'm trying to tell you here is do not say there is no data. There is some data is a different scale. You could still use it for rainfall. So of these satellites, most of the satellites are from the US, let's say NOAA, NASA, JAXA, and then TRIM is a very successful rainfall monitoring satellite. You have NOAA, you have JSON, JPSS, etc. Then you have the Indian French satellite MAGA. So MAGA tropics is a satellite which is between India's mission between India and France, and it is a very good satellite that you can collect data from Israel website itself. So there are multiple platforms that can support the estimation of rainfall using remote sensing products. So in this lecture, what we came across is precipitation occurs by different methods. We looked at the key methods that occur in India, even though they discuss the methods overall, the more dominant methods. And then we looked at orography and frontal precipitation methods. Once precipitation occurs, it is important to capture the precipitation. So we discussed about rain gages. We looked at how a rain gauge collects data, and then we showed the map of where the rain gauges are present for India through IMD. Then we said, okay, there might be some issues to counteract it or to say where, how you could use other data products. We looked at the remote sensing or satellite products. And with this, I am showing the satellites that are available for free, but to download data for rainfall estimations. We will conclude the precipitation-related lecture today and move on to the other parameters in the next lecture. Thank you.