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  • View in gallery

    Photo credit: Henry Reges

  • View in gallery

    CoCoRaHS precipitation map showing daily observations for the period ending 0700 LT 6 May 2015. Precipitation amounts ranged from 0.00 to 7.93 in. (201.4 mm). Total number of reports: 13,030 (many reporting daily) with 6,914 observers measuring greater than a trace.

  • View in gallery

    ETgage (atmometer) used by selected CoCoRaHS volunteers to measure ETo. (Photo courtesy of Henry Reges.)

  • View in gallery

    2012 summer water balance for Illinois CoCoRaHS station IL-CP-1. Daily precipitation amounts are shown with blue bars, and daily evapotranspiration rates are shown red with bars. Water balance is shown with a green line. This is the difference between incoming precipitation and outgoing evapotranspiration. Graph depicts occurrence of flash drought during Jul–Aug, when evapotranspiration greatly exceeded precipitation.

  • View in gallery

    CoCoRaHS training animations have made learning about measuring precipitation fun and simple for all ages. A full suite of instructional shorts are available to stream via YouTube.

  • View in gallery

    CoCoRaHS 4-in.-diameter plastic rain gauge—required equipment for each CoCoRaHS observer. The gauge measures to the hundredth of an inch and has an 11.30-in. (287 mm) capacity, with any amount greater than 1 in. flowing into and collecting in the outer cylinder. The funnel and inner cylinder are removed in cold weather for capturing frozen precipitation. (Photo courtesy of Henry Reges.)

  • View in gallery

    Comparison of unique CoCoRaHS SWE stations reporting to NOHRSC. Of the SWE reports received, 18% came from CoCoRaHS stations in 2006–07, whereas 58% came from CoCoRaHS stations in 2013–14. (Graphic courtesy of NOHRSC.)

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    CoCoRaHS gauge outside the visitor’s dugout at Target Field in Minneapolis, MN. The gauge has a clear, unobstructed view of the sky. (Photo courtesy of Henry Reges.)

  • View in gallery

    2013 Colorado flood map with CoCoRaHS stations showing 48-h totals, 0700 MDT 11 Sep 2013–0700 MDT 13 Sep 2013. Analysis based on integrated data from multiple sources, including radar. The dense network of volunteer gauges along the Front Range of Colorado provided a rich resource of precipitation observations for detailed mapping.

  • View in gallery

    CoCoRaHS map showing 24-h rainfall totals reported by CoCoRaHS observers ending at 0700 CDT 30 Apr 2014. Area includes counties in the Alabama and Florida Panhandles (including Mobile and Pensacola metropolitan areas). Several reports exceeded 18.00 in. (457.2 mm) in 24 hours.

  • View in gallery

    Example of one station making a difference. Observer in eastern Comal County, TX, near New Braunfels reporting 7.12 in. (180.8 mm) of precipitation in 24 hours ending at 0700 CDT 6 May 2008, whereas stations nearby received less than 0.1 in. (2.5 mm).

  • View in gallery

    2010–14 national number of active observers and reports entered. Blue bars show total number of active observers by month. Yellow bars show number of observers who have reported an observation each month. Dashed lines show 12-month averages.

  • View in gallery

    2010–14 national number of new sign-ups per month. Blue bars show total number of new volunteer observers signing up each month. Yellow bars show those who have signed up during that period who have actually reported. Blue dashed line shows 12-month average total sign-ups. Yellow dashed line shows 12-month average sign-ups reporting.

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CoCoRaHS: The Evolution and Accomplishments of a Volunteer Rain Gauge Network

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  • 1 CoCoRaHS, Colorado Climate Center, Colorado State University, Fort Collins, Colorado
  • 2 Wyoming State Climate Office, Laramie, Wyoming
  • 3 CoCoRaHS, Colorado Climate Center, Colorado State University, Fort Collins, Colorado
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Abstract

The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is a large and growing community of volunteers measuring and reporting precipitation and is making this information broadly available for the research and operational community. CoCoRaHS has evolved through several phases since its beginnings in 1998, first starting as a flood-motivated local Colorado Front Range project, then through a 5-yr nationwide expansion period (2005–09), followed by five years (2010–14) of internal growth and capacity building.

As of mid-2015, CoCoRaHS volunteers have submitted over 31 million daily precipitation reports and tens of thousands of reports of hail, heavy rain, and snow, representing over 1.5 million volunteer hours. During the past 10 years, there has been wide demand for and use of CoCoRaHS data by professional and scientific users with an interest in its applicability to their different areas of focus. These range from hydrological applications and weather forecasting to agriculture, entomology, remote sensing validation, city snow removal contracting, and recreational activities, just to name a few. The high demand for CoCoRaHS data by many entities is an effective motivator for volunteer observers, who want to be assured that their efforts are needed and appreciated.

