Climate Change Threatens Health

Climate change is one of the most serious public health threats facing the nation, but few people are aware of how it can affect them. Children, the elderly, and communities living in poverty are among the most vulnerable.

Six Ways Climate Change Threatens Health

Air Pollution

Rising heat worsens smog. Burning coal and oil emits carbon and particle pollution; plants produce more allergenic pollen, affecting respiratory health threats like asthma.

Rising temperatures can make smog pollution worse and increase the number of "bad air days" when it's hard to breathe. This puts many of us at risk for irritated eyes, noses, and lungs—but it is particularly dangerous for people with respiratory diseases like asthma. As the climate changes, unhealthy air pollution will get worse. Here's how:

Ozone smog forms when pollution from vehicles, factories, and other sources reacts with sunlight and heat. Increasing temperatures speed this process and result in more smog. Added to the mix are ragweed and other allergens in the air—which are expected to worsen as rising carbon dioxide levels cause plants to produce more pollen. Also, as dry areas get dryer, wildfire risks go up and smoke from burning landscapes intensifies poor air quality.

Exposure to increased smog, pollen pollution, and wildfire smoke puts a wide range of people at risk for irritated eyes, throats and lung damage (the U.S. EPA likened breathing ozone to getting a sunburn on your lungs). This includes outdoor workers, children, the elderly, and those who exercise outside.

But people with asthma, allergies, and other respiratory diseases face the most serious threats, since exposure to increased pollution heightens sensitivity to allergens, impairs lungs, triggers asthma attacks, sends people to the hospital, and even results in death. In 2010, the American Lung Association estimated that about 23 million Americans suffered from asthma.

Communities must take steps to improve air quality, but everyone should know the risks that climate change poses and learn how to best protect themselves when bad air days get worse.

Eleven states and various local governments have developed preparedness measures to address the air quality impacts associated with climate change. The most frequent recommendation is developing or strengthening statewide air monitoring programs; gathering information is often the first step towards preparing for climate change related threats.

Extreme Heat

Heat waves send thousands to emergency rooms and cost health care systems millions of dollars; climate change brings longer, more intense heat waves.

Across the nation, climate change is making hot summer days hotter and stretching their numbers into heat waves that never seem to end. And the heat is causing more than just discomfort—as temperatures rise, so are the number of illnesses, emergency room visits, and deaths.

At least 37 states saw record highs in the summer of 2010, and in many regions, it didn't cool off at night. Nationwide, over 28.5 million people lived in counties where 2010's average temperature set records, and over 36 million people lived in counties where the hottest summer nights ever were recorded.

The record heat experienced in the United States in the summer of 2010 was no isolated event. Global temperature data compiled by NASA show that 2010 was tied with 2005 as the hottest year on record. This comes on top of the warmest decade on record (2000-2009).

Extreme heat waves cause the most harm among elderly people and young children. City dwellers are at particular risk because of elevated temperatures in cities, known as the "urban heat island effect" due to the magnifying effect of paved surfaces and the lack of tree cover.

In the United States, an average of 400 deaths per year are directly related to heat, and an estimated 1,800 die from illnesses made worse by heat—including heat exhaustion, heat stroke, cardiovascular disease, and kidney disease. Deadly heat waves swept across most of the nation in 2006, hitting California the hardest; the state saw an additional 16,000 emergency room visits during the two-week heat wave.

Scientists predict that average temperatures in the United States will rise between 5 and 9°F (3-5°C) over the next century; these hot summer days and heat waves could be the norm by 2100.

Communities across the nation must educate themselves about the risks from extreme heat and learn how to protect their most vulnerable residents.

Twelve states and several local governments have developed preparedness measures to prevent the health impacts of increasing extreme heat associated with climate change. The most frequent recommendation is developing or strengthening statewide heat early warning systems, with an emphasis on alerting the most vulnerable populations.

Infectious Diseases

Hotter summers can make disease-carrying insects more active, for longer seasons; illnesses like dengue, West Nile, and Lyme can spread into new areas.

