Water Scarcity

Hoover DamWater scarcity is an enormous challenge in many parts of the world, with many of the world’s most important aquifers being drained much faster than they can be replenished. These trends in water availability will have effects on food production systems, water-borne illness patterns, and other water-related diseases.  For example, the aquifer under the North China Plain, where half of China's wheat is grown, is falling at up to three meters/year, and it is estimated that each year 300 million Indians and Chinese are being fed on fossil water that is not being replenished.  Demographic changes are driving sharp increases in global water demand at a time when climate change promises to increase water scarcity in a variety of ways, including more extreme forms of precipitation, dry areas becoming drier, earlier spring runoff from winter snow pack, loss of glacial contributions to dry-season flow, sea level rise and inundation of coastal aquifers with salt water, and hotter temperatures leading to increased evapotranspiration. 

These complex changes in quantity, quality, and timing of water availability, overlaid on significant existing water scarcity and increasing demand, are likely to impact food production, water-borne disease exposure, and water-related diseases.  Changes in land use (e.g., deforestation) also impact water quality and quantity and exposure to water-borne disease in ways that are inadequately understood.  Research to better characterize these challenges and identify approaches to reducing vulnerability is urgently needed.

Learning Objectives

  • L1: Relate and analyze the linkages between drivers of water scarcity and health implications.
  • L2: Describe how water availability and quality affect economic opportunities and human well-being, and how human activity affects water resources.
  • L3: Understand the natural systems and physical properties of water that contribute to its fundamental role in driving Earth systems.
  • L4: Explore how availability of and demand for water resources is expected to change over the next 50 years and what this means for health.

 

McMichael AJ, Patz J, Kovats RS. Impacts of global environmental change on future health and health care in tropical countries. Br Med Bull [Internet]. 1998;54 :475-88. Publisher's VersionAbstract

The aggregate human impact on the environment now exceeds the limits of absorption or regeneration of various major biophysical systems, at global and regional levels. The resultant global environmental changes include altered atmospheric composition, widespread land degradation, depletion of fisheries, freshwater shortages, and biodiversity losses. The drive for further social and economic development, plus an unavoidable substantial increase in population size by 2050--especially in less developed countries--will tend to augment these large-scale environmental problems. Disturbances of the Earth's life-support systems (the source of climatic stability, food, freshwater, and robust ecosystems) will affect disproportionately the resource-poor and geographically vulnerable populations in many tropical countries. Ecological disturbances will alter the pattern of various pests and pathogens in plants, livestock and humans. Overall, these large-scale environmental changes are likely to increase the range and seasonality of various (especially vector-borne) infectious diseases, food insecurity, of water stress, and of population displacement with its various adverse health consequences.

Rosegrant MW, Ringler C, Zhu T. Water for agriculture: maintaining food security under growing scarcity. Annual Review of Environment & Resources [Internet]. 2009;34 :205-22. Publisher's VersionAbstract

Irrigated agriculture is the main source of water withdrawals, accounting for around 70% of all the world's freshwater withdrawals. The development of irrigated agriculture has boosted agricultural yields and contributed to price stability, making it possible to feed the world's growing population. Rapidly increasing nonagricultural demands for water, changing food preferences, global climate change, and new demands for biofuel production place increasing pressure on scarce water resources. Challenges of growing water scarcity for agriculture are heightened by the increasing costs of developing new water, soil degradation, groundwater depletion, increasing water pollution, the degradation of water-related ecosystems, and wasteful use of already developed water supplies. This article discusses the role of water for agriculture and food security, the challenges facing irrigated agriculture, and the range of policies, institutions, and investments needed to secure adequate access to water for food today and in the future.

Markelz RJC, Strellner RS, Leakey ADB. Impairment of C-4 photosynthesis by drought is exacerbated by limiting nitrogen and ameliorated by elevated CO2 in maize. Journal of Experimental Botany [Internet]. 2011;62 :3235-3246. Publisher's VersionAbstract

