Open Water Data in Space and Time1

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION

OPEN WATER DATA IN SPACE AND TIME1

David R. Maidment2

ABSTRACT: An Open Water Data Initiative has been established by the federal government to enhance water information sharing across the United States (U.S.) using standardized web services for geospatial and temporal data. In a parallel effort, the National Weather Service has established a new National Water Center on the Tuscaloosa campus of the University of Alabama, at which a new National Water Model starts operations in June 2016, to continually simulate and forecast streamﬂow discharge throughout the continental U.S. These two developments support the interoperability of streamﬂow and hydrologic information in time and space from modeled and observed sources through the use of open standards to share water information.

(KEY TERMS: data management; geospatial analysis; monitoring; web services; water data.)

Maidment, David R., 2016. Open Water Data in Space and Time. Journal of the American Water Resources Asso- ciation (JAWRA) 1-9. DOI: 10.1111/1752-1688.12436

INTRODUCTION Alabama, which was formally opened in May 2015. The aim of this Center is to “improve water resource forecasts, understand how water moves across the Several events occurring during the spring and land and rivers, and facilitate creative and informed summer of 2014 spurred the establishment of an decisions — all utilizing the best available science” Open Water Data Initiative in the United States (http://www.nws.noaa.gov/oh/nwc/, accessed August 6, (U.S.). In March 2014, President Obama launched a 2015). The National Water Center is intended to sup- Climate Data Initiative and invited leaders of high port the combined efforts of federal water agencies technology firms and representatives of community working together in the Integrated Water Resources organizations to the White House to explore how Science and Services partnership, whose founding information from the climate data holdings of the fed- members were the U.S. Army Corps of Engineers, eral government could be made more accessible to cit- U.S. Geological Survey (USGS), and NWS, joined in izens so that they could better adapt to climate the summer of 2015 by the Federal Emergency Man- change, especially with respect to the effects of sea agement Agency. level rise. This event was part of a larger emphasis The first two goals of this Center are an “opera- on Open Data in the federal government and tions center with situation rooms” to develop a com- prompted the question: what could be achieved by an mon operating picture of water conditions from floods Open Water Data initiative? to droughts, and a “geo-intelligence laboratory” to In May 2014, a new National Water Center was support the effort with state-of-the-science enterprise established by the National Weather Service (NWS) GIS information (http://www.nws.noaa.gov/oh/nwc/, on the Tuscaloosa campus of the University of accessed August 6, 2015). A National Water Model is

1Paper No. JAWRA-15-0123-P of the Journal of the American Water Resources Association (JAWRA). Received August 7, 2015; accepted April 20, 2016. © 2016 American Water Resources Association. Discussions are open until six months from issue publication. 2Hussein M. Alharthy Centennial Chair in Civil Engineering, University of Texas, Austin, Texas 78712 (E-Mail/Maidment: [email protected]).

