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Good groundwater management makes for good neighbors

Good groundwater management makes for good neighbors

Post by Samuel Zipper, postdoctoral fellow at both McGill University and the University of Victoria, in Canada. You can follow Sam on Twitter at @ZipperSam.

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Dedicated Water Underground readers know that this blog is not just about water science, but also some of the more cultural impacts of groundwater. Keeping in that tradition, today’s post begins with a joke*:

Knock, knock!

Who’s there?

Your neighbor

Your neighbor who?

Your neighbor’s groundwater, here to provide water for your plants!

Figure 1. Typical reaction to joke written by the author.

Ahem.

Perhaps this joke needs a little explanation. As we’ve covered before, groundwater is important not just as a supply of water for humans, rivers, and lakes, but also because it can increase the water available to plants, making ecosystems more drought resistant and productive. However, we also know that groundwater moves from place to place beneath the surface. This means that human actions which affect groundwater in one location, like increasing the amount of paved surface, might have an unexpected impact on ecosystems in nearby areas which depend on that groundwater.

Imagine, for example, two neighboring farmers. Farmer A decides retire and sells his land to a developer to put in a new, concrete-rich shopping center. Farmer B continues farming her land next door. How will the changes next door affect the groundwater beneath Farmer B’s land, and will this help or hurt crop production on her farm?

In a new study, my colleagues and I explored these questions using a series of computer simulations. We converted different percentages of a watershed from corn to concrete to see what would happen. Our results showed that the response of crops to urbanization depended on where the land use change occurred.

Figure 2. Conceptual diagram showing how urbanization might impact crop yield elsewhere in a watershed. From Zipper et al. (2017).

In upland areas where the water table was deep, replacing crops with concrete caused a reduction in groundwater recharge, lowering the water table everywhere in the watershed – not just beneath the places where urbanization occurred. This meant that places where the ecosystems used to be reliant on groundwater could no longer tap into this resources, making them more vulnerable to drought. However, places where the water table used to be too shallow saw boosts in productivity, as the lower water table was closer to the optimum water table depth.

In contrast, urbanization happening in lowland areas had a much more localized effect, with changes to the water table and yield occurring primarily only in the location where land use changed, because the changes in groundwater recharge were accounted for by increased inflows from the stream into the groundwater system.

So, what does this mean for the neighboring farmers we met earlier?

For Farmer A, it means the neighborly thing to do is work with the developers to minimize the effects of the land use change on groundwater recharge. This can include green infrastructure practices such as rain gardens or permeable pavement to try and mimic predevelopment groundwater recharge.

For Farmer B, the impacts depend on the groundwater depth beneath her farm. If the groundwater beneath her farm is shallow enough that her crops tap into that water supply, she should expect changes in the productivity of her crops, especially during dry periods, and plan accordingly.

*Joke written by scientist, rather than actual comedian.

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For More Information:

Zipper SC, ME Soylu, CJ Kucharik, SP Loheide II. Indirect groundwater-mediated effects of urbanization on agroecosystem productivity: Introducing MODFLOW-AgroIBIS (MAGI), a complete critical zone model. Ecological Modelling, 359: 201-219. DOI: 10.1016/j.ecolmodel.2017.06.002

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Sam Zipper is an ecohydrologist. His main research focuses broadly on interactions between vegetation and the water cycle, with a particular interest in unintended or indirect impacts of land use change on ecosystems resulting from altered surface and subsurface hydrological flowpaths. You can find out more about Sam by going to his webpage at: samzipper.weebly.com.

Groundwater & Education – Part One

Groundwater & Education – Part One

Post by Viviana Re, postdoctoral researcher at the University of  Pavia (Università di Pavia), in Italy. You can follow Viviana on Twitter at @biralnas.

Part one of a two part series on groundwater and education by Viviana.

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Education /ɛdjʊˈkeɪʃ(ə)n
The process of receiving or giving systematic instruction, especially at a school or university.

  • from Latin educatio(n-), from the verb educare
  • Educare is a combination of the words e (out) and ducare (lead, drawing), or drawing out.

Based on this definition, I should change the title of this post to: Drawing out groundwater (from the well). This is actually the main occupation of groundwater scientists, isn’t it? Not only are we always withdrawing groundwater from a well or a borehole while sampling, but we also often have to “draw it out” when dealing with managers and policy makers, as sometimes they seem to forget about this hidden (but very important) component of the water cycle. Therefore, we are quite used to these forms of “drawing out” – but what about education? Are we really that effective in “drawing out” groundwater in explaining its peculiarities, issues, and connections within the whole water cycle and, more generally, with the environment?

