In one case a major metropolis was flooded within hours, leaving thousands homeless, millions without power, transportation and businesses shut down, and a mass human crisis. In the other case, three years of sunshine and blue skies have left water supplies at record lows, crops shriveled and, for the most unfortunate, taps dry. It may seem that Superstorm Sandy in the New York area and the current California drought do not have anything in common, but they do. Understanding why can teach us how to reduce the future risks we face.
In California and the wider American West and in New York and the Northeast, there is a history of development without regard to environmental risk.
In New York and New Jersey, much housing and critical infrastructure was built in low-lying, flood-prone areas, with little or no defense against rising waters. These include barrier islands (the Rockaways, the Jersey Shore), former coastal wetlands (the areas that flooded in Staten Island, South Brooklyn and Queens) and landfill (the fringe of lower Manhattan).
In California, water has been allocated since the 19th century on a first-come, first-served basis, with no rational pricing — or no price at all. This allocation system was not designed for the current levels of population and agricultural use in a chronically drought-prone region. Agriculture accounts for more than 70% of water use in California, although it is less than 2% of California's economy.
In both cases, it will be challenging to overcome the legacy of poor planning and to move toward a more sustainable future. Powerful interests are vested in the status quo.
In the East, protecting flood-prone areas — whether through physical measures such as flood walls or dunes, or financial ones such as continued government subsidies for flood insurance — will be expensive, while moving people and facilities away from those areas is very difficult politically. In the West, investment is needed to build a sustainable water supply system that meets multiple, competing needs. In the process, those who get large allocations of cheap water stand to lose a lot from any system that distributes it more rationally.
In both cases, human-induced climate change is increasing the risks of future disasters, and reductions in greenhouse gas emissions are critical to avert the worst. Yet neither the drought nor the hurricane can be blamed on the warming to date.
In the New York area, there has been about a foot of sea level rise since preindustrial times, the better part of which is because of the warming climate. That rise added a small but significant increment to Sandy's 9-foot storm surge. Beyond that, current science doesn't justify any strong statements about a role for greenhouse warming in the storm itself. The current drought in California also appears to be largely explainable as a result of natural variability in the climate system.
But we can gain clarity if we understand that many of the actions we need to take to adapt to climate change are similar to ones we would be wise to take even if the climate were not changing.
Climate change is increasing the risks of future droughts and floods. The sea will continue to rise, increasing flood risk along the East Coast, perhaps made worse by intensifying hurricanes. And the best science indicates that California's wet season will become shorter and sharper. Spring drying will be exacerbated as more water is lost to evaporation into a warmer atmosphere and less is stored as winter snow.
There are significant uncertainties in the details of these predictions, including how rapidly they will occur. But certainty is not needed to justify stronger measures to manage the increasing risks of flood and drought. Sandy and the California drought make clear that we are poorly prepared to handle such events when they occur in the current climate, let alone the future climate.
How do we reduce the harm that results when the climate delivers too much or too little water?
First, by bringing science into the political process and not allowing political leaders to duck their responsibilities with "Well, I'm not a scientist" excuses. It also requires the political will to make job-creating public investments in infrastructure upgrades whose payoffs in protection come in the long term.
Building a proper accounting for climate change into these investments would mandate stronger measures than would be needed if the climate were staying constant. That would mean, for example, higher flood barriers or more retreat from inundated coastlines in the East, and stricter water management and more rational allocation in the West.
What nature can throw at us already has us reeling from coast to coast.
Improving on that score now would prepare us better for the graver risks ahead.
Adam Sobel, a professor at Columbia University's Lamont Doherty Earth Observatory and School of Engineering and Applied Sciences, is author of "Storm Surge: Hurricane Sandy, Our Changing Climate, and Extreme Weather of the Past and Future." Richard Seager is a professor at the Lamont Doherty Earth Observatory and the lead author of the NOAA report on the 2011-14 California drought.