[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. Today, I am delighted to welcome Lorenzo Rosa to the Water Resources Podcast.
Lorenzo is a principal investigator at the Department of Global Ecology at Carnegie Institute for Science at Stanford. And prior to that, he was a postdoc fellow at ETH in Zurich. He has a PhD in Environmental Science from UC Berkeley and a BS and MS in Environmental Engineering from Politecnico di Milano in Italy.
Lorenzo has received numerous awards, including the 2021 American Geophysical Union Science for Solutions Award, and I think that is fantastic, because I would really like to focus a lot of discussion on solutions. And then he was also listed among the most influential young leaders in science and technology of 2020 by Forbes, 30 under 30.
So Lorenzo's research focuses on potential benefits and unintended climate and environmental consequences of innovations engineered to satisfy increasing global demands for water, energy, and food. And today we're going to focus on water and food issues. And I hope we're going to discuss green, blue and economic water scarcity under past and future climates, and potential solutions to building more resilient water and food security.
Thank you so much for joining me, Lorenzo. I really appreciate it.
[00:01:50] Lorenzo Rosa: Thank you very much, Bridget. It's a pleasure for me to be here.
[00:01:53] Bridget Scanlon: Right. So I very much enjoyed reading many of your papers and you're so prolific that was a bit of a career. But maybe we have first started the discussions about scarcity estimates and water scarcity and food scarcity.
Maybe you can first describe what you mean by scarcity and how you estimate scarcity.
[00:02:13] Lorenzo Rosa: Yes, so scarcity is defined when we have a supply that is lower than demand, and you can quantify scarcity at different timescales and at different spatial scales. And if we talk about water scarcity, we mean that water demand in a certain region and a certain time is greater than water availability.
And so in these regions, there is an unsustainable use of water resources. So humans are using water that should be used by other systems like ecosystems, or humans are using more water than that one that is available from the annual renewable cycle of water.
If we talk about food, we can think about a similar concept. So for food scarcity, we mean that we don't have enough food to meet the demand. And importantly, for food, we need to consider also the four pillars of food security, that are not only:
- availability, so you have enough food to meet demand, but are also
- accessibility,
- utilization, and
- stability
For accessibility, I mean that people need the economic means to buy the food, to get the food.
It's not only necessary, but there is enough food in a certain region or countries. Utilization is more about the nutritional value of the food. So we need the food that has enough nutritious value to meet biophysical requirement by our bodies. And stability is also very important and is needed because, as for example, we saw last year with the price shock after the invasion of Russia in Ukraine, we need stability in food because we need the permanent and durable access to food.
[00:04:02] Bridget Scanlon: Right, and so it's important then how we define supply and demand. And Malin Falkenmark in her water footprint calculations way back when, she indicated water scarcity when demand exceeded 40 percent of supply. But so you, in your calculation, then you just, you simply look at a demand versus supply, not a fraction of it.
[00:04:27] Lorenzo Rosa: Yes. So in my calculation, first of all, our global analysis is at the pixel level. So we divide the world in a mesh of small 10 kilometers, 10 times 10 kilometers or 50 times 50 kilometers. And here we basically solve a simple hydrological balance where you have precipitation, that is the water that is going into the system, and then we have evaporation. That is the water, that is going out of the systems. And from this we can quantify how much water is present in rivers, lakes, and aquifers. So this is the water available. And then we have the component that is the human component.
So is the water used by humans, which is mainly from irrigation on a global level. Irrigated agriculture accounts for 90 percent of water consumption. And then we have other uses like domestic, industrial, manufacturing, and energy. We can basically solve a balance, a hydrological balance, to quantify if there is enough water locally available to meet the human water demand. And importantly, there is also a fraction that needs to be left to the environment and the so called environmental flows. And so this fraction needs to be left in the environment to preserve aquatic ecosystems. In my calculation, I use different methodologies depending on the spatial scale and the temporal scale. But usually around 60 to 80 percent of the water available, so of the renewable water available, should be left in the environment to preserve environmental flows.