Predictions of future ecosystem function and food supply from staple C(4) crops, such as maize, depend on elucidation of the mechanisms by which environmental change and growing conditions interact to determine future plant performance. To test the interactive effects of elevated [CO(2)], drought, and nitrogen (N) supply on net photosynthetic CO(2) uptake (A) in the world's most important C(4) crop, maize (Zea mays) was grown at ambient [CO(2)] (∼385 ppm) and elevated [CO(2)] (550 ppm) with either high N supply (168 kg N ha(-1) fertilizer) or limiting N (no fertilizer) at a site in the US Corn Belt. A mid-season drought was not sufficiently severe to reduce yields, but caused significant physiological stress, with reductions in stomatal conductance (up to 57%), A (up to 44%), and the in vivo capacity of phosphoenolpyruvate carboxylase (up to 58%). There was no stimulation of A by elevated [CO(2)] when water availability was high, irrespective of N availability. Elevated [CO(2)] delayed and relieved both stomatal and non-stomatal limitations to A during the drought. Limiting N supply exacerbated stomatal and non-stomatal limitation to A during drought. However, the effects of limiting N and elevated [CO(2)] were additive, so amelioration of stress by elevated [CO(2)] did not differ in magnitude between high N and limiting N supply. These findings provide new understanding of the limitations to C(4) photosynthesis that will occur under future field conditions of the primary region of maize production in the world.

Rijsberman FR. Water scarcity: Fact or fiction?. Agricultural Water Management [Internet]. 2006;80 :5-22. Publisher's VersionAbstract

It is surprisingly difficult to determine whether water is truly scarce in the physical sense at a global scale (a supply problem) or whether it is available but should be used better (a demand problem). The paper reviews water scarcity indicators and global assessments based on these indicators. The most widely used indicator, the Falkenmark indicator, is popular because it is easy to apply and understand but it does not help to explain the true nature of water scarcity. The more complex indicators are not widely applied because data are lacking to apply them and the definitions are not intuitive. Water is definitely physically scarce in densely populated and areas, Central and West Asia, and North Africa, with projected availabilities of less than 1000 m(3)/capita/year. This scarcity relates to water for food production, however, and not to water for domestic purposes that are minute at this scale. In most of the rest of the world water scarcity at a national scale has as much to do with the development of the demand as the availability of the supply. Accounting for water for environmental requirements shows that abstraction of water for domestic, food and industrial uses already have a major impact on ecosystems in many parts of the world, even those not considered "water scarce". Water will be a major constraint for agriculture in coming decades and particularly in Asia and Africa this will require major institutional adjustments. A "soft path" to address water scarcity, focusing on increasing overall water productivity, is recommended. 

Wu D-X, Wang G-X, Bai Y-F, Liao J-X. Effects of elevated CO2 concentration on growth, water use, yield and grain quality of wheat under two soil water levels. Agriculture, Ecosystems & Environment [Internet]. 2004;104 :493-507. Publisher's VersionAbstract

Wheat (Triticum aestivum L.) is one of the most important food sources in the world. The potential impacts of elevated CO2 on wheat yield and grain quality will have profound influences on the supply and nutritional value of wheat products as well as on many industrial sectors. A growth-chamber experiment was designed to estimate how soil moisture influences the potential effects of elevated CO2 concentration ([CO2]) on wheat growth, water use and grain yield. Spring wheat (T. aestivum cv. Ganmai 8139) was grown in pots placed in controlled growth chambers and was subjected to two [CO2] (approximately 350 and 700 μl/l, respectively) and two soil water levels (80 and 40% of field water capacity (FWC), respectively). High [CO2] increased plant shoot dry weight by 89% under 80% FWC and by 53% under 40% FWC. Grain yield of wheat was markedly increased under elevated [CO2] with greater grain number and harvest index. The ratio of plant shoot dry weight to height was increased by 75% under high [CO2] at high soil moisture, and by 54% at low moisture. Water use efficiency of shoot (WUEs) and grain yield (WUEg) were increased under high [CO2] because the magnitude of the increase in shoot dry weight and grain yield was greater than that of the cumulative consumption of water under high [CO2] conditions. When wheat plants were under high [CO2] conditions and maintained at high moisture, the WUEs and WUEg were increased by 62 and 128%, respectively. Elevated [CO2] resulted in lower concentrations of mineral nutrients (N, P, K and Zn), lysine and crude protein in mature grains. This was probably caused by a dilution effect induced by great increment of carbohydrate in grains. The total quantity of mineral nutrients, lysine and crude protein accumulated in grains per hectare were still increased under high [CO2] due to increase in grain yield. Our results indicate that high [CO2] is beneficial to plant growth, yield and WUE, while grain quality was lowered under high [CO2] conditions as reflected by the increased crude starch content, and corresponding decreases in mineral nutrients, lysine and crude protein concentrations. The analysis of yield components suggested that the yield increase was mainly attributable to an increase in the number of grains. However, the effects of CO2enrichment on plants depend on the availability of soil moisture, and plants may benefit more from CO2 enrichment when sufficient water is supplied.

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