Going forward, CoCoRaHS hopes to continue to play a leading role in the evolution and growth of citizen science while contributing to research and operational meteorology and hydrology.

CORRESPONDING AUTHOR: Henry W. Reges, Colorado State University, 1371 General Delivery, Fort Collins, CO 80523-1371, E-mail: hreges@atmos.colostate.edu; antonius@uwyo.edu

Abstract

The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is a large and growing community of volunteers measuring and reporting precipitation and is making this information broadly available for the research and operational community. CoCoRaHS has evolved through several phases since its beginnings in 1998, first starting as a flood-motivated local Colorado Front Range project, then through a 5-yr nationwide expansion period (2005–09), followed by five years (2010–14) of internal growth and capacity building.

As of mid-2015, CoCoRaHS volunteers have submitted over 31 million daily precipitation reports and tens of thousands of reports of hail, heavy rain, and snow, representing over 1.5 million volunteer hours. During the past 10 years, there has been wide demand for and use of CoCoRaHS data by professional and scientific users with an interest in its applicability to their different areas of focus. These range from hydrological applications and weather forecasting to agriculture, entomology, remote sensing validation, city snow removal contracting, and recreational activities, just to name a few. The high demand for CoCoRaHS data by many entities is an effective motivator for volunteer observers, who want to be assured that their efforts are needed and appreciated.

Going forward, CoCoRaHS hopes to continue to play a leading role in the evolution and growth of citizen science while contributing to research and operational meteorology and hydrology.

CORRESPONDING AUTHOR: Henry W. Reges, Colorado State University, 1371 General Delivery, Fort Collins, CO 80523-1371, E-mail: hreges@atmos.colostate.edu; antonius@uwyo.edu

This article discusses the evolution of CoCoRaHS, the nationwide citizen science network of precipitation observers, during the past 10 years.

fig13

Photo credit: Henry Reges

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is a precipitation monitoring network composed of thousands of volunteers manually measuring precipitation in a consistent way and reporting data online (www.cocorahs.org). The network, which began as a local community project in response to a local flash flood (Kelsch 1998), has expanded over time to provide informal weather and climate education opportunities for the public, and it has evolved to provide high-quality daily precipitation data that are used and depended upon by numerous entities throughout the country. CoCoRaHS was first described in the Bulletin of the American Meteorology Society (BAMS) 10 years ago (Cifelli et al. 2005). What was at that time a small five-state network of volunteer observers has grown into a nationwide leading citizen science example with approximately 20,000 active participants (many reporting every day), throughout the United States, Puerto Rico, the U.S. Virgin Islands, and 13 Canadian provinces. CoCoRaHS is now the largest provider of daily manual rainfall measurements in the United States and is one of the larger citizen science networks in the world (Fig. 1). In March 2015 the federal government even became part of the program with a gauge located in the First Lady’s vegetable garden at the White House (station DC-DC-19). A total of 37,500 observers have made observations as part of the network during its 17-yr history with over 31 million daily reports recorded and archived. Assuming conservatively that each daily observation takes about three minutes to measure and report online, this represents a volunteer contribution on the order of 1.5 million hours. In addition, there have been tens of thousands of supplemental reports of hail, heavy rain, snow, and drought conditions.

Fig. 1.
Fig. 1.

CoCoRaHS precipitation map showing daily observations for the period ending 0700 LT 6 May 2015. Precipitation amounts ranged from 0.00 to 7.93 in. (201.4 mm). Total number of reports: 13,030 (many reporting daily) with 6,914 observers measuring greater than a trace.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

This article looks at the evolution and accomplishments of this maturing network.

NATIONAL EXPANSION: 2005–09.

The landscape of CoCoRaHS was very different 10 years ago. A staff of two and a handful of volunteer leaders oversaw the development of a network of rain gauge volunteers in Colorado, Wyoming, and Kansas. At the same time, Nebraska followed the Colorado model by establishing its own network—the Nebraska Rainfall Assessment and Information Network (NeRAIN) (http://nerain.dnr.ne.gov/nerain/). Texas and New Mexico were just joining the network then. Thanks to National Science Foundation funding, CoCoRaHS became more visible to the scientific community though participation in several national conferences. Scientists and educators were just beginning to hear of the oddly named organization—CoCoRaHS (pronounced KO-ko-rozz)—that most could neither spell nor pronounce.

