Roman aqueducts, such as this photo of the > 160 foot tall aqueduct at Pont du Gard near Nimes (Figure 1), symbolize the engineering advances and glory of the Roman civilization (Smith, 1978). The aqueducts accounted for only 5% of the 300 miles of water systems supplying ancient Rome, which are considered one of the great engineering achievements in antiquity. Their hydraulic technology was not duplicated until the 17th century, after engineers tried to pump water from the Seine and the Thames to sustain rapidly expanding populations in Paris and London, respectively. Unfortunately, the water from those rivers was inferior in quality - when it was not lethal.

Aquatic origins of humanity

Potable fresh water was, is, and, for the foreseeable future, will be a limited commodity for civilization. It first developed in the "Fertile Crescent" in southwest Asia, where water resources facilitated the development of agriculture; and that civilization then declined when its water resources became depleted. That pattern has been repeated elsewhere throughout history up to the present, and it is projected to continue into the future.

Human history began approximately 7 million years ago with the evolution of protohuman species (Australopithicus africanus, Homo habilis, and Homo erectus) in Africa, with the subsequent evolution into humans (Homo sapiens) that spread throughout the world (Figure 2). That global expansion began with the "Java man" (H. erectus), who migrated into Asia between 1 and 1.8 million years ago. Modern humans (H. sapiens) are then believed to have evolved from H. erectus approximately 500,000 years ago, and populated all corners of the world by 2,000 BC (4,000 years ago).


Figure 2. Historic migration of humans


However, human society did not evolve past a tribal level until approximately 10,000 to 6,000 BC) with the development of organized food production in the "Fertile Crescent" of Mesopotamia (Figure 3). It was located between the Tigris and Euphrates rivers, which is now referred to as the "cradle of civilization". Diamond(1997) primarily attributes the development of that early civilization to (1) the presence of native plants that had evolved in a Mediterranean climate, where mild, wet winters and long, hot dry summers selected for hermaphroditic, rapidly growing plant species (3 cereals and 4 pulses) with large seeds that were suitable for foraging and agriculture; (2) the presence of large mammals (goat, sheep, cow and pig) that could be domesticated; and (3) the difficulty of sustaining competing hunter-gatherer lifestyles in an area with few large rivers and a small coastline, which provided meager aquatic resources (fish and shell fish). In summary, the origins of human society in Mesopotamia appear to have been catalyzed by the availability of water resources that that were sufficient to initiate crop cultivation and animal husbandry, but insufficient to sustain a large population of hunter-gatherers.


Figure 3: The Fertile Crescent


Historic droughts


"You don't know the worth of water, until the well runs dry"

(Ben Franklin)


While Mesopotamia became known as the 'breadbasket of southwestern Asia" and by the constructs of it's advanced societies, including the hanging gardens of Babylon that arose in the middle of the third millennium BC, it then crumbled around 2200 BC during a 300 year drought. The drought has been associated with a rapid climate change that affected areas between the Aegean Sea , Nile and Indus Valley. Associated droughts have been correlated with concurrent declines of the Old Kingdom in Egypt, early Bronze Age cities in Palestine, and the early Minoan civilization in Crete.

The global extent of that climate change has been derived from analyses of variations in oxygen isotope ratios in Greenland ice cores. The ratios show temperature changes extending to end of last ice age 11, 700 years ago and then relatively stable warm temperatures during the Holocene. This indicates that the entire span of human civilization appears to have occurred within a relatively stable, mild environment, in spite of those devastating droughts.

There is evidence of comparable historic droughts in the New World. While associated paleoindian hunter-gatherer populations throughout the Americas were able to respond rapidly to the changes in resources with resultant heterogeneous patterns of population densities and subsistence strategies, many of the more complex, agricultural-based societies either dramatically declined or even collapsed (Markgraf, 1998). This is illustrated by the following case study.


