[00:00:00] Bridget Scanlon: Welcome to the Water Resources Podcast. I am Bridget Scanlon. In this podcast, we discuss water challenges with leading experts, including topics on extreme climate events, over exploitation, and potential solutions towards more sustainable management. I am delighted to welcome Abhijit Mukherjee to the Water Resources Podcast today.
Abhijit is a professor at the Indian Institute of Technology in Kharagpur, close to the city of Kolkata, formerly Calcutta, in eastern India. Abhijit has received numerous awards over his career and will be receiving the prestigious Devendra Lal Memorial Medal at American Geophysical Union meeting this fall for outstanding research in earth sciences.
Abhijit and I have known each other for a couple of decades now since he was a postdoc in our group in the mid-2000s. And we worked together on a book titled Global Groundwater. So welcome to the podcast, Abhijit, and I really appreciate your taking the time. Thanks
[00:01:07] Abhijit Mukherjee: Thanks.
[00:01:12] Bridget Scanlon: It's a number of different topics ranging from water scarcity in India, the role of groundwater, food security and poverty alleviation, and then some comparisons between India and Sub Saharan Africa. Abhijit has done a lot of work on water quality issues, and then try to discuss some potential solutions towards more sustainable groundwater management.
So, Abhijit, first, maybe let's talk about water scarcity concerns in India. You have an estimated 18 percent of the global population, 1.4 billion people, similar to China and Africa, but only about 4 percent of the estimated water resources. Irrigation, as always, is the elephant in the room, the dominant water consumer and has been since the Green Revolution in the 70s.
But then you have been able to develop food security in India and a lot of people have moved out of severe poverty. And so that has been a help. So can you describe a little bit about how irrigation has evolved with the green revolution in India.
[00:02:20] Abhijit Mukherjee: Yeah, so at present, India is considered to be the most intensive groundwater using countries in the world. And the estimate was like about 240 billion cubic meters of water, groundwater is consumed every year. So the idea is that once India got its independence back in 1947, our forefathers tried to kind of framework, frame ideas and policies that would kind of make people self-sufficient in terms of food.
Now, those days, the food production in India was mostly dependent on canals, the canals that were constructed during the, the colonial period, the past 200 years. And accordingly, like irrigation, and cultivation was only possible in and around the canals, not in the lands far from the canals.
So in the 1960s, late 1960s, early 1970s, the planners and the policy makers, they realized that with an exponentially growing population, you need sufficient water supply for food production. So till then, like India was a food deficient country. They were importing food from various parts of the world, like Mexico, like US, Africa, and so on.
And the population was growing, growing quite fast. So in the late 1960s, the policy, both the policy as well as scientific advancement, led to drilling of groundwater wells all across the country, and subsequently using those wells as the source of water for irrigation, mostly in northern India, but also in other parts of India.
So subsequently, by the turn of 1990s, just in 20 years, those number of 25 million wells, and at present, I don't think there is a number counted. It's definitely more than 25 million. So, what happened is, within these, like, 50, 60 years, groundwater, which was kind of very less exploited before the 1960s, became the prime commodity for food production, like a primary source for food production.
And since India being a more equatorial or tropical country, much of the food production is related to rice production, which is typically known to be pretty water intensive crop. And back in the 1990s, there were some more water intensive, high yielding rice varieties were introduced, which would need more water to survive and to grow.
So consequently, what happened, the groundwater usage increased without any bound, and consequently, what we see today, back from 2010 onwards, through the GRACE satellite mission and the groundwater monitoring that the government of India started, that groundwater has declined at an unforeseen rate, possibly one of the highest rates in the world. And consequently, many of the places, many of the parts of India, specifically in other parts of India, which are trailed by the big rivers like the Indus, the Ganges and the Brahmaputra, they are actually drying out in terms of groundwater. So as the cultivation and irrigation dependent cultivation has been progressing, which made India a food sufficient country, pretty much, Northern India has now become the big basket of Asia, but with the cost, the cost of groundwater.
[00:05:54] Bridget Scanlon: Right. Well, thanks for describing that. I mean, it has been a long road. And so initially under the British rule, you had the canal irrigation systems and heavy reliance on that. But then with the expansion of groundwater use, then people were able to access groundwater anywhere. And so that expanded the crop cultivation, and made it more food secure. So that's really interesting. And I think a recent World Bank report mentioned that maybe 50 percent of urban dwellers in India rely on groundwater, 80 percent of the rural population rely on groundwater for domestic use, and then irrigation accounts for about 65 percent of groundwater use.