While many infectious diseases were once all but eliminated from the United States, there's evidence that climate change is a factor that could help them expand their range and make a comeback.

Mosquitoes capable of carrying and transmitting diseases like Dengue Fever, for example, now live in at least 28 states. As temperatures increase and rainfall patterns change—and summers become longer—these insects can remain active for longer seasons and in wider areas, greatly increasing the risk for people who live there.

The same is true on a global scale: increases in heat, precipitation, and humidity can allow tropical and subtropical insects to move from regions where infectious diseases thrive into new places. This, coupled with increased international travel to and from all 50 states, means that the U.S. is increasingly at risk for becoming home to these new diseases.

Nearly 4,000 cases of imported and locally-transmitted Dengue Fever were reported in the U.S. between 1995 and 2005, and that number rises to 10,000 when cases in the Texas-Mexico border region are included. In Florida, 28 locally-transmitted cases were reported in a 2009-2010 outbreak, the first there in more than 40 years. Dengue Fever, also known as "Breakbone Fever", is characterized by high fever, headaches, bone and joint aches, and a rash. Recurrent infection can lead to bleeding, seizures, and death.

Lyme disease—transmitted primarily through bites from certain tick species—could expand throughout the United States and northward into Canada, as temperatures warm, allowing ticks to move into new regions.

West Nile virus, which first entered the U.S. in 1999, expanded rapidly westward across the country. By 2005, over 16,000 cases had been reported. Warmer temperatures, heavy rainfall and high humidity have reportedly increased the rate of human infection.

Communities across the nation must educate themselves about the risks from climate change and spreading infectious diseases and learn how to protect their most vulnerable residents.

Eleven states and several local governments have developed preparedness measures to address the spread of infectious diseases associated with climate change. The most frequent recommendation is improving statewide surveillance for vectors such as mosquitoes, and the presence of vector-borne diseases.

Drought

Hotter days and nights, and changing rainfall patterns reduce water supply quantity and quality, and diminish food security.

Water is life, and climate change is threatening this precious resource. Nearly every U.S. region is facing some increased risk of seasonal drought.

Climate change will significantly affect the sustainability of water supplies in the coming decades. As parts of the country get drier, the amount of water available and its quality will likely decrease—impacting people's health and food supplies.

Parts of the Western U.S. are already experiencing water crises because of severe dry-spells, but with climate change, the entire country will likely face some level of drought. NRDC's Climate Change, Water, and Risk report found that 1,100 counties—one-third of all counties in the lower 48 states—face higher risks of water shortages by mid-century as the result of climate change. More than 400 of these counties will face extremely high risks of water shortages.

As temperatures rise and precipitation decreases, water quality can be jeopardized. Shrinking amounts of water can concentrate contaminants such as heavy metals, industrial chemicals and pesticides, and sediments and salts. During drought, drinking water supplies are susceptible to harmful algal blooms and other microorganisms.

Of course, drought means more than not having access to clean drinking water. Changes in precipitation and water availability could have serious consequences for commercial agriculture – crops yield less and food security suffers. Drought conditions can also help fuel out-of-control wildfires.

Local communities across the country can prepare for drought by learning to conserve water and improving drinking water safeguards.

Nine states and several local governments have developed preparedness measures to address the drought impacts associated with climate change. The most common recommendation is improving general preparedness measures for droughts and ensuring an adequate water supply.

Flooding

Climate change intensifies rainfall; heavy rains increase risk of drinking water contamination and illness; floods can force communities to relocate.

Climate change has contributed to a rise in extreme weather events—including higher-intensity hurricanes in the North Atlantic and heavier rainfalls across the country. Scientists project that climate change will increase the frequency of heavy rainstorms, putting many communities at risk for devastation from floods.

Flooding can cause a range of health impacts and risks, including: death and injury, contaminated drinking water, hazardous material spills, increased populations of disease-carrying insects and rodents, moldy houses, and community disruption and displacement.

As rains become heavier, streams, rivers, and lakes can overflow, increasing the risk of water-borne pathogens flowing into drinking water sources. Downpours can also damage critical infrastructure like sewer and solid waste systems, triggering sewage overflows that can spread into local waters.