Case Study: Collapse of the Maya Civilization

The sudden collapse in of the Classic Maya civilization in Mesoamerica around 800 AD has been associated with a protracted drought (Hodell et al., 1995). It was documented with a reconstruction of temporal variations in calcite (CaCO3), gypsum (CaSO4), sulfur (S), fossil organisms (foraminifera, ostracods, and gastropods), and oxygen isotopes ( 18O) in a radiocarbon dated sediment core from Lake Chichancanab, Mexico. That paleoclimate record was consistent with other measurements of low lake stands in central Mexico and increased forest fires in Costa Rica during the same period, 1400 to 800 BP. In toto, these analyses indicate the period between AD 800 - 1000 AD was the driest episode in the region over the past 8,000 years (Figure 4).

Figure 4: May1998 NG

It is now believed the drought exacerbated several interrelated factors that resulted in the remarkable demise of an advanced civilization that had developed 3,000 years ago. Hieroglyphic texts indicate those factors included population growth, environmental degradation, and inter-city conflict. Since the same factors exist throughout the world today, the drought and decline of the Maya civilization is more than an esoteric interest, as noted by Sabloff (1995).

"The research by Hodell and colleagues contributes to scholarly attempts to understand why and how the Classic Maya successfully adapted to their tropical environment for so many centuries, overcoming numerous problems and reaching population levels that far exceed modern ones in the same area, and why they ultimately failed. Their research also raises an anthropological question that is relevant not only to the ancient Maya but to the contemporary world as well, and is certainly deserving of continued attention - namely, how severe do internal stresses in a civilization have to become before relatively minor climate shifts can trigger widespread cultural collapse?"


Disappearance of the Anasazi

Recent studies have revealed that much of North America was much drier prior to its European colonization. This is illustrated by a reconstruction of the climatic history in the Great Plains over the past 2,300 years, using variations in fossil diatoms in a North Dakota lake (Laird et al., 1996) which show that the last 100 years have been atypically wet and that there was a much greater frequency of relatively extreme droughts prior to 1200 AD (Figure 5). The longest of those droughts lasted for centuries (200 to 370, 700 to 850, and 1000 to 1200 AD) and were markedly drier than the relatively brief dry period during the 1930's Dust Bowl period, which had such a devastating impact in US history. Similar climatic records in precipitation have been found in California, using analyses of temporal variations in flooding in San Francisco Bay (Ingram et al., 1996) and the Sierras that parallel the historic record of droughts in Patagonia (Stine, 1994) As in the Old World, the paleoclimate record indicates the development of North America coincided with an unusually wet period in history and that recent devastating droughts in North America are inconsequential compared to droughts that can be expected in the future.

Figure 5: Laird et al., Nature Dec 12, 1996.

From time series analyses of Indian populations and environmental change in the Southwest, it appears that environmental fluctuations in precipitation affected human demography throughout the past two millennia (Martin, 1994). Prior to 1000 AD, populations were presumably low enough to have allowed fairly simple behavioral responses that primarily involved the relocation of small groups to nearby areas that were less affected by environmental degradation and human occupation. After 1000 AD, when growing populations filled habitable areas and curtailed settlement mobility as an adaptive response, other behavioral adjustments were necessary. These included subsistence intensification, increased inter-group interaction, and increased sociocultural complexity

However, the long period of relatively moderate environment in the Southwest ended around 1130 AD, when conditions worsened in all the major habitat zones (Figure 6). A severe drought caused a dip in alluvial groundwater levels, reduced water flow, and a severe and prolonged downcutting of floodplain sediments. Again, this marked water scarcity coincided with the desertion of pueblos in the US southwest, as it had with the abrupt decline of the Classic Maya civilization (in Guatemala, Mexico, Belize, and Honduras) a few centuries (Sabloff, 1995).

The scarcity of water in the that region was subsequently reported by Spanish explorers (e.g., Don Francisco Vasquez de Coronado) in the 1500s and 1600s and by US explorers (e.g., Lewis and Clark, General Pike, Jedediah Smith, and John Wesley Powell) in the 1800s (Reisner, 1993). Perhaps, the most extensive account of the limited amount of water in that area was by John Wesley Powell, as recounted in the histories of DeVoto (1952), Stegner (1953), and Reisner (1993). In addition, European disease vectors and the presence of Europeans, themselves, contributed to the failure of native populations to grow appreciably until the introduction of modern health care practices in the late nineteenth century (from Martin, 1994).