With the hiring of a full-time national coordinator late in 2004, the vision for CoCoRaHS shifted from local and regional to national. A nationwide network could potentially fill gaps where precipitation was not being measured by “official” networks, and it could possibly be done with a volunteer force of interested citizens who would learn about their climate while doing something useful for their community. The National Weather Service (NWS) also played a significant role. One of its forecasters from the Boulder (Colorado) NWS Forecast Office wrote some computer code that effectively made CoCoRaHS real-time reports of heavy rain, freezing rain, heavy snow, and/or hail immediately available as an alert message to the appropriate forecast office anywhere in the country. This provided NWS offices immediate motivation to participate in CoCoRaHS and to encourage its expansion. And so the national expansion began (CoCoRaHS 2013). Methodically, on a state-by-state basis CoCoRaHS grew. An Environmental Literacy grant from the National Oceanic and Atmospheric Administration (NOAA)’s Office of Education in 2006 gave the network funding and further motivation to enlarge its footprint across the country. Through partnerships with the National Weather Service and state climatologist offices (both of which needed, appreciated, and had the immediate capacity to use more and better precipitation data from widespread locations in each state), teams of volunteer state leaders were developed. Recruiting and publicity strategies were developed, press releases were issued, and the recruitment of observers intensified. States such as North Carolina and Kentucky launched large CoCoRaHS kickoff campaigns (ASU 2007; http://wwwagwx.ca.uky.edu/cocorahs.mp3). With the addition of Minnesota in December of 2009, all 50 states were part of the network. Along the way several smaller existing precipitation networks in parts of the country saw the advantage of utilizing data collection and management functions of a larger and more developed network with an established and staffed infrastructure. Some of these networks combined their operations into CoCoRaHS. Over these four years, active observers grew from 2,000 to over 15,000 (“active” is defined as registered, with a rain gauge installed and submitting at least one report during the specified year). This definition was chosen from a citizen science education perspective, with about three-quarters of these observers reporting regularly.

2009 survey.

Over 7,000 observers took an online survey conducted in the late summer of 2009 to help gauge the motivations of CoCoRaHS volunteers, to determine what they were learning from participation, and to identify areas for improvement. The survey helped determine the focus for the next phase of CoCoRaHS. The survey results pointed out a need for better cyberinfrastructure and improved educational materials. It also exposed a relative lack of diversity among the participants.

INTERNAL EXPANSION: 2010–14.

In 2010 new grants from the National Science Foundation’s Advancing Informal Science, Technology, Engineering and Math (STEM) Learning (AISL) grant program and NOAA’s Office of Education provided support for a multiyear effort to build up the cyberinfrastructure of the network, to bolster its educational content, and to attempt to reach broader and younger audiences.

Cyberinfrastructure.

The ongoing growth in the number of observers and data users, and the increasingly large data archive necessitated improvements to the CoCoRaHS cyberinfrastructure. The need for improved cyberinfrastructure was also driven by new protocols, new data analysis and quality control tools, and improved data mapping and interactions. These improvements, which included a move to dedicated server hardware, performance tuning the database, and more versatile data mapping and graphing tools, led to a significant increase in both performance and capacity of the network.

Educational/outreach initiatives.

The challenge of bolstering the network’s educational content to improve the public’s climate literacy was next on our list. Several initiatives were undertaken during this period. A webinar series called “CoCoRaHS WxTalk” began in late 2011 (www.cocorahs.org/Content.aspx?page=wxtalk). The webinars provide volunteers a chance to link personally to experts in the fields of weather, climate, hydrology, and related fields though presentations with question-and-answer sessions afterward. Many American Meteorological Society (AMS) members have been featured speakers. Topics span the gamut, from clouds, radar, lightning, and severe weather to backyard rainwater harvesting and “So you want to become a Meteorologist?” The webinars are recorded and are available on YouTube.

Another focus was on encouraging weather observers to advance from being weather observers only to also being climate data analysts and investigators. Several data analysis tools were developed to help observers explore their own data and data from other sources. For example, detailed summaries are produced each year at the end of each October–September water year for every station, making it easy to explore daily and seasonal patterns as well as year-to-year and geographic differences (http://cocorahs.org/WaterYearSummary/).

A natural educational path was to go beyond just precipitation to emphasize the function and importance of the water cycle. A popular YouTube animation on the water cycle was developed in 2013 and has had well over 400,000 views (https://youtu.be/ZzY5-NZSzVw). Working with a small company in Colorado, we added the measurement of reference evapotranspiration ETo to the CoCoRaHS suite of observations. Motivated observers were encouraged to purchase a fairly inexpensive atmometer (∼$220) known as an ETgage (Gavilan and Castillo-Llanque 2009) to deploy during the growing season months (Fig. 2). A reporting site was developed along with an in-depth web page on ETo (http://cocorahs.org/Content.aspx?page=et). This measurement protocol was pilot tested in 2011 and volunteers were recruited in 2012. By 2015, over 130 CoCoRaHS locations across the country were observing ETo. A great example of the added value of these reports was the Midwest “flash drought” during the summer of 2012 (Fig. 3). CoCoRaHS observations of rainfall and ETo pointed out the quick onset of extreme drought during July and early August, and the rapid alleviation later that summer and autumn. These reference ET data and graphs show clearly the profound differences in water balance around the country, which relates directly to vegetation, landforms, and the number and size of rivers and streams.