Cities like New York City and Chicago, where older sewer systems carry sewage and rain water in the same pipes, are at greater risk for sewage spills. During heavy rains, these pipes cannot handle the volume of stormwater and wastewater, and untreated sewage is often discharged into local waters where people swim and play.

Exposure to pathogens from sewage and unclean water can sicken vulnerable communities with illnesses like cryptosporidiosis, giardiasis, and norovirus (which cause diarrhea, abdominal pain, nausea, vomiting, headache, and fever).

Local communities across the country can prevent floods and heavy rains from devastating their homes and buildings by updating infrastructure, improving drinking water safeguards, and creating public plans for what to do in case disaster strikes.

Eight states and various local governments have developed public health preparedness measures to address increased flooding risks associated with climate change. These measures are a good start at addressing some of the risks but comprehensive response plans addressing the multiple threats and hazards highlighted above are lacking.

Extreme Weather: Record-Breaking Events in 2011

In 2011, thousands of record-breaking extreme weather events harmed communities and health in the US. Climate change is contributing to more intense and frequent extreme weather events.

2011 was a year of unparalleled extremes: 14 disastrous weather events in the US each resulted in over a billion dollars in property damage. This was an all-time record breaking number—and their estimated $53 billion price tag did not include health costs. When health-related costs of extreme events are calculated, the total tally increases by billions more dollars, as shown recently, in a first-of-its-kind study published in the journal Health Affairs.[1] Costs will likely continue to climb as climate change continues.

Since climate is the baseline for weather, alteration of the climate affects extreme weather events, too. Some people have likened the effects of climate change to "weather on steroids": taking steroids makes hitting a home run more likely for a ball player, and climate change makes some types of extreme weather events more likely.

A troubling trend has been identified by the international reinsurance company MunichRe[2]; they concluded that from 1980 through 2011, the frequency of damaging extreme events increased substantially in the U.S. Many of the 2011 extreme events, such as record temperatures, devastating storms, wildfires, and extreme droughts and floods, are among the types expected to worsen as climate change continues. A newly-released analysis by international climate scientists (the IPCC)[3] concluded that climate change will amplify extreme heat, heavy precipitation, and the highest wind speeds of tropical storms.

We need to be prepared. Emergency planning must incorporate risks from climate change. For example, maps describing flooding zones need to account for increased risks caused by extreme rainfall and sea level rise resulting from climate change. While these plans are made at the local level, the Federal Emergency Management Agency (FEMA) must also prioritize addressing and preparing for climate change by providing guidance and resources to state and local governments.

  1. Knowlton K, Rotkin-Ellman M, Geballe L, Max W, Solomon GM. 2011. Six climate change-related events in the United States accounted for about $14 billion in lost lives and health costs. Health Affairs 30(11):2167-2176.
  2. Munich Re. 2011.Half-Year Natural Catastrophe Review, July 12, 2011. MR NatCatSERVICE. Available at: http://www.munichreamerica.com/webinars/2011_07_natcatreview/MR_III_2011_HalfYear_NatCat_Review.pdf. A webinar regarding the entire year of 2011 by MunichRe is available at: http://www.iii.org/presentations/2011-natural-catastrophe-year-in-review.html.
  3. IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, Summary for Policymakers (Nov. 18, 2011), available at: http://ipcc-wg2.gov/SREX/.

Air Pollution: Smog, Smoke and Pollen

In NRDC's 2007 issue paper, Sneezing and Wheezing: How Global Warming Could Increase Ragweed Allergies, Air Pollution, and Asthma, pages 14-16 describe the methodology by which we created the online air pollution map on our pages. "Unhealthy ozone days" are those sites where at least one day per summer, on average, did not meet the US EPA's health-based standard for ground-level ozone smog, in the five study years from 2002-2006. The presence of ragweed in an area can mean allergenic pollen is also being produced in late summer and into autumn, which is often the same time that ozone smog is at its worst, posing a "double-whammy" to health for people with allergies and asthma.