European Colonization of North America

The mysterious fate of the first English speaking settlers in the New World also appears to have been caused by a severe drought. As history books note, Virginia Dare, the first English child born in America on August 18, 1587, along with every one else in Lost Colony of Roanoke disappeared. That disappearance has, recently, been correlated with the most extreme three year drought in 800 years on Roanoke Island, using tree ring growth measurements (Stahle et al., 1998). The relatively high mortality of the later colony at Jamestown, also, appears to have been, at least partially, due to another extended drought from 1606 to 1612.

In spite of those initial set backs and previously noted reports of water scarcity in the southwest by Spanish and American explorers, large numbers of Americans emigrated to the Great American Desert in the 1860s during an unusually humid weather pattern in that area (Reisner, 1993; Laird et al., 1996). Some scientists mistakenly concluded that fluke coincidence was causal, and they founded a new school of meteorology to explain it. Their motto was:

"Rain Follows the Plow."

The leading proponent of that idea was Professor Cyrus Thomas. He observed: "Since the territory (of Colorado) has begun to be settled…towns and cities built up, farms cultivated, mines opened, and roads made and traveled, there has been a gradual increase in moisture…I therefore give it as my firm conviction that this increase in moisture is of a permanent nature, and not periodical, and that it is in some way connected to the settlement of the country, and that as population increases the moisture will increase (as cited in Reisner, 1993). Several explanations were proposed to account for this covariance. These included plowing the land, which released moisture to the atmosphere; planting trees; which increased rainfall; train smoke, which caused rain to form, and commotion on land from human activities. Based on the latter hypothesis, "dynamiting the air became a popular means of inducing rain to fall (Reisner, 1993). Unfortunately, a return to normal weather conditions and associated drought disproved the hypothesis.*

The limited amount of water in the American west quickly lead to competition among individuals and interest groups. One perspective on that conflict, which continues today, is Marc Reisner's (1993) Cadillac Desert, which was made into a PBS series with the same name in 1997. Other global perspectives on current problems associated with declining fresh water resources are those of Postel (1992), Last Oasis: Facing Water Scarcity; Clarke (1993), Water: The International Crisis; and Gleick (1993) Water in Crisis.

* Recent studies indicate that it rains more often on the week-ends due to anthropogenic emissions during the week that serve as nuclei for precipitation (Cerveny and Balling, 1998).


Environmental Consequences of Diminishing Freshwater Resources

The preceding titles, and those of other recent texts, instill an attitude of desperation and gloom that is, at least partially, supported by some facts. The 1975 WHO study of 90% of developing countries (excluding China) determined that only 35% (1.4 billion people) of the global population had access to relatively safe drinking water and that only 32% (1.2 billion people) had proper sanitation (Clarke, 1993). Moreover, total water use in the world has quadrupled over the last 50 years (Clarke, 1993), and is projected to parallel future increases in population growth and industrialization.

However, Rogers (1993) argues that when US cases (irrigation, domestic supply, wildlife support) are examined, there are usually good alternatives available at a relatively small cost. This perspective is consistent with that of Vogel (1993), who observes:

"An emerging theme in U.S. water policy and management appears to be a return to what was once called integrated or unified river basin management and is now couched in terms of watershed management and sustainable yield."

Hence, the US does not appear to be facing a water crisis on the same scale as that being confronted by some other water scarce areas.


Current Vulnerability of U.S. Water Resources

The vulnerability of U.S. water resources has been exacerbated by projected climate changes associated with global warming (Waggoner, 1991). The principal indicators, or "warning lamps", of that vulnerability are:

  1. consumption: supply
  2. storage: supply
  3. variability of runoff
  4. dependence upon hydroelectricity
  5. overdrawing of groundwater

"In today's climate and in all of the 21 American water-resource regions, at least one warning is flashing, and in the Great Basin, Missouri, and California regions four of five are flashing."