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1 JAWRA MAIDMENT starting operations in June 2016, which will continu- some of the elements of an Open Water Data Initia- ally simulate and forecast land surface hydrology and tive might consist, and to examine whether there streamflow discharge across the continental U.S. This might be developed a National Water Data Infras- requires an underpinning foundation of continually tructure with similar goals for water to those that updated geospatial and temporal information about the NSDI embodies for geospatial information to water conditions throughout the nation. underlie the operation of the National Water Model. The Open Water Data Initiative was launched during the summer of 2014 by Anne Castle, then Assis- tant Secretary for Water and Science of the Department of the Interior, in her capacity as Chair WATER DATA IN SPACE of the Federal Geographic Data Committee and of the Advisory Committee on Water Information, the two bodies within the federal government which coordi- The geographic information encapsulated in the nate national geographic and water information, NSDI is divided into a set of themes describing infor- respectively. The Initiative is coordinated through a mation of particular kinds, divided into core and sup- Subcommittee on Spatial Water Data, which serves plemental framework themes. The two Core to represent water within the Federal Geographic Framework Themes relevant for water are Hydrogra- Data Committee and spatial data within the Advisory phy and Elevation Terrestrial. Hydrography is com- Committee on Water Information. This Subcommittee prised of map layers depicting water features of the has established use cases for open water data in the landscape — streams, rivers, lakes, bays and the areas of flooding, water supply, and water quality, coastline, connected into a flow network. Elevation and seeks by a series of experiments to find the open Terrestrial describes vertical position above or below water data services which best inform decisions in a datum surface. The interaction of these two themes these areas. captures the age-old duality — water flows downhill The NWS collaborated with the academic commu- directed by the slope of the landscape, while the ero- nity coordinated through the Consortium of Universi- sive power of flowing water has itself been a major ties for the Advancement of Hydrologic Science, Inc. force in shaping the landscape over millennia. Sup- (CUAHSI) to conduct a National Flood Interoperabil- plemental Framework Themes relevant to water ity Experiment from September 2014 to August 2015 include Watersheds and Wetlands, which along with focused on developing a near real-time, high spatial Hydrography are part of the Inland Waters theme, resolution flood data, modeling, forecasting and inun- and Flood Hazards, Soils, Earth Cover, Geologic and dation mapping system. This experiment informed Climate, themes whose properties influence and are the flooding use case of the Open Water Data Initia- influenced by the movement of water through the tive. The results of the experiment will be reported in landscape. a later Featured Collection of articles in this Journal. During the first 10 years of the NSDI (1994-2004), The Federal Geographic Data Committee coordi- the focus was on the development of the framework nates the National Spatial Data Infrastructure themes, in particular the National Elevation Dataset, (NSDI), initiated in 1994 during the period of transi- National Hydrography Dataset, and later the Water- tion from paper maps to digital datasets in the U.S. shed Boundary Dataset. During the subsequent 10 Subsequently, “the NSDI has come to be seen as the years (2004-2014), the focus was on the integration of technology, policies, criteria, standards and people these datasets — the National Hydrography Dataset necessary to promote geospatial data sharing Plus (NHDPlus) dataset was formed as a synthesis of throughout all levels of government, the private and the elevation, hydrography, watershed boundary, and non-profit sectors, and academia” (http://www.fgdc. land cover datasets. gov/nsdi/nsdi.html, accessed August 6, 2015). A major The NHDPlus dataset partitions the nation’s drai- transition is occurring currently in GIS from provi- nage system into 2.67 million reach catchments, each sion of datasets to provision of data services, which is reach catchment draining to a single stream reach or acknowledged in the strategic plan for 2014-2016 for water feature, which are connected by the movement the NSDI whose first goal is to “develop capabilities of water through the sequence of reaches from any for national shared services” (Federal Geographic point in the landscape to the coast. Each reach catch- Data Committee, 2013). ment and the flowline within it carries a unique iden- In recent years, the capability for developing data tifier, or COMID, and by this means the land and services for water information has also been devel- water systems of the nation are connected. What oped, so it is useful to examine how data services for emerges is a single flow network across the continen- geospatial and water information could be inter- tal U.S., from atmosphere to oceans and from coast to linked. The purpose of this article is to explore what coast. The National Water Model computes the flow