Fig. 2.
Fig. 2.

ETgage (atmometer) used by selected CoCoRaHS volunteers to measure ETo. (Photo courtesy of Henry Reges.)

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

Fig. 3.
Fig. 3.

2012 summer water balance for Illinois CoCoRaHS station IL-CP-1. Daily precipitation amounts are shown with blue bars, and daily evapotranspiration rates are shown red with bars. Water balance is shown with a green line. This is the difference between incoming precipitation and outgoing evapotranspiration. Graph depicts occurrence of flash drought during Jul–Aug, when evapotranspiration greatly exceeded precipitation.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

During 2012, a partnership was formed with Oregon State University’s Parameter-Elevation Regressions on Independent Slopes Model (PRISM) organization (Daly et al. 2008). The PRISM-CoCoRaHS Climate Portal was developed that provided CoCoRaHS participants with a sophisticated tool for precipitation analysis and research. CoCoRaHS volunteers were provided exclusive access to estimates of “normal” (recent 30-yr average) precipitation for any location in the contiguous United States as well as gridded estimates of monthly and annual precipitation for any location from 1895 to the present. Volunteers, even if they had only helped collect data for a few months or years, could compare their local observations to regional and historic patterns. The portal helps connect volunteers’ daily precipitation measurements (weather) to seasonal patterns, long-term averages, and year-to-year variations (climate)—a very important step toward climate literacy. For example, observers hearing of heavy rains in their states could go to the portal and, based on historic data, see how extreme they actually are. CoCoRaHS participants could have a climate reference to compare to for their locations to determine if their recent rainfall totals were greater or less than average, how they compared to wet and dry years of the past, and if there was any evidence of long-term trends in their areas.

To expand the reach of the network to other communities, a guide to climate resources for master gardeners (http://cocorahs.org/Content.aspx?page=MasterGardener) was developed. The climate guide was used as part of the training materials by several master gardener organizations (www.extension.org/mastergardener) across the country, including those in the Colorado State University Extension. Additional outreach to public and community gardens was initiated, resulting in collaborations with the American Horticultural Society and a presentation at the 2014 annual meeting of the American Public Gardens Association in Denver, Colorado. A relationship with the National Association of Conservation Districts (NACD) was established in a strategic effort to connect with landowners in rural communities. Precipitation was a natural connection to its mission. There are now many examples—such as Erie County, Ohio; Adams County, Pennsylvania; and Weld County, Colorado—where local conservation districts embraced the need for better local monitoring of precipitation and helped recruit and train dozens of volunteers.

Leadership/coordination.

A key to growth and sustainability of CoCoRaHS is a strong and motivated corps of regional, state, and local volunteer leaders (coordinators). A focused effort has been made to personally meet, visit, and encourage as many of the local, state, and regional volunteer leaders as possible during travels to conferences and other meetings. In addition, leadership webinars and conference calls have been organized a few times each year. Many coordinators have attended one or more in a series of yearly national workshops on managing and utilizing precipitation observations from volunteer networks sponsored by the Cooperative Extension’s Western Education\Extension and Research Activities Committee (Delheimer 2014). This has been a highly effective means for building and maintaining partnerships between states, universities, local organizations, and NOAA’s National Weather Service and National Centers for Environmental Information. It has also cemented the relationship between NOAA’s historic Cooperative Observer Program network (National Research Council 1998) and the more recent and less formal CoCoRaHS.

CoCoRaHS and schools.

The 2009 CoCoRaHS participant survey showed that our participant demographics consisted mainly of well-educated middle-age to retirement-age Caucasians. As a result, we set goals to reach younger and more diverse audiences. This has proven to be a significant challenge. The most effective approach so far has been targeted outreach to kindergarten through grade 12 schools through the development of educational materials and a “CoCoRaHS Schools” web page (http://cocorahs.org/Content.aspx?page=CoCoRaHS_Schools). In Colorado, 2012 provided a unique opportunity to reach every school with a donated rain gauge during the state’s “Year of Water” celebration (www.cocorahs.org/Content.aspx?page=CoCoRaHS-Schools-Water2012). This statewide campaign allowed us to test various methods for students to collect and enter data, and it helped us to learn how to best disseminate “CoCoRaHS for Schools” to school districts around the country. Nationally, opportunities to reach teachers and school districts continue to expand. As of November 2015, more than 900 schools across the country were registered in the CoCoRaHS database with 550 of them having submitted data (60% participation). Schools are not well suited for continuous year-round participation, but a biannual campaign called “Rain Gauge Week,” where all registered schools are contacted and encouraged to take observations during this time frame, significantly boosts participation.

