A drought is a deficiency of precipitation over an extended period resulting in a water shortage.
The National Weather Service describes five types of droughts: meteorological, agricultural, hydrological, socioeconomic, and ecological – most of which can significantly affect New York City.i
Meteorological, or climatological, drought is defined in terms of the departure from a normal precipitation pattern and the duration of the hazard. This is where climate change may be considered. Simply, it is when dry weather patterns dominate a given geographic area. This type of drought has a slow onset—it usually takes at least three months to develop—and may last for several seasons or years.
Agricultural drought links meteorological drought to agricultural impacts due to precipitation shortages, reduced groundwater, and soil-water deficits. This drought has a minimal direct impact on New York City because there is no significant agricultural activity within the city’s boundaries.
Hydrological droughts, which often trail behind meteorological and agricultural droughts, involve surface and sub-surface water supply deficiencies. The frequency and severity of hydrological drought are often defined on a watershed basin scale. Although the climate is a primary contributor, other factors—such as changes in land use, land degradation, and the construction of dams—all affect the hydrological characteristics of the basin.
Socioeconomic drought occurs when a water shortage begins to affect the supply and demand of various commodities within the population, individually and collectively. This type of drought takes into consideration all previously listed types of droughts.
Lastly, ecological drought is an episodic deficit in water availability that drives ecosystems beyond thresholds of vulnerability, impact ecosystem services, and triggers feedbacks in natural and human systems.ii
What is the Hazard?
Drought differs from other hazards in many ways. Its effects take a considerable time to develop, and the extent of the hazard can linger for prolonged periods after the drought itself has ceased. For example, most definitions of socioeconomic drought associate the hazard with supply, demand, and economic good. The absence of a definitive and universally accepted definition complicates the determination of whether a drought is occurring and the level of its severity. Compared to other natural hazards, the geographical area, impacts, and duration of drought are difficult to quantify. This is especially true in New York City because its water comes from three upstate sources.
The city’s complex water supply system is a remarkable feat of engineering. It originates in upstate reservoirs and extends over 125 miles to supply New Yorkers with high-quality water.iii Water shortages and disruptions are possible due to a failure of a major component of the water system’s infrastructure due to age, a planned outage for scheduled repairs, maintenance, capital work, or other factors. A water shortage can also be caused by an upstate drought, which can affect reservoir water levels. Droughts have occurred in the past and may occur again – in a future shaped by climate change.
The New York City Department of Environmental Protection (DEP) manages our water supply system, ensuring the steady flow of water from large upstate watersheds through a complex network of reservoirs, aqueducts, tunnels, and neighborhood water mains (or distribution water mains).
DEP developed the Water Shortage Emergency Rules to guide the City’s response to drought.iv The current Water Shortage Emergency Rules, updated recently in May 2022 in preparation for the Delaware Aqueduct shutdown has three phases: drought watch, drought warning, and drought emergency.v Drought emergencies are subdivided into three stages, each with increasingly severe mandated water-use restrictions. Factors such as prevailing hydrological and meteorological conditions inform the guidelines. DEP declares a drought watch when there is less than a 50% probability that either of the two largest reservoir systems—the Delaware (Cannonsville, Neversink, Pepacton, and Rondout reservoirs) or the Catskill (Ashokan and Schoharie reservoirs)—will fill by the following June 1, the start of the water year. DEP declares a drought warning when there is less than a 33% probability that the Delaware or the Catskill system will fill by the start of the water year (June 1).vi
Each day, more than one billion gallons of water is delivered to New York City, almost all by simple gravity.vii We use water daily for our basic needs – drinking, bathing, cooking, and laundry. Therefore, it comes as no surprise that residential buildings are our largest water consumers, accounting for 86 percent of total water usage.viii Water is also used for institutional, commercial, and manufacturing purposes. For example, hospitals use steam to sanitize medical equipment and water is also used in some manufacturing processes, including bottling plants in New York City.
Pie chart showing water usage by land use (million gallons per day, percentage of daily usage.
Water shortages could be caused by drought or failures in our water-supply infrastructure. Water contamination is beyond the scope of this brief profile, which focuses on drought and infrastructure.