Indeed, the effort of shedding light on something that is not so visible nor easily studied has the side effect of forcing us to focus solely on it, with a resulting tendency of developing sectorial approaches to water management.

In the preface of a UNESCO Technical paper, I found the following excerpt: “Water resources schemes are now increasingly considered as integrated systems and consequently, civil engineers, geologists, agricultural engineers and hydraulic engineers engaged in planning and design no longer work in isolation”. The document is dated 1974 but, still in 2017, we are somehow struggling to fitting groundwater into Integrated Water Resources Management (IWRM) and to connecting mental and structural “silos”. Quoting Daly (2017), the latter is particularly relevant (especially when education is at stake): if on the one hand, specialization can be the driver for a sound knowledge; on the other hand, this can encourage people to get stuck in their own individual disciplines (or said in other words, their “silos”). Indeed, “silos” exist in their structures, but can also exist as a state of mind that can go hand in hand with tunnel vision (Tett, 2015).

Therefore, in my opinion, the new generation of groundwater scientists (and teachers) should have a new mission: to work (and therefore, to teach) coherently with the integrated and complex nature of the water cycle. In fact, the role of hydrogeologists and groundwater scientists in times of increasing freshwater demand, exacerbated by population growth and climate change effects, requires a serious shift towards a more holistic approach targeting sound groundwater assessment and long-term management.

Arguably, if we are still discussing possible ways of practically implementing this integration, we should definitely start asking ourselves if the the “business as usual” way of working and teaching is effective.  If it is not, we must begin investigating how we can go beyond classical approaches to draw groundwater out of the well.

Playing with kids while sampling … can we call it capacity building?!

 

To be continued …

[Read More]

What is the difference between ‘water withdrawal’ and ‘water consumption’, and why do we need to know?

What is the difference between ‘water withdrawal’ and ‘water consumption’, and why do we need to know?

Post by Inge de Graaf, University of Freiburg, Environmental Hydrological Systems group

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Last week I had to teach my first class in global hydrology. When I showed the global trend on increasing demands and withdrawals (see Figure) I needed to explain the different terms as sometimes the term “water use” gets, well, misused.

The term “water use” often fails to adequately describe what happens to the water. So I told the students; if you see or hear to term ‘water use’ always ask yourself what’s actually being said. The term is often used for water withdrawals or water consumption, and it’s important to understand the difference.

Water withdrawal describes the total amount of water withdrawn from a surface water or groundwater source. Measurements of this withdrawn water help evaluate demands from domestic, industrial and agricultural users.

Water consumption is the portion of the withdrawn water permanently lost from its source. This water is no longer available because it evaporated, got transpired or used by plants, or was consumed by people or livestock. Irrigation is by far the largest water consumer. Globally irrigated agriculture accounts for 70% of the total water used and almost 50% is lost either by evaporation or transpiration.

Understanding both water withdrawal and consumption is critical to properly evaluate water stress. Measurements of water withdrawal indicate the level of competition and dependence on water resources. Water consumption estimates help to quantify the impact of water withdrawals on downstream availabilities and are essential to evaluate water shortage and scarcity. For example, most water used by households is not consumed and flows back as return flow and can be reused further downstream. However, water is rarely returned to watershed after being used by households or industry without changing the water quality, increasing water stress levels.

Already more than 1.4 billion people live in areas where the withdrawal of water exceeds recharge rates. In the coming decades global population is expected to increase from 7.3 billion now, to 9.7 billion by 2050 (UN estimate). This growth, along with rising incomes in developing countries, is driving up global food demands. With food production estimated to increase by at least 60% (FAO estimate), predicting water withdrawal and consumption is critically important for identifying areas that are at risk of water scarcity and where water use is unsustainable and competition amongst users exist.

Global trend I showed in my class, published in Wada et al (2016).

Ref:

Wada, Y., I. E. M. de Graaf, and L. P. H. van Beek (2016), High-resolution modeling of human and climate impacts on global water resources, J. Adv. Model. Earth Syst., 8, 735–763, doi:10.1002/2015MS000618.

 

Is highway de-icing ‘a-salting’ our aquifers?