So, in India, you have a lot of different aquifer systems throughout the country. And I think that's very important to recognize that and acknowledge that. And you spend a lot of your time working on geology or hydrogeology. Maybe you can describe the different aquifer systems of India.
[00:06:56] Abhijit Mukherjee: Right. So, India is a pretty diverse country.
I mean, Yeah. Maybe it's not as extensive or something like some of the bigger countries in the world, but in terms of the geology, it is pretty diverse. So in the northern part of the country, we have the Himalayas, which marks the northern edge, but to the south of the Himalayas, we have what we call the northern Indian plains. And these plains are actually developed because of alluvial deposits from the Himalayan rivers, the mega rivers. So we have some of the largest river systems in the world just draining through these northern Indian plains. And this includes the Indus, the Ganges, the Brahmaputra, and of course their tributaries.
And these rivers have brought down humongous volumes of sediments over the last few million years and have filled up this North Indian Plain to make one of the most fertile aquifer systems in the world and most extensive aquifer system in the world. Now, if you go south of that, we have these really ancient rocks, what we call the Precambrian rocks.
And these Precambrian rocks and, the subsequent crystalline rocks, these actually make up the bulk of India, what we call the peninsular India. And these crystalline rocks, which vary from granite to metamorphics, at some places they have a lot of fractures and discontinuities, but in other places they are very crystalline.
So consequently, as far as the estimate goes, that the North Indian Plains occupies about 27 percent of the Indian landmass, but it holds almost 70 percent of the groundwater locked into it. Whereas the rest of the coastal aquifers, which makes the most of the rest of India, is about like 70 percent of the landmass, but just have only 30 percent of the groundwater share.
So it's a very polarized system. Consequently, over the years, it's from the Indus Valley, which is like 5,000 years or more, most of the civilization actually prospered in these North Indian Plains. And historically, this is the cradle of human civilization in some sense.
And you have all these ancient civilizations that grew in the North Indian Plains of the Indus, the Ganges. And even today, if you look at the population of India, more than 50 percent of Indian population is actually clustered.
[00:09:29] Bridget Scanlon: Right. So that's really important to recognize the differences then in these groundwater systems across India.
So very thick aquifer systems in the north with the sediments coming off the Himalayas. So these are up to several kilometers thick.
[00:09:42] Abhijit Mukherjee: Yeah, the usable groundwater is up to about even take 500 meters. We know that the quality deteriorates.
[00:09:50] Bridget Scanlon: Okay, right. So you have about 500 meters of thick groundwater in that region, but then in the basement rocks in peninsular India, then much thinner aquifers, maybe 50 meters.
[00:10:02] Abhijit Mukherjee:Even less, even less. Yeah. So you have basement regolith aquifers, which are no more than 10 meters thick, below which you will have the more crystalline aquifers. Which will be pretty much dependent on the fracture systems, connected fracture systems. So they can vary somewhere from 50 meters to 100 meters, maybe.
[00:10:21] Bridget Scanlon: Right, right. And I think we see a parallel in Africa with the very thick aquifers in the north, the Nubian aquifer and these other aquifer systems in the north Africa. But then basement aquifers that Alan MacDonald suggested were about 40 percent of the landmass. But thin aquifers and regoliths, like you mentioned, from erosion of those crystalline basement rocks, and then the fracture system, which really depends on finding those fractures and having a productive well. So that's a bit more difficult to accomplish. But so understanding the geology is critical then to managing the resource. And you mentioned earlier Abhijit that you've been able to greatly reduce poverty in India and a recent report on the multi dimensional poverty index indicates that about 400 million people have moved out of extreme poverty between 2005 and 2019.
So having their global multi poverty index in 15 years. And so that's really great, that food security that you get with irrigation and everything and helping alleviate poverty. But as you say, it's a trade off at the expense of water. And so, I mean, how do you see this evolving at current times? It's very important to have food security, but how can we manage the water?
[00:11:48] Abhijit Mukherjee: Yeah, well, it's a kind of a double edged sword. And you go for food security. And if you don't have any other water sources, which is the case here, you heavily rely on the groundwater. Now, there is one thing that I should mention here that it's not true everywhere where they're having irrigated cultivation, you have just food production for food purpose or domestic purposes.
Much of the places would have actually cultivation for food that they're going as cash crop. So you The cash crop, I mean the food itself, but it's getting exported to other places, possibly to other countries, would actually emit a huge water footprint, groundwater footprint. So if you look at some of Dalin's calculations, India is one of the largest groundwater exporters in the world.