DEP declares a drought emergency when there is a reasonable probability that a protracted dry period would drain the New York City’s reservoirs without the implementation of stringent measures to reduce consumption. DEP estimates this probability during dry periods in consultation with the New York State Drought Management Task Force and the New York State Disaster Preparedness Commission. Analyses of the historical record, the pattern of the dry-period months, water quality, sub-system storage balances, delivery system status, system construction, maintenance operations, snow cover, precipitation patterns, use forecasts, and other factors inform the estimation.
Occasional drought is a normal, recurrent feature of virtually every climate in the United States. According to the New York State Department of Environmental Conservation (NYS DEC), New York’s Average Annual Precipitation ranges from 60 inches in the Catskills to 28 inches in the Lake Champlain Valley.ix
However, even with a temperate, moist climate, normal fluctuations in regional weather patterns can lead to periods of dry weather. The last severe droughts in New York State occurred in the mid-1960s, again in the early and mid-1980s, and early 2000s. According to the National Drought Atlas, a guide to the severity, frequency, and duration of droughts for the continental United States, weather that brings 62% of normal precipitation or less occurs one year out of 50 in New York City. The US Drought monitor began in 2000.x
Water Shortage caused by Drought
Occasional drought is a normal feature of many climates in the United States. It results from climate conditions that can develop over several months or years. A drought can last briefly, or for a long time. A brief drought’s impacts can be worsened by extreme heat and/or wind.
Water shortages due to a drought affect New York City on a citywide basis. Because the reservoirs that supply our water are upstate, rainfall in that region, not within our city, is what determines how adequate our water supply is.
New York State has a generally temperate, moist climate. Since 1963, New York City has experienced seven periods of drought.xi The last severe drought in New York State occurred from 2001-2003. Four less severe drought emergencies have occurred since the 1960s. Following the drought in the 1960s, the region has experienced a wetter period.
The most recent period of dryer weather occurred in December 2001, when DEP issued a Drought Watch because reservoir water-storage levels were at 44 percent. A month later DEP issued a Drought Warning; a Drought Emergency was issued in April 2002. Over the next eight months, increased precipitation and reduced water consumption alleviated drought conditions. Normal conditions were restored on January 2, 2003, ending a 14-month drought event.
A 2011 study by the Lamont-Doherty Earth Observatory (referencing tree ring historical record evidence) predicts that a severe drought similar to the one in the 1960s could easily return to the greater Catskills region without warning, and its duration cannot be forecast.xii That is, the wetter conditions that have prevailed since the 1970s may not persist in the future.
Water Shortage Caused by Infrastructure Failure
New York City’s water supply system dates back to the 1840s, when the Croton Aqueduct in Westchester County opened.xiii Water travels daily through a complex system of reservoirs, aqueducts, tunnels, and water mains to New York City as well as many upstate communities. Due to the system’s age, size, and extent, parts of it may be subject to failure.
A water shortage can occur from a failure at any point in the water systems infrastructure. Depending on its location and scale, a failure can have varying degrees of impact. For example, a water main break may only impact a specific area of the city, while a dam failure or a collapse of tunnels or aqueducts could impact the distribution of water to all of New York City.
Of particular concern now is the Delaware Aqueduct, which delivers approximately half of the city’s drinking water – 500 million gallons per day. It is leaking as much as 35 million gallons per day.xiv New technologies have permitted DEP to perform inspections of it. NYC DEP has announced a planned shutdown of the Delaware Aqueduct in October 2024 until the spring of 2025 to connect a bypass tunnel and repair leaks in the aqueduct.xv
Among other portions of the system that need repair, most notable are City Water Tunnel No. 1, completed in 1917, and City Water Tunnel No. 2, completed in 1936. They have been delivering water to our homes, businesses, and institutions continuously since they were placed in service. Because of the creation of Water Tunnel No. 3 in 2013, it allows the NYC DEP to shut down, inspect and repair city tunnels nos. 1 and 2.xvi
Water main breaks occur frequently. Some of the causes include the age of the mains and pipe material. For instance, 46 % of the City’s 6,785 miles of water main were built before 1941.xvii Most mains are composed of unlined cast iron or cement-lined cast iron, which is susceptible to internal corrosion and leaks.
DEP’s decades-long, intensive efforts and multi-billion-dollar investments in maintaining and repairing our water supply system are discussed below in “How Do We Manage the Risk?”