Is highway de-icing ‘a-salting’ our aquifers?

Post by Mark Cuthbert, Cardiff University, and Michael Rivett, GroundH20 plus Ltd; University of Strathclyde.

If you live in a cold climate, have you ever wondered where all the de-icing salt (or ‘grit’ as we call it in the UK) that gets spread on the roads in winter time ends up, aside from that accumulating salty grime that coats your car? As you might expect, most of the salt gets washed off the highways as the salt has the desired effect of melting the ice, or carried away by rain. This salty ‘runoff’ ends up in streams nearby via pipes which drain the highway. However, that is not the end of the story…

We studied a major highway intersection on the edge of UK’s second largest city, Birmingham (more than a million people), to see how much of the salt spread on the highway ends up in groundwater. Our interest stems from concerns of the national regulator to understand not only how much salt ends up in streams, but also the potential long-term build-up of salt in underlying groundwater resources that are pumped for public and private water supply. Although the origin of salt in streams and lakes is relatively well studied, the pathways by which salt moves from highways to groundwater are poorly understood and quantified.

The various ways salt could be getting in to the groundwater are shown in Figure 1 and a bit of detective work was required to find out what was going on.

Figure 1*

This involved dressing in silly (and warm) clothes, and pulling our equipment around on a sledge, which was a lot of fun (see photos below).

The authors, Mark (left) and Mike (right), enjoying some urban winter fieldwork.

Our main field activities were fortuitously timed to include the severe winters of 2009-10 and 2012-13. We collected information about the amount of salt spread on the roads and measured the salt concentrations in the local streams, as well as in the shallow and deep groundwater wells in the area around the highway network.

7 km of motorway drained to the studied stream. Over the winter of 2012-13 we estimated that around 510 tonnes of de-icing salt was applied to the highway and major road network across the catchment. Most of that washed off the road via drains when it next rained or as the snow and ice melted, and ended up in the stream which flows under the highways. Some of it ended up on the roadside verges – this was not quantified, but would likewise eventually leach into the underlying groundwater over time.

We estimated about 12% of the de-icing salt, that’s around 63 tonnes over the 2012-13 winter, leaked through the bottom of the stream channel into the groundwater in the sandstone aquifer beneath, and may pose a risk to groundwater supplies in the area (see “9” in Figure 1, and results in Figure 2). While increases in groundwater chloride concentrations observed to date have been modest, and fortunately remain far below the drinking water standards, the steady year-upon-year build-up of salt in groundwater remains a concern. This is especially the case as the UK’s de-icing salt applications reached record levels in the recent severe winters and add to a potential de-icing salt legacy in our aquifers that has accumulated now over some 50 plus years.

Figure 2*

So how concerned should we be that so much salt is flowing down these streams and into the groundwater around our highways? There isn’t yet a simple answer to that but, with a global trend towards increasing urbanisation, this is an important area of ongoing and future research.

 

Further details of our published research to date on the Birmingham case study may be found at:

Rivett, M.O.,  Cuthbert, M.O., Gamble R., Connon, L.E., Pearson, A., Shepley, M.G., Davis, J., 2016. Highway deicing salt dynamic runoff to surface water and subsequent infiltration to groundwater during severe UK winters.  Science of the Total Environment 565, 324-338. http://dx.doi.org/10.1016/j.scitotenv.2016.04.095 (*figures reproduced with permission) [Read More]

Groundwater Speed Dating! Can you find a match?

Groundwater Speed Dating! Can you find a match?

Post by Matt Herod

Welcome to the first edition of groundwater speed dating. In today’s post I introduce you to a motley crew of isotopes and chemicals that hydrogeologists and geochemists use to date the age of groundwater. After meeting all of the contestants it will be up to you to pick your favourite and perhaps propose a second date. On your groundwater samples that is.

Starting to find some answers on water chemistry of baseflow samples from the Yukon. The first step in groundwater dating…picnic style. (Photo: Matt Herod)

Before I introduce you to our contestants I should briefly make it clear why groundwater dating is important. Understanding how old groundwater is may be one of the most, if not the most important aspect of protecting groundwater as a resource and preventing depletion of groundwater reserves from overpumping. For example, pumping an aquifer with a groundwater age of 10 years can be done semi-sustainably as any water extracted will take ~10 years to replace. However, pumping water with an age of 100,000 years is exploiting a nearly non-renewable resource. There may be lots of it, but the aquifer could take a long time to recover. Think of it like this: the water being pumped has to come from somewhere. Pumping could draw more water into the aquifer from recharge (not always an option) to replace what is lost, the water pumped could be from groundwater already stored in the aquifer, or it could be groundwater that was leaving the aquifer via discharge into a river or lake that is now diverted to your well.