And this water, this groundwater actually comes from much of these northern parts of India, where we already mentioned about that the groundwater Is depleting at an alarming rate. So it's a balance between the food, the water and the poverty and the livelihood. So, the way I look at it, if you are trying to address the sustainable development goals (SDGs), literally, like, groundwater in India, at least, and possibly in other parts of the world, too, is actually linked to all the 17 SDGs, just not SDG number six.
But it's very obvious what the food production, the poverty alleviation, the gender gap, the education, the well being, and so on. And you can literally see all of this in a microcosm in India. Right.
[00:13:27] Bridget Scanlon: And that's very important, I think, to point out the linkage, how groundwater goes across many of the 17 sustainability development goals.
And we think about water security, but then that's linked to food security. And then there's a gender issue because oftentimes women are required to fetch water. And if that takes them a long time, then they can't get educated. And so if we can address the water issues, then that will help with many of these other sustainability development goals.
So a lot of people are looking at India and seeing how they have gotten food security and improved the poverty situation. And then I was just recently talking with Jude Cobbing, who suggested that in Sub Saharan Africa, they have water resources, but a reluctance to develop them in case it would become unsustainable.
But there are a lot of parallels, I think, between India and Africa. And so what can Sub Saharan Africa learn from India, and how can they improve their situation in Sub Saharan Africa?
[00:14:38] Abhijit Mukherjee: Well, like you said, Africa also has these heterogeneities in terms of the aquifers, right? So if you are looking at the crystalline aquifers, there is not much that you can do in a natural sense because you get the groundwater where the fractures are and you would not know that upfront.
In contrast to Africa, what we have in India is this huge population load. Like we are at present like 1.4 billion, the most populous country in the world. And predictions are that up to 2060, the population is going to almost double possibly. So you have this huge population. You have a very limited landmass where people can stay because most places are kind of inhabited anyway.
So there are very little opportunities for further development, at least for the horizontal development. So what people are doing, specifically in the northern parts of India, they are going for drilling deep, going deep and trying to get more water. More groundwater. Now what that has happened, and that has been a trend in many places of the country.
But what that has done is literally made this deep groundwater, which are literally fossil groundwater, possibly just thousands to millions of years age, potentially depleting at a faster rate than the shallower ones. Because shallower ones still have a chance to get rejuvenated through, through the seasonal rainfall or through other unintended artificial means, but this deep groundwater, which is literally disconnected from the surface, once that is depleted, you'd have no way to go back to it.
So what possibly Africa can learn and again, population is possibly the single most standing point within this. Africa population is nowhere close to what we have in India, but as the population grows, also in Africa, it is very important that the groundwater and the surface water are treated as a like a conjunctive source. And treated us pretty much as one water and this governance needs to be placed from day one in India to my understanding. The only planners did not understand this conviction by the time they did, it was, I would not say it's too late, but it's quite late.
Definitely one of the more groundwater starving countries in the world, at least in the time to come.
[00:17:09] Bridget Scanlon: Right. You bring up an excellent point, Abhijit, is considering surface water and groundwater as one resource, acknowledging the interconnection between the two. And I think very few places globally have governance regulations that regulate them as one unit.
And so understanding those linkages is extremely important. So currently I think in Sub Saharan Africa, Northern Africa is like Northern India. They have thick, deep aquifers and they're exploiting fossil groundwater that was recharged millions of years ago. So that is a similar situation. But Sub Saharan Africa, with a lot of basement, crystalline basement, these are thin aquifers, shallow aquifers, crystalline, when they go after the fractures, they can go deeper. So they could manage that those are recharged. Like you say, the shallow system is recharged more on a regular basis. So they could possibly use that. But as some people point out, and Jude Cobbing points out, that there are many issues, not just the groundwater resource, but also economic issues, cost of pumps, entrepreneurial spirit, market for their crops, and all that, which I think is much more advanced in India. And you have a much more developed trade system and things like that, that has encouraged crop production. Maybe you can speak to that just a little bit.
[00:18:35] Abhijit Mukherjee: Sure. Well, so the first thing I'd like to emphasize here is again, the population. Again, I cannot remember from the top of my head, what the density in sub Saharan Africa, but if you look at Northern India, the density can go as high as 2000 people per square kilometers, that's the densest in the world.
Water supply for that such a dense population, you need to actually produce a lot of groundwater because surface water is limited. And one more thing is from some of our study, and we can talk about this later that the surface water is also dependent on groundwater in some way or other.
And if you are taking out groundwater, you're literally also taking out surface water and vice versa. So consequently what has happened is, yes, like possibly there are more advanced technologies. The economic power is much higher. There is economic growth in many industries that India is becoming a like economic powerhouse in the world.