Since the potential size of those water resources are the residual precipitation after evaporation, the effect of increasing temperature on those water resources is not linear (Waggoner, 1991). "An international appraisal "concluded that a 1ß to 2ßC warming coupled with 10% less precipitation could reduce runoff 40 to 70%." This is especially important in the western states, where much of the surface runoff is derived from snow that would "store less water if it melted sooner".

The magnitude of those projected decreases pale in light of recent discoveries of much larger natural droughts in California. Based on analyses of relic tree stumps in California's Sierra Nevada, Stine (1994) concluded that extremely severe drought conditions extended for more than two centuries before ~1112 and for more than 140 years before AD ~ 1350 and that runoff from the Sierras during those periods was "significantly lower than during any of the persistent droughts that have occurred in the region over the past 140 years." Similarly, Ingram et al. (1996) concluded, from their analyses of variations in the isotopic composition of fossil shells in San Francisco Bay, that "alternate wet and dry (drought) intervals typically have lasted 40 to 160 yr." in the San Francisco Bay drainage area (Sacramento and San Joaquin valleys) over the past 750 years. In other words, the size and extent of "record" droughts that have disrupted California since the Gold Rush are inconsequential compared to prehistoric droughts in the area.


Societal Impacts of Future Water Scarcities

White (1968) has observed that the historical roots of our ecological crisis are based on the Western view that nature was ours to exploit and consume, but that it was not until science and technology united in the nineteenth century that "the impact of our race on the environment has so increased in force that it changed in essence". The resultant ecological crisis is creating social problems. These, in turn, are increasing pressures on the environment.

The societal consequences of current and projected water deficiencies have recently received a great deal of attention. Two of the most widely read articles on these escalating problems are those by Homer-Dixon et al. (1993) and Kaplan (1994). The latter was published in The Atlantic Monthly, whose cover consisted of a picture of a shriveled globe on fire and the following caption:

"The coming anarchy: Nations break up under the tidal flow of refugees from environmental and social disaster. As borders crumble, another type of boundary is erected - a wall of disease. Wars are fought over scarce resources, especially water, and war itself becomes continuous with crime, as armed bands of stateless marauders clash with the private security forces of the elites. A preview of the first decades of the twenty-first century."

This dire prediction has been partially substantiated by recent events (e.g., tribal wars and cholera epidemics in water scare regions of Rwanda). New calculations also indicate the degree of water scarcity on a global scale is now greater than the previous WHO estimates (Postel; 1992; Clarke, 1993; Gleick, 1993). Again, that scarcity is projected to increase along with the expanding global population.


Limitations in Projected Population Growth

Those estimates of the impact of future water scarcities are severely constrained by limitations in projections of population growth. Most population projections avoid assigning a probability to the projections of a single projection or a set of low, medium, and high variants, and rarely provide a probabilistic interpretation. That limitation was addressed by Lutz et al. (1997), who incorporated expert opinions on trends in fertility, mortality, and migration, and derived the 90% uncertainty range for those trends on world population growth between 1995 and 2100 was unlikely. Specifically, they determined there is a two thirds probability that the population will not double again in the twenty-first century. Therefore, projections of water scarcity based on current exponentially increasing growth rates may be erroneously high.

Those global projections also contrast with many regional projections. For example, some regions are projected to more than double and other regions are projected to decline during that period. The median projection for North Africa is a growth from 162 millions to 439 millions and the Middle East is projected to increase from 151 millions to 515 millions. Conversely, the population of the former Soviet Union is projected to decline from 238 millions to 188 millions. The population of North America is projected to increase from 297 to 403 millions, with 95% confidence limits of increases from 303 millions to 534 millions; and a disproportionately large fraction of that increase is projected to occur in California.


Minimizing Water Shortages

While all of the preceding accounts provide a relatively bleak outlook on the environmental health of a world with increasing demands for a declining supply of fresh water, others are more optimistic (Byerly, 1995). Reisner, who has just completed a study for maintaining water subsidies for some agricultural interests in California that has reportedly put him at odds with some environmental groups, has also reportedly stated that his perspective on the problem is "evolving" (San Jose Mercury, September 13, 1997). Additionally, both Gleick's and Postel's books include descriptions of ways to conserve and recycle water. The latter includes the following table listing examples of companies saving water in San Jose, California.