Another great reason to know the groundwater age is to assess the vulnerability of an aquifer to contamination. If groundwater is young it is likely that the host aquifer is more vulnerable to contamination. Furthermore, knowing the age of groundwater throughout an aquifer will also allow a hydrogeologist to assess how quickly contamination will spread and if it can be contained. There are other reasons that it is beneficial to know the age of groundwater and if you’re interested I refer you to some of the references below.

I should also mention that the clock on a groundwater age starts once it becomes groundwater. That means that once my rain drop infiltrates into the ground and reaches the water table. The time it takes for the water to infiltrate through the soil layer is not included in the date which can add several months. Therefore, when I say groundwater is one year old, this means that it was likely rain from last year that has now reached the well, but it may be slightly older when you factor in the vadose zone travel time.

Are you ready to meet your speed dating contestants!? Pick the one that you’d like to date (the best isotope for your particular groundwater sample).

Note: You’ll see reference to cosmic rays a lot below. For reference see this primer in a previous blog post.

Name: Carbon-14
Nickname: 14C, The Cool One
Personality: Bada^s, Awesome
Half-life: 5730 years
Groundwater age range: 100 -100,000 years
A little about me:
14C, nicknamed radiocarbon, is the isotope that everyone wants to meet. Used by hydrogeologists in a vast range of dating applications for almost any organic material (organic = has carbon in it) it can also be used to date groundwater. 14C is produced by cosmic ray interactions with nitrogen in the atmosphere. 14C was also produced in significant quantities by atomic weapons testing and created a “bomb pulse” like our contestant tritium below which is also used to date groundwater. The great thing about radiocarbon is that since we know exactly how much is produced we can always estimate an age. However, dater beware. The age obtained from 14C and many other groundwater dating tools is the apparent age, which means it is inexact and vulnerable to aggregation errors when mixing young and old water mix, and requires the dater to consider other sources of inorganic carbon that contain no 14C such as ancient limestone. There are ways to correct for these issues, but great care must be taken so don’t be deterred from choosing 14C…maybe a bit of that coolness will rub off on you!? (Of course, as hydrogeologists we don’t need any extra coolness).

Name: Krypton 85 and Krypton 81
Nickname: 85Kr and 81Kr, The Twins
Personality: Different, One short tempered, the other slow to anger
Half-life: 81Kr: 10.75 years, 85Kr: 230,000
Groundwater age range: 10 – 100 and 10,000 -1,000,000 years (using different Kr isotopes)
A little about me:
These two twins could not be more different. Both are isotopes of krypton but with hugely different applications. You won’t see them in Twins magazine (twinsmagazine.com). The source of 85Kr is low level emissions from the nuclear industry, mainly fuel reprocessing. It has a short half-life meaning it can only be detected in groundwater a few decades old.

On the opposite end of the spectrum 81Kr is used for dating extremely ancient groundwater and is a relatively new dating tool for hydrologists. See me previous post on atom trap trace analysis for the details on this method that has made 81Kr dating possible. 81Kr is produced by cosmic ray interactions with gases in the atmosphere that become incorporated into rain that can recharge groundwater. 81Kr is the newest tool in the isotope hydrologists kit and has been used to date waters over 100,000 years old! It isn’t often you see twins so different than this pair. Nevertheless, they may be worth a longer look in your future?

Name: Tritium
Nickname: 3H, The Friendly One
Personality: Popular, Nice
Half-life: 12.3 years
Groundwater age range: 10-100 years
A little about me:
Tritium is the popular isotope in groundwater dating. Of all the isotopes in this competition, 3H is picked more often than the rest combined. Tritium has a short half life making it an ideal tracer and dating tool of young groundwater. Before the 1950’s all tritium in groundwater was natural and produced by cosmic ray interactions in the atmosphere. However, following the atomic weapons testing in the 1950’s and 60’s the tritium concentration in the atmosphere, rain and groundwater increased drastically. This made it possible to date groundwater using what hydrogeologists know as the “bomb peak”. This method has been enhanced using the decay product of tritium, 3He, as well to overcome the loss of tritium by decay over the time since weapon’s testing ended. While 3H may become less useful in the northern hemisphere as the bomb peak decays, the natural variability of 3H production in the southern hemisphere with fewer anthropogenic sources suggests 3H may become ever more useful! http://www.hydrol-earth-syst-sci-discuss.net/hess-2016-532/. Don’t be deterred by it’s popularity and the crowds, tritium is the real deal!