[00:06:06] Bridget Scanlon: Right, and we're increasingly recognizing that many years ago, we didn't acknowledge that we needed to leave water for environmental flows. And so then we overestimated the supplies and probably underestimated scarcity issues. So in your work, you have covered both rain fed cropland and irrigated cropland, and then you also emphasize economic water scarcity.
So maybe we'll first start off with describing green water scarcity related to rain fed agriculture.
[00:06:40] Lorenzo Rosa: Yes, so first is very important to distinguish water into green water and blue water. So green water is the root zone soil moisture and this is basically precipitation water that is retained in the soil and can only be used by plants. Humans cannot use this water directly. And so this water is called green water.
And then we have blue water, that is the water that humans use in their activities directly. And this is blue water. So this is the water that we take from rivers, lakes, and aquifers.
And when we talk about green water scarcity, we mean that rainfall is not enough to meet the crop water requirements in agriculture. So in other words, the rainfall regime is not sufficient to meet the demand of crops of water. So in these regions, if you don't provide additional water through irrigation, you face green water scarcity. And agricultural production, therefore, is reduced. So productivity is not at potential. And just to give you an idea about half of crop plants globally face green water scarcity at least one month per year. So here you don't have enough rainfall to meet the crop water demand. And again, productivity is reduced.
When we talk about blue water scarcity, we talk about what they're used by humans directly, and in this case is mainly irrigation, as I mentioned, but also domestic, industrial and energy use and where blue water scarcity when human water use is larger than availability after accounting for the water that you need to leave in rivers, lakes and aquifers to preserve aquatic ecosystems.
[00:08:25] Bridget Scanlon: So green water scarcity then refers to water scarcity in dryland cropland systems. And so the rainfed croplands account for about 80 percent of global cropland and produce about 60 percent of the food. Whereas I guess irrigated accounts for 20 percent of the cropland and produces 40 percent of the food.
Is that correct?
[00:08:50] Lorenzo Rosa: Yes, this is correct. So irrigation on average is twice as productive as rainfed croplands because here croplands can have a stable and reliable supply of water. And so they are less susceptible to climate variability in precipitation, but also temperature. And indeed, only 20 percent of global croplands are irrigated, but 40 percent of food is produced over irrigated croplands.
At the same time, rain fed croplands, they produce 60 percent of the food. So they are very important and they deserve a lot of attention, especially in the context of climate change. Because under climate change, we will have an increase in temperature. And also a change in precipitation patterns. So in many regions, we will have an exacerbation of green water scarcity.
[00:09:41] Bridget Scanlon: Right, so you have looked at changes in green water scarcity under different temperature regimes like 1.5°C warming or 3°C warming and how that would increase water scarcity. So your baseline is 50 percent of rainfed cropland is currently water scarce. It's not producing at potential yield and considered water scarce.
So then when you increase the temperature, then by 1. 5 to 3 degrees, how much does green water scarcity change?
[00:10:12] Lorenzo Rosa: Yes. So first I would like to explain why we choose 1.5 degrees warming and what they represent. So 1.5 degrees warming is basically the Paris Agreement climate target. And that is the goal that global economies have set to limit the warming. So we are aiming as a global economy to limit the global warming to 1.5 degrees compared to the preindustrial era. While 3 degrees warming is basically the warming we are going to reach if we continue as business as usual policies. So 1.5 and 3 degrees warming, they represent the two scenarios where we are going to be likely end up in this century.
And if we talk about green water scarcity under 1. 5 degrees warming, our calculation basically has found that we will have an additional 100 million hectares affected by green water scarcity from the current 400 million hectares, okay? And so these 100 more million hectares of croplands facing green water scarcity are mainly located in Russia, Argentina, Ukraine, and in some regions of the Midwest of the United States.
And we also quantify the number of people that are fed over these croplands that will face green water scarcity under 1. 5 degrees warming. And basically we found that climate change due to green water scarcity will affect food production for 340 million people under 1. 5 degrees warming.