Selected Cases of Industrial Water Savings in San Jose California

(from Postel, 1992)

-----------------Water Use-------------------


Water Savings
Payback Period on

(thousands of cubic meters per year)



California Paperboard Corporation


Gangi Brothers Food Processing




Advances Micro Devices


Tandem Computers


Dyna-Craft Metal Finishing



Byerly, R. Jr. 1995. U.S. science in a changing context: A perspective. In: U.S. National Report to International Union of Geodesy and Geophysics 1991-1994: Contributions in Hydrology. American Geophysical Union, Washington, D.C. , pp. A1-A16.

Cerveny, R.S. and R.C. Balling, Jr. 1998. Weekly cycles of air pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region. Nature 394: 561-563.

Clarke, R. 1993. Water: The International Crisis. The MIT Press, Cambridge, MA, 193 pp.

De Voto, B. 1952. The Course of Empire. Houghton-Mifflin, Boston, MA

Gleick, P.H. (editor).1993. Water in Crisis - A Guide to the World's Fresh Water Resources. Oxford University Press, New York, 473 p.

Hodell, D.A., J.A. Curtis, and M. Brenner. 1995. Possible role of climate in the collapse of Classic Maya civilization. Nature 375: 391-393.

Homer-Dixson, T.F., J.H. Boutwell, and G.W. Rathjens. 1993. Environmental change and violent conflict. Scientific American, Feb., pp. 38-45.

Ingram, B.L., J.C. Ingle, and M…E. Conrad. 1996. A 2000 yr. record of Sacramento-San Joaquin river inflow to San Francisco Bay estuary, California. Geology 24: 331-334.

Kaplan, R.D. 1994. The coming anarchy. The Atlantic Monthly, February, pp. 44-76.

Laird et al. 1996. Nature Dec12, 1996

Lutz, W., W. Sanderson, and S. Scherbov. 1997. Doubling of world population unlikely. Nature 387: 803-805.

Markgraf, V. 1998. Researchers investigate inter-hemispheric climate linkages in the Americas and their societal effects. EOS 79:371, 378.

Martin, G.J. 1994. Adaptive stress, environment, and demography. In: Themes in Southwest Prehistory (G.J. Gumerman, editor), School of American Research Press, Santa Fe, NM.

Moreau, D.H. 1995. National water policy: Shifts continue. In: U.S. National Report to International Union of Geodesy and Geophysics 1991-1994: Contributions in Hydrology. American Geophysical Union, Washington, D.C. , pp. 937-940.

Postel, S. 1992. Last Oasis: Facing Water Scarcity. W.W. Norton & Company, New York, NY. 239 pp.

Reisner, M. 1993. Cadillac Desert. Penguin Books, New York, NY, 582 pp.

Rogers, P. 1993. America's Water - Federal Roles and Responsibilities. The MIT Press, Cambridge, MA, 285 p.

Sabloff, J.A. 1995. Drought and decline. Nature 375: 357.

Stegner, W. 1953. Beyond the Hundredth Meridian. Houghton-Mifflin, Boston, MA

Stine, S. 1994. Extreme and persistent drought in California and Patagonia during mediaeval time. Nature 369: 546-549.

Truelson, S. 1997. Are American students learning facts or fears ?. Register-Pajaronian, March 17, 1997, pp. 11.

Vogel, R.M. 1995. Recent advances and themes in hydrology. In: U.S. National Report to International Union of Geodesy and Geophysics 1991-1994: Contributions in Hydrology. American Geophysical Union, Washington, D.C. , pp. 933-936.

Waggoner, P.E. 1991. U.S. water resources versus an announced but uncertain climate change. Science 251: 1002.

White, L., Jr. 1968. Dynamo and Virgin Reconsidered, MIT Press, Cambridge, MA 186




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