Extreme Heat: More Intense Hot Days and Heat Waves

Background: The frequency, duration, and intensity of heat waves in the U.S. are projected to increase substantially by 2090 due to climate change.[1] Extreme heat is a significant public health threat and has been linked to increases in premature mortality, hospitalizations and emergency room visits.

Extreme Heat Vulnerability Indicator: The percentage of the U.S. affected by heat waves has risen since the 1970s, distinguished by a rise in extremely high nighttime temperatures, as well as daily high temperatures well above normal.[2] We applied the 90th percentile value of daily maximum summer temperatures as a measure of extreme heat, that is, daily temperatures exceeding those values were considered "extreme." Summer was calculated as June, July and August (JJA) temperatures at each meteorological station for which data were available, as is common practice in climate analyses. In addition, a 30-year period was used as a baseline, in this case a 1961-1990 reference period against which the most recent decade of data was compared, namely 2000-2009 summer daily temperatures.

Data Source: Data from all cooperative weather stations for all years historically from the National Climatic Data Center was collected. The data through 2008 was purchased from EarthInfo, a private vendor that collects NCDC data and makes it available on DVDs. 2009 data was downloaded manually from NCDC. Geographic detail for sites was also from NCDC. The NCDC defines cooperative stations as: "U.S. stations operated by local observers which generally report max/min temperatures and precipitation. National Weather Service (NWS) data are also included in this dataset. The data receive extensive automated + manual quality control."

Data Preparation: Data was assembled in an SQL data base. Each record represented a single site-month of data. The total was 24 million site-month records or a total of more than 720 million site-days of data.

Calculations: For each site we calculated the 90th percentile for the maximum temperature during the reference period of June, July and August of 1961-1990. All days June, July and August 2000-2009 at the same site were then compared against the reference period 90th percentile value. The total number of days that exceeded the 90th percentile reference value was computed. County-level averages were then computed by averaging site-level data within the county.

Sites were excluded from the analysis if A) they had less than 75% of possible reference days; B) one entire year from the 2000-2009 period was missing; or C) they had less than 75% of possible current period days.

Map: In a summer defined as June, July and August, there are a total of 92 days, so the "expected" number of days that would exceed the 90th percentile is 10% of 92, or 9.2 days. Rounding to the nearest whole number of days, locations with over 9 days on average per summer with temperatures above that station's 90th percentile reference value had "more than expected" number of days of extreme heat. The highest category (greater than 13.8 days) gives a sense of those locations with over approximately two weeks of these "more than expected" hot days in a recent decade, relative to temperatures in the 30 years from 1961-1990.

Note, too, that "extreme heat" is defined by local temperatures at each site; the map does not compare temperatures in one part of the U.S. to those in another region.

Infectious Diseases: Dengue Fever, West Nile Virus, and Lyme Disease

For NRDC's 2009 issue paper, Fever Pitch: Mosquito-Borne Dengue Fever Threat Spreading in the Americas, we created an online Appendix that describes the method we used to create the map of dengue fever vulnerability you're viewing now.

Drought: Threats to Water and Food Security

Background: Global warming is projected to alter precipitation patterns, increase the frequency and intensity of major storm events, and increase risks of floods throughout the U.S. and particularly the Midwest and Northeast.[1] Over the period from 2000 to 2009, roughly 30 to 60% of the U.S. land area experienced drought conditions at any one time.[2]

Drought Vulnerability Indicators: Drought vulnerability is indicated by the extreme low flow days that are defined as less than the 5th percentile for each monitoring station. This category is classified by USGS as "severe hydrological drought".[3] Current conditions (2000 -2009) were compared to historical conditions using a thirty-year reference period (1961-1990, in this case), consistent with other climate change-related studies.

Streamflow Data

Data Source: Data from all streamflow gauging stations for all years historically from the United States Geological Survey was collected. The data through 2009 was purchased from EarthInfo, a private vendor that collects USGS data and makes it available on DVDs. Watershed data also comes from the USGS (http://water.usgs.gov/GIS/huc.html). The original watershed data was at the HUC12-level (high resolution). These watersheds were aggregated to HUC4 based on HUC ID.