Name: Chlorine-36
Nickname: 36Cl, The Hard to Get
Personality: Evasive, Sends Mixed Signals
Half-life: 301,000 years
Groundwater age range: 10,000 – 1,000,000
A little about me:
36Cl is produced in the atmosphere by cosmic rays and has been used widely for dating ancient groundwater that is tens to hundreds of thousand years old. However, chlorine-36, while popular, is also “high-maintenance”: 36Cl requires more than just a run of the mill accelerator mass spectrometer (AMS) to measure. Indeed, in order to measure 36Cl on an AMS it needs to have the ability to remove the isobar sulphur-36 that interferes with the measurement of the much rarer (and thus sought-after by hydrogeologists) atoms of 36Cl in a sample. Only the highest energy AMS instruments or those with special capabilities, such as an isobar separator, can perform the measurement of 36Cl accurately. Nevertheless, sometimes it is worth putting in the extra effort for the reward. Will you?

Name: Uranium 234-238 Disequilibrium
Nickname: U-Disequilibrium (234U/238U), The Complicated One
Personality: Confusing, Game Player
Half-life: N/A
Groundwater age range:
A little about me:
You don’t come across U-disequilibrium dating that often, but when you do have a beer. U-disequilibrium is a bit mind-bending and requires a very thorough understanding the of the nuclear and geochemical processes at work in your sample location. Basically, it works because as 238U decays in rocks it shoots out alpha radiation, aka. 4He nuclei, at high energies. These bullets of helium break the crystal lattice of the minerals around the 238U atom allowing groundwater the get in. The groundwater then preferentially dissolves some of the 238U grand-daughter, 234U. This means there is more 234U than 238U dissolved in the water (by activity). The (activity) ratio of 234U/238U is greater than one and is predictable over time if you know the geochemical and hydrogeological characteristics of the system. This means you can correlate the ratio you measure to an age. This is an oversimplification of the method, but at it’s core that’s how it works. If you’re persistent, and work hard to understand U-disequilibrium the date is worth it. Will you put in the hard work?

Name: Iodine-129
Nickname: 129I, The Forgotten One
Personality: Quiet, Interesting
Half-life: 15,700,000 years
Groundwater age range: < 80,000,000 years
A little about me:
My personal fave but so forgotten it didn’t merit the figure above! See my PhD thesis for why. The short of it is that I think 129I has a wide variety of applications but we don’t yet fully understand its transport in groundwater and thus applying it is difficult. Therefore, people often overlook 129I for groundwater dating. It is similar to 36Cl in that it requires an AMS to measure, and they are both halogens. 129I has a very long half life and it is interesting because it is produced in three ways: cosmic rays, 238U fission in rocks, and nuclear fuel reprocessing. This makes it a tracer of modern groundwater and allows it to constrain the age of water that is less than 80 million years old as well! If you’re willing to take a chance and explore, perhaps 129I could be the one for you!?

Pick the isotope you’d like to date and leave a comment below!

Feature image from warsaw social.

Crop kites

Crop kites

Post by WaterUnderground contributor Mikhail Smilovic. Mikhail is a PhD  candidate in the Department of Civil Engineering at McGill University, in Quebec.

Crops use water for photosynthesis, absorbing nutrients, and transpiration, or the plant-equivalent of sweating. A crop may experience water-stress if the soil surrounding the roots is not adequately wet, and this stress will affect the crop differently depending on the crop’s stage of growth. Irrigation is the watering of plants to ultimately avoid such water-stress.

Non-irrigated crops are more vulnerable to intervals of dry and hot weather, and the increasing unpredictability of a changing climate will further complicate other crop management tools, such as choosing different cultivars (the particular variety of crop, some which may deal with certain stresses in an improved way) or changing planting dates.