Again, that came with a resource. Cost and one of the resource that has been kind of understated is actually groundwater until just about 10 years back. There are barely people talking about groundwater until, some seminal papers came out and the government also realized that something wrong is happening. So it is just in the last 10 years or so, a little more than 10 years that people have been trying to talk about groundwater and how to manage the groundwater. So what they have done in last six, seven years, they are putting in a governance strategy where all the water resources under one ministry. So that way you can go on the surface water, the groundwater, the drinking water under one umbrella.
Now, how much that has been effective. That's something only future can say, but that means the idea is coming in place and hopefully it will see some good things in the future. One more thing that I should mention here from an Indian context in this developing and so the power situation is so there are more power stations that are coming up, hydropower, thermal powers, and some nuclear power, nuclear power is less, but then solar power. So India is one of the leading fields in terms of solar power generation at present times. So the global solar power alliance, India is kind of leading. Now, when the solar power is kind of leading to grids, possibly you have some control.
But then if you send the same technology to the local farmers, then you just lose the control. And if you have free electricity, you can do anything with your pump, which is free. So it is kind of again, like a toxicituation when you want to bring people out of poverty, you want to impact them, of course, give them livelihood and so on. So you make the electricity free, but that again, on a different note, is going to cost the groundwater resource.
[00:21:41] Bridget Scanlon: Right. And many people have talked about that India provided free electricity to the farmers and that promoted overexploitation of the resources. So that was an important concept. So, one other thing you mentioned groundwater and surface water being one resource and I was talking with Shamsudduha or Shams about the Bengal Water Machine recently. In the mid-70s, some people introduced the concept of the Ganges Water Machine and how that might help with the water management. Can you describe that a little bit? Sure. And you commented recently on its potential in India. So that would be great.
[00:22:24] Abhijit Mukherjee: Right. So the concept of Ganges Water Machine possibly had a role as a piece of a theoretical sense in kind of bringing in the green revolution in India.
So the idea is that on this North Indian Plains, the Indus, the Ganges, the Brahmaputra, the flood plains, they have enormous thickness of sediments. And the idea in this Ganges water machine was that these aquifers are to begin with saturated at time zero, it's saturated, and as the summer progresses, you desaturate it, you take out the water for your agricultural purposes, but then you have a heavy monsoon coming up, and this monsoon should be able to fill up the aquifers back to its original level.
So, you are basically using the subsurface as a transient groundwater repository. Now, in case that does not happen, you go for augmentation, you go for artificial recharge. But at the end of the day, you are again back to saturation level, and you are not losing anything. The net loss, in terms of the groundwater level zero, is zero.
Now, the whole hypothesis, while it sounds quite exciting and interesting, it kind of has some inherent assumptions. And one of those assumptions is that you do need to have a homogeneous system. A homogeneous system where there is seamless flow of water between the groundwater system and the surface water system and the irrigation system.
While the reality is that most of the places it's pretty heterogeneous. So the Ganges Water Machine in theory possibly works, but from my own experience and some of the people that I've worked with, it has a lot of inherent problems. Specifically the geological, the hydrogeological problem. Now you mentioned about Shams paper and Shams a very good friend of mine.
We work together quite often. So through Shams work and my previous work, like when I was working with you actually, so we kind of demonstrated numerically that it's a possibility. It's a possibility in places where you have a sediment, a continuous sand aquifer. So like a thick sand aquifer without much barrier. So it is going to work there, but in other places where you have intervening aquicludes or confining layers, that would be a challenge. And it is not going to be just a challenge in terms of restarting the method system. But even if you are going for augmentation and artificial research, because in some places, it's confined, you have to be 50 meters to 60 meters thick clay, there is no way in a human timescale that you are going to bypass that. So in those places, this concept might not be a practical thing to work on.
[00:25:12] Bridget Scanlon: So you bring up some important aspects to that. The Ganges Water Machine or the Bengal Water Machine, I mean, the basic concept is very interesting that the more you use the groundwater during the dry season for irrigation, the more space you create in the subsurface for the following monsoon, which can recharge that groundwater and then replenish it.
And so you can even it out, but that relies on a homogeneous subsurface geology, like a uniform sand type of aquifer, then that would allow that water, that monsoon water to replenish the system. And so you continue the cycle. But the subsurface is very heterogeneous, and so you have clay layers that could prevent subsurface recharge and things like that.
And so I think this gets at the idea, the UN has “Groundwater: Making the Invisible Visible, and Rosemary Knight has been doing a lot of airborne electromagnetics to try to map the subsurface geology so we can understand the potential to either artificially recharge or to have incidental recharge from surface irrigation practices or these sorts of things.