While under 3 degrees warming, which is where we are going to be with global warming according to current emission scenarios, we find that an additional 150 million hectares, compared to baseline conditions, will face green water scarcity. The regions mostly impacted are going to be Northeastern US and Russia. And this additional warming will affect food production for about half a billion more people compared to the 1.5 degrees warming. So here, I think it's also very important to highlight that different temperature targets will have very different impacts on agricultural productivity and also on adaptation. So on how much adaptation we will have to do and varies as you can see, there is a disproportional need of adaptation from 1.5 to 3 degrees warming. So again, this shows how important is to keep global warming within 1.5 degrees Celsius.
[00:12:50] Bridget Scanlon: Right. And so when you say where the impacts are going to be, I think it's important to recognize that these are areas that probably have large rain fed agriculture.
And so places like India, where a lot of the cropland is irrigated or the North China Plain or regions like that, won't be as impacted because they're already irrigated.
[00:13:11] Lorenzo Rosa: These are very good points. So when I listed the countries like Russia, US, Argentina, these are countries that obviously they are, they have a very large extent of rainfed agriculture. And so when you make a global statistics, the areas more impacted are going to be, in these regions.
And, and then obviously there are other regions like China and India where agriculture is already mainly irrigated, so they are not going to face green water scarcity because they already face it today, right? But they face today huge blue water scarcity. So in these regions, irrigation is unsustainable because it's depleting groundwater stocks or usurping environmental flows. So not leaving enough water in rivers, lakes, or aquatic ecosystems. And just to give you an example of environmental flow depletions.
So many rivers worldwide for some months per year don't reach the ocean. One example here in the U. S. is the Colorado River that does not reach Mexico and the Gulf of Mexico because there is so much consumption of water upstream, mainly for irrigation along the Colorado River, that does not indeed reach the ocean.
And so this is an example. is the emblematic example of environmental flows depletion, but along with the Colorado, there are many other rivers like the Yellow River in China, the Nile River, and many others that are so strongly depleted that we have environmental flows depletion.
[00:14:38] Bridget Scanlon: Right. So when you look at the impacts of temperature increases, climate change on green water scarcity, these temperature increases may result in expansion of rainfed crop and I know you haven't looked at it in your paper, but you're maybe doing some current research and so that would be interesting to see what impact those temperature increases have in northern latitudes, maybe Canada and places like that.
[00:15:02] Lorenzo Rosa: Yes, so this is a good point and we are actually working on a study on these. So basically we are quantifying how warming is going to benefit some regions compared to others. And obviously tropical and subtropical regions are going to be strongly impacted by warming because the optimal temperature to grow crops is going to shift to higher temperature and so it's going to go out the niche of optimal temperature to grow these crops.
While for other regions, like Russia and Canada, we are finding that for some crops like wheat and barley, that are mainly winter crops, there is going to be a substantial increase in productivity because indeed the temperature is going to warm in this region and is going to end up in the optimal niche of temperature. And so these regions close to the poles, like Russia, and for Russia I mean the regions in Russia, north of China. So between Mongolia and China, Soviet region and Canada, but also Argentina in the south are going to be winners. And I think it's going to be very interesting to see what are going to be the product productivity implications, global food security and the trade implications if these countries actually are going to invest in these regions and intensify and expand agricultural productivity there.
[00:16:19] Bridget Scanlon: Right. It really could change the picture quite a bit. And then because rain fed cropland is so important, I mean, it's 80 percent of the cropland, you mentioned then that there are ways to adapt to green water scarcity.
Maybe you can describe some of these nature based solutions to try to make the systems more resilient and reduce green water scarcity.
[00:16:43] Lorenzo Rosa: Yes. So basically we have green water scarcity when there is an issue between supply and demand of water, right? As we mentioned at the beginning of the podcast and to reduce green water scarcity, there are some ways that the farmers can implement.
And some of these ways are basically aimed to reduce evaporation and increase infiltration. So in this way, you increase the moisture, the green water in the root zone. And then the majority of these techniques are so called green approaches because they don't require a large infrastructure and they are a soft path to adaptation in agriculture.