In late 2012, CoCoRaHS formed an informal partnership with National Aeronautics and Space Administration (NASA)’s Global Precipitation Measurement (GPM) satellite mission’s education and outreach team (http://gpm.nasa.gov/education/rain-engauge) where schools were recruited to take part in a ground validation campaign. Additional funding opportunities in 2014 (Rolston 2015) allowed the targeted recruiting of students in rural Colorado counties by providing gauges and prize incentives for consistent reports. While the quality and continuity of precipitation measurements from schools have been found to be less than from adult backyard volunteers, the educational experience and the diverse participation are highly valued.

Social media/cellular technology.

To further encourage the participation of broader audiences, the addition of social media (Facebook, Twitter, YouTube) and the development of mobile device applications (apps) were introduced. Mobile device apps not only enticed new observers but older ones as well. Farmers and ranchers, for example, many of whom had not used personal computers or did not have high-speed Internet access in the earlier years of CoCoRaHS are now much more connected by cellular communications. They can immediately record their daily rainfall amounts standing at their rain gauge or while working on their farms and ranches.

TRAINING.

Training of volunteers is very important to the success of the network and to providing accurate high-quality observations. In the early days of CoCoRaHS in-person training sessions were provided by coordinators on a county-by-county basis. As the network grew and more of our demographic became computer savvy, online training materials were developed. To simplify the training, short topical cartoon animations have been developed. These informative, fun-to-watch “shorts” (Fig. 4) delivered via YouTube (www.youtube.com/user/cocorahs) have helped cover a wide variety of important topics for our new volunteers in a concise and entertaining way. In-person training continues to be useful where volunteer leaders are able to provide it. Continuing education for existing volunteers is delivered in several ways, including the “Message of the Day” (http://cocorahs.org/Content.aspx?page=mod&mod=1) and monthly electronic newsletters (http://cocorahs.org/Content.aspx?page=catch).

Fig. 4.
Fig. 4.

CoCoRaHS training animations have made learning about measuring precipitation fun and simple for all ages. A full suite of instructional shorts are available to stream via YouTube.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

HIGH-QUALITY DATA.

CoCoRaHS from its infancy was never envisioned to be a national and international monitoring network, but it has headed in this direction. The primary reason has been the high quality of data provided by CoCoRaHS volunteers and it has been recognized by data users. Observers are typically highly motivated and interested in accuracy. Furthermore—and this has been very important to the success of the network—the required rain gauge used by CoCoRaHS volunteers—a clear plastic range gauge with a 4-in. diameter and 11.30-in. (287 mm) capacity (Fig. 5)—meets the National Weather Service’s precipitation measurement requirements and is also listed in the World Meteorological Organization’s Catalogue of National Standard Precipitation Gauges (Sevruk and Klemm 1989). This gauge is, by design, a scaled-down version of the NWS historic standard rain gauge. With appropriate care it is effective for measuring all forms of precipitation (rain, hail, and snow) in all seasons of the year. As such, the data can be utilized and combined with data from traditional NOAA official sources, such as the Cooperative Observer Program (COOP) network. Under most circumstances, this type of gauge performs comparably (±4%) when compared to the official National Weather Service’s standard 8-in.-diameter rain gauge that has been used for over 125 years to document our nation’s climate (Doesken 2005). As a result, the data collected by CoCoRaHS have been found to be consistently of high quality and suitable for both climate monitoring and research. Comparisons have been conducted examining how CoCoRaHS data compare with observation from automated gauges. In 2002, an extremely dry year in Colorado, an unpublished comparison showed that the tipping-bucket rain gauges used by the Fort Collins, Colorado, stormwater utility read 10%–20% lower than CoCoRaHS gauges. Some of this bias was attributed to the screens that keep insects and debris from blocking the orifice but which increase undercatch and evaporative loss. More recently, the West Texas Mesonet (www.mesonet.ttu.edu/) systematically compared multiday accumulations collected in the CoCoRaHS gauge with the totals observed from its adjacent automated gauges. It has noted a systematic low bias of its automated gauges when compared to the CoCoRaHS gauge of approximately 5%–10% over a wide range of precipitation amounts (J. Lipe, National Weather Service, Lubbock, Texas, 2015, personal communication). The Urban Drainage and Flood Control District of Denver (http://udfcd.org/) operates an Automated Local Evaluation in Real-Time (ALERT) network of about 200 automated tipping-bucket gauges in the Denver area. It has provided encouragement and financial support for CoCoRaHS since the early 2000s, resulting in a very dense observing network in its target area. The Urban Drainage and Flood Control District uses Weather Surveillance Radar-1988 Doppler (WSR-88D) data in combination with its automated rain gauge data to produce a gauge-corrected product. CoCoRaHS data are then used to independently verify precipitation totals and patterns (http://udfcd.org/wp-content/uploads/uploads/resources/flood%20hazard%20news/FHN_2007.pdf). There are many obvious operational advantages to real-time data from automated networks. However, the added value of spatially dense and consistent quality daily precipitation totals from CoCoRaHS and the National Weather Service’s COOP network help meet the high standards for many climatological and research applications (Burt 2012).