Water shortages may also occur due to planned outages for system repair.
Droughts tend to affect New York City on a city-wide basis. This is largely because the City gets its water from outside its jurisdiction. As described in New York City’s Hazard Environment, major components of the city’s water supply system are located upstate, making the system vulnerable to weather conditions to the north. As part of its New York State Drought Plan, NYS DEC subdivided the state into drought management regions. New York City is in Drought Region IIA; however, most of its watershed lies to the north in Region II (see Figure 3.8.59).xviii
Major droughts affected the state of New York in the 1930s and, to a greater extent, the 1960s, which is considered to be the drought of record.xix During the 1960s drought, New York City reservoirs were down to 25% capacity. Since this time, New York City reservoirs have had improvements that make them much more resilient to dry conditions. There were short-lived drought periods in the 1980s and 1990, as well as several throughout the early 2000s. In August 2012, over 80% of the state experienced drought or abnormally dry conditions, with over 30% in moderate drought. This brought wildfires, low lake levels, and crop disaster designations across the state.
A drought in 2016–2017 brought attention to the state from state and government officials, as conditions quickly deteriorated and extreme drought occurred for the first time since 2002. There were major impacts to farming, with crop yields down for many producers, as well as record-low streamflows and impacts to smaller reservoir systems. The state also experienced moderate to severe drought from the summer of 2020 through the summer of 2021, and again in the summer of 2022. During this time farmers felt the economic impacts of having to purchase feed they couldn’t grow and needing to take in water.
The table below is a list of NYC specific droughts, provided by NYC DEPxx:
The previous tables exhibit the history of drought in New York. The spiked line graph shows the variations in dry and wet years. Lighter colors representing potential drought-like conditions and blue representing precipitation. The spikes in drought activity align with our recorded history of occurrence throughout the state. Accompanying the spiked line graph are two legends. The “D” aspect of the legend illustrates the intensity of dryness, whereas the “W” focuses on wetness. Including both these diagrams provides a digestible visual of dry and wet patterns across the State.
What is the Risk?
Each drought produces a unique set of impacts on New York City, depending on its severity, duration, and spatial extent and on ever-changing social conditions. As shown in Figure 3.8.60, drought can directly or indirectly affect New York City’s social, economic, built, natural, and future environments.
Drought can negatively affect the population of New York City in many ways. The harmful effects of this hazard may be particularly acute among vulnerable populations, including the very young, seniors, low-income populations, and those with pre-existing or chronic health conditions.
Severe droughts can adversely affect public health. They can lead to a diminished quantity and quality of potable water, which can increase the likelihood of dehydration, compromise sanitation and hygiene and lead to an increase in illness and disease. According to the Centers for Disease Control (CDC), decreased rainfall can cause groundwater and surface water to become polluted with viruses, protozoa, and bacteria, increasing the risk of disease outbreaks.
According to the CDC, prolonged drought can also diminish air quality, increasing particulates suspended in the air, such as pollen, smoke, and fluorocarbons.xxi These substances can irritate the bronchial passages and lungs. This can also increase the risk of acute respiratory infections like bronchitis and bacterial pneumonia. The health effects of drought may be most pronounced among those with pre-existing health conditions or those who may be more susceptible to illness and the spread of disease. Poor air quality due to drought may exacerbate conditions for people with chronic respiratory diseases such as asthma. Given droughts’ prolonged and chronic nature, indirect health effects may not be readily identified, making it challenging to monitor and plan for these events.
Droughts may also affect the population by compromising food and nutrition availability. Limits on growing season, low crop yields, and increasing food prices could result in food shortages. This could adversely affect low-income populations, which may lack the resources to contend with these drought impacts.
Within our tri-state region, severe drought would harm the hundreds of farms that supply food to us, limiting growing seasons and suppressing crop yields, with consequences for the many farmers markets that operate within the city, and the many Community Assisted Agricultures that transport farm goods to us from tri-state area farms.
It should be noted that, because New York City imports most of its food, a prolonged severe drought in any region of the world that supplies a significant quantity of our food supply could produce some shortages and higher prices. Higher prices may create further hardships for low-income households and strain the budgets of commercial and institutional kitchens.
