Over the past decade it has become obvious that the world is warming - Arctic and Antarctic ice is shrinking steadily and glaciers are retreating worldwide. Climate models predict a significant increase in global temperature this century, raising concerns that global climate will reach "tipping points:" major changes (like shifts in ocean currents) which could take centuries to reverse. Unfortunately, the models, while improved, are still clearly imperfect and the actual amount of warming remains controversial. Even more controversial is the degree to which human activities, particularly greenhouse gas emissions, contribute to this warming trend. With these uncertainties, the probable effects are also uncertain and controversial. Ocean level rises and more powerful storms are likely, as well as changing climate patterns which will affect water supplies, agricultural patterns, wildfire frequency and intensity, and the distributions of pests and diseases.

The potential impacts of these effects range from minimal to catastrophic. Prudence requires that we address these challenges, but also requires that we avoid committing large resources to uncertain projects. A key objective is to make our response systems more resilient without major expenditures. This will be beneficial even if effects turn out to be milder than current projections and will improve our capacity to address other unexpected challenges. Improving system resilience will also be critical if worse effects do materialize. What can be done now, at relatively modest cost, to provide maximum improvements in current capabilities?

Water Challenges: Houses without water are uninhabitable; fields without water are infertile; most business require water to operate and industrial plants typically use large quantities. Conflicts between these users can only increase if supplies diminish. Global warming will shift rainfall patterns, reducing water availability in numerous areas; the general consensus is that the already dry southwest will become drier and northern areas will become wetter.

The good news is that there is already in place an extensive network of institutions addressing these issues at the national, regional, state and local levels. As detailed in a 2007 report by the National Academy of Sciences on the Colorado River Basin, this network actively manages water resources and is well aware of amelioration technologies, including desalination and the use of water efficiency devices. The report also acknowledges that sustained, severe drought has been a recurring feature of the region, even in the absence of current global warming trends.

Unfortunately, the focus of the report is how to maintain more or less the current usage patterns in the face of routine regional droughts. None of the planning which is discussed addresses the actions which would be necessary in the face of sustained, severe drought which could force the relocation or even abandonment of homes, facilities, and industrial operations. Questions of aquifer depletion, the environmental impact of large-scale desalination operations, or research on water efficiency technologies are not even addressed.

The main challenge is at the grass roots, user level.

There has been much research on energy efficient dwelling or commercial buildings. Thanks to solar radiation (as well as local wind or geothermal resources) it is possible to construct buildings requiring zero energy input. But it is virtually impossible to construct buildings with zero requirement for water input. Even buildings which today seem self-sufficient thanks to wells or local streams ultimately depend on rainfall and ground water resources. There is already wide availability of some water saving technologies (e.g., low-flow shower heads or toilets, waterless urinals). Other amelioration approaches have been evaluated in detail, such as rain capture (presently illegal in some localities) or re-use of gray water, but rarely put into practice. Most of the responsibility lies at the state or local level and a few states have systematic programs; perhaps the best is California's Office of Water Use Efficiency. But overall, the amount of on-going research pales in comparison to research on energy efficiency. Municipalities take measures for addressing short-term droughts, such as restricting or prohibiting certain activities (e.g., landscape watering or car washing); some longer term measures are also used, particularly withholding construction permits or reducing the allowance for preferential water rates and so encouraging the application of water saving technologies. But there is little planning or even discussion on how to address hard questions of water allocation in the face of sustained, severe drought.

Agricultural use raises even more challenging questions. Water stress, combined with increased heat, pests, diseases, and weather extremes will pose adaptation challenges for crop and livestock production. This can severely affect crop suitability, forcing shifts in agricultural patterns, necessitating changes not only in crop, livestock and forestry operations in specific regions, but in equipment requirements, marketing arrangements, industrial locations and manpower needs. In extreme cases, such as California's Imperial Valley, desert areas have been turned into productive agricultural regions thanks to extensive irrigation. Through the years, these areas have typically worked hard to improve water usage - lining irrigation ditches, for example, or using soil moisture measurements to maximize irrigation efficiency. Nevertheless, pressures of growing populations have steadily forced reductions in water use, even without the impact of global warming. In the face of declining water availability, private groups and the US Department of Agriculture have initiated wide ranging research into plant varieties requiring less water or alternative crops. These measures, however, have focused on making more efficient use of present agricultural facilities and rarely address the question of large-scale shifts which might be forced by water shortages. The National Association of Wheat Growers, for example, strongly supports efforts to limit global warming. It systematically looks at research priorities but none of these address potential major shifts in growing areas. Among the states, California is again in the lead with systematic assessments of future challenges and plans to address them. For agriculture, a 10-20% reduction in water availability would force some reductions in planted acreage and undermine the economic viability of some farms; but a 40-80% reduction would force realignments of irrigation networks and the closing of outlying farms.

Many industrial processes require large amounts of water; industry accounts for roughly 10% of all water usage. Industry has put a significant effort into energy efficiency, but much less into water efficiency. The American Chemistry Society (the largest professional organization in the world), for instance, has almost nothing of water efficiency on its web site or on the web site of its weekly news magazine. The American Chemistry Council, the corresponding industrial organization, touts its major reductions of overall emissions and extensive work on energy efficiency but also has almost nothing to say on water efficiency. Similarly, the National Association of Manufacturers stresses energy efficiency; its handbook mentions water efficiency but gives it scant attention. California has done some evaluations of industrial water usage and set up a Water Desalination Task Force which has had little activity in the last several years. Overall, industrial water efficiency efforts lag considerably behind industrial energy efficiency efforts.

In summary, there is a recognition that sustained, severe drought is possible and that shifts in water availability and agricultural patterns are likely. But there is little systematic effort to address this, even though there are a number of relatively low cost efforts which could be implemented promptly, including:

• Systematic efforts at developing and installing water efficiency technologies in existing and new buildings.




• Severely restricting new building permits in areas of projected water shortages.




• Research and implementation of new water efficiency technologies, which include technologies to reduce home water use, to develop and promote landscape and agricultural plants which require less water, and to realign industrial processes to minimize water usage.




• Increase water availability by improving reuse and recycling as well as research to improve desalination technologies.




• Encouraging gradual shifts in agricultural use patterns before any large-scale shifts are urgent.




• Encouraging systematic efforts to minimize industrial water use.




• Discussion and contingency planning on principles and procedures for addressing water allocation challenges which could force relocations or abandonment of buildings, facilities, or operations.

These actions all build on existing programs and institutions, they all make sense in their own right, and they would require only modest resources. They could be integrated into a National Water Contingency Plan with relatively little effort. This could incorporate systematic assessments of water demand management as envisioned by David Brooks and his colleagues . The Department of the Interior with its Water 2025 program is also systematically addressing the challenge and the need to implement measures such as those outlined above.

Overall, global warming poses a range of challenges to water availability. Even without addressing the questions of what is causing global warming and what we could do to halt it, there is much we can do now to minimize its impact on water resources by increasing the flexibility and resilience of our water consuming systems.