Overview of the Problem
Many formerly dry areas are suitable for crop production only because of techniques such as irrigation. Irrigation allows for improved crop yields in areas where rainfall does not provide reliable water for plant growth. Humans have been irrigating land for millennia, and it contributes greatly to present and future food security prospects. According to a Food and Agriculture Organization report released in 2009, 20 percent of cropland worldwide is irrigated and irrigated land accounts for 50 percent of production (Food and Agriculture Organization of the United Nations, 2009). The percentage of irrigated land varies greatly across regions (Figure 1).
In order to feed the growing world population over the coming decades, it will be necessary to increase crop yields, especially in less developed countries where there is high potential for growth. Crop yields may be greatly increased by maximizing the effectiveness of the irrigation and the portion of cropland that is irrigated. Herein we discuss methods of accomplishing these goals in the context of both developing and developed countries and present Mission 2019’s plan for irrigation in the next century.
While addressing the overarching issue of irrigation in relation to food security, we have taken a number of factors into account. Major concerns are the effects of a changing climate on the ability to irrigate, and the effects irrigation will have on the environment. Another important factor we considered is the economic feasibility of various irrigation techniques. A third aspect we considered is what sources of water will be used for irrigation purposes for crops. Our solution attempts to address all of these problems to facilitate the establishment of sustainable irrigation systems for the future around the world.
Types of Irrigation
There are a wide variety of irrigation methods practiced globally. The type of irrigation most suitable for a plot of land depends on its size, crop types and location. In most cases, the type used in a certain area is due more to tradition and location of water sources than it is to the method’s effectiveness. Below is an overview of the most common methods of irrigation.
Flood irrigation supplies water to crops at surface level, using gravity to cause movement from higher ground to lower. Water is distributed in large quantities across the surface of farmland. This method tends to cause erosion and is the oldest and most basic form of irrigation, and is commonly used in less developed countries (USGS, 2015). The types of flood irrigation include: sheet irrigation, an appropriate method for hay and pasture crops; and furrow or ditch irrigation, used for row crops, in which water is moved from a main ditch to perpendicular canals. Erosion can be reduced by contouring the furrows.
Sprinkler irrigation is the application of water in small quantities across land. This method is appropriate for steep slopes, but is costly. It also loses large amounts of water to evaporation . The various types of sprinkler irrigation include: overhead irrigation, in which sprinklers are mounted above cropland, commonly with a center pivot; buried sprinklers that emerge from underground when water pressure rises; and rotary irrigation, a circular motion to increase reach. The rotary sprinkler method is best suited to large areas of land, as it can reach up to 100 feet (USGS, 2015).
Terraced irrigation is used for contoured land; the land is formed into a series of flat terraces so that water will flow down each step. This method is very labor-intensive but is useful for crops like rice that grow in very wet areas such as paddies (USGS, 2015). Spate irrigation uses excess river water during floods to irrigate, and silt in the water fertilizes crops. Wastewater irrigation makes use of unfiltered water to irrigate crops, which greatly improves conservation of such a precious natural resource, but can have adverse health effects if it is not regulated properly. This method is not recommended in developing countries due to the high risk of mismanagement (USGS, 2015).
Drip irrigation is a one of the most efficient, direct methods of delivering water and prevents excessive loss. Fifty percent less water is used with drip irrigation than flood irrigation to produce the same yield of crops (Howeler, Lutaladio, & Thomas, 2013). Perforated pipes deliver water at or near the crop surface, meaning up to one-fourth of the water used can be saved and re-used (USGS, 2015). Because of the technical complexity of drip irrigation compared to other types, it is mostly used in developed and high-income countries or regions. We encourage its use in all areas with enough agriculture funding to feasibly implement drip irrigation.
All of these methods require advanced technology, investment, and correct materials in order to be effective at watering various crops. Most irrigation systems are set up to bring water from a river into a canal, then progressively smaller lateral canals, to supply various systems for many farmers’ crops. Irrigation worldwide is between 40 to 95 percent efficient. In many low-income or poorly maintained areas, water is lost to evaporation, seeps into the ground in transit, runs off into other waterways, or supplies other plants like weeds (Hemmerly, 2015).