Irrigated crops do not experience water stress (they may in fact experience water stress under a non-perfect irrigation system, but forgive this for now), but the water is necessarily derived from somewhere else. This somewhere else may also experience water withdrawals from municipalities, industry, and other agriculture. The source of water may be underground, or water from a river, lake, or spring, but a connection between both underground and surface waters shares with us that water removed from a system somewhere will have a response somewhere. This somewhere may very well be an ecosystem. Irrigation may also be costly related to the abstraction, transportation, and on-farm distribution.

Between non-irrigated and irrigated is a curious place where we can increase the resiliency of our agricultural systems to periods of drought and heat with limited irrigation, while allowing crops to experience well-timed water stress. Agricultural productivity or yield is determined as the amount of crop produced per area of land, say 3 tons/hectare for wheat. When water is a limiting factor, we would be sensible to also consider water productivity, that is the ratio of crop yield and water use, or, the amount of crop produced per drop of water. The practices of limited irrigation, also known as supplemental or deficit irrigation, makes an effort to increase this water productivity.

This space in-between non-irrigated and irrigated, however, has been often poorly explored or simplified. Crop kites is a novel tool to determine and quantify the potential agricultural and water productivity associated with different irrigation practices. This is important for regions interested in shifting investments into or away from irrigation, as well as for researchers interested in evaluating limited irrigation practices as initiatives to establish food and water security, both currently and with changing climates.

A first thought might be, if a crop uses three quarters of the water than it would under ideal conditions, does the crop produce three quarters as much as the crop under ideal conditions? In fact, the answer depends very much on when this water is used.

Let us take the example of winter wheat in northern Africa. Winter wheat can be broadly characterized into five different growth stages. We can illustrate water use throughout the season with the following figure:

Water use is represented by the bottom blue colour, and the associated deficit is represented with the upper orange colour – the top line of the shape is the amount of water the crop would use under ideal conditions on the associated day. This example shows a 0, 10, 20, 30, and 40% deficit occurring in stages 1 to 5 respectively, representing a 78% water use across the entire growing season as compared to ideal conditions. Understanding both the amount of water used and when the water was used, we are able to determine the associated yield, for this example, we reach 68% of potential yield.

Now, what if we were to simulate the yield using all reasonable water uses and all reasonable distributions of the timing of this water use? The resulting shape is our crop kite, with each point associated with a water use distributed throughout the growing season in a particular way:

 

This shape illustrates the incredible range of yields associated with each water use; for example, 80% of potential water use relates to between ~20 and 90% of potential crop yield.

Water distributed through canals are often delivered according to a schedule, and not necessarily related to growth-stage sensitivities or actual weather. From the crop kite we can derive estimates on how the crop yield will be affected by adopting certain irrigation schedules. We elaborate on this with three examples: S1) water use is distributed to optimize yield, S2) the deficit is distributed evenly across all growth stages, S3) water is used preferentially for the earlier growth stages. The resulting crop-water production functions are illustrated in the following figure:

 

Although the first schedule optimizing for crop yield may be in line with the motivations of the irrigating farmer, it is often an unreasonable assumption for farmers delivered water according to predetermined schedules, but may be appropriate for farmers irrigating with a privately owned well. Evaluating the potential of supplemental irrigation necessitates estimating the ability of farmers to manage both the amount and timing of irrigation applications. Otherwise, non-reasonable assumptions may be used to evaluate and over promise estimates for agricultural production, with the fault not in the practice of limited irrigation, but in the criteria used to evaluate the system.

Crop kites demonstrate the wide range of water use-crop yield relationships, and can be used to evaluate the potential of limited irrigation to shift both food and water security.

 

Mikhail Smilovic is a PhD candidate at McGill University and the University of Victoria . Mikhail’s work investigates the interplay between foot security, water resources, and energy, and evaluating and integrating initiatives that increase agricultural production while reducing demands on water resources.

Limits to global groundwater use

Limits to global groundwater use

Post by WaterUnderground contributor Inge de Graaf. Inge is a postdoc fellow at Colorado School of Mines, in the USA.

Groundwater is the world’s most important source of freshwater. It supplies 2 billion people with drinking water and is used for irrigation of the largest share of the world’s food supply.

However, in many regions around the world, groundwater reserves are depleting as the resource is being pumped faster than it is being renewed by rain infiltrating through the soil. Additionally, in many cases, we are still clueless about how long we can keep drawing down these water reserves before groundwater depletion will have devastating impacts on environmental and socio-economic systems. Indeed, these devastating effects are already being observed.