So I think we have a long ways to go. And so you underscored the importance of understanding the geology of the system to see what's possible and what's not possible. Yeah,
[00:26:36] Abhijit Mukherjee: Yeah, maybe I'll just add one point to this. So that's an excellent summary of what I tried to say. Now, what the government of India did, and this is from back from 2008, to my understanding. And like many other countries, they have started something called National Aquifer Mapping Mission. And since 2008, using Heliborne geophysics, surface geophysics, as well as drilling, they have tried to map the aquifers of the country. Now, I'm not saying that it is complete, or we know what is the status everywhere. But at least in many places, they did a real good job and had a lot of data. Maybe not in public domain, but they do have a lot of data, which they have accrued, which possibly would give a lot of information on the subsurface. So my understanding, they have drilled at least a few tens of thousands of observatory wells.
And again, like they had six geologic and geomorphic terrains, where they tried to explore the effectiveness of the heliborne geophysics. And they got mixed results. In some places they worked very well, some places did not. So yes, it's a long way to go, but there are efforts already in place where data are being collected.
[00:27:53] Bridget Scanlon: Right. I think that's similar to the airborne electromagnetic program in California where they're trying to map these aquifers and see how feasible it is to recharge and replenish the depleted aquifers. And when you mentioned Heliborne systems, so basically geophysical systems in on helicopters to, to map the subsurface. And so geophysics provides the eyes then to try to map the heterogeneity that's in the system. And so, and then ground-based geophysics is another great tool and then ground truthing that with the borehole data. So a comprehensive approach, and I think that's a great way to move in that direction so that we understand the systems better.
So you mentioned earlier that the GRACE satellite data in the late 2000s, Matt Rodell's work in 2009 made people realize that the degree of groundwater overexploitation. And that was a great visual that people could understand that satellites were showing how much groundwater had been depleted since the GRACE mission began in 2002.
And I think more recently than McAllister and others and Alan MacDonald at the British Geological Survey have looked at a much longer record of the development of the canals over the last 100 and the development of the tube wells. And they suggested that there was an overall increase in groundwater storage of about 450 cubic kilometers or billion cubic meters, like you mentioned earlier. That's similar to 450 million acre feet for US listeners. And then only in the decade that they were reporting on, between 2000 and 2010, did they see about a hundred cubic kilometers decline in storage. So, So that would suggest that there's a net increase in storage over that entire time period? So have you seen data to support that
[00:29:57] Abhijit Mukherjee: Well, honestly, like I didn't get a chance to look through the data that I did look through the paper and they heavily dependent on some published reports, specifically two reports that are possibly in the US archive on which they based their observations.
Now, I don't say that that's not possible, I'm supposing it's highly possible. Now, here is one thing that you have to realize here. That unlike many other parts of the world, the Indian subcontinent is highly influenced by a tropical climatic system, which is the monsoon. And the idea is that when the monsoon comes, at least the shallow aquifers, they will get recharged up to the surface.
Basically, they're not necessarily flat. But to be fully saturated and it's still visible, like it still happens in many parts of the country. So when you say that you have these leakages from the camels, which is highly possible and possibly did take place. Now, where was the space? Because if you have this multilayered system kind of replenishing aquifers years after years for millions of years, where is the space? Because the groundwater possibly was already close to the surface. Or very near to the surface. Now, of course, in places and specifically in places where they did the study, which is the more arid areas like the desert areas. Yeah, I can imagine that there will be more subsurface space where groundwater could have built up.
But in other parts, more wetter or humid parts of the country, I would have a pinch of salt to understand where the space would be. If you were to first create the space to put in more water. Sure. Again, like not seeing the data and not fully understanding what the process was. Maybe I'm not in a very good position to comment on what might have happened.
But what did happen since the 1960s and until the 1990s when documentation started, because from 1960s to 1990s, there was not a lot of monitoring for groundwater. And before that, since people were not using groundwater, why would anybody monitor it? So when the monitoring started back in 1984 or 85, They already started seeing some depletion trends, but of course, people did not realize because.
And like you said, so the materials work that was possibly one of the first time that they could see an aggregated visual interpretation of what this depletion might be taking place in a larger system or larger space. And that is when people realize that, yes, these have a far reaching implication and it is just not like a point that is depleting, but it's the whole space and the three dimensions that is getting depleted.
So wherever we started, so assuming like the aquifer was in a full situation, which is the case in much of Northern Indian Plains. So the groundwater has depleted somewhere in some places up to 30 meters to some places up to 50 meters and that has been observed in all reports and all data sources.
