 Hello everyone. Welcome back to rural water resource management course. This is week one and lecture four. In the previous lectures we looked at why do you need to study rural water resource management. We looked at some components of a hydrological cycle just to give a brief introduction and then we looked into the composition of water availability of water, LPCD rates to show why and how water resource management are needed for rural India. Today we would look into more specifics on the hydrology cycle. We would first start with definition of it and then get into how you would like to use hydrology to understand water management. What is the hydrological cycle? How do you define it? The definitions can be simplistic or more in detail. In simple definition hydrology is the study of the movement of water. Very simple four or five words you can explain people what hydrology is. So we know water moves from high potential to low potential and then by force by pumping etc. To study this movement two different phases is called. The general subject is called hydrology and there are scientists and researchers who focus on particular aspects of the hydrology or hydrological cycle and that could be coined as a subsection hydrology. For example there is surface hydrology which means study of the movement of surface water. So how water comes from snow melt to rivers and then rivers to lakes dams and then oceans. So all of this would constitute surface hydrology. When there's a subsurface or soil moisture that part of the hydrology where water goes in and out of the soil and people look at it as subsurface flow those very focused studies are there. So I am a groundwater hydrologist wherein I focus more on groundwater. So how water from the surface goes into or from the surface or atmosphere goes into the earth and through infiltration and percolation and then how different compartments are filled and converts from one form to the other. So that is groundwater hydrology. So these are specific terms but there are also some interdisciplinary terms also. Let's look at some few. We have social hydrology and hydro sociology. So how hydrology impacts the sociology and those kind of aspects people will discuss about it. And you have a geohydrologist, a scientist who has some aspects of geology on groundwater those kind of things but mostly he or she is a hydrologist. So a person who studies hydrology is called a hydrologist and then the subsection wise also you could be labeled. For example, I'm labeled as a groundwater hydrologist and then there is a geohydrologist where a geo means geological terms and they study mostly well below the depth of groundwater which means like where magma flows, petroleum, those kind of studies. And then you have hydrogeologists. So if you see the word geohydrologist, hydrogeologist, it can be interchanged but when it's interchanged the dominant science comes at the back. So a geohydrologist is still a hydrologist. However, a hydrogeologist is mostly in the domain of geology, not hydrology. So you have this interdisciplinary also approach but in general it is called hydrology and then there is subsection, surface hydrology, soil moisture movement and then groundwater hydrology and then the people who work on it are called hydrologists. Let's get into some of the more technical terms of hydrology. Describes the continuous movement of water on above and below the surface of the earth USGS. This definition clearly tells that you study the continuous movement of water on above, so above the earth surface which is your lithography or on the top and then just below, just below the earth surface which is your groundwater hydrology. They don't go too much in the depth because that constitutes as I said a geologist. So the continuous movement of water, the interactions between water, all of this comes in the terms of hydrology because when it interacts it moves and then by movement also you can have more interactions, those kind of things. Let's take a definition from a dictionary. So some people would like to have a dictionary reference and I'm going to read it out because these are dictionary terms. The sequence of conditions through which water passes from vapor in the atmosphere through precipitation upon land or water surfaces and ultimately back into the atmosphere as a result of evaporation and transpiration called as hydrological cycle, medium dictionary. So each dictionary would give different terms and if you look at it here clearly, they look at water which comes from the atmosphere as precipitation it comes down and then goes into the rivers and lakes and oceans as surface hydrology and then goes back as evaporation because of evaporation, transpiration driven by the sun, it goes back into the atmosphere. So here there's no dimension of groundwater, there's no mention of storage because it is just a brief overall definition of hydrological cycle. That is why it is always very important to draw it out. When you draw a hydrological cycle, any physical cycle I would say, then you understand where the priorities are and how you could put more focus on different aspects of the hydrological cycle depending on your area. As I said, if in India in a rural region, all these places I would remove, frozen land basically and ice, snow and glaciers not much, we don't have an active volcanic steam so I can remove all this. So when you sit for and draw or discuss a hydrological cycle of a