Okay, and for example, we have solutions that aim to increase infiltration. So, for example, in regions where you have steep agriculture, like when you are in hilly areas or in mountains, when it rains, you have a lot of runoff. And this water, when there is runoff, does not have enough time to infiltrate into the soil and be retained as soil moisture.
So by, for example, creating terracing, contouring, and you can slow the runoff and so let the water infiltrate in the soil. And then most of these techniques are indigenous techniques. For example, pitting. It's a technique that is indigenous in the Sahel region. And the technique is called Zai pitting.
And basically, farmers, they create holes in the farm with their tools. And when it rains, and when it rains very high rate there, the rain, instead of creating a runoff, is going to form these small ponds. So it has time to infiltrate in the soil and therefore have more green water later in the dry season to meet the crop water demand without irrigation. Then there are other techniques that can reduce evaporation. And for example, no till farming, mulching. And the cover crops basically create a shading in the soil and then reduce evaporation. Another technique, which is more technological, is called agrivoltaics. And basically, this technique consists in combining solar photovoltaics panels with agriculture. And so you have the mutual benefit of producing renewable energy from solar, but at the same time, the solar panels, they create a shading to reduce temperatures below the panels. So where we are, the crops, and therefore reduce evaporation.
There are also other ways to increase green water availability. And these are, for example, weed control. So as well, to grow, we use water. So by removing weeds, you can leave only water to crops. So you remove the non beneficial water that is used in a non productive way by weeds. And then the other way that can be adopted is to switch to less water intensive crops.
For example, wheat is less water intensive than corn. Or sorghum and millet are less water intensive than wheat. So by switching crops you can save water. But here then comes other issues like societal issues because you have cultural preferences and in some regions you need to grow some types of food because the local population are adapted to eat that kind of food.
But ideally switching crops you can save water and you can save a lot of water.
[00:20:15] Bridget Scanlon: Yeah, we can solve a lot of problems on a desktop analysis, but then we have to consider the socioeconomic factors, then it becomes another challenge and maybe much more difficult to implement to get behavioral changes and to consider the societal needs. So that's quite a lot of potential solutions then to address the green water scarcity. And we see maps of these oftentimes. I mean, the Loess Plateau, there's a lot of terracing, it's steep topography. And so they do a lot of terracing. And I've seen the pitting is kind of like a miniature managed recharge type of system that gives the time for water to infiltrate and also reduces erosion, which is a big issue when you have these intense rains and you lose when you lose nutrients and you lose organic matter, so there can be multiple benefits to these approaches. And the nice thing about them is that they can be adopted in a decentralized way and that they're not that expensive.
But as you mentioned earlier, in terms of water use, irrigation is the elephant in the room.
And even though it only accounts for 20 percent of cropland, it generates about 40 percent of the food. And then you mentioned that it's 90 percent of global water consumption and 70 percent of global water withdrawal. So really, if we could manage irrigated agriculture better, we could resolve maybe many water issues, overexploitation of water. Maybe you can describe how you come up with the estimates of blue water scarcity and what you consider in your calculations.
[00:21:56] Lorenzo Rosa: Yes, for a blue water scarcity, for irrigation, we first have to quantify the irrigation water consumption. And for irrigation water consumption, we develop, in the PhD group where I was, we develop a crop water model that basically quantify by crop the demand of water needed by this crop. And we quantify the demand of water divided by green water. And if there is enough green water, obviously, you don't need irrigation. But if there is not enough green water, you need the supplemental water. And the hypothesis here is that the supplemental water is met with irrigation. So over irrigated croplands, the assumption is that farmers irrigate, providing this supplemental water needed to meet the crop water requirements.
And we are able to quantify these from temperature and precipitation, solving at a pixel level, a water balance, okay? And we use the Penman Monteith equation to calculate evaporation on temperature, latent heat, and wind speed. And obviously crop type during the growing season of the crop. And then to quantify water availability, we solve our water balance starting from precipitation. So from precipitation, we know the digital elevation model, we know the soil type, so we can estimate the runoff, making a difference between precipitation and evaporation. And once we generate the runoff, we need to quantify the runoff and how it's going to move downstream based on the digital elevation model.
