List of Projections:

1 - Evidence of Water on Mars - islands
2 - Evidence of water on Mars - canyons
3 - Major floods in U.S.
4 - Major Floods in China
5 - Inventory of water on Earth
6 - Earth's hydrologic cycle
7 - Residence time calculations (general form): t = Reservoir / Flux.

Water as basis for life

Water played an essential role in the development of life on Earth. Evidence of past or current occurrence of water on other planets is seen as an indicator for the potential presence of life.  Space craft exploring the surface of Mars transmitted images of surface features very similar to those produced by rivers on Earth [Projection 1, Projection 2].

Source of compilations: Munich Re-Large reinsurance company.

USA since mid 19th century: Johnstown, PA flood from a mine tailings dam collapse, resulted in about 2200 deaths; Mississippi River floods during summer of 1993 caused about $16 billion of losses; total of about 5000 deaths in USA from 25 major floods since 1899 and cumulative losses in excess of $32 billion. [Projection 3]

China since mid 17th century: 4 floods with deaths for each exceeding 500,000; at least three major floods on Yangtze-Kiang River during 20th century (1911, 1931, 1996); total deaths from 23 major floods of the order of 4 million people (almost 800 times greater than those from the USA since 1899); cumulative economic losses in excess of $64 billion. [Projection 4].

Other examples are the major floods in Europe in 2002.

How do we deal with these catastrophes? Should we build more dams or levees for flood control? Should we restrict settlements in areas (flood plains) that are often subject to flooding?

Major floods as stimulus for construction of dams.

Hydroelectric generation: largest electricity source other than fossil fuels & nuclear energy (about 20% of global and 10% of USA electricity supplies).

Construction of large dams on rivers primarily occurred during the 20th century, representing one of the major perturbations of the natural environment by humans. In the late 1990's there were globally 47655 dams above 15m. Construction of dams results in the displacement of people, affects ecosystems and fisheries.

Glen Canyon used to be one of the most beautiful canyons of the Colorado River  attracting many tourists. Building the Glen Canyon Dam resulted in formation of Lake Powell, which sparked the development of a new local tourism economy, but also almost eliminated native fish populations etc. Should this dam be removed to restore the original beauty of the canyon and the natural ecosystems? What will happen when Lake Powell has been filled with silt?

Given the dominance of short-term economic and political issues in most decisions about water resources, how can issues such as long-term sustainability be explicitly considered. Or should they be at all? Nearly all reservoirs will eventually fill up with sediments, leading to nearly total loss of the economic value of those investments, and requiring major new capital input just to prevent further downstream disruptions. Yet, to the first approximation, this issue is ignored as a serious consideration in assessing the viability of dam construction for particular projects.

Rainfall and river discharge in a number of semi arid and arid areas where water resources are very highly valued, such as Australia and the SW USA, experience large inter annual variations that have strong, but not perfect correlations with the El Nino-Southern Oscillation cycle. Thus probabilities of higher or lower rainfall amount could be explicitly included in water management decisions. Episodes will occur, however, where inclusion of such information could make management more difficult, especially in the political environment. How can we develop water management practices that incorporate new understanding of natural climate variability, as well as the significant uncertainties of our understanding of all natural systems.

Global warming may result in many sensitive regions becoming drier. Sea level rise is likely to affect freshwater resources in Pacific Islands.

Irrigation water is generally provided in arid regions of the USA and most other countries, at a small fraction of its actual cost to supply (usually less than 10%). Although this tends to significantly reduce the local cost of agricultural production, it often leads to accelerated depletion or degradation of water resources. Urban water supplies are delivered at much higher costs, usually much more than a factor of 10 greater per unit volume than irrigation water. Thus in areas such as CA and AZ, a substantial fraction of irrigation water supplies will be diverted to cities in the coming decades. Is this a trend that public policies should attempt to accelerate, retard, or passively accept?

Fossil groundwaters in many parts of the world are being rapidly depleted, mostly by pumping for irrigated crops. Should there be public policies that explicitly address this issue, or should we accept the loss of these resources as a natural economic outcome of intensive development and attempt to deal with the supply disruption consequences as they unfold? A major fraction of the water for new golf courses in Phoenix and other SW USA areas is derived from fossil groundwaters that are being rapidly depleted.

In the developing world, water quality issues have a huge impact on public health. About 80% of all disease in the developing world in water borne! Water contamination can be biological (e.g. cryptosporidium, Milwaukee, 1993; cholera, etc.) or chemical (Arsenic, solvents, gasoline, pesticides).

Provision of clean water resources to rural populations in the developing world is a very high priority to improve health conditions. In Bangladesh, a major international effort over three decades to stimulate use of shallow groundwaters as a source of pathogen-free domestic water supplies has led to more than 95% of rural populations having access to these new supplies. Although water-borne microbial diseases have been greatly reduced, there is now a huge epidemic of arsenic poisoning, derived from natural sources, affecting tens of millions of rural people from Bangladesh and West Bengal (India). How can affordable, safe water be provided to these people? How can the international community help avoid future "development" crises such as this?

More than 200 river basins are shared by several countries, for example Lebanon, Israel, and Palestine; Turkey and Iraq; US and Mexico and so forth. The frequency of water related conflicts is increasing (see Gleick, 2002). These conflicts are also very important on the local levels, for example between states (Colorado River) or within states (upstate New York versus New York City).

How can we manage river basins across international or state borders to reduce these conflicts?

The goal of water section of this course  is to help provide some scientific basis to contribute to better policy decisions on water related issues.

2. The Earth's water (hydrologic) cycle

Most of the Earth's water is in the oceans. Only a tiny fraction of all water (<< 1% of the global total) is available for our use [Projection 5].

Of all water on land, less than 1% is in rivers, lakes, and soils, but 25% is in groundwater. Why are we using mostly surface waters? One reason is that the residence time of surface waters (days to years) is so much shorter than that of groundwater (years to millions of years). Hence, surface waters are replenished much more rapidly then groundwaters.

Representative reservoirs (water amount) and fluxes (water amount transported per time) in the Earth's hydrological cycle provide some insight about global water resources [Projection 6].

Basic Principle of residence time calculations: residence time = reservoir/flux [Projection 7]

Updated September 10, 2003
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