Water shortages may also increase recreational risks for swimmers and boaters. People who engage in water-related recreational activities during drought may be at increased risk for waterborne disease caused by bacteria, protozoa, and other contaminants such as chemicals and heavy metals. Exposure can occur through accidentally or intentionally swallowing water, direct contact of contaminants with mucous membranes, or breathing in contaminants.
Untreated surface water can be a health threat in drought conditions. In untreated surface waters, some pathogens, such as a type of amoeba (Naegleria fowleri), are more common during drought because low water levels may create warmer water temperatures that encourage their growth.
As the levels of surface waters used for boating, swimming, and fishing drop, the likelihood of injury increases. Low water levels in lakes can put people at risk for life-threatening injuries resulting from diving into shallow waters or striking objects that may not be immediately visible while boating. Low surface water levels can also expose potentially dangerous debris from the bottom of lakes, rivers, and ponds.
During a severe drought, reservoir levels may be so low that water pressure is not high enough to suppress fires. Localized disruptions in the distribution system such as a water main break or illegally opened fire hydrants may also impact water pressure. It’s important to consider that NYC system pressure is maintained at one reservoir (Hillview). Widespread impacts may not impact NYC unless it also includes Hillview.
Drought can also have direct and indirect economic impacts. Businesses reliant on water—such as car washes, landscapers, and manufacturers—may be forced to suspend all or a portion of their activities due to reduced water levels and subsequent curtailment of water usage. The indirect impacts associated with drought may be far-reaching.
In general, drought does not cause structural damage and does not affect infrastructure such as highways, bridges, and electric conveyance systems. Drought can, however, impact water-borne transportation systems, including ferries and barges, due to periods of low water. In addition, droughts can affect the functioning of the energy and steam supply systems in New York City. Several power-generation plants rely on potable water to produce power. In the event of a drought, water use restrictions can cause disruption or reduction in the power supply. The steam system in New York City relies heavily on the water at certain times of the year. During winter, the steam system consumes a peak of 1.6 million gallons of water per hour.
In general, a water shortage does not cause structural damage to buildings, highways, and bridges. But it does pose a risk, albeit very low, of aggravating “soil shrinkage,” the reduction in soil volume that occurs as soil loses moisture.xxii The condition can compromise the foundations on which infrastructure stands, including retaining walls and bulkheads, affecting their stability.
The ability to cool equipment and buildings that use water-dependent cooling systems may be disrupted during a water shortage.
Our city’s energy and steam supply systems could be affected by a water shortage. A number of power-generation plants rely on our water supply to produce power. Water-use restrictions during a prolonged severe drought would disrupt or reduce that power supply. This includes the city’s steam system, which relies heavily on water during winter months, when it consumes a peak of 1.6 million gallons of water per hour to heat homes and buildings in parts of Manhattan. Hospitals also rely on steam to sterilize medical equipment.
Drought can also cause severe soil shrinkage, which can compromise the foundation upon which infrastructure stands, including retaining walls and bulkheads. However, soil shrinkage only causes real damage if soils shrink and swell as the moisture content decreases and increases. According to the U.S. Geological Survey, New York City soils typically are not high-swelling in nature. Therefore, there is a very low risk of structural damage associated with drought.xxiii
Droughts can also affect green roofs. In New York City, green roofs contain vegetation that provides insulation, combats the urban heat island effect, and improves air quality. Droughts impair plants on green roofs, disrupting their ability to reduce air pollution and provide other benefits.
Drought has a much more severe impact on the natural environment than on the built environment. Effects may include loss of wetlands, damage to plant species, and reduction in biodiversity. For example, New York City’s waterfront mainly consists of wetlands that range from approximately 5,600 acres to just over 10,000 acres, located in Jamaica Bay, on Staten Island, and along the Long Island Sound.xxiv These wetlands provide wildlife protection, protect coastal communities, provide recreation, reduce the impact of the Urban Heat Island Effect, and improve water quality. In Jamaica Bay Park alone, 325 species of birds, 50 species of butterflies, and 100 species of finfish inhabit the wetlands.xxv
Droughts can threaten community gardens. There are nearly 500 community gardens in New York City. Like green roofs, these gardens help reduce air pollution, combat the urban heat island effect, and increase access to fresh produce.xxvi
Climate change projections indicate future disruptions in precipitation patterns and increasing temperatures. The New York City Panel on Climate Change (NPCC) projects future disruptions in precipitation patterns and rising temperatures for New York City. While annual rainfall is predicted to increase here, along with the intensity of severe storms, the frequency of drought will approximately double by the 2050s and will be five times greater by the 2080s.xxvii
How do we manage the risk?