Potential for Negative Impacts
Irrigation does have some adverse effects. For example, the residue of salt left behind after evaporation (called salinization) diminishes the productivity of soil over time, and can render some fields unsuitable for future crops. Leached salt can pollute other sources of water. Many farmers who can afford it now use genetically selected crops which are adapted to salinized soil (Hemmerly, 2015), but for those who cannot afford GM crops or live in areas in which they are illegal, salinization remains a detriment to high production. A way some farmers prevent such damage is the drainage of salty water to evaporation ponds or in some cases to the ocean (Dougherty, 1995), although this is quite damaging to marine ecology. Alkalization (the deposition of soluble mineral salts that reduce crop production) also occurs in soils, but can be remedied by preventing seepage and inefficiencies of systems that require maintenance. Waterlogging, or excessive and damaging quantities of water in soil caused by low irrigation efficiency, is a major problem in some areas, but in others is beneficial to reduce salinization, soil acidification, and alkalization. Water-related disease is unfortunately common; helpful preventions are health facility improvements and education about the causes (Dougherty).
The demand for water in a given area changes when it supplies irrigation systems. The normal flow of rivers and streams is reduced, leading to reduced biodiversity and alterations in ecology, as well as disputes over water rights downstream (Hemmerly, 2015). Other sources people have found to supply water include deep wells and aquifers, but drilling is very expensive and leads to subsidence, or sinking of land, over time. In addition, groundwater sources are far from infinite and are quickly depleted. The southern and western United States have experienced damage to urban areas, a common result of such a problem, due to subsidence from underground piping and wells. Drilling also causes the intrusion of salt water into wells in some coastal areas (Hemmerly, 2015). This can be helped by adjusting abstraction changes (Dougherty, 1995).
As mentioned, irrigation modifies natural ecosystems and in some instances causes long-term ecological problems, such as pollution from pesticides and fertilizers (Dougherty, 1995). Revolutionary gains in crop production can be achieved with modern irrigation techniques, but most advantages are in fact only temporary, as millions of dollars are spent each year to repair broken systems (Hemmerly, 2015). Irrigation efficiency can cause increases in energy consumption and even a decrease in employment in agriculture (Dougherty, 1995).
The monetary and environmental costs of irrigation (implementation, upkeep, et cetera) often nearly outweigh any increase in production. In addition, about 70 percent of all freshwater consumed worldwide is used for irrigation, a major part of our most precious resource (Stauffer, 2013, Gowing, 2006). Ensuring sustainable operation depends on everything from people, infrastructure, education, and other support services to a region’s legal system (Dougherty, 1995). The environmental impacts of irrigation are great and unfortunately a major contributor to climate change, which is the primary cause of desertification and increased need for irrigation.
It is important to note that irrigation has some secondary effects that can be greatly beneficial, such as the potential for flood prevention. Uncontrolled floods can be devastating, but reservoirs built to supply irrigation systems often stop them before they occur (Dougherty, 1995). Flood plains also allow a groundwater “recharge” of sorts, and dams can provide hydroelectric power (Dougherty, 1995). These are merely the unintended positive effects of irrigation, as it fulfills its true purpose with increases in crop production that are vital to future food security worldwide. Irrigation also allows the poor in dry areas to be employed in agriculture that they otherwise would not have, improving economic stability as well as alleviating poverty. Irrigation also improves economic stability by creating agricultural jobs in previously non-arable regions.
Methods of Efficiency
There are many techniques farmers and governments use to try to increase the efficiency of irrigation systems, including:
Leveling of fields: equipment guided by a laser beam scrapes a field flat before planting to allow gravity to most efficiently transport water down a gradual hill. Flood irrigation then flows evenly throughout fields.
Surge flooding: releasing water onto a field at prearranged intervals and preventing unnecessary runoff.
Capture and reuse: Much of the flood-irrigation water used ends up wasted because it runs off the edges of fields. Farmers can capture the runoff, store it in ponds, and pump it back up to the top of the field for reuse in the next cycle of irrigation (USGS, 2015).