particular region, you should have good understanding of these factors and which are relevant and not relevant to your system. Most importantly, you can write it in very simpler terms as given by the dictionary which is precipitation. So you have precipitation as the input water cycle to the water cycle and then you have your surface flows which is your rivers, fresh lakes, oceans and then goes back into the atmosphere as evaporation and transpiration then comes back as precipitation so you close the loop. So this is how you relate to a definition of hydrological cycle, studying the movement and also target which ones are very important for your area. Suppose you cannot draw in detail, for example, you could not draw in detail the mountains, the slopes, I don't know how much comes in, you can still do pathways. So this is a pathway diagram or a flowchart kind of a diagram and you have to be clear on mentioning what is 1, 2, 3, which comes 1, 2, 3 first. So let's look at this, this is from the FAO, Food and Agriculture Organization. I would have a lot of references from FAO because many governments including government of India has a lot of recommendations taken from the FAO's booklet. FAO is an international organization like your WHO for health, for food and agriculture it is the FAO and they give a lot of research outputs recommendations where a lot of these governments are taking into action. So let's first look at the hydrological cycle representation from them. It's a very simplistic take, so which means you don't need to be very artistic to draw rivers, lakes, etc. But you could draw it as a simple arrow diagram. So here you have rain in that particular example from Shaxon, you have only rain, no snow. So the precipitation is coming in as rain and because of the slope, let me bring out the definitions. So direct evaporation from a dead leaf surface is the first one. So what happens is when rain happens, the first, the first before it touches the ground, so your slope is your ground, what does it touch? The rainfall falls on the leaf of the plants or trees and there is evaporation, not transpiration. Transpiration is when plant takes the water through the soil and then gives it off. We'll come to that later, you could see it here. What is evaporation? The leaf is a little bit warmer and then there's active sunlight, so when water comes and hits your leaf, it evaporates. So just evaporation, conversion of water into vapor. So that direct evaporation from a vetted leaf surface is the first because it interacts on your rain, the first. Then whatever rain remains would come down. That is why when you go to, when it rains, you stand under a tree because the leaves kind of shade you. Initially all the water would be falling on the leaf, it vets the surface and then there's evaporation. That's what this is telling. You might be amazed to see how much this vetted leaf evaporation is. Sometimes it might be tremendous, so that's why we still have to account for it. In some reasons, it may not be that important. For example, a coconut tree may not give you that much shade as a banyan tree. So you could neglect in a coconut tree because the leaf shape is like this, water falls and then it comes down, so it doesn't, it doesn't wet and evaporate. So those kind of things, analogies, as I said, you should have from your field experience. So the second dominant process becomes your slope, surface runoff, stream storm flow. So that is the land. Now the rainfall has hit the leaf and then come down into the land and then starts to flow as runoff. Runoff is a process where rainfall converts into a flow, surface flow. It can be storm flow, it can be rivers, those kinds of things is counted as surface runoff. So that is number two. Here the arrow size is the same. It doesn't mean the equally volume is equal. So please don't look at the arrows. In some diagrams, you will see a bigger arrow, which means more water goes into runoff. Here we're not doing that. We are only looking at the pathways. Then what happens? Number three is direct evaporation from the soil. So as the plant leaf or the tree leaf is warm and it evaporates, same way your soil can also evaporate. So if you look at it, the first drops on the road, the first drops on the soil can evaporate. That's why you have the smell of the soil comes. When rainfall occurs, you suddenly smell the wetted soil. That's because the some of it gets evaporated. So that evaporation happens. So that is number three. Now four, five, six is plant available soil moisture within the root range of existing weeds, crops, and trees. So for this area, the author has seen weeds. Weeds are grasses or crops that are not necessary, invasive, whatever it is. So it's not that necessary in a plot. Then you have crops and then you have trees. So the water after it goes to runoff, after the evaporation, water starts to slowly move down. When it moves down, the plants take it up and then transpire. So this is the difference between evaporation and transpiration. Evaporation is on the surface. The plant doesn't use it. It just evaporates. Transpiration is when the plant takes the water from the soil and then it pumps it to the shoot and then transpires. This breeds it out. So those are because of growth. As here clearly mentioned, because of the growth, four, five, six happens. And this one happens because of the slope. Because of the slope, you have runoffs. So let's move on. We have