Data Preparation: Data was assembled in an SQL data base. Each record represented a single site-month of data. The total was 7 million site-months or a total of more than 210 million site-days of data.

Calculations: A 95th and 5th percentile value for the reference period (1961-1990) was calculated for each site for each day of the year using a moving average of 7 days before and after the day. For example, the reference period percentiles for June 15th would be calculated by selecting all days June 8-June 22 for the years 1961-1990 (15 x 30 possible days = 450 days contribute to the percentile calculations). June 16th would be based on all days June 9-June 23 and so on. For the first and last six days of the year (Jan 1- Jan 6 and Dec 26-Dec 31), the reference period moving average included days from 1960 and 1991. Current flows at a site were then compared against the reference period percentiles day by day. For example, the ten possible June 15th values from 2000-2009 would be compared against the 95th and 5th percentiles for that day from the reference period. Watershed-level averages were then computed by averaging site-level data within the watersheds.

Analysis was limited to stations that make up the Hydro-Climatic Data Network, a subset of stations that are unaffected by artificial diversions. See appendix for a description of these sites below.

Sites were excluded from the analysis if A) they had less than 75% of possible reference days; B) two entire years from the 2000-2009 period were missing; or C) they had less than 75% of possible current period days.

Map: Color gradations reflect terciles of the data distribution.

Flood Stage Data

Data Source: Data was collected from the USGS WaterWatch website (http://waterwatch.usgs.gov?/new/?id=wwdp2_2).

Data Preparation: We developed Python scripts to iterate through all states and download/format all available flood data 2000-2009. Tabular data was converted to geographic data by linking to the dataset described above on USGS station number.

Calculations: No additional calculations were performed. Graduated circles were mapped based on the "No. of days above flood stage" variable from USGS.

Map: Graduated circles reflect natural data breaks in the distribution. Note: flood stage information is not currently available for all Hydro-Climatic Data Network (HCDN) streamflow gauge sites.

Appendix: Definition of HCDN sites

HCDN Description: Pasted from USGS Hydro-Cliatic Data Network: Streamflow Data Set 1874-1988 by By J.R. Slack, Alan M. Lumb, and Jurate Maciunas Landwehr. USGS Water-Resources Investigations Report 93-4076

The potential consequences of climate change to continental water resources are of great concern in the management of those resources. Critically important to society is what effect fluctuations in the prevailing climate may have on hydrologic conditions, such as the occurrence and magnitude of floods or droughts and the seasonal distribution of water supplies within a region. Records of streamflow that are unaffected by artificial diversions, storage, or other works of man in or on the natural stream channels or in the watershed can provide an account of hydrologic responses to fluctuations in climate. By examining such records given known past meteorologic conditions, we can better understand hydrologic responses to those conditions and anticipate the effects of postulated changes in current climate regimes. Furthermore, patterns in streamflow records can indicate when a change in the prevailing climate regime may have occurred in the past, even in the absence of concurrent meteorologic records.

A streamflow data set, which is specifically suitable for the study of surface-water conditions throughout the United States under fluctuations in the prevailing climatic conditions, has been developed. This data set, called the Hydro-Climatic Data Network, or HCDN, consists of streamflow records for 1,659 sites throughout United States and its Territories. Records cumulatively span the period 1874 through 1988, inclusive, and represent a total of 73,231 water years of information.

Development of the HCDN Data Set: Records for the HCDN were obtained through a comprehensive search of the extensive surface- water data holdings of the U.S. Geological Survey (USGS), which are contained in the USGS National Water Storage and Retrieval System (WATSTORE). All streamflow discharge records in WATSTORE through September 30, 1988, were examined for inclusion in the HCDN in accordance with strictly defined criteria of measurement accuracy and natural conditions. No reconstructed records of "natural flow" were permitted, nor was any record extended or had missing values "filled in" using computational algorithms. If the streamflow at a station was judged to be free of controls for only a part of the entire period of record that is available for the station, then only that part was included in the HCDN, but only if it was of sufficient length (generally 20 years) to warrant inclusion. In addition to the daily mean discharge values, complete station identification information and basin characteristics were retrieved from WATSTORE for inclusion in the HCDN. Statistical characteristics, including the monthly mean discharge, as well as the annual mean, minimum and maximum discharge values, were derived for the records in the HCDN data set. For a full description of the development and content of the Hydro-Climatic Data Network, please take a look at the HCDN Report.