And we have to quantify these also considering upstream human water use, okay? Because if upstream you use all the water, downstream you're not going to get the water. So solving this flow accumulation algorithm, so it's called like this flow accumulation algorithm, we are able to quantify renewable water availability. As I mentioned before, from renewable water availability, there are different thresholds to quantify environmental flows. So a fraction of renewable water availability has to be left in the environment to preserve environmental flows. And this water remaining is compared to water consumption from human uses, mainly irrigation.
And when the water consumption indeed is greater than water availability, we have a blue water scarcity.
[00:24:17] Bridget Scanlon: Right. And so we have read a lot in the past about these hotspots of overexploitation, North China Plain, Northwest India, Central Valley in California, where we've been irrigating a lot in these semi-arid regions. I mean, they have a lot of positives in terms of crop production, in terms of solar energy, good soils, and we can add the nutrients through fertilizers. But then initially when they started irrigating, for example, the Central Valley in California, they thought there was lots of water because it was under artesian pressure and it was flowing at the surface.
But then over time, then they realized that they were depleting the aquifers. So we could grow more, we could irrigate more humid regions where water could be used more sustainably. And I think you've mentioned in the past that there's been an expansion of irrigated agriculture in the humid Eastern U S have you seen that in other regions also?
[00:25:15] Lorenzo Rosa: Yes, so these are very important. So irrigation is an important adaptation strategy to global warming. We've been adapting to global warming, right, in the past few years because the current temperature is about 1. degrees warmer compared to pre industrial era. So we are already affected by global warming.
Indeed, in some regions of the world, they are expanding irrigation as an adaptation strategy. For example, in the U. S., we've been adapting in the past 20 years of moving of irrigation eastward. So in the southwest, irrigation is contracting, but is increasing in these regions in the eastern part of the U.S. And this is indeed because farmers they have more reliable access to water, obviously they have also technology, they have irrigation, they have pumping technology, which was not available, for example, until 80 years ago. They are expanding irrigation because it's very important also as insurance. So some insurance companies actually require farmers to be insured to have irrigation systems. And so, for example, this is happening in the United States.
But there are other regions in the world where irrigation is actually expanding, or where there are projects where institutions like the World Bank are investing to expand the irrigation, so to build infrastructure to expand irrigation. For example, there are projects in Ethiopia, in Kenya, Armenia. And where they are actually working on expanding irrigation. And in some of my work I find where water will be locally available in the future to expand the irrigation and where this water will be locally available to expand irrigation in a sustainable way. So without depletion of groundwater and, environmental flows and basically solving the same water balance that I mentioned before, but running the model using climate impacts. From 1. 5 and 3 degrees warming, we were able to quantify globally and map globally where there are these hotspots for irrigation expansion.
I can list some of these countries. So previously I mentioned that the United States will be strongly impacted by green water scarcity. Yes, but the United States actually is going to be also the country with the greatest potential for sustainable irrigation expansion. About 40 million hectares will be suitable for irrigation expansion in the U.S., mainly in the northeast of the U. S. Because water here will be locally available to meet irrigation water requirements. Similarly, also in Russia, Brazil, Nigeria, and India, we will have some potential in the future to expand irrigation. So some countries obviously are going to be very strongly impacted by green water scarcity and their warming, but they have at the same time the potential to adapt. If they invest in adaptation strategies that can be green water management technologies, as we mentioned, terracing, pitting, agrivoltaics, not tillage, but also at the same time, they can have the potential to adapt using more infrastructure based approaches like irrigation, which obviously are more expensive from the economic point of view, but also they provide a more reliable production.
[00:28:32] Bridget Scanlon: Right. So I mean, irrigation makes you sort of independent of the climate. It makes you more climate resilient. And then expanding into these areas where it can be done more sustainably is really helpful. And I know in my own work, we looked at irrigation in the Mississippi embayment aquifer system and also compared it to the Central Valley.