weeds, crops, and trees plant available soil moisture. So the water from the soil, which is from the rainfall, gets into the transpiration cycle. Let's go to eight, sorry, seven soil moisture within root range of existing plants, but held at tensions unavailable to them, which means in the soil, not all water can be taken up by the plant. So there is some tension because the soil also wants to hold on to the water and the plant can only exert some pressure to take the water out. If it is too much pressure, it cannot. It will wilt. So it would rather not take the water from the soil and some water is held in the soil. I wouldn't get into the soil physics because that is beyond the course. But just understand that if I give one liter of water to the soil, not all the water I can pump out, some water still remains in the soil. And that is what is happening here, number seven. So this is the one which contributes to the soil moisture and also to the properties of soil, depends on the properties of soil. Soil moisture held at all tensions, but below root depth of existing plants. So this is below the root depth. So seven and eight, what is the difference? It's just the depth. Seven is at the root zone. The plant cannot take the water, still remains. And then there is some water which moves still down. Why does water move down? Because of gravity. So gravity exerts and then it moves down in the column, soil column. And then at eight, it stays there. So you have water staying in the soil moisture at seven and eight, not being taken up. So number nine and 10, here is the groundwater dynamic. So if you see from the slope until the upper groundwater, it is purely soil water where plants can take it up, soil can take it up, and some stored in the soil. After that phase is done, water still moves down. So when it moves down, it goes into nine and 10. And nine is where the water which is not captured by the roots and the small pores in the soil, the small holes in the soil, moves downwards to the groundwater. And there are two types of groundwater. There is shallow groundwater and then there is deep. So number nine is shallow. That's why it stands here. And number 10 is your deep groundwater. It is interesting to see that some part of your nine, which is your shallow groundwater, goes back into the river as base flow or stream flow. So here it says moving to the groundwater and stream flow. So now you've seen that you're discussing about, when we discuss about hydrological cycle, we start from atmosphere, which is rain. Then we go to the ground and ground dynamic slope angle, etc. And then we look at warmth, the radiation, and then that driving the evaporation. And then you go to transpiration. So a lot of plant dynamics. And then you go down more further into the geological aspects. So where does this science stay? Is it a civil engineering topic? Is it a plant science topic? Let's look at it. So what is hydrological science? Someone asked you, a water resource management person can have multiple, multiple, as I said, it's interdisciplinary. So you can have sociology and hydrology together. Hydro economics is a topic. So all of this constitutes your water resource management. So to be a good water resource management, you need to understand the hydrology, but not alone the hydrology, but all these other sciences. Then what do you have? You have fluid mechanics. So some part of the engineering hydrology, where a lot of engineers are built. So what is the difference between hydrology as a science and hydrology as an engineer? Irological science is driven by physics and other laws, mathematics. Whereas engineering hydrology, a lot of engineering components would come in, construction, those kind of things. So hydrological science is right in between your fluid mechanics, the physics, the hydrological engineering, and the atmospheric sciences of metrology, oceanography, all those things. So it is a very, very interdisciplinary science. And as I said, where you want to apply defines your boundary. If you want to apply more in the groundwater, you become a groundwater hydrologist. If you want to be in the surface water, you'll be a surface water hydrologist. And if you just want to be a general, you know, everywhere I would like to contribute, you're a hydrologist. So same like a doctor, you're a general doctor, you can be a surgeon, you could be a diabetics specialist, pediatrics for children. So same thing, you have different doctors and very specific. So here, hydrological science is not a science by itself. It is a combination of different sciences, different engineering aspects. And what are they in the basic sciences, it includes mathematics, as I said, mathematics drives all the science without equations, without solving equations, it is very difficult. So math is mathematics driven physics, chemistry, biology, etc. Some people do a lot of statistics. But again, it depends on how you want to use your statistics. So please understand if you would like to use statistics, you understand the limitations and strengths of our statistics before jumping into applying it. So that's the basic sciences and the basic sciences are helping out or probing more the geosciences. The geosciences start with the geology. The geology would be your ground, the earth, composition, soil, etc. So it comes as soil science, atmospheric science, ocean science, glaciology, geochemistry. So what do you understand from this diagram? To