Fig. 5.
Fig. 5.

CoCoRaHS 4-in.-diameter plastic rain gauge—required equipment for each CoCoRaHS observer. The gauge measures to the hundredth of an inch and has an 11.30-in. (287 mm) capacity, with any amount greater than 1 in. flowing into and collecting in the outer cylinder. The funnel and inner cylinder are removed in cold weather for capturing frozen precipitation. (Photo courtesy of Henry Reges.)

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

A very important niche that CoCoRaHS fills is measurements of snow accumulation and snow water content. Quantitative measurements of snowfall in the United States have traditionally been limited to National Weather Service cooperative observers, some NWS forecast offices, and several major U.S. airports. Thanks to CoCoRaHS volunteers, who take year-round measurements (about 20% of the CoCoRaHS volunteers take a break during the winter season, but the rest stick with it; Fig. 11), the number of daily snowfall observations in the United States has more than doubled. As with all snow observations, measurements may sometimes be imperfect. But by having many volunteers and greater spatial coverage, it is easier to spot possible errors and biases and, where needed, provide volunteer training.

USEFUL DATA.

CoCoRaHS volunteers’ observations are making a difference on a daily basis. Survey results have shown that a key reason that volunteers stick with rain gauge observations day after day and year after year is because the data they collect are important and are being put to good use. Observations are immediately made public and observers’ data are ingested in many products on a daily basis. These data provide critical information where it may previously have been lacking, helping scientists and others to continually sharpen their knowledge of precipitation patterns and processes across the country.

Thus, it is excellent for a wide range of uses. Weather forecasters and hydrologists, water managers and research scientists, farmers and ranchers, climatologists, insurance adjustors, engineers, recreationists, and many others, use CoCoRaHS observations regularly. Some specific examples include NOAA’s River Forecast Centers (RFCs). A critical input to river stage and flow prediction models is mean areal precipitation—the precipitation averaged across a watershed. The more rain gauge reports there are, the more accurately NWS RFCs can assess mean areal precipitation, which equates to better river forecasts. The National Operational Hydrologic Remote Sensing Center (NOHRSC) uses CoCoRaHS data during winter and spring to improve mapping of snow water equivalent (SWE) over North America. Accurate assessment of SWE is essential to supporting effective hydrologic modeling and prediction. Manual measurements of the water content of snowpack are taken by many CoCoRaHS volunteers in snow areas. Core samples of snow on the ground are taken at least once per week and then melted or weighed to determine water content. These data are then combined with SWE measurements taken by some National Weather Service cooperative observers and from extensive automated SWE data collected by the Snow Telemetry (SNOTEL) system [of the U.S. Department of Agriculture Natural Resources Conservation Service (Pagano et al. 2004)] as well as the Airborne Gamma Radiation Snow Survey Program (GAMMA, which makes airborne SWE and airborne soil moisture measurements from low-flying aircraft across the country; Carroll 2001). The result is a robust ground validation dataset that enhances NOHRSC’s remote sensing, snow modeling, and spatial analysis programs. In 2011 over half of the ground-based observations used by NOHRSC came from CoCoRaHS (Fig. 6). One of NOHRSC’s products is the Snow Data Assimilation System (SNODAS) model (Clow et al. 2012). The observations that are incorporated into this model include satellite imagery, airborne remote sensing, and ground-based observations, which include those collected by CoCoRaHS.

Fig. 6.
Fig. 6.

Comparison of unique CoCoRaHS SWE stations reporting to NOHRSC. Of the SWE reports received, 18% came from CoCoRaHS stations in 2006–07, whereas 58% came from CoCoRaHS stations in 2013–14. (Graphic courtesy of NOHRSC.)

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

Municipal water providers, such as Denver Water, and regional water managers, including the Lower Colorado River Authority in Austin, Texas, use CoCoRaHS reports daily. CoCoRaHS data help assess available water supplies and current and projected customer demands based on local and regional precipitation patterns and water balance (i.e., during wet periods municipal demand decreases and during dry periods municipal demand increases). Daily observations are important in water management, but so is precipitation accumulated over weeks, months, and seasons. CoCoRaHS observations help by providing these seasonal hydrologic panoramas. Those concerned with agricultural interests, such as the developers of the U.S. Drought Monitor, use not only CoCoRaHS observations in helping chart drought throughout the country, but also reports of drought impacts by CoCoRaHS volunteers (Smith et al. 2014).