In the United States, 65 percent of all cropland harvested in 2013 (55.3 million acres) received water from irrigation (Hemmerly, 2015). About 39 percent of fresh water in the US goes toward irrigation (USGS, 2015). In 2005, about 26.6 million acres were irrigated with flood systems, 4.05 million acres with microirrigation systems, and 30.5 million acres with sprinkler systems. The average application rate was 2.35 acre-feet per acre (USGS, 2015).
The Imperial Valley in Southern California is a prime example of the success of irrigation, in terms of quantity of crop production; it was considered a desert wasteland, full of arid-adapted wildlife, but was converted into a highly fertile area after engineers completed the All-American Canal in 1940 to bring 2.5 million acre-feet of water annually from the Colorado River (Imperial Irrigation District, 2015). Now, over 1.29 million hectares produce fruits and vegetables year-round (Hemmerly, 2015), and provide much of the winter produce in America (Imperial Irrigation District, 2015). Because the climate is warm and temperate, the region is able to grow crops all year long using the added water. Many current deserts around the world could be transformed into equally productive regions if irrigation systems could be implemented, since the moderate climate in areas with little precipitation is beneficial for a variety of crops. Thus water resources in developing countries could be spread to greater areas rather than being concentrated and only helpful to one agricultural region. Mission 2019 proposes that residents in or near desert regions begin attempts to bring effective irrigation to those areas, through techniques such as contacting policymakers and fundraising.
Other countries produce more than half of their crops with the necessary help of irrigation: in the northern Jordan Valley of Israel, canals and pipelines now bring much-needed water to the arid south, transforming the country’s food production. In Pakistan’s Indus Basin, underground water is increasingly being pumped up to supply irrigation systems, leading to an intensification of the current shortage in energy. The region has the world’s largest contiguous network of river-fed irrigation canals (Stauffer, 2013).
Farmers in South Asia and other regions have also begun pumping up groundwater to supplement their low yields from rivers and lakes, causing a worrying drop in the water table. Great amounts of energy are consumed using this pumping method, as mentioned, which only exacerbates the existing power problem (Stauffer, 2013). Over the entirety of Asia, 60 percent of production requires irrigation, making the understanding of these issues vital to a food secure future (Gowing, 2006).
Large-scale, industrial irrigation systems supply fields, home gardens, livestock, fishing, aquatic plants/animals, and enterprises like brick-making, laundry, and bathing. Within these systems, four functional subsystems are usually distinct: water source, delivery, use, and disposal. They are usually continuously operational throughout the irrigation season and have existing water storage options. These can help with gaps in supply and demand and act as a buffer between primary and secondary canals or systems. On-farm storage lies in the “use” subsystem, and can include ponds or paddy basins that may be used for aquaculture as well (Gowing, 2006).
Less Developed Countries
In less developed countries in which use of irrigation is not yet widespread, there is great potential for better production. Many regions contain renewable water resources that may be used for this purpose (Figure 2). By implementing irrigation systems, the amount of arable land may be increased. For example, in Imperial Valley, California, desert was converted into fertile land by the creation of a canal directing river water to the desert (Hemmerly, 2015). In addition, the yields on land already under cultivation can be maximized to increase gross sales, value and employment (See figure 3). In some cases, yields increase two or three fold due to use of irrigation (Hart, 2001).
It is especially important to irrigate land because of the conditions of this decade. Irrigating land can reduce poverty by helping rural farmers increase their yields. When done efficiently, it also allows for urbanization. Since demand is constantly shifting toward vegetables and livestock from staple crops, modernized irrigation must be put in place to produce food with less water. It also makes it possible to diversify crops, which can add value to a farm (Hart, 2001). Climate change makes it necessary to use water resources more efficiently than in the past to stabilize crop growth conditions (Molden, 2007). Finding the best methods of irrigation is essential to feed a growing population in a warming world.
Figure 3. An example of the benefits of irrigation. Study of Alberta, Canada. (Hart, 2001)
The ideal method of irrigation will increase crop yields without depleting sought-after water resources. Currently 1.4 billion people live in areas with depleted groundwater. This number will only worsen with climate change (FAO, 2009). Mission 2019 suggests using alternative sources of water and efficient methods of irrigation as the best way to irrigate without further diminishing available water resources.