And actually they were pumping more groundwater in the Mississippi embayment than they were in the central Valley. But when they were pumping that groundwater water, they were capturing surface water because the Mississippi is a humid region. And so they could do it more sustainably and not have these huge groundwater depletion that we've seen.
And I do remember many years ago talking to the water use people at the USGS, and they mentioned that in Alabama, the banks were requiring the farmers to install irrigation to make sure that they could pay back their loans. So whether it's the insurance industry or the banks, they want that reliability.
And I guess irrigation is one of the ways to do that. In your work, Lorenzo, you mentioned that demand for food production will possibly double by 2050. And you also talk about a number of ways to meet that increasing demand, which is going to be very challenging. Maybe you could describe some of those approaches.
[00:29:55] Lorenzo Rosa: Yes, so we are facing a huge challenge that indeed we will need to double food demand by 2050. Or, in other words, in the next 30 years, we will need to produce the same amount of food that we did cumulatively over the past 8,000 years. So this is a huge challenge in addition to climate change. And to meet this demand, obviously, there are different ways.
One way is to intensify agricultural productivity. So it's basically to produce more over carrying croplands. And this is because in many regions, especially in the Global South, croplands and agricultural productivity are not at potential. So by providing water with irrigation and by providing nutrients, mainly with fertilizers, these croplands have the potential to increase agricultural productivity and feed billions more people. And this is the concept of yield gap closure or sustainable intensification of agriculture.
And then this concept is opposite to the other concept, which is agricultural extensification. So for this, we mean that we expand agricultural land in regions where before we were not doing agriculture. For example, the deforestation in the Amazon rainforest is an example of agricultural expansion. So here we use more land to produce food and the opposite concept of intensification. We use the same amount of land or less land, but here we produce more food. And then there are, and these are techniques to increase production from the supply point of view.
There are also ways to meet this future demand, considering the demand point of view. And these are more social techniques. For example, reducing meat consumption, reducing animal-based products can indeed reduce the amount of crop plants we need and the amount of crops we need to grow. The other way is to reduce food waste, 40 percent of global food today is wasted. So if we just reduce food waste from 40 to 30%, we can feed several million more people per year. And at the same time, they have lower impacts because that 40 percent of food that is wasted is also water, is also energy, is also greenhouse gas emissions. So it's all connected. And so these are the main techniques.
Then there is also another technique that is very controversial, which is the about controlling a population. So in, in some countries, basically we have a high fertility rates, for example, in the Sahel region. And that we publish actually a comment in nature where basically we lay out the issues that this region is facing. And one of these is indeed that we have a booming population. And this is because Mostly of the conditions of women. So in here, women are not educated and they have in many cases, the first child at 13, 14 years old and the fertility rate for a woman, there is about eight to 10 kids. So it has been proven that by sending women to school, some. The fertility rate decreases. So, in this commentary, for example, we show how helping these, younger girls can actually not only improve the life of these women, but also have the benefit of, reducing this issue of overpopulation and at the same time increase food security in the region.
[00:33:24] Bridget Scanlon: Right, so, so that's a lot of different approaches, I guess. So your two main approaches are either intensification or extensification of agriculture. And intensification then will probably mean more irrigation, increased fertilizer use to close the yield gap that we find in many regions today. And then extensification, I'm not sure how much opportunity there is for extensification, except maybe you said earlier, we could expand crop production in northern climates with changing temperatures, possibly. And then, so both of those are on the supply side, and then on the demand side, reducing food waste, post harvest losses, being able to have refrigeration and energy sources to manage food so that we don't lose so much of it would be great, especially considering that it's currently about 40 percent of food production.
And then that also includes all the other footprints that you mentioned, energy, carbon, greenhouse gases, and all of those sorts of things. And I think one of the reasons that women have reduced opportunities to become educated and stuff in developing countries is because oftentimes they spend a lot of their time collecting water from distant sources and stuff, and so they had a readily available water, then they could spend their time in school rather than walking miles to get fetch water.
So it's easy on paper to see what we can do, but then it's another thing to actually realize some of those changes. Another aspect that you mentioned that you've looked at in your work is large scale storage of water in reservoirs and how that helps irrigation. And I'm not sure if you looked at that also with the future projections and projected increases in reservoir storage.