Flooding: Devastating Floods and Heavy Rains

Background: Global warming is projected to alter precipitation patterns, increase the frequency and intensity of major storm events, and increase risks of floods throughout the U.S. and particularly the Midwest and Northeast.[1] Flooding can cause a range of health impacts and risks, including: death and injury, contaminated drinking water, hazardous material spills, increased populations of disease-carrying insects and rodents, moldy houses, and community disruption and displacement. In recent years, a higher percentage of rainfall in the U.S. has come in the form of intense single-day events.[2]

Flooding Vulnerability Indicators: Vulnerability to flooding is indicated by the frequency of extreme high flow days and the frequency of days where flood conditions were recorded, consistent with the USGS WaterWatch program.[3] Extreme high streamflow is defined as above the 95th percentile for each monitoring station. Flood conditions are indicated by days above flood stage, which is defined by the Nation Weather service as the level of surface water where there is a hazard to lives, property, or commerce. Current conditions (2000 -2009) were compared to historical conditions using a 30-year reference period (1961-1990 in this case), consistent with other climate change-related studies.

Streamflow Data

Data Source: Data from all streamflow gauging stations for all years historically from the United States Geological Survey was collected. The data through 2009 was purchased from EarthInfo, a private vendor that collects USGS data and makes it available on DVDs. Watershed data also comes from the USGS (http://water.usgs.gov/GIS/huc.html). The original watershed data was at the HUC12-level (high resolution). These watersheds were aggregated to HUC4 based on HUC ID.

Data Preparation: Data was assembled in an SQL data base. Each record represented a single site-month of data. The total was 7 million site-months, or a total of more than 210 million site-days of data.

Calculations: A 95th and 5th percentile value for the reference period (1961-1990) was calculated for each site for each day of the year using a moving average of 7 days before and after the day. For example, the reference period percentiles for June 15th would be calculated by selecting all days June 8-22 for the years 1961-1990 (15 x 30 possible days = 450 days contribute to the percentile calculations). June 16th would be based on all days June 9-June 23 and so on. For the first and last 6 days of the year (Jan 1-6 and Dec 26-31) the reference period moving average included days from 1960 and 1991. Current flows at a site were then compared against the reference period percentiles day by day. For example, the ten possible June 15th values from 2000-2009 would be compared against the 95th and 5th percentiles for that day from the reference period. Watershed-level averages were then computed by averaging site-level data within the watersheds.

Analysis was limited to stations that make up the Hydro-Climatic Data Network a subset of stations that are unaffected by artificial diversions. See appendix for a description of these sites below.

Sites were excluded from the analysis if A) they had less than 75% of possible reference days; B) two entire years from the 2000-2009 period were missing; or C) they had less than 75% of possible current period days.

Map: Color gradations reflect terciles of the data distribution.

Flood Stage Data

Data Source: Data was collected from the USGS WaterWatch website (http://waterwatch.usgs.gov?/new/?id=wwdp2_2).

Data Preparation: We developed Python scripts to iterate through all states and download/format all available flood data 2000-2009. Tabular data was converted to geographic data by linking to the dataset described above on USGS station number.

Calculations: No additional calculations were performed. Graduated circles were mapped based on the "No. of days above flood stage" variable from USGS.

Map: Graduated circles reflect natural data breaks in the distribution. Note: flood stage information is not currently available for all Hydro-Climatic Data Network (HCDN) streamflow gauge sites.