The most direct effect of groundwater depletion is the decline in groundwater levels. As a direct impact, groundwater-pumping cost will increase, so too will the cost of well replacement and the cost of deepening wells. One of the indirect consequences of declining water levels is land subsidence, which is the gradual sinking of the surface. In many coastal and delta cities, increased flooding results in damages totaling billions of dollars per year. Next to this, declining groundwater levels lead to a decrease in groundwater discharge to rivers, wetlands, and lakes, resulting in rivers running dry, wetlands that are no longer sustained, and groundwater-dependent ecosystems that are harmed.

Over the past decades, global groundwater demands have more than doubled. These demands will continue to increase due to population growth and climate change.

The increase in demands and the aforementioned negative effects of groundwater depletion raise the urgent question: at what time in future are the limits to global groundwater use reached? This is when and where groundwater levels drop to a level where groundwater becomes unattainable for abstraction, or that groundwater baseflows no longer sustain river discharges.

In my PhD research, I predicted where and when we will reach these limits of groundwater consumption worldwide. I defended my dissertation last year April at Utrecht University, in the Netherlands.

Where and when are the limits reached?

Results show that many large aquifer systems are already highly depleted, especially for intensively irrigated areas in dryer regions of the world, like India, Pakistan, Mid West USA, and Mexico (see Figure 1). New areas experiencing groundwater depletion will develop in the near future, such as Eastern Europe and Africa. Future predictions show that some areas, like the Central Valley, and the High Plains Aquifer, partly recover when more recharge will becomes available. Notwithstanding, environmental groundwater demands will increase as to buffer more irregular streamflow occurrences due to climate change.

Figure 1: Estimated groundwater depletion (1960-2010) in [m], masked for aquifer areas, and zooms for hotspot regions, which are the intensively irrigated regions of the world.

In 2010, about 20% if the world population lived in groundwater depleted regions, where groundwater dropped below the economical exploitable limit. As a rule of thumb: the economic limit is reached when groundwater becomes unattainable for a local farmer, which is approximately when the water level drops to 100 m below the surface. In 2050, 26% to 36% of the world’s population will live in areas where the economic exploitable limit is reached (see Figure 2). Evidently, this persistence and increasing level of groundwater stress will impair local development and generate tension within the global socio-economic system.

Figure 2: First time that groundwater falls below the 100m limit.

 

Global-scale simulations

To answer my main question, I studied the effects of groundwater abstractions on river low flows and groundwater levels worldwide, as well as which trends in river low flow frequency and groundwater level change can be attributed to groundwater abstractions.

I used a newly developed physically based surface water-groundwater model to simulate i.a. river flows, lateral groundwater flow, and groundwater-surface water interactions at a high resolution (approx. 10×10 km) at the global scale. Total water demands were estimated and account for agricultural, industrial, and domestic demands. I simulated groundwater and surface water abstractions based on the availability of the resource, making the estimate reliable for future projections under climate change and for data-poor regions where we do not know how much groundwater or surface water is abstracted. Next, I developed a global-scale groundwater model. I estimated alluvial aquifer thickness worldwide, as no data at the global scale is available (see Figure 3). Aquifer thickness is one of the parameters you need to estimate groundwater flow and storage.

Figure 3: Estimated alluvial aquifer thickness. White areas are mountain regions, where no aquifers are simulated.

Simulations were done for the recent past and near future (1960-2050) and the results include maps and trends of groundwater heads, groundwater fluctuations, and river discharges.

In conclusion, most of our water reserves are hidden underground and most of our groundwater abstractions rates exceed groundwater renewing rates, leading to depletion. The growing demand and the expected climate change bring our groundwater reserves under mounting pressure. More than two-thirds of all abstracted groundwater is used for food production. Every year the world’s population is growing by 83 million people.

Improving our knowledge about how much water we can use in the near future while avoiding negative environmental and socio-economic impacts is therefore extremely important. A study like this contributes to the knowledge gap and can help guide towards sustainable water use worldwide to overcome potential political water conflicts and reduce potential socio-economic friction, as well as to secure future food production.

Want to read more? Check out the recent AGU press release or if you have more time… read my papers on dynamic water allocation (click here), development of a global groundwater model (click here, or here), or read my PhD thesis (here).