[00:33:10] Bridget Scanlon: Right. So you mentioned an important point. I mean, if we want to have recharge, increased recharge, we need a reservoir in the subsurface and depleted aquifers can provide that reservoir now. So we depleted them like the Central Valley in California and now we can try to replenish them and we have space in the subsurface.
And sometimes that space is much greater than surface reservoir storage. So you need space to accommodate the increased recharge. So I'd like to shift a little bit, Abhijit, we've talked a lot about water quantity issues and water scarcity, food production and stuff. But I would like to shift to water quality because I know you've spent a lot of your career focusing on water quality issues.
And maybe you can describe a little bit your early work on arsenic issues in India. and then we can talk about some other water quality aspects.
[00:34:10] Abhijit Mukherjee: So unlike the water scarcity, the groundwater scarcity, the water quality issue was known in the 1980s.
And people, specifically in parts of eastern India, actually the state I come from, West Bengal, they saw signatures of arsenicosis. That's a disease that happens when you drink water which is polluted by elevated concentrations of arsenic. Actually, being a natural element that is present and can cycle to the groundwater.
So since 1980s, 1984 to be more precise, people did understand that the groundwater, at least in the Bengal area was polluted with arsenic. Eventually, that pollution was also detected in Bangladesh in a very, in a very extensive way. And other parts of the Ganges aquifers, the Gangetic aquifers, the Indus aquifers, and the Brahmaputra river aquifers.
At one time back in 2001, there was a World Bank publication by Smith, Alan Smith, where he quoted the problem of this pollution as the largest mass poisoning in human history, which is possibly a very correct statement because by then almost 250 million people were exposed to the risk of arsenic poisoning by natural means. So when I started my study during my PhD times with my professor Alan Fryer and then subsequently with you, what I tried to do was to look at a geologic angle to it, like a hydrogeologic and geologic angle to it. So what I tried to do is try to find out not only the the distribution of the arsenic in the subsurface in the Bengal area and its upstream areas but also try to understand what might be the geologic control because till then most of the research was done by people who are mostly from chemistry background like geochemists and so on who are very heavily dependent on geochemical processes and how they might be influenced by other geochemical means and biogeochemical means. So there was not a lot of information that was available on aquifer structures, groundwater flow, and how that might be modulating. And by then, there was a very popular hypothesis that arsenic is a very shallow aquifer stream, and you don't encounter polluted groundwater below a depth of 80 to 100 meters.
So when that happened, what that made in practice is that the government decided that, okay, if the shallow groundwater is polluted, let's go deep. And consequently, since the 1990s, early 2000s, the government of India, like the state governments, as well as government of Bangladesh, to my knowledge, they drilled a lot of very deep drinking water wells, like 200, 300 meters, which is quite deep in a sense that you do have groundwater available at a depth of five meters.
The simple reason was the hypothesis being that arsenic-free water exists below a depth of 80 meters. Now, that observation was made by the early workers based on certain geochemical parameters. So, when I started my studies during the early 2000s, so that was my kind of hard work is to figure out whether the deep groundwater is a safe drinking water source or not.
So, what I found out through that study is that arsenic exists even in the deep aquifers. In some places, they were detected up to a depth of 300 to 350 meters, and people are literally drinking that polluted water in many places when that is true in some other places that may not be the case and the groundwater was actually less polluted in the deeper horizons.
And what I was able to find out that this difference between whether that will be polluted or not depends pretty much on on the aquifer structure. What is the framework of the aquifer? And depending whether it's like a continuous aquifer system that will form in the upper part of the delta versus more sites where you have multi-layer system, you have the distribution of arsenic kind of regulated by that and the regional groundwater flow systems.
So what I was able to do was to kind of map out the areas which might have still got some safe drinking water sources in the deeper horizons in contrast to areas where you might not. Subsequently, through one of my very recently graduated students, I expanded that study to up to Bangladesh, in the major parts of Bangladesh, so the whole Ganges Delta.
And we kind of mapped out those safe aquifers versus non safe aquifers across the transboundary system.
[00:39:03] Bridget Scanlon: Right. So that's extremely interesting, Abhijit. It's interesting to consider that they shifted from surface water use initially to avoid all the contamination in the surface water bodies and all the bacterial contamination and the health issues related to that to groundwater.
And it took them a while to figure out that the groundwater had natural arsenic in it from a geologic source. And then, as you said, the initial hypothesis was that only the shallow groundwater had elevated arsenic and the deeper groundwater was safe, but then your more in-depth analysis then showed where that was not always the case.
