New York City, New YorkNew York City’s heightened awareness of climate change issues over the past four years has led to extensive discussions about how regional changes in temperature, precipitation, sea level, and frequency of extreme weather events will impact the City’s water supply, drainage and wastewater management systems. Under the leadership of Commissioner Emily Lloyd, the subject of climate change is institutionalized at New York City’s Department of Environmental Protection. Climate Change Impacts could be significant - new climate and sea level extremes could be experienced that the systems are not designed to accommodate. The City’s existing awareness of system vulnerabilities, from observing the effects of past climate variability and extreme weather events, has guided the City’s initial assessment of how climate change could impact the City’s and its water systems.
With more than 600 miles of coastline, rising sea levels caused by increased temperatures resulting in thermal expansion of the oceans and ice melt along with regional geologic subsidence pose a significant threat to New York City. Already, over the past century the water level at Battery Park in Lower Manhattan has risen approximately one foot influenced in part by local subsidence, and continued warming could intensify water level rises in future years.
In addition, 60 percent of the City’s sewer network is comprised of combined sewers that frequently overflow and discharge untreated waste during heavy rain events – which are predicted to increase as a result of global warming. Between 1900 and 2005 total rainfall in New York City grew an average of .4 inches per decade, and precipitation intensity in the city could increase between 8% and 9.9% by 2050.
Daily per capita water consumption in the City has already fallen from 189 gallons per day (gpd) in 1979 to 133.5 gpd in 2006, but conservation efforts will continue. Soon, a new billing notice program will automatically alert customers with unusually high water charges of potential leaks in their pipes, and a new rebate program will help customers purchase more water efficient clothes washers and toilets, with special incentives for apartment buildings aimed at reducing citywide water use by 5%. In the future, the City hopes to devise a method to recycle water that seeps into the subway system, potentially capturing and reusing 25 million gpd.
Most of the global climate models examined by the City indicate that New York City and its watersheds will experience higher annual rainfall by the 2050s. In addition, current climate science suggests that the rainfall events experienced now may become larger and more intense, with a longer interval between the rainfall events during this century. Climate change may also affect the length of the growing season and the ecology of the watershed. These changes could affect evapotranspiration and, thus, reservoir inflows. Longer growing seasons could increase plant uptake, reducing soil moisture and reducing the availability of groundwater and surface flows to resupply reservoirs.
Further compounding the issue of water supply is the prediction of warmer winter temperatures that may result in more precipitation falling as rain and less as snowfall. Thus, there will likely be less storage of water in the form of snow pack, and therefore reduced inflows to reservoirs during the spring thawing season.
An associated concern is water quality from changes in precipitation patterns, particularly the potential for larger and more intense storms, which could cause more erosion and increased turbidity, increased loadings of pathogenic bacteria and the parasites Cryptosporidium and Giardia, more phosphorus and eutrophication in the City’s reservoirs. Other concerns include: 1) changes in the ecology of the watersheds; 2) increased water temperature in streams and reservoirs could change temperature stratification, reduce dissolved oxygen, etc.; and, 3) increased temperature can also alter the migration habits of waterfowl, such as Canada geese, which can have a major influence on fecal coliform levels in the City’s reservoirs.
To address these concerns, the City, through its Department of Environmental of Protection (DEP) will: