Current Surface Water Conditions

090E030N

By G. R. Brakenridge and A. J. Kettner

 

Display 1: Flooded Areas

Map layers, bottom to top: Light gray: Satellite record of flooding, 1999-2016. Red: Currently-observed flooding (past 14 days). Blue: Bankfull reference water.

Click on colored dots to retrieve daily discharge or reservoir extent values. Click on reservoir, wetland, and lake areas to retrieve Flood Observatory Web Map Server displays. A large, simplified Geotif of this map is also available.

 

Display 2: Seasonally flooded, Now-Dry Land

Map layers, bottom to top: Light gray: Satellite record of flooding, 1999-2016. Yellow: New dry Land (the bankfull water layer). Blue: Current water (past 14 days).

Click on colored dots to retrieve daily discharge or reservoir extent values. Click on reservoir, wetland, and lake areas to retrieve Flood Observatory Web Map Server displays. A large, simplified Geotif of this map is also available.

 

Explanation

Purpose:

These maps and displays provide satelllite-based water information to a variety of water professionals. Since late 1999, satellite data have been obtained by the Dartmouth Flood Observatory, processed to detect water/land boundaries, and analyzed to produce flood inundation limits in vector GIS format. Current Surface Water Conditions compiles this information to produce both a permanent record of the Earth's surface water variability, and on-going observations of changes as they occur.

Many areas of both maps include hyperlinks to more detailed map or river flow status information: hover with the mouse to locate active links

Map Coverage:

The map sheet number gives geographic coordinates of the upper left corner of map. Most maps measure 10 degrees longitude and latitude and are in plate-carree (equirectangular) projection. Sheets above 60 degrees north are in UTM projections and measure 20 degrees longitude.

Uses:

Flood Response: In the Flooded Areas display, red areas are flooding compared with bankfull conditions. In some cases, new reservoirs also appear in red. Red areas in mountainous terrain, or during winter in the higher latitudes may be "false positive" water detections. Visit also the Web Map Server (WMS) for more detailed examination, or download the larger scale geotif file.

Flood Hazard: In either display, the light gray aresa indicate observed surface water during the period of record. Download the full resolution geotif file to retrieve this important information about flood hazard. Where River Watch sites monitor floodplain reaches, recurrence intervals can also be calculated for the mapped flooding.

Reservoir and Lake Monitoring: In the Low Water Areas display, reservoirs with yellow fringes are low compared to the bankfull water layer. In contrast, those with red fringes in the Flooded Areas display are experiencing unusually high water. The maximum reservoir extents recorded are also shown, in light gray.

For additional information, click on many of the reservoirs and lakes to access the Web Map Server (WMS). Select appropriate water layers for display. For example, to compare current surface water with the maximum in the year to date, display only two layers: "January till current" and "Two week water extent", which is the last 14 days of MODIS water detection.

Many rivers and reservoirs are also being monitored daily by microwave radiometry. Click on the dot symbols to retrieve this information. The microwave data provide updates even when cloud cover is present.

Notes:

Twice-daily (NASA Terra and Aqua) MODIS data used here are first processed by NASA's LANCE system. A specially-produced daily surface water outcome is then transmitted to the Flood Observatory and further processed and archived. The "current" water layer is an accumulation of such data over 14 days to remove cloud obscuration. The map date refers to a two week period ending on that date. The file is updated each day and replaces the previous one.

A variety of additonal water data products are produced from this information, and including annual maximum surface water extent files. The bankfull water product is created by comparison of four such annual files (2013-2016). Water shown on this bankfull file was observed as water in at least 3 of the four files.

Known errors: Floods in mountainous regions are difficult remote sensing targets and not always observable at MODIS spatial resolution of 250 m/pixel. Also, cloud cover sometimes restrict the ability to capture peak inundation, even using the rolling-forward 14 day accumulation. The maps do not illustrate all areas of possible flood hazard. They do provide an objective record of where flooding has been observed..

Terrain shadows in upland areas may produce abundant "false positive" water detections using MODIS data. Quite commonly, these are obvious errors when compared to the shaded relief base map, and should be disregarded.

GIS Data Access:

Click here for access to the automated daily MODIS-derived .shp file GIS record (record commences in 2011; processor is now located at NASA LANCE). Choose appropriate 10 deg x 10 deg map sheet directory and dates of interest.

Data from the Global Surface Water Explorer is included in both displays as part of the light gray satellite-mapped water extent. These data are based on Landsat data at a spatial resolution of 30 m (Jean-Francois Pekel, Andrew Cottam, Noel Gorelick, Alan S. Belward, High-resolution mapping of global surface water and its long-term changes. Nature 540, 418-422, 2016).

NASA NRT Global Flood Mapping annual maximum water extent for the years 2013-2015, at 250 m spatial resolution, also are included in the light gray water extent. These data are produced at DFO and also provided separately via the Web Map Server.

Since late 1999, DFO has produced flood extent files through mapping of individual floods. All of these are included in the light gray "satellite record of flooding" layer.

River and Reservoir Watch Measurements (colored dot symbols):

At selected locations, a time series of satellite microwave-based daily river discharge or reservoir area measurements are available from the Flood Observatory. See River and Reservoir Watch Global Display for more information. A sample from Site 26 in this map sheet is shown below. White triangles: ice covered. Yellow dots: low flow (< 5th percentile discharge for this date, or < 20th percentile reservoir area). Blue dots: normal flow or reservoir area. Purple dots: moderate flooding (>1.5 year recurrence interval or > 70th percentile reservoir area). Red dots, major flooding (> 5 year recurrence interval, or > 90th percentile resevoir area).

Funding, Data, and Institutional Support:

The NASA Earth Sciences Program, the Latin American Development Bank, the World Bank, the European Commission (Global Disaster Alert and Coordination System, GDACS), the Google Earth Engine research awards program, the Committee on Earth Observation Satellites (CEOS) Disasters Working Group-Flood Pilot, the Japanese Space Agency, and the European Space Agency all have supported this work via research grants and contracts or by provision of free satellite-derived data.

The Dartmouth Flood Observatory was founded in 1993 at Dartmouth College, Hanover, NH USA and moved to the University of Colorado, INSTAAR, CSDMS in 2010. The institutional support of both universities is gratefully acknowledged.

Creative Commons License
This work, web site, and associated data are by G. R. Brakenridge and A. J. Kettner and are provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. With attribution, they can be used and shared for non-commercial purposes. Commericial use is available by permission.

 

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