And are you suggesting then that in regions where you had multi-layer aquifer systems that you're more likely to have good quality, deeper groundwater than in systems that are more homogeneous,
[00:39:54] Abhijit Mukherjee: Yeah, absolutely. so what I tried to do through my studies, I tried to create this mask, three dimensional maps to show like where you can still have good quality groundwater, even in the mid level to deeper aquifers, however, there is a catch.
The catch is that you have to make sure that you don't over exploit that intermediate to deep aquifers, because if you do so, you can have cross formational flows or you can have leakage, like, well bore leakage, and you can, again, have create a possibility where you cross contaminate that deep aquifer down the road.
So we did some mathematical analysis and subsequently one of our collaborators did some studies, like isotope studies to show that on a well that can be in one of these aquifers and are safe from arsenic when they were constructed, they can actually get polluted even at a depth of 150 meters, within just a time frame of 5 to 30 years of construction. So with all the pumping going on in the surrounding, you cannot really bet on the groundwater, unless you make sure that you use the water from that day, only for drinking water purposes.
[00:41:11] Bridget Scanlon: Right.. So basically to limit irrigation then to the shallow system, because that is of course always the elephant in the room and consuming the most water, and then limit groundwater for drinking use then to the deeper system.
And so try to protect that so that if you extract a lot of groundwater from the deep system, then that will promote water from the shallow system to move into the deep system and bring the arsenic with it. So that was an important concept and help with understanding and managing the issue to some extent.
So we've talked about quantity and quality issues. And then it would be nice to talk about how you think that they can move towards more sustainable management in India. And I know the World Bank has a program. I'm not sure if I pronounced it correctly at all. Atal Bhujal Yojana or something like that, where they, it seems over multiple states that they are providing up to 420 million was what I could read in a thousand systems so that the communities would manage the system and promote that.
And so that they would understand the system. And I think that's really promising so that the local communities can understand what the resource is, the dynamics of it, and what they can extract sustainably. Maybe you can describe that program a little better.
[00:42:36] Abhijit Mukherjee: So this is a Sanskrit word. It started about seven, eight years back (2019). The whole idea is to govern the groundwater and even the surface water in a better way. Now, when you say that, and like we have been saying it, that we have to consider this as one water system, and it's just on the groundwater, but also the surface water and just on the quantity, but also the quality.
So, along with the Atal Bhujal Yojana mission, there's also another mission that has started, which is called the Jal Jeevan mission, which is basically Water for life. And these two missions or these two policies are kind of going hand in hand, with what they're trying to do, first of all, is try to find out the quantity of groundwater that is available, or might be available, and then how to protect it, how to govern it, possibly how to augment it.
And then out of that groundwater, how much is usable? Because we talked about arsenic, but then there are other geogenic and human force pollutions that are also available. Besides arsenic, you also have a lot of fluoride in the groundwater. Many of the places, you have salinity problems. And, microbial, like sanitation, soil microbes are the only present thing.
So, taking everything together, what is a net safe, sustainable groundwater? That would be available on water. I would say that would be available to the people. So what I've been doing when I get to work with the government of India officials intermittently, I try to promote this understanding of the availability of net water, just not the whole water, because at the end of the day, when you are supplying that water to the people, that water needs to be safe going by every statistics of the day, like there is almost like 50 percent or even more parts of India. I mean, it's a continent. I would say they don't have access to clean water, right? For domestic purposes, mostly for drinking water purposes. So it is very important to understand not just the quality of the groundwater, but also the safety of the water.
So through this, they are trying to go for a governance of groundwater in a village level scale, like coming down from the top level, like a state level to the village level scale and involving the local stakeholders, like local communities and so on. To manage it. Now, while these are all very promising ideas, the devil lies in the details.
I mean, many of the places what is happening is the scientific acumen is not fully recognized, and many of the things are more governed by economic realities, I would say. Consequently, what is happening, many of the good things that could have been done are getting bypassed or short circuited, literally ruining the groundwater systems forever.
So what I've been trying to do in my own capacity is to sensitize that. The top policymakers that look when you were trying to do something which is in all good faith. If I'm good, but you have to implement that in a proper way. And you literally have to have like a scientific basis of what you're doing.
I'm going to do that. You are going to basically destroy a resource that is irrecoverable. You cannot go back to the resource. You cannot really pump a few billion cubic meters of water to give it to the people. So. What is done is done. But whatever water is still available, what is safe is still available.
You must use it extremely judiciously, plan it judiciously, go on it for a future time. Right. Just like to give you an example of the numbers. We did a health risk study two years back just from the arsenic. We calculated that just out of India, we have about 270 million people who would be exposed to arsenic in this groundwater.