Strategies for managing the risk of water shortage include measures to protect infrastructure; regulatory controls and programs to promote and incentivize long-term water conservation; robust protocols for monitoring reservoir water levels; contingency planning for drought conditions; and communication efforts designed to inform water users of water shortage conditions and actively enlist them in water conservation efforts.
Maintaining our water supply system, repairing leaks and cracks, and creating redundancy are crucial to ensuring the system’s continued performance under normal conditions, and to reducing the impacts of any water shortages.
DEP’s largest and longest-running project – one of the country’s largest infrastructure projects – is City Water Tunnel No. 3. Initiated in 1970, was completed and activated in 2013 with the final portions to be completed sometime this decade, at an estimated total cost of $5 billion.xxviii The tunnel is a critical piece of infrastructure. When it is completed, it will add capacity to the system, deliver water to customers, and allow DEP to inspect and repair as needed City Water Tunnels No. 1 and 2.
Tunnel No. 3 is being constructed in stages. The construction of City Water Tunnel No. 3 began in 1970. The first section of the Tunnel serving the Bronx and upper portions of Manhattan went into service in 1998.xxix The portion of the Tunnel serving midtown and lower Manhattan went into service in 2013. The tunnel for Queens/Brooklyn was completed in 2001, and since then 7 of the 9 shafts needed to support the tunnel have been completed (including 15B).
The two final shafts, 17B and 18B, demonstrate DEP’s ongoing long-term planning. To that end, in 2018–2019 the decision was made to build these two shafts in a manner that will allow for this future connection.
DEP’s Water for the Future program addresses the leak in the Delaware Aqueduct. In 2013, DEP began building a three-mile tunnel, the Delaware Bypass Tunnel, to bypass the section of the aqueduct that is leaking in Orange County.xxx To connect this tunnel, the Aqueduct will shut down next year, during which time DEP augmented available supply and minimize demand.xxxi Additional construction will continue in October 2024.xxxii
DEP completed construction that increased the capacity of the Catskill Water System in 2021.xxxiii Workers cleaned 59 miles of the aqueduct’s concrete lining and repaired structural defects and leaks at several locations. One of the major shutdowns during the construction process included a special effort to reconstruct much of the Catskill Influent Weir — the structure that discharges water from the aqueduct into Kensico Reservoir. The inside of the weir was cleaned and the piers that hold the weir together were completely reconstructed with new concrete.
Additional projects to increase resiliency include: Kensico Eastview Connection, CDIS4-Delware Connection, upgrades to Croton Falls and Cross River Pump Stations, the Catskill-Delaware Interconnection, and the planned tunnel between Kensico Reservoir and the Catskill-Delaware Disinfection facility (currently in design).xxxiv
DEP’s Water Distribution System Optimization program targets local water main leaks, implements system repairs, and upgrades water distribution infrastructure.
The New York City Department of Buildings’ (DOB) Retaining Wall Rule regulates inspections and filing requirements for retaining walls to determine safety and maintenance conditions. The rule requires regular inspections of retaining walls that are 10 feet or higher and that face a public right-of-way (sidewalk or entrance).xxxv
Reducing demand through regulatory controls and programs
Long-term water conservation strategies help reduce water demand and thus extend how long water remains available during a prolonged water shortage. They also help to meet the demands of a growing population. They take the form of regulatory controls and programs that encourage conservation.
Both building design and the equipment used in buildings can reduce water use, with bathrooms a key target. The DOB Construction Codes encourages water conservation strategies in new buildings as part of an approved water conservation plan.
