Water Shortages in Northeast Linked to Human Activity

May 12, 2006
Recent water shortages in Rockland County, N.Y., reveal an increasing mismatch between water demand and supply
Graph of Drought Severity

The Palmer Drought Severity Index (dsi), a measure of dryness shown here for the Hudson Valley that incorporates rainfall and temperature and in which normal conditions appear as 0, clearly indicates the drought that occurred during the 1960s. In contrast, recent declared water emergencies (first three arrows), appear far less severe. Moreover, even though the monthly dsi registered only a small downturn in September 2005 (right-most arrow) conditions were dry enough for Rockland County to issue a drought watch, which was only averted by extremely heavy rainfall in October.

With the summer approaching, new research has shown that recent water emergencies in the Northeast have resulted from more than just dry weather. Instead, researchers from The Earth Institute at Columbia University found droughts had more direct, human causes. The result is a condition known as demand-driven drought that may catch more water managers and residents off-guard in coming years.

The study, which appeared in a recent issue of Journal of the American Water Resources Association was conducted by Bradfield Lyon at the International Research Institute for Climate and Society (IRI), Nicholas Christie-Blick at Lamont-Doherty Earth Observatory and Yekaterina Gluzberg from the Department of Ecology, Evolution and Environmental Biology. They examined precipitation variability and drought in Rockland County, N.Y. over the last 100 years and found that factors such as development, population growth, and failing water supply systems played as significant a role as climate in creating the water emergencies.

"The balance between water demand and supply is now so finely tuned that even a few months of lower than normal precipitation is sufficient to trigger an emergency," said Christie-Blick. "Rockland County is ill-prepared to deal with the severe drought conditions that we know recur on a scale of tens to hundreds of years."

Located 24 miles northwest of New York City, Rockland County is in many respects a typical suburban county in the Northeast. In a landscape dotted with lakes and ponds, traversed by the Ramapo River and bordered by the Hudson River, the region might appear to be highly resilient to drought. However, between 1995 and 2002, the county declared three drought emergencies, the most recent of which one county official called "the worst on record." Research shows, however, that, although unusually dry weather contributed to these emergencies, their severity indicates an increasing imbalance between water demand and supply driven largely by human factors.

"There were certainly droughts during the three recent water emergencies, but by several measures, they were far from exceptional," said Lyon. "In terms of accumulated rainfall deficit and duration, the drought from the 1960s was larger by a factor of three than what we've seen more recently."

By examining tree-ring and rain-gauge records, the researchers found that the most rapid increase in the population of Rockland County occurred over a 30-year period that was relatively wet for the region. Another significant cause was that the aging water supply system had not been upgraded to keep pace with growing demand, thus making it more vulnerable to failure, even within the normal range of climate conditions.

The result is that the criteria for declaring a drought emergency—when water demand is anticipated to exceed supply—are expected to be met in Rockland County with increasing frequency, a situation that is likely to become more common throughout the Northeast. The researchers' findings also reinforce the fact that, instead of pointing to climate forces that are beyond local control, groups most concerned with water demand, such as community planners and developers, and those that focus on supply, such as water resource managers, must work together more effectively to come up with solutions.

"It’s going to require taking a hard look at the options and deciding you either have to increase your supply or deal with the demand side of the equation to keep things in balance," said Lyon.


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