In certain regions, we suggest that groundwater continue to be used for irrigation. Groundwater is water pumped from underground aquifers to the surface of land to be used for irrigation or other purposes (See figure 4). In South Asia and the North China Plains there are good aquifers that can be used to irrigate farmland. Irrigation can help reduce the high poverty rates in the these areas (Molden, 2007). With new technologies and improved farming practices, the efficiency of groundwater use can be improved to ease environmental effects. Additionally, we propose that water-saving crops should be used in conjunction with groundwater irrigation to lessen its adverse effects (Molden, 2007).
Figure 4. A simplified diagram of groundwater extraction (Austin, 2015).
Alternatively, less pure sources of water can be used to irrigate. We propose that the use of alternate water sources is strongly considered in less developed regions. Options besides groundwater include wastewater, saline drainage water, canal water and floodwater (Molden, 2007). The benefit of using these sources of water is that they would not otherwise be used for human consumption. Additionally, they do not cause aquifer depletion, which in turn causes the ground to sink. A downside of using alternate sources of water is that they have the potential to contaminate crops if not regulated properly (Shuval, Adin, Fattal, Rawitz, & Yekutiel, 1986). In the case of wastewater irrigation, arid to semi-arid regions should receive a low-rate application of wastewater. This can improve crop growth, while keeping contamination risk to a minimum (Shuval, Adin, Fattal, Rawitz, & Yekutiel, 1986). Similarly, we recommend that spate irrigation is used to maximize the benefits of flood waters. In flood-prone areas, during peak floods, water can be diverted to fields for irrigation purposes (International Fund for Agricultural Development, 2015). Both wastewater and spate irrigation are particularly suitable methods for less developed countries. Their advantages are twofold: they provide water to the field and add nutrients to the soil. In poorer areas, fertilizers and fresh water are difficult to obtain, so this is an ideal solution. Ultimately the use of floodwater or wastewater to irrigate will help with long term soil fertility (Shuval, Adin, Fattal, Rawitz, & Yekutiel, 1986).
In most areas of less developed countries, we propose the implementation of drip irrigation systems as a reliable method to water crops. Drip irrigation systems are designed to provide water directly to the root area of plants, ensuring that plants take in the water. The water is applied frequently, in small quantities (Figure 5). This minimizes water loss due to evaporation. For example, in India, drip irrigation methods used 50 percent less water to produce the same yields as traditional methods (Howeler, Lutaladio, & Thomas, 2013). We suggest that a number of things are considered to make drip irrigation a viable option. The technique can be expensive because it tends to require advanced technology. It also often requires relatively pure water (Shuval, Adin, Fattal, Rawitz, & Yekutiel, 1986). With the development of improved drip irrigation, the systems will be able to use water with more suspended solids, like wastewater and floodwater. In the case of drip systems that cannot distribute wastewater, we recommend using sprinkler systems instead. Sprinkler systems provide the same advantage of a controlled rate of application, but more easily distribute wastewater at low pressure settings (Shuval, Adin, Fattal, Rawitz, & Yekutiel, 1986).
Figure 5. A model of inexpensive drip irrigation systems (Polak, Nanes, & Adhikari, 1997).
In order to benefit from irrigation in areas that have not previously used advanced farming techniques, we propose that governments strictly regulate its implementation. If not already present, legislation should be enacted specifying how water is used. This includes but is not limited to resource allocation and delivery of water in large quantities to farms (Molden, 2007). Legislation should also be in place ensuring best management practices for small and large farms (Molden, 2007). Specifically, in the case of wastewater, we propose that only certain types of crops should be irrigated. It is necessary to minimize contact between wastewater and crops and workers. We suggest that there be laws enacted requiring the disinfection of crops that have been overly exposed to wastewater. In addition, there needs to be wastewater treatment specifications to minimize the risks of wastewater irrigation (Shuval, Adin, Fattal, Rawitz, & Yekutiel, 1986).