[00:35:16] Lorenzo Rosa: Yes, so these are a part of work that we recently started after we quantified where you can potentially expand irrigation under warming. And basically from that analysis in 2020, we found that yes, there will be still potential to meet irrigation water demand in the future, but there will be a huge intra-annual variability in water availability.
So while today we can meet water demand. Within a few weeks, within a few months in the future, you will have maybe all the water available in January, and then you need it in the summer season when you have agriculture. So these all brings in the issue that you need to store water. from the wet season where when you have surplus to the dry season when you have a water gap.
And one way to meet, indeed, this water gap is through water storage. And recently we quantified these using historical climate, considering large dams. So large dams, today there are about 6, 000 large dams worldwide, and the other 3, 000 are planned or under construction. And basically, we quantify the water that is contained in these reservoirs that can be used for irrigation because of this, a fraction of this water is used for either power or other uses like recreation.
So considering the water available in these reservoirs for irrigation, we quantify how much dam base reservoir can contribute to irrigation and food production. And we did it only under current climate conditions. We are currently working on future climate conditions, considering not only large dams, but also smaller dams, or check dams, or more in general, water storage.
So how much water storage we will need is enough water storage to meet the water gap that we will have in a certain time along the year.
[00:37:11] Bridget Scanlon: So I guess what you're saying is that you're seeing increasing seasonal amplitude of water availability and to resolve the temporal disconnect between supply in the winter and demand in the summer, then we need to store water.
Traditionally, that's been surface reservoirs. But maybe in the future, maybe more small check dams or even groundwater storage, we've depleted a lot of aquifers and that creates a reservoir that we could fill that the Central Valley is looking at to store water. And I think even Oregon, with the reducing snow availability, or I mean, earlier snow melt, they are using managed aquifer recharge to help resolve that temporal disconnect to store the snow melt for the demands in the late summer for crop yield.
So a lot of different ways to manage. I would like to ask you just briefly, you used a lot of different tools and data to do these analysis and maybe for just briefly, and I think you've maybe already described it, but you have developed a databases of crop water needs over time historically and using some of your water balance models and make those data available.
I think that's really nice to make data accessible to others.
[00:38:29] Lorenzo Rosa: Yes. So in my work, obviously, when we publish, our goal is to provide the data. So they are mainly just spatial data. So they are maps that we provide in the data availability of our study. For example, in the past, we provided irrigation water requirements, by year, by crop, under current and future climate.
We provided the extent of where you have blue water scarcity, green water scarcity, economic water scarcity. At annual time step or monthly time step on their current future climate. So we provide these data and they are actually being used because for example, there are institutions like I mentioned before, the World Bank are actually using these data to start their project.
So we find where we are in these regions that they have potential and then they go more local scale. They are collected with local census data of agriculture and basically they refine the quantification and did more at the global level for their projects more at the local or regional level. So they are actually being used and they have an impact.
And this makes me very happy. I think the main issue with these global studies is that we rely, all of us working on this topic, we rely on maps, geospatial maps of irrigation around the year 2000. And so this is a big issue because irrigation is 90 percent of water use, but we are more than 20 years behind.
So I think there is a need to update these maps and create updated irrigation maps to better inform decision making, decision making around water and food security issues.
[00:40:06] Bridget Scanlon: And I think you mentioned when we talked previously that you've been doing that in some countries and that you don't, you think it's feasible, it's not a huge task, it's doable, maybe we should just invest in that, I think.
[00:40:20] Lorenzo Rosa: Yes, I think this can be a good project, like for example, we recently did a project in collaboration with the World Bank to map irrigation in Ukraine. And obviously, this is a project that started once Russia invaded Ukraine. And the idea is to build back better in Ukraine. And one of the main programs of this reconstruction plan is indeed around agriculture and irrigated agriculture.