 

Author Inge de Graaf receiving her PhD degree from her advisor, professor Marc Bierkens (at Utrecht University, Netherlands). Note Tom Gleeson’s bald head in the lower left…

The great American groundwater road trip: Interstate 80 over the Ogallala Aquifer

The great American groundwater road trip: Interstate 80 over the Ogallala Aquifer

 


Authored by: Sam Zipper – Postdoctoral Researcher in the Department of Civil & Environmental Engineering at the University of Wisconsin-Madison


In late July, my wife and I loaded the dog into the car, cranked up the water-related tunes, and drove over a few million cubic meters of water. No, we haven’t traded in our sedan for an amphibious vehicle – rather, we were driving west, across Nebraska, on the Interstate 80 highway. While this may be a relatively boring road trip by conventional standards, it does provide an opportunity to drive across the famous Ogallala Aquifer, a part of the High Plains Aquifer system.

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The wide reaching Ogallala Aquifer 1. The red line shows Interstate 80’s route.

While the geological history of the Ogallala is described in more detail elsewhere; the short version is that sediment, eroded off the Rocky Mountains over many millions of years, filled in ancient river channels, eventually creating the flat plains that characterize much of Nebraska today. Despite the flat landscape, however, the sights you’ll see along I-80 exist in their present form almost entirely due to this vast underground supply of water.


Irrigation

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A center-pivot irrigation sprinkler. A common sight over the Ogallala 2.

It’s estimated that upwards of 90% of the water withdrawn from the Ogallala is used for agricultural irrigation. Driving through western Nebraska, 90% seems like an underestimate. Center-pivot systems stretch away from the interstate as far as the eye can see, and it’s hard to imagine what this landscape would look like without the water from the Ogallala. While groundwater levels have declined in the most heavily irrigated parts of Nebraska compared to predevelopment conditions, they’ve fortunately stabilized over the past ~30 years; the most serious drawdowns are occurring further south, in Western Kansas, Oklahoma, and the Texas Panhandle.


The Mighty Platte

PlatteRiver

The mighty Platte River. Photo by Sam Zipper.

The Platte River stretches from the Rockies to its confluence with the Missouri River in eastern Nebraska, and I-80 follows the Platte through most of Nebraska. Along the way, the Platte is receiving water from surrounding groundwater systems.  This process of groundwater discharge to streams (often called baseflow), is particularly important for sustaining flow in the river during dry periods, along with the ecosystems, agriculture, and municipalities that depend on this water supply. For a more beautiful look at the Platte than my cell phone camera offers, check out the Platte Basin Timelapse project, which uses photography to explore the movement of water through the basin.


The Namesake

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Ogallala Nature Park welcome sign. Photo by Sam Zipper.

The Ogallala is named after Ogallala, NE, a tiny town about a half hour’s drive from the Colorado border. The aquifer is named after Ogallala because that’s where the geologic “type locality” is – a fancy way of saying, they found the Ogallala formation here first. While we didn’t venture into the town of Ogallala itself, we did stop at the lovely Ogallala Nature Park just off the interstate for a stroll among the phreatophytic vegetation lining the banks of the Platte. Phreatophytes, such as the cottonwoods common to Nebraska, have evolved to have special roots which can extract water directly from groundwater when soil moisture supplies are low, thus allowing them to survive in the sandy, well-drained banks of the Platte.

Do you have any hydrogeologic highlights we should investigate on our drive back to Madison? Let me know via the comments below!


Picture Sources

https://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Ogallala_saturated_thickness_1997-sattk97-v2.svg/2000px-Ogallala_saturated_thickness_1997-sattk97-v2.svg.png

http://water.usgs.gov/edu/pictures/full-size/irrigation-sprinkler-large.jpg


About the author:

Sam Zipper‘s research interests lie broadly at the intersection of humans and the environment, focusing on feedbacks between subsurface hydrology, vegetation dynamics, soil water retention characteristics, and climate & land use change that cut across the disciplines of hydrology and hydrogeology, soil science, agronomy, and ecology.  He is an ecohydrologist at the University of Wisconsin-Madison.

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Nature Geoscience digging into water underground this month!

Nature Geoscience digging into water underground this month!

Nature Geoscience is digging hard into water underground – the February issue is part of a special focus on groundwater. The cover this month is a gorgeous (groundwater-filled?) waterfall by Glen Jasechko, Scott’s brother.  The groundwater focus includes:

As part of the focus the journal made our paper on modern groundwater free to registered users for a month – so go download it an check out this and the other papers too!

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