JAWRA 2 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION OPEN WATER DATA IN SPACE AND TIME in all these reaches as a connected whole, each reach Information System for water quantity and quality, being fed by the drainage from the catchment that and the U.S. Environmental Protection Agency surrounds it. (USEPA) Storet (Storage and Retrieval) database for Attributes of the catchments describe properties of water quality. Beyond this information about moni- the local area while attributes of the flowlines toring the properties of the nation’s water, there are describe properties of the total upstream drainage important data on water operations, such as the vol- area. As the National Water Model is further devel- umes of storage and release from reservoir systems, oped, it is expected that the present continental scale and on water use in cities, agriculture, and industry surface water model will be complemented by a con- that form an important part of the nation’s water nected continental scale groundwater model. information base. Water information is collected by The strategic plan for 2014-2016 for the NSDI is all levels of government and there are hundreds if defined by Federal Geographic Data Committee not thousands of web sites that contain water data of (2013). The first goal of this plan is to “develop capa- various kinds collected for various purposes. bilities for national shared services.” The desired Data vital to performing functions such as flood future state of the NSDI includes: emergency response is contained in a myriad of local databases each with their own web site. Rapid federal 1. Leverage shared and open standards-based ser- response to local and regional emergency situations vices and focus on applied information for requires open access to this real-time local informa- improved decision making tion, and the capacity to synthesize it rapidly across 2. Use real-time data feeds and sensor webs for the nation. improved monitoring, control, situational aware- ness, and decision making 3. Facilitate access to and use of multi-temporal information linked to place WATER DATA IN TIME 4. Facilitate use of community-driven open standards with multiple implementations The principal source of water quantity information These goals could equally well have been written for the U.S. is the National Water Information Sys- for nationally shared data services for water informa- tem (NWIS) of the USGS. This information has tra- tion. ditionally been accessed through the web (http:// The water-related information in the NSDI www.usgs.gov/water/, accessed June 8, 2016), includ- describes the “water environment,” that is, the land- ing a WaterWatch map, shown in Figure 1, in which scape features through which water flows but it does the current value of streamflow discharge recorded at not describe the properties of water itself — the flow, each USGS gage is compared to past values recorded water level, and quality of water that are vital for at that gage on that calendar day and plotted as a understanding the impact of water on human life, percentile value to show how high or low the current and the reverse — the impact of humans on water discharge value is compared to those recorded previ- systems. The principal federal datasets containing ously. This WaterWatch map can be thought of as this information are the USGS National Water the forerunner of a new class of “Water Maps,” which

FIGURE 1. USGS WaterWatch Map for June 8, 2016. (http://waterdata.usgs.gov/nwis/rt, accessed June 8, 2016).

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 3 JAWRA MAIDMENT describe a water property across space and through Consortium (OGC) (http://www.opengeospatial.org/s- time, enable current conditions to be compared to tandards/waterml, accessed August 6, 2015). This stan- those of the past, and act as a point of departure for dard was developed in collaboration with the World forecasts of the future. Meteorological Organization through an OGC/WMO Besides streamflow discharge the USGS also has Hydrology Domain Working Group, which since its websites for real-time water quality (http://water- establishment in 2009 has become an effective forum watch.usgs.gov/wqwatch/, accessed January 18, 2016) for development of international standards for and groundwater (http://groundwaterwatch.usgs.gov/, exchange of water and hydrologic data. The original accessed January 18, 2016). WaterML language for water resources time series Besides accessing USGS data through traditional was developed by the CUAHSI, an organization repre- web pages, this information can also be accessed senting 125 U.S. universities, sponsored by the through water data services (http://waterservices. National Science Foundation. WaterML2 was usgs.gov, accessed August 6, 2015). These services endorsed by the Office of Science and Technology Pol- include real-time and daily time series information icy (2013) as part of a national strategy for civil earth from continuously operating gages, water quality and observation of the U.S. The WMO is presently process- groundwater data collected at irregular intervals, and ing the WaterML2 standard through its approval pro- information on measurement site locations. For cess under a new name, TimeSeriesML, to become a example, a request for real-time information on WMO standard for all forms of time series. At present, instantaneous values (iv) in the WaterML2 language this format is intended for regularly collected time ser- (format = waterml, 2.0) for the Colorado River at ies and is not intended for use with data that are irre- Austin, Texas (sites = 08158000), for the most recent gularly sampled in time, such as for water quality and one day (period = P1D), and for streamflow discharge groundwater levels. (parameterCD = 00060) can be expressed as follows: Water quality data can be downloaded from a Water http://waterservices.usgs.gov/nwis/iv/?format=waterml, Quality Portal (http://waterqualitydata.us/, accessed 2.0&sites=08158000&period=P1D¶meterCd= January 18, 2016) which is jointly operated by the 00060. USGS and USEPA and provides a common access The resulting time series of values returned from point for water quality data from both agencies. This this web request is presented as a set of Time-Value is typically point information that is collected in indi- Pairs as shown in Figure 2, in which the time is spec- vidual water samples and analyzed for many con- ified according to the ISO time convention so that stituents in a water quality laboratory. USEPA has June 7, 2016 at 5:20 in the Central Time Zone is spe- developed a set of web services for conveying this cified as 2016-06-07T05:20:00-05:00, where the information called WQX (for Water Quality eXchange). À05:00 refers to the time offset from Universal Coor- These are not time series data and less well suited for dinate Time of this particular time stamp. The second conveying in the WaterML2 time series language. part of the Time-Value Pair is the discharge, 26100.0 cubic feet/s (739 cubic meters/s), and information elsewhere in the response gives the units of measure, location of the station, source of the data, and other SPATIAL AND TEMPORAL WATER DATA descriptive information about the time series. SERVICES The WaterML2 language used for this USGS water service is a standard of the Open Geospatial Open standards for conveying geospatial information as services have existed for some time. These include the Web Map Service, Web Feature Service and Web Coverage Service of the OGC. The OGC also supports a Sensor Observation Service and the WaterML2 standard is a profile of the Observations and Measurements model that underlies the Sensor Observation Service. It can thus be seen that an open standards framework exists for conveying both map and observational data. The application of this framework is not limited to water information on the land surface — the U.S. Integrated Ocean Observing System FIGURE 2. Real-Time Streamflow Data in the WaterML2 (http://www.ioos.noaa.gov/, accessed August 6, 2015) Language for the Colorado River at Austin, Texas also uses this standards framework although in a (accessed June 7, 2016). slightly different form. The Open Water Data

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Initiative relies on open geospatial and water infor- information is through “push” services in which mes- mation systems, which are produced using commer- sages are sent in the SHEF language (Standard cial and open source software linked through open Hydrologic Exchange Format) from one part of NWS standards. to another. More recently, the NWS adopted a “push” It follows that to serve a “Water Map” that con- system for file distribution called the Local Data tains information distributed in both space and time, Manager, developed by Unidata, NSF’s data center requires a combination of services for presenting first for atmospheric science. These “push” services are a map service that contains the geospatial observa- not compatible with the “pull” system for data ser- tion points, in which the feature attributes of each vices that the USGS uses and which is more common point have links to the temporal information. There in the commodity Internet. In push services, the data are generally three types of such links — one that supplier determines the timing of the data distribu- produces a chart, a second that produces a comma- tion and the data consumer accepts the pushed infor- separated variable listing of the data, and a third mation, generally on a preset timing basis. In pull that produces the WaterML2 time series service, as services, the data consumer makes a request for shown in Figure 3. The chart service is for quick information and the data producer responds — this visual appreciation of the data, the .csv service is for can be thought of as a “just in time” response. In downloading and ingestion into a spreadsheet such as other words, the schedule of pull services is controlled Excel or a statistical package such as R, and the by the data consumer and for push services by the WaterML2 service is for complete description of the data producer. time series. A new development, however, changes this picture. It happens that many of the USGS gaging loca- The NWS has adopted the Flood Early Warning Sys- tions shown in Figure 3 are also forecast points of tem (FEWS) developed by Deltares in the Nether- the river forecasting system of the U.S. NWS. There lands, and has deployed FEWS at all of its River are about 3,600 such forecast points in the nation, Forecast Centers. FEWS has the capability to both and approximately three-quarters of them are co- ingest and produce WaterML2 data services. During located with USGS stream gages. The NWS River the summer of 2015, the NWS used this mechanism Forecast Centers are continually running hydrologic to assemble forecast information on precipitation, models on the watersheds above these points and pro- land surface runoff, and streamflow discharge from ducing five-day ahead forecasts of flows. The tradi- all 12 of its River Forecast Centers in the continental tional way that the NWS has distributed its U.S. and produced a prototype web service, using the

FIGURE 3. Water Map and Data Services.

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WaterML2 language that conveys this forecast infor- encompasses the entire domain, such as North Amer- mation in exactly the same way as depicted in Fig- ica, or the globe, and contains all the variable dimen- ure 2 for USGS streamflow observations. This is a sion values for a particular day or other short time remarkable development in itself, and a significant interval. This is a “broad in space, shallow in time” accomplishment of the Open Water Data Initiative, approach. For hydrology and water resources, the which fosters this adoption of open standards for fed- focus is often the reverse — the need is for informa- eral water information. There is a long-standing dis- tion on individual variables in a particular small area tinction of missions as agreed upon between the such as a local watershed, and the need is to see the USGS and NWS, by which the USGS focuses on the time history of those variables. past and present, and the NWS on the present and One example of this information is the National future. Through the use of water services integration Aeronautics and Space Administration (NASA)/ between these two agencies, the consumer of water National Oceanic and Atmospheric Administration information can cross over this divide and have a con- (NOAA) Land Data Assimilation System (NLDAS). tinuous picture through time of water information NLDAS presents information on a 1/8 degree grid for through time, past, present, and future. North America and 1/4 degree grid globally, and on a Another important aspect of this development is 1 h time interval for North America and 3 h time that it makes possible the development of a national interval globally. It contains information for about 80 map of river forecast data and information services variables defined on this grid, from atmospheric con- where the map covers forecast information from the ditions, weather forcing functions such as precipita- River Forecast Centers, and the user could choose tion and solar radiation, and the land surface any combination of forecast points, large or small. response in the form of the water and energy balance, The provision of national water map and data ser- including evaporation, soil moisture levels, and sur- vices will be critical to the operation of the National face and subsurface runoff. The information is com- Water Center. piled from 1979 onwards and is continually refreshed by NASA with new data produced from numerical weather modeling and land surface modeling done at the National Centers for Environmental Prediction WATER DATA AS A SPACE-TIME CONTINUUM (NCEP). For each variable in each grid cell, there are more than 300,000 values in the hourly time series since 1979 in this dataset. At NASA Goddard Space The foregoing discussion applies to water informa- Flight Center, a new method of presenting this infor- tion at point locations in the landscape, or more gen- mation called “Data Rods” has been developed. The erally to discrete geospatial objects (points, lines, entire NLDAS database is being reconstituted to pro- areas), whose temporal properties are described by vide access through time at particular points in space time series. A parallel development for shared data and to provide time series data services, including services is happening for continuously gridded infor- charts, comma-separated variable and WaterML2 ser- mation, such as that describing weather and climate. vices. An illustration of data rods for NLDAS soil This information is defined on multidimensional moisture for Texas is shown in Figure 4 (Espinoza- arrays, where for each point in the coordinate dimen- Davalos et al., 2016). Knowing the whole time history sions (latitude, longitude, altitude, time) data for a at each cell enables probability-based interpretation set of variable dimensions are specified (temperature, of the current map values in the context of past val- precipitation, humidity, wind speed, etc.). ues, in an equivalent manner to the Water Watch A widely used server for publishing this kind of infor- Map shown in Figure 1. mation is THematic Real-time Environmental Distribu- ted Data Services (THREDDS), produced by Unidata in Boulder, Colorado (http://www.unidata.ucar.edu/software/thredds/current/tds/, accessed August 6, 2015). DATA ON WATER OPERATIONS AND USE Access to gridded information in THREDDS is provided either through Open Data Access Protocol (OpenDAP), or the OGC Web Map Service and Web Coverage Ser- Besides the functioning of the natural water sys- vice, or through direct http://requests. A response from tem, there are vital parts of the nation’s water infra- THREDDS for time series in the WaterML2 language structure system whose data are needed to form a has been programmed at Unidata. complete picture of water conditions. A critical data Typically, gridded information is distributed in file layer needed to understand the impact of climate formats such as netCDF or Grid where each grid file change on the water security of the U.S. is the

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FIGURE 4. Data Rods for Texas from NLDAS Soil Moisture Simulation. volume of water storage in the nation’s reservoir sys- Beyond the reservoir data, there is a large variety tems. As shown in Figure 5, there are nearly a thou- of information concerning water use from surface and sand of these reservoirs operated by the U.S. Army groundwater to supply the needs of cities, agriculture, Corps of Engineers and U.S. Bureau of Reclamation, industry, power generation, and other needs. An ini- and many more reservoirs operated by regional agen- tiative of the Western States Water Council called cies such as the Tennessee Valley Authority, and Water Data Exchange (WaDE) has created a data local entities. These reservoirs are the backbone of schema for exchanging water use information among the surface water supply system of the nation and the Western states that may serve as a prototype for they respond regionally to drought conditions. Data wider adoption. on their operation, including storage volumes and releases, are compiled by the agencies that operate these reservoirs but there is no consistent system for accessing this information as already exists for USGS DATA FOR FLOOD INUNDATION MAPPING water data. Indeed, the information is held in regional offices, and is continually updated as further operations occur, so one way to build a nationally One of the data layers in the NSDI is Flood federated reservoir information system is to build Hazards — the boundaries of the flood inundation consistent water data services at each reservoir infor- zones for extreme floods, especially for the base flood, mation location and then federate them nationally whose chance of occurrence in any year is 1%. These with a single web map, the attributes of whose points maps are compiled by the Federal Emergency Man- contain links to the appropriate reservoir information agement Agency, which has spent approximately services, in a similar way to that shown for USGS $2 billion on digital flood mapping since 2003 under streamflow in Figure 3. The Lower Colorado Region the Map Modernization and later the RiskMAP pro- of the Bureau of Reclamation has completed a pilot grams. This large investment, said by some to be the study to establish how to publish its reservoir infor- largest civilian mapping program in the world, has mation as a water data service. An alternative inspired the development of the Lidar (Light Detec- approach is to compile the reservoir information into tion and Ranging) industry in the U.S. for precise a national repository and provide information ser- mapping of land surface terrain. About one-third of vices from that, as the Australian Bureau of Meteo- the nation now has Lidar data coverage, and a great rology has done for that nation’s reservoir deal of engineering effort has been expended in inter- information. pretation of this information to define stream

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FIGURE 5. Locations of Reservoirs of the U.S. Army Corps of Engineers and U.S. Bureau of Reclamation. channels in three dimensions, with both profile lines RAPID for river flow routing. It was demonstrated and cross-sections, and to add to that information that the flow could be forecast for 15 h ahead in each about structures in the floodplain, including bridges of the 2.67 million stream reaches of the NHDPlus and culverts. dataset in the continental U.S. in a single operation The USGS and NWS also have a real-time flood taking 10 min of computational time at the Texas forecasting and inundation mapping program in Advanced Computation Center in Austin. This com- which for a region upstream and downstream of a putation was updated every three hours. In June USGS gage, a flood map is drawn from a precom- 2016, a further developed version of that model is puted library of such maps for the water surface ele- being made operational at the National Water Center vation forecast at that location by the NWS. The in Tuscaloosa, Alabama for continual simulation of NWS Advanced Hydrologic Prediction Service cur- land surface hydrology and streamflow discharge rently has such maps at 130 locations in the nation. throughout the continental U.S. The open sharing of The terrain surface is the origin of watershed rep- computational results and observational and opera- resentation for hydrologic computation and channel tional water data in space and time across the nation definition for hydraulic computation. Hydrologic mod- will be needed to use this information to improve els convert storm precipitation into flood discharge in water resources decision making and water science. streams and rivers, and hydraulic models determine the resulting water surface elevations. Floodplain maps are created by transposing the computed water surface elevations back onto the terrain surface, and CONCLUSIONS delineating the resulting inundation boundaries. Hydrologic and hydraulic models capable of being applied at the continental scale have been developed Two recent developments, the Open Water Data in recent years, including the Weather Research and Initiative, and the new National Water Center, have Forecasting Model Hydrological modeling extension created a platform for the open sharing of water data package (WRF-Hydro) developed at the National Cen- in the U.S. The Open Water Data Initiative does so ter for Atmospheric Research (NCAR) by Gochis et al. by encouraging adoption of the data standards of the (2013), Routing Application for Parallel computation Open Geospatial Consortium for sharing geospatial of Discharge (RAPID) developed by David et al. data, and the WaterML2 language for time series (2011), and Simulation Program for River neTworks data. (SPRNT) developed by Liu and Hodges (2014). These A National Water Model is starting operations at models are optimized for very high-speed processing the National Water Center in June 2016, in which of information on large landscapes and river net- land-atmosphere hydrology and streamflow discharge works. are computed and forecast continually in a near real- During the National Flood Interoperability Experi- time, high spatial resolution manner across the conti- ment, a high spatial resolution, near real-time flood nental U.S. The streamflow is computed in this model modeling forecasting system was developed for the in each of the 2.7 million reaches of the NHDPlus, a U.S. by combining the High-Resolution Rapid Refresh geospatial dataset covering the continental U.S. precipitation and weather forecast, with the WRF- In collaboration with the NWS, the academic com- Hydro framework for land-atmosphere modeling and munity, coordinated by the CUAHSI, conducted a