So the first question is, how much is irrigated? How much irrigation was lost because of the conflict? And basically we were able to map at a very high resolution irrigation in 2000, before the invasion, so in 2021. And also using remote sensing, we were able to see what happened in 2022 and 2023. For example, we found that about 2 percent of agriculture is irrigated.
in Ukraine was irrigated before the invasion, only 2%. And due to the invasion, a lot of irrigated agriculture is located in regions that were part of the conflict of the invasion. So in 2022, Ukraine lost a lot of irrigation. And also this year, after In June, the Kaklova Dam was destroyed, a lot of irrigation was lost because indeed this dam was providing water to a lot of irrigation districts that rely on these dams here in the south of Ukraine, in the Kherson region.
[00:41:46] Bridget Scanlon: So it sounds like there's a potential then to build back better and to expand irrigation. And I think you mentioned maybe a couple of decades ago that there was more irrigation, but it was destroyed way back.
[00:42:01] Lorenzo Rosa: Yes, so. Before the collapse of the Soviet Union in 1991, Ukraine had more irrigation. But after the collapse, basically socio economic and political reasons caused a disuse of irrigation.
And actually irrigation decreased by 85 percent from the collapse of the Soviet Union till 2021. And this is for various reasons. mainly socio economic, but also political reasons. For example, in some places the metals used to produce, to build the channels was dug up and used as a scrap metal and sold on the market.
So here brings in also the issue of economic water scarcity, right? So where you have water available for irrigation, but in many regions, you don't have irrigation infrastructure for socioeconomic and political reasons. And about 25 percent of croplands are affected by economic water scarcity. So you add green water scarcity, you have a lower productivity because of these less precipitation to meet crop water demand.
You need irrigation and you have the water locally available for irrigation, but you don't have the infrastructure. And indeed, I think there is huge potential to make target investments in some target regions to build this infrastructure and sustainably intensify agriculture. Right.
[00:43:23] Bridget Scanlon: I would guess that sub-Saharan Africa is one of those regions where currently we only have one to 2 percent irrigation.
And in some regions, the water is probably there for sustainable irrigation expansion, but the economic factors are probably a barrier.
[00:43:40] Lorenzo Rosa: Yes, and also training for farmers, because in many regions, farmers don't know how to manage these new technologies that can be irrigation, but also fertilizers, they don't know how to apply it.
And so it's very important also to build this infrastructure, adapting to the local context. Okay. So maybe some techniques that works in a region are going to work in another region. And one of the, I think one way to expand irrigation in a very sustainable way is a solar power drip irrigation. So you have renewable energy because we didn't mention this, but irrigation use a lot of energy to pump water, especially when it's deep groundwater.
So it's a lot of energy and a lot of greenhouse gas emissions. And this energy today is mainly from diesel. So it's mainly from fossil fuels. So the way forward there is a solar power drip irrigation because drip irrigation is very efficient irrigation and basically reduce the amount of water that you need to pump and also reduce water scarcity.
So I think this has a lot of potential, but there's a very large capital cost, but on the other end, very low operational costs. Well, we've
[00:44:49] Bridget Scanlon: covered a lot of different topics, Lorenzo, and your research, and we still haven't covered probably a quarter of your research. I really appreciate how you bring so many factors together.
And today we focused on water and food, and green, blue, and a little bit on economic water scarcity. But also, I think there's some positives. And your work helps identify where we could improve situations to increase food production with sustainable irrigation and make more climate resilient systems.
And so I think that's extremely valuable. And I know you've done a lot of work on greenhouse gases and agriculture and energy and everything. And maybe that could be a topic for another podcast, but I really appreciate your time and greatly admire your work and bring so many insights. And it's fantastic that you are working with the World Bank then, because I mean, when they work in developing countries, there's often very little data available for them to start off these projects.
And so the analysis that you do with these different remote sensing datasets and other datasets really gives them a kickstart. Those projects. I'm sure. So our guest today was Lorenzo Rosa, who works at the Department of Global Ecology at Carnegie Institution for Science. Thank you so much, Lorenzo, for taking the time to chat.
[00:46:13] Lorenzo Rosa: Thank you very much, Bridget.