CoCoRaHS rain and snow reports are used by hunters, fisherman, snowmobilers, and other outdoor recreationalists. One very interesting recreational use is by Major League Baseball’s Minnesota Twins. During the season the grounds crew keeps a CoCoRaHS gauge mounted near the visitor’s dugout at Target Field (Fig. 7) to help it determine how much rain has fallen on the field and also to access possible poststorm flooding data, which can occur with slow-moving summer storms. During winter, skiing and snowmobilers use CoCoRaHS data and maps to determine where fresh snow has fallen.

Fig. 7.
Fig. 7.

CoCoRaHS gauge outside the visitor’s dugout at Target Field in Minneapolis, MN. The gauge has a clear, unobstructed view of the sky. (Photo courtesy of Henry Reges.)

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

There are many examples, from Atlantic tropical storms and Pacific atmospheric rivers to midwestern thunderstorms, where CoCoRaHS has proven to be a great resource in mapping extreme rainfall. In September 2013, unprecedented weeklong rainfall flooded the Front Range of Colorado (Fig. 8). Lives were lost and damage reached into the billions of dollars (Gochis et al. 2015). An army of over 1,000 CoCoRaHS observers helped provide amazing detail for mapping this storm. Other recent extreme event examples captured by CoCoRaHS observers include the Navarro County (Texas) floods of 24 October 2015 [18.95 in. (481.33 mm) in 24 hours], the Palm Beach County (Florida) floods of 10 January 2014 [14.79 in. (375.7 mm) in 24 hours], the Mobile Bay (Alabama)–Pensacola (Florida) extreme event of 30 April 2014 [12.33–18.93 in. (313.2–480.8 mm) in 24 hours] (Fig. 9), and the Islip, New York, flood of 13 August 2014 [13.02 in. (330.7 mm) in five hours]. Finally, in 2008, a New Braunfels, Texas, observer recorded 7.12 in. (180.8 mm) of rainfall in two hours, while stations nearby recorded only 0.1 in. (2.5 mm) or less (Fig. 10). Having a dense, widespread network of volunteers provides amazing detail that might otherwise go undetected. It also provides calibration and validation support for both radar and satellite remote sensing.

Fig. 8.
Fig. 8.

2013 Colorado flood map with CoCoRaHS stations showing 48-h totals, 0700 MDT 11 Sep 2013–0700 MDT 13 Sep 2013. Analysis based on integrated data from multiple sources, including radar. The dense network of volunteer gauges along the Front Range of Colorado provided a rich resource of precipitation observations for detailed mapping.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

Fig. 9.
Fig. 9.

CoCoRaHS map showing 24-h rainfall totals reported by CoCoRaHS observers ending at 0700 CDT 30 Apr 2014. Area includes counties in the Alabama and Florida Panhandles (including Mobile and Pensacola metropolitan areas). Several reports exceeded 18.00 in. (457.2 mm) in 24 hours.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

Fig. 10.
Fig. 10.

Example of one station making a difference. Observer in eastern Comal County, TX, near New Braunfels reporting 7.12 in. (180.8 mm) of precipitation in 24 hours ending at 0700 CDT 6 May 2008, whereas stations nearby received less than 0.1 in. (2.5 mm).

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

A highlight in CoCoRaHS’s history occurred in July 2010, when we learned that our data were being archived by NOAA’s National Centers for Environmental Information (NCEI) and made publically available as a part of the Global Historical Climatology Network (GHCN)-Daily (Menne et al. 2012). As of December 2014, CoCoRaHS was contributing 25,335 station time series to the GHCN-Daily database. These data can be accessed directly by the public from the National Weather Service website (weather.gov) via “NOWData.”

VOLUNTEER SUPPORT AND SUSTAINABILITY.

With an ever-growing network (Figs. 11 and 12), logistical challenges remain (Doesken and Reges 2010). How to most effectively manage large numbers of volunteers spanning the entire country and representing all ages and walks life—and doing this with only two full-time staff members—is an ongoing question. The excitement of Internet communications in the 1990s and early 2000s helped launch CoCoRaHS nationwide. Direct e-mail and web page communication were very effective in the early years of CoCoRaHS, but they now seem to be waning a bit as more people are burdened with excessive e-mail and prefer other forms of social media.

Fig. 11.
Fig. 11.

2010–14 national number of active observers and reports entered. Blue bars show total number of active observers by month. Yellow bars show number of observers who have reported an observation each month. Dashed lines show 12-month averages.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

Fig. 12.
Fig. 12.

2010–14 national number of new sign-ups per month. Blue bars show total number of new volunteer observers signing up each month. Yellow bars show those who have signed up during that period who have actually reported. Blue dashed line shows 12-month average total sign-ups. Yellow dashed line shows 12-month average sign-ups reporting.