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National Flood Interoperability Experiment in 2014- Liu, F. and B.R. Hodges, 2014. Applying Microprocessor Analysis 2015. This experiment demonstrated that the flow in Methods to River Network Modeling. Environmental Modelling the 2.7 million stream reaches of the continental U.S. & Software 52:234-252. Office of Science and Technology Policy, 2013. National Strategy could be computed in 10 min at the Texas Advanced for Civil Earth Observation: Executive Office of the President. Computing Center. National Science and Technology Council, Washington, D.C., p. This information will be distributed by geospatial 21. and temporal data services in standardized formats defined through the Open Water Data Initiative. Other data sources, such as reservoir operations information, the National Land Data Assimilation System, and real-time flood inundation mapping, should also form part of the emerging open data sharing system. Hence, it can be said that a flow-continuum model in time and space is emerging, from atmosphere to oceans and from coast to coast. This is an unprece- dented development for the nation — the emergence of a field of study that might be called real-time continental hydrology. This will require the very rapid assembly and processing of time series of precipitation, water levels and flows recorded across the nation by the USGS, other federal agencies, and by many hundreds of state and local agencies, and thus the sharing of data through open standards as defined by the Open Water Data Initiative.

ACKNOWLEDGMENTS

The research described in this article was supported in part by NSF grant 1343785 “EarthCube Building Blocks: Integrating Dis- crete and Continuous Data,” and by contributions supporting the author’s research by ESRI, Kisters, and Microsoft Research. The author acknowledges the helpful contributions of Jerad Bales, Anne Castle, Don Cline, and Peter Colohan for the formation of the Open Water Data Initiative; to Anne Linn for her insights concerning relevant information about open geographic information systems; and to Fernando Salas for help in preparing the example water map and data services.

LITERATURE CITED

David, C.H., D.R. Maidment, G.-Y. Niu, Z.-L. Yang, F. Habets, and V. Eijkhout, 2011. River Network Routing on the NHDPlus Dataset. Journal of Hydrometeorology 12(5):913-934, DOI: 10.1175/2011JHM1345.1. Espinoza-Davalos, G.E., D.K. Arctur, W. Teng, D.R. Maidment, I. Garcıa-Martı, and G. Comair, 2016. Studying Soil Moisture at a National Level through Statistical Analysis of NASA NLDAS Data. Journal of Hydroinformatics 18(2): 277-287, DOI: 10.2166/ hydro.2015.231 Federal Geographic Data Committee, 2013. National Spatial Data Infrastructure Strategic Plan 2014-2016. Reston, Virginia, 19 pp. http://www.fgdc.gov/nsdi-plan/nsdi-strategic-plan-2014-2016- FINAL.pdf, accessed June 2016. Gochis, D.J., W. Yu, and D.N. Yates, 2013. The WRF-Hydro Model Technical Description and User’s Guide, Version 1.0. NCAR Technical Document, 120 pp. https://www.ral.ucar.edu/projects/ wrf_hydro/, accessed June 2016.

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