Appendix: Definition of HCDN sites

HCDN Description: Pasted from USGS Hydro-Cliatic Data Network: Streamflow Data Set 1874-1988 by By J.R. Slack, Alan M. Lumb, and Jurate Maciunas Landwehr. USGS Water-Resources Investigations Report 93-4076

The potential consequences of climate change to continental water resources are of great concern in the management of those resources. Critically important to society is what effect fluctuations in the prevailing climate may have on hydrologic conditions, such as the occurrence and magnitude of floods or droughts and the seasonal distribution of water supplies within a region. Records of streamflow that are unaffected by artificial diversions, storage, or other works of man in or on the natural stream channels or in the watershed can provide an account of hydrologic responses to fluctuations in climate. By examining such records given known past meteorologic conditions, we can better understand hydrologic responses to those conditions and anticipate the effects of postulated changes in current climate regimes. Furthermore, patterns in streamflow records can indicate when a change in the prevailing climate regime may have occurred in the past, even in the absence of concurrent meteorologic records.

A streamflow data set, which is specifically suitable for the study of surface-water conditions throughout the United States under fluctuations in the prevailing climatic conditions, has been developed. This data set, called the Hydro-Climatic Data Network, or HCDN, consists of streamflow records for 1,659 sites throughout United States and its Territories. Records cumulatively span the period 1874 through 1988, inclusive, and represent a total of 73,231 water years of information.

Development of the HCDN Data Set: Records for the HCDN were obtained through a comprehensive search of the extensive surface- water data holdings of the U.S. Geological Survey (USGS), which are contained in the USGS National Water Storage and Retrieval System (WATSTORE). All streamflow discharge records in WATSTORE through September 30, 1988 were examined for inclusion in the HCDN in accordance with strictly defined criteria of measurement accuracy and natural conditions. No reconstructed records of "natural flow" were permitted, nor was any record extended or had missing values "filled in" using computational algorithms. If the streamflow at a station was judged to be free of controls for only a part of the entire period of record that is available for the station, then only that part was included in the HCDN, but only if it was of sufficient length (generally 20 years) to warrant inclusion. In addition to the daily mean discharge values, complete station identification information and basin characteristics were retrieved from WATSTORE for inclusion in the HCDN. Statistical characteristics, including the monthly mean discharge, as well as the annual mean, minimum and maximum discharge values, were derived for the records in the HCDN data set. For a full description of the development and content of the Hydro-Climatic Data Network, please take a look at the HCDN Report.

Extreme Weather: Record-Breaking Events in 2011

This map was generated based on "NRDC's Extreme Weather Map 2011" project which created an animated graphic that tracked "record-breaking" weather events over the course of 2011 within the 50 United States. The following modifications to the original methods were made to enable the geographic specificity of this map:

Monthly temperature, rain and snowfall records were compiled into a single map. Multiple monthly records at a single meteorological station are marked by a single icon.

Extreme drought point locations were replaced by a shaded polygon representing the geographic areas found to experience "Exceptional Drought" (D4) in 2011 by the National Drought Mitigation Center's Drought Monitor. http://droughtmonitor.unl.edu/dmshps_archive.htm

Extreme flood point locations to mark the Lower Mississippi Floods (http://www1.ncdc.noaa.gov/pub/data/cmb/special-reports/2011-spring-climate-extremes/ustatus_miss-II.jpg) and Upper Midwest floods (http://www.noaa.gov/extreme2011/midwest_flood.html) were replaced with shaded polygons created by digitizing maps produced by the National Climatic Data Center. Because flooded area maps were unavailable, the flood point locations marking record high peak flows due to the impacts of Hurricane Irene and Tropical Storm Lee were retained as point data.

  1. Karl TR, Melillo JM, Peterson TC, editors. Global climate change impacts in the United States. New York: Cambridge University Press; 2009.
  2. EPA "Climate Change Indicators in the United States" (2010), EPA 430-R-1—007. www.epa.gov/climatechange/indicators.html
  3. US Geological Survey (USGS) WaterWatch: Flood conditions website. http://waterwatch.usgs.gov/new/index.php?id=ww_flood

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