Now, I'm not saying that all 270 million people are suffering from poisoning, but who knows, like maybe a large number and it's undocumented. These 270 million people are actually drinking arsenic laden groundwater in some sense or other. So it's very important to manage and govern it in a very scientific, appropriate way.
[00:46:56] Bridget Scanlon: So, so on a promising note, Abhijit, some of your students have looked at GRACE data in peninsular India. and a noted rejuvenation of some of the aquifers in the peninsular parts of India. And that's, and I was just looking at the GRACE data recently. And so I see continued increases in water storage in peninsular India.
And you attribute some of that to digging of ponds and government program. Maybe you can describe that a little bit for us.
[00:47:28] Abhijit Mukherjee: Right, so this is through the work of one of my former students, who is now in one of the labs in the US and working with Matt Rodell team in NASA. We were trying to get a more updated estimate of the groundwork reserve in India.
And while doing so, we did realize that while everybody was talking about all this depletion all across the country, but then we found out that that is, well, that is true and it's very strong in some parts of the country, specifically the northern Indian plains. Maybe there is a more promising picture that is something that we got to see in the southern parts of the country, some parts of the southern parts of the country. And there we saw maybe, I am not saying it's negligible, but at least there is a reversal of trend. From depletion to rejuvenation, and we did see that quite widespread. It's not just one village or one state, but in several of the states that has been taking place in the last 20 years or so. Not 20 years, but more like 15, 16 years now.
People have tried to explain that in many ways. I know there are a lot of contention on that. Some people say that the pattern has changed. Some people say, well, the data are not correct and so on. But we try to verify that through multiple data sources, including satellite-based data, the ground based data, the state level data collections and so on, and we kind of came to the conclusion that yes, there are irregularities in the data, but by and large, there are rejuvenation that are happening. Now, the question was, how is that happening then? Because you still have all this cultivation, like irrigation for cultivation going on.
And then we realized that, and this is where I think the SDGs get connected, that back in the early 2000s or late 1990s. There are certain social employment schemes that were deployed for the very poor people, the poor people in the villages. And the idea was that the villages will be given a mandated 100 days of minimum work in a year, and that's kind of secured from the government side. So you have at least 100 days that you would be working. But then there was not much work because these are all unskilled laborers. So what both the state and the central government did is they made these people to dig ponds because possibly that would on an immediate note would act as a like a reservoir for rainwater and that rainwater can be used for multiple purposes.
And that would also give this 100 days’ work kind of secured. Now, what happened and what we think happened is that when that was kind of intended more for water reservoir or just giving employment to those people. These points also acted as more focused drought related structures. In many places, we believe that this unintended application and going for digging ponds actually helped to rejuvenate the groundwater in the locality.
Now. So since our study got published back in 2017, there was a lot of interest in various policy makers. And since 2017, a major chunk of the money that is used for this special employment scheme, which is a pretty big amount actually has been actually diverted for digging ponds now intended for rejuvenating the groundwater.
Well, this is again like a possible story for many of the places in some other states we observe, which are more the western states, we observe that the groundwater rejuvenation is possibly linked with some rationing of the electricity. So, like I said earlier, so electric current is free for agricultural purposes in many parts of India.
So, in some of the states, they started rationing it, not, giving the free electricity or giving the free electricity, but only for limited time periods. Now, that potentially helped to kind of back up the groundwater in those areas.
[00:51:34] Bridget Scanlon: Right. Very, very interesting. And we are trying to replenish a lot of aquifer systems in Central Valley and other regions and to have aquifer storage and recovery.
So it's really nice to see that it seemed like this had a regional impact. And as you say, there's a lot of controversy about it. Some people may not agree and others, but so, but you see it in the GRACE satellite data and it seems to be fairly widespread. And if that's the case, then that's a really a positive note.
So our guest today is Professor Abhijit Mukherjee from Indian Institute of Technology, and he's given us a great overview of many of the water issues in India, including the water quantity issues and emphasizing the importance of the understanding the geology. and the linkage between surface water and groundwater, and then also considering water quality issues, and then solutions then with local governance like the World Bank is promoting, and this developing ponds to recharge the aquifer systems.
So thank you so much, Abhijit, for your time today, and really appreciate all your work, and I hope you will get to San Francisco to receive the Devendra Lal Memorial Medal at the American Geophysical Reunion meeting. Thank you. Thank you so much.
[00:52:53] Abhijit Mukherjee: It's a real pleasure to talk to you.