During the 1980s and 1990s, DEP instituted a number of programs to incentivize water efficiency and reduce water demand by 30%.xxxvi Even during the droughts of 1989, 1991, and 1995, water demand decreased when restrictions were put in place despite population increases during this period. The timeline shows that as New Yorkers began to use water more efficiently, water demand was reduced as the population grew – demonstrating the success of regulatory controls and programs that incentivize water conservation.xxxvii
DEP’s water conservation programs now include these:
- Toilet Replacement Program. Because residential buildings account for the largest share of water use, DEP has identified opportunities to conserve water in these building types. Older toilets can use 3.5 to 5.0 gallons of water per flush; high-efficiency models consume as little as 1.28 gallons per flush. From 1994-1997, DEP ran a Toilet Rebate Program that successfully reduced water demand. In 2013, DEP launched a Toilet Replacement Program. The program provides discounts for owners of residential and multi-family buildings who replace old toilets with high-efficiency models.
- The Municipal Water Efficiency Program is retrofitting City-owned properties, with savings estimated at up to nine million gallons of water a day.
- The Residential Water Efficiency Program offers building owners free surveys that identify opportunities for water savings, including leak detection.
- The Non-Residential Water Efficiency Program encourages major water users such as hospitals, hotels, universities, and restaurants to implement water-efficiency measures.
- DEP’s website enables customers to see how their behavior is affecting their water use and helps them identify leaks by providing daily and sometimes hourly information. DEP is conducting a pilot program to help customers evaluate monthly billing, so that by better understanding their usage patterns they can reduce their demand.
Reservoir monitoring, backup supplies, and water shortage protocols
DEP closely measures and monitors reservoir levels. Its Operations Support Tool is a collection of predictive modeling and data tools that help the agency monitor reservoir levels. The tool automatically delivers continuous, real-time projections. Improved forecasts from the National Weather Service have recently been incorporated into it. DEP also closely monitors the condition of our in-city water distribution system.
Alternative water supplies
New York City has alternative drinking water sources. The Queens system is not usable because of water quality issues and disuse; Chelsea can only be used in the most extreme conditions (e.g. to maintain pressure for firefighting), also due to water quality issues and need to filter. While these alternative supplies do exist, they would require substantial time and resources to make them usable.
- DEP’s groundwater supply system in southeast Queens County consists of 68 wells. It has a State Department of Environmental Conservation permitted capacity of 68 million gallons per day on an annual basis.
- Several interconnections between private utilities in Nassau County are available during an emergency.
- The Chelsea Pump Station in Dutchess County near Poughkeepsie can tap water from the Hudson River. Filtration capacity does not exist. This could increase the city’s water supply by 100 million gallons per day under emergency conditions. This pumping station was used during the droughts of 1985 and 1989.
Water shortage protocols
During a planned or unplanned water shortage, reducing the amount of water we consume is imperative. DEP’s Water Demand Management Plan describes formal operational phases (the phases are “defined” in the Water Shortage Emergency Rules and soon to be revised Drought Management and Contingency Plan) for managing a water shortage and actions for each phase.
Actions in the plan will address all water system customers, including City agencies, the private sector, and households. Action items will change with each phase as water shortage conditions progress. Some of the actions include reducing water usage, communication with customers, enforcement of emergency rules, and implementation of alternative water sources. DEP also evaluates the option of raising water rates to encourage water conservation and increase revenues to maintain operations, specifically for the Emergency phase. The plan will be expanded to address issues related to infrastructure failure and planned system repairs.
One of the New York City’s main utility providers, Con Edison, supplies steam to customers in Manhattan. It implements protocols during water shortages to prioritize all water leaks requiring urgent repairs, to modify operations to conserve water, and to encourage steam customers to reduce steam usage.
As a water shortage initially develops, clear communication with water users is essential. They must be informed about the potential seriousness of the situation and about steps they can take to curtail their water use.
Since water shortages can vary in duration, location, and severity messaging may have to be tailored. For situations where the water shortage is localized such as a water main break, messaging is targeted to the affected customers.
During a drought, DEP employs many strategies to inform customers of water supply status, water restriction rules, and steps for conserving water. Additionally, DEP works with other City agencies and the Mayor’s office to ensure that messaging is clear, concise, accurate, and reaches a broad audience. The agency develops messages intended for residents, community groups, and elected officials using many communication tools: media announcements, social and digital media posts, notifications to elected officials, direct community outreach (including meetings), direct mail, phone calls, and emergency alerts.
Notify NYC and the Advanced Warning System would be used to inform the public of emergency conditions. The City would use social media, notifications, alerts, and targeted outreach tools to communicate updates on water shortage conditions and practical information on how the public can conserve water.