be a water resource management person, we have to understand hydrology. And hydrology is not a one discipline. It is a combination of other engineering and science factors. And so it's very easy to understand. So that's what I've done. I'm a physics, by training physicist, masters, masters in physics, but then my PhD was in hydrology because such an easy transfer because a lot of physics is there, applied physics is there in hydrology. Hydrology, I would say, is an applied science, applied engineering. So think about those terms. So those who want to become a water resource person do not refrain saying that maybe I'm not an engineer, I'm not an engineer too, but you can still do good hydrology by understanding the science or mathematics part of it. Wherever you're strong, you could still contribute to the hydrology. This is from the Dingman book. So analysis of hydrological cycle. Now you've seen that, okay, there are different components of hydrological cycle and different pathways. But before that, you need to arrest a particular area. What would happen if you don't arrest a particular area? You don't have a boundary. So how do you know what crops? I told in the previous example, you have weeds, you have crops, entries. That is because my area of focus is having all these. So it is very, very important to first, foremost, determine your area of interest or area of research. So that is because the unit of analysis. Mostly it is the watershed. It's not a district. It is not a nation, not a continent. It is a watershed. Why? Because within the watershed, you have a clear demarcation of the rainfall pattern. You have a clear demarcation of flow, where the rainfall converts to runoff, and all the other parameters can be just within that unit. But where's the problem? The problem comes because the average land holding size in India is around 1.08 hectares, according to the agricultural census 2015. This is such a small area. So when you want to do rural water resource management, a watershed might be too big. I'll come into definitions of watershed, but as a unit, it can be too big. So there is a need for small scale understanding of hydrological phenomena. Small scale understanding means what are the priority pathways? What are the key variables in your system? So that is where you understand where in your particular area, small scale, small scale means smaller area. In your smaller area, what are the key hydrological drivers? Is it rainfall? Is it snow? Is it stream flow, groundwater, anything? So that is very important to understand. So first and foremost, fix your unit of analysis. If watershed is too big because your average land holding size in India is 1.08 hectares, then you have to go to the field and understand what is your analysis size. So that is what is very, very key for rural water management because I can sit in my office here and then say, I want to do a rural water resource assessment somewhere in Orissa. Without going there, how do I know what crops are growing? What are the trees? How much water do they consume? Someone can give me the data. That's fine. But it is fine if it is a bigger area. But if it is a very small scale, it is best to go there and understand what are the key factors. That is where the science is driven now. So the government hydrological parameters can change from rural scale to district size. So this is very important. If someone says, Nuno in Tamil Nadu, for example, the rainfall on the border of the Western Ghats is very, very high because the water rainfall comes from the Kerala side and there's a lot of Western Ghats deposition of rainfall. Does that mean entire Tamil Nadu gets the same rainfall? No. Not even half of it comes to the other region. So it's very, very dry in the center of Tamil Nadu and along the coast of Chennai and other things is semi-arid, which is around 600 to 700 millimeters. Whereas along the Western Ghats, along the Kerala border, it is around 2000. So you see how different it is. So your unit of analysis is very important because your rainfall is the key parameter into the system. So therefore, it is important to understand the key drivers and monitoring is important. For a larger-scale size project, it is okay to escape with the data you get. But for a smaller scale, it is very, very important because the drivers may be different. So with this, I would like to conclude and stress on the fact that it is best to have a field level understanding of the rural drivers. What are the key crops? When do they grow? How much water do they consume? When you want to discuss the hydrological cycle? If you do not do this, what would happen is everything is assumed or estimated as an assumption, which would derail your understanding of the hydrology. The very, very small components, very small rainfall would be in a plot. If it is a district, okay, some of the rainfall can be converted to groundwater. So there is give and take. You can lose here, give there, etc. It's fine. So we call it as a noise, which is smooth talk. But in a small, small size, it is very, very difficult to let go of these exchanges. So you have to understand what are the key exchanges and document it. After you document it, you do a flow chart of how we did in class today, slide 3, 4, etc. So you write it down. This is the key products. And then you stop there. Then you put the volume of water coming. All this we would be discussing in the future classes. Thank you.