Thursday, April 26, 2012

Utilizing online resources for hydrological research [Part 1]

Introductory words:

Many of us familiar that online resources available for water resources/hydrological research but the same way many of us don’t really know where and how to get those data easily in a usable format. Various problems we face when we desperately need some data, among them finding the exact site and getting the exact data is most notable. Often it happens  that we become ambiguous to see too many information given in the web site and we could not find the required one that we need. Here in this post we will see how to get some environmental data needed to build a hydrological model and process them in a usable format. There are varieties of data available but we will focus only the listed below. Once again these data`s are completely FREE OF CHARGE!!

[1] Administrative Area Map (Shape file)
[2] Digital Elevation Model (DEM)
[3] River Network
[4] Land use Map
[5] Digital Soil Map

[1] Administrative Area Map
Administrative area maps are very useful to when we want to have basic information for some specific region. It is often difficult to find administrative area of developing countries or some specific island therefore a group of researcher made it possible geo referencing all the region of the entire earth and putting them all together in the GADM website [1A]. The file formats are ESRI shape file [1B], or (.kmz) files for Google earth plugin.



[2] Digital Elevation Model
Digital elevation model (DEM) represents the elevation of Earth’s surface, including features (vegetation, buildings, etc.).A DEM can be represented as a raster a grid of squares, also known as a height map when representing elevation [2A]. They are very useful for watershed/hydrological modeling [2B]. Especially they play significant role for flood mapping and modeling spatial extent of food [2C]. Traditionally elevation was derived by direct survey of the land, and then photogrammetry techniques allowed for terrain extraction with a pair of images with stereoscopic techniques. Today, highly accurate digital elevation can be achieved with light detection and ranging (LIDAR) and interferometry synthetic aperture radar (IfSAR). The SRTM digital elevation data, produced by NASA originally, is a major breakthrough in digital mapping of the world, and provides a major advance in the accessibility of high quality elevation data for large portions of the tropics and other areas of the developing world [2D]. Beside academia DEMs are commercially used for geographic analysis especially urban and regional planning [2E]. Globally available DEMS has approximately 1 km resolution from GTOPO30 and 90 m accuracy from the Shuttle Radar Topography Mission (SRTM) [1].
There are various ways we can download DEM from SRTM site but I found the easiest way of quick download using Google earth plugin [2F]. Here is the video clip to have quick access of SRTM DEM and processing steps to make better use of it.



[3] River Geometry Map:
Steam geometry maps are extremely important for flood modeling and management. [3A]. River network is useful for basin delineation [3B]. HydroSHEDS is a mapping product that provides hydrographic information for regional and global-scale applications in a consistent format [3C] It offers a suite of geo-referenced data sets (vector and raster) at various scales, including river networks, watershed boundaries, drainage directions, and flow accumulations. HydroSHEDS is based on high-resolution elevation data obtained during a Space Shuttle flight for NASA's Shuttle Radar Topography Mission (SRTM). The goal of developing HydroSHEDS was to generate key data layers to support regional and global watershed analyses, hydrological modeling, and freshwater conservation planning at a quality, resolution and extent that had previously been unachievable. Available resolutions range from 3 arc-second (approx. 90 meters at the equator) to 5 minute (approx. 10 km at the equator) with seamless near-global extent.



[4] Land cover map:
Land use maps often called zoning maps are basically derived from the satellite images and classifying them [4A]. Wide application of land use maps mostly for demographic features and Eco hydrological research[4B ]. They are often used for impact assessment of climate change due to vegetation change and demographic features [4C]. Environmental impacts and land at risk from land degradation such as salinity, flood, drought, and erosion studies can be done with land use maps. Land use maps are prepared by several government agencies, for a variety of reasons. Individual groups and organizations can also generate maps with land use information. Often, such maps are publicly available, so that people who are interested in land use trends can access them. For global application European Space Agency (ESA) provides maps in different time slice. They 



[5] Digital Soil Map
Digital soil map provides type of soil and their physical properties. Soil properties have immense importance for agricultural productivity and application of fertilizer. Soil map can be prepared by survey or classifying the remote sensing images [5A] robust application of soil maps is most often related to irrigation requirement and scheduling. Food and Agricultural Organization of united nation provides soil map with 1:10000 scale classifying 6998 soil classes for entire world. This can be obtained from the geo network web portal of FAO [5B]. Organic and inorganic components are including with the attribute table provided by FAO which is very useful for agricultural research [5C].


Concluding remarks [For part: 1] 

Few issues needed to be discussed, among them projection system and resolution of data needs attention. In most cases the standard projection system is GCS WGS 1984 where the distances are calculated on Arc second. Usually 1 degree equals to 100 km. Since I used ArcGIS they have a default projection of GCS WGS 1984. There might be some error messages or dis placement of maps if the projection system is not similar with the data frame and the extracted data from different sources!!

Here it ends the part 1 of extraction of freely available online geographic data for Environmental/Hydrological/Geographical research, the next section I will be focusing CLIMATIC data [Precipitation, Temperature, Wind speed Solar radiation etc etc.] freely available. So keep tuned....


  1. Excellent effort. Thank you for sharing!

  2. Great work. However, is there any way to obtain all the SWAT required parameters for each of the FAO soil types?

  3. Yes!
    If you download the zip file u can find a csv file that has exactly SWAT parameters in it.
    For any difficulty I can send you from my computer
    In that case I need your mailing ID
    thanks and kind regards

  4. hello...
    sir em waiting for ur reply...Abid Sarwar

  5. Abid
    I do not see your question
    Please let me know what you want then I can reply

    1. sir i've mail you a detail help which i required
      at ur gmail accout

    2. Abid
      I tried to looked at my account but could not find anything from ur account. DO you mind sending me again?

      Here is the mailing ID u can send your question

  6. em an agricultural engineer from Pakistan em very new comer for ArcSWAT nd need ur kind and valuable guidance about the ArcSWAT for start my research...

  7. But thats not any technical question!
    In that case I would suggest you to follow this post
    where I mention how to start with...
    Good Luck Abid

  8. hello...
    sir how can i study climate change in SWAT..
    i mean's can it provide us projections like GCM's?....but they r difficult to use plz guide me some literature for study, climate change only with SWAT..

  9. hello!
    sir would u plz guide me about the basic inputs required by SWAT for flow simulation of a watershed

  10. This comment has been removed by the author.


    I'm one of PhD research students in Universiti Teknologi Petronas, Malaysia. I found your video tutorial on "" on how to download Soil Map from

    For more than two weeks now, several efforts have been made to download the free Global Digital Soil Map from the said website as demonstrated in your tutorial BUT TO NO AVAIL. I usually got hooked when I get to "download summary" in the website in an attempt to download it.

    Sir, Kind assist me with the downloaded version of the global soil map so that I can process my case-study-area for my own use in ArcGIS.

    I shall be very glad if you could attach a copy of global soil map (in zipped folder) to my mail.

    Thanking you for the anticipated favorable consideration and prompt responded.

    NOTE: I have sent you an email on your gmail account 0n the 4th Sept, 2015.

    Thank you sir

  12. Pls you may attach the Digital Soil Map to my email as requested above sir: My email address:

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    Geospatially Referenced Radiation Surveys