With improvements in technology, there is a potential to greatly decrease the cost of irrigation systems. For example, it may be possible to cut the cost of drip irrigation from 2500 USD to 250 USD per hectare by use of simple innovations. This would favor small farmers, and would be especially helpful in areas where irrigation water has high value, like in India and sub-Saharan Africa (Polak, Nanes, & Adhikari, 1997). We recommend that government grants paid for by internal taxes are made available to help make irrigation systems viable in less developed countries. Compounded with temporary international aid, grants and new technologies can be successful in transforming farming in less developed nations (World Bank, 2007).
Austin, C. (2015). Groundwater Banking. Retrieved from http://mavensnotebook.com/the-notebook-file-cabinet/groundwater-banking/#top.
Dougherty, T. C., Hall, A. W., & Wallingford, H.R. (1995). Environmental impact assessment of irrigation and drainage projects. FAO.
Food and Agriculture Organization of the United Nations. (2009). How to Feed the World in 2050. Retrieved from http://www.fao.org/fileadmin/templates/wsfs/docs/expert_paper/How_to_Feed_the_World_in_2050.pdf.
Gowing, J. 2006. A review of experience with aquaculture integration in large-scale irrigation systems. In M. Halwart & A.A. van Dam, eds. Integrated irrigation and aquaculture in West Africa: concepts, practices and potential, pp. 7–16. Rome, FAO. 181 pp.
Hart, J. R. (2001). Benefits of Irrigation Development. In Irrigation into the 21st Century: Economic Benefits and Opportunities (7). Retrieved from http://www.aipa.ca/wp-content/uploads/2013/11/21st_Century_Economic_Benefits_and_Opportunities.pdf.
Hemmerly, T. E. (2015). Irrigation. Salem Press Encyclopedia, 2011.
Howeler, R., Lutaladio, N. B., & Thomas, G. (2013). Water Management. In Save and grow: Cassava (Chapter 4). Retrieved from http://www.fao.org/ag/save-and-grow/cassava/en/4/index.html.
http://www.fao.org/docrep/v8350e/v8350e09.htm#chapter 4: major impacts of irrigation and drainage projects
Imperial Irrigation District. (2015). Colorado River Facilities. Retrieved from http://www.iid.com/water/water-transportation-system/colorado-river-facilities.
International Fund for Agricultural Development. (2015). The Sudan: Making large-scale irrigation work for poor communities. Retrieved from http://www.ifad.org/english/water/sdn.htm.
Lipton et. al. (2003). Preliminary Overview of the Impact of Irrigation on Poverty. Food and Agriculture Organization of the United Nations, Land and Water Development Division.
Molden, D. (2007). Comprehensive Assessment of Water Management in Agriculture. In Water for Food, Water for Life: A Comprehensive Assessment of Water Management in Agriculture. Retrieved from http://www.iwmi.cgiar.org/assessment/files_new/synthesis/Summary_SynthesisBook.pdf.
Polak, P., Naner, B., & Adhikari, D. (1997). A Low Cost Drip Irrigation System for Small Farmers in Developing Countries. Journal of the American Water Resources Association, 33(1). Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1752-1688.1997.tb04088.x/abstract.
Shuval, H. I., Adin, A., Fattal, B., Rawitz, E., & Yekutiel, P. (1986). Wastewater Irrigation in Developing Countries: Health Effects and Technical Solutions. World Bank Technical Paper, 51. Retrieved from http://www-wds.worldbank.org/servlet/WDSContentServer/WDSP/IB/1999/09/17/000178830_98101904164938/Rendered/PDF/multi_page.pdf.
Stauffer, N. W. (19 August 2013). Large-Scale Irrigation. Energy Futures, Spring 2013. Retrieved from http://news.mit.edu/2013/large-scale-irrigation.
United States Geological Survey. (27 July 2015). Irrigation Techniques. U.S. Department of the Interior. Retrieved from http://water.USGS.gov/edu/irmethods.html.
World Bank. (2011). MZ PROIRRI Sustainable Irrigation Development (P107598) [Implementation Status & Results Report]. Retrieved from http://www-wds.worldbank.org/external/default/WDSContentServer/WDSP/AFR/2015/02/06/090224b082a6842d/1_0/Rendered/PDF/Mozambique000M0Report000Sequence007.pdf.