Citation: Bulletin of the American Meteorological Society 97, 10; 10.1175/BAMS-D-14-00213.1

Approximately 260 state and regional volunteer coordinators, primarily made up of professionals from the climate, weather, and water community, help manage the network on a local basis. Sustaining relationships between the coordinators and CoCoRaHS headquarters is imperative. Texas alone has over 1,400 volunteer observers in 254 counties. It is divided into 13 regions with 18 regional coordinators and dozens of county coordinators. Having these local coordinators who know their communities and understand the local weather and climate patterns is very valuable. The local coordinators in each state, although under the CoCoRaHS umbrella, have been given autonomous liberties to shape the program in their state. This has led to the development of creative approaches to volunteer recruiting, engagement, and retention. Newsletters, get-togethers, state web pages, training events, and volunteer recognition vary from state to state; however, without local leadership, it would be much harder to maintain this network.

Figure 11 shows the growth in participation in CoCoRaHS. A recent analysis of our data showed that during the years 2010–13, 71% (19,217 sign-ups; 13,719 making their first report) of those who signed up to join the network made their first report and 71% (9,705 reporting a year later from those 13,719 who made their first report) of those who made their first report were still reporting after one year. In other words, only about half of all initial recruits are still participating a year later. This rate of retention seems discouragingly low, but leaders of other citizen science projects, such as the USA National Phenology Network, are very impressed with CoCoRaHS’s volunteer retention. Also on the bright side, of those who stay with CoCoRaHS for a full year, they are likely to continue for many more years.

On a national level, events like CoCoRaHS March Madness, an annual 31-day recruiting contest in March to win the “CoCoRaHS Cup” (http://cocorahs.org/Content.aspx?page=Marchmadness15), trigger many coordinator interactions between states in the form of friendly competition (Fig. 12). This annual spring event helps recruit hundreds of new volunteers and helps offset attrition from those volunteers who lose interest, move, or are no longer able to perform the duties of a rain gauge volunteer. Long-established CoCoRaHS states like Colorado, New Mexico, Wyoming, and Texas have observers who have made thousands of reports and have been observers for over 10 years. Still, a comprehensive, nationwide effort to recruit new volunteers is continually needed.

THE FUTURE OF COCORAHS.

As CoCoRaHS soon completes its second decade, there are both opportunities and challenges ahead. Automated rain gauge networks are proliferating, supporting real-time hydrometeorological requirements. The greater accuracy of CoCoRaHS measurements from manually read gauges is still recognized and appreciated but will that be sufficient? CoCoRaHS fills a major observational gap when it comes to snow and hail but will that be supported? Federal grants helped start the network. Now volunteer donations and support from data users are becoming the primary sources for sustaining the network.

CoCoRaHS is interested in helping enhance, develop, and supplement other volunteer observing networks worldwide (Doesken and Reges 2011). Current examples include supplementing observations from NOAA’s Cooperative Observer Program network and developing the 2016 CoCoRaHS expansion across the Bahamas in collaboration with the Bahamas Department of Meteorology through the support of the World Meteorological Organization (WMO), the Global Climate Observing System (GCOS), and NOAA. Expansion on a continental or global scale is technically feasible, but it would only be effective with very strong local interest and leadership. Given time and resources, there are many other opportunities for improvement, including better mapping and data display; more tools for data analysis; research on floods, drought, and climate variability; a revamped web interface; and furthering relationships with collaborators.

CoCoRaHS needs more volunteers. To sign up to become a rain gauge reader, go to the CoCoRaHS website (http://cocorahs.org/) and click “Join CoCoRaHS.” CoCoRaHS data are freely available for research, education, and application. Please direct any questions to info@cocorahs.org.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the dedication of CoCoRaHS volunteers and coordinators for making this project a success. This project has been supported by grants from the National Science Foundation (0229723, 1010888), NOAA’s Office of Education (NA06SEC4690004, NA10SEC0080012), the Colorado Agricultural Experiment Station, the National Institute of Food and Agriculture, the U.S. Department of Agriculture, our philanthropic donors, Colorado State University, the PRISM organization at Oregon State University, the National Drought Mitigation Center, NOAA’s National Weather Service, NOAA’s National Centers for Environmental Information (NCEI), NOAA’s National Operational Hydrologic Remote Sensing Center, NOAA’s Climate Program Office, the World Meteorological Organization (WMO), the Bahamas Department of Meteorology, the Global Climate Observing System, the American Association of State Climatologists and state climate offices throughout the United States, the National Association of Conservation Districts, the USDA, NASA, K–12 school districts, Weather Innovations (WIN), Environment Canada, Denver Water, Denver Urban Drainage and Flood Control District, and our other partners, of which there are too numerous to mention.

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