How to use WaPOR portal
|Site:||IHE DELFT OPEN COURSEWARE|
|Course:||WaterPIP ToT2 – FAO WaPOR for Water Productivity - Part 1|
|Book:||How to use WaPOR portal|
|Printed by:||Guest user|
|Date:||Sunday, 1 August 2021, 12:51 AM|
WaPOR is FAO's portal to monitor Water Productivity through Open access of Remotely sensed derived data, monitors and reports on agriculture water productivity over Africa and the Near East. It provides open access to the water productivity database and its thousands of underlying map layers.
The video below introduces you to the data components of WaPOR database. The detailed information on the spatial and temporal resolution for the different data layers can also be found in the WaPOR Catalog.
The WaPOR portal not only provides interactive web-based maps but also analysis tools to extract time-series data and compute customized water productivity maps when specific crop parameters in a study area are known.
After this lesson, you will learn how to:
- navigate on the WaPOR portal
- use WaPOR analysis tool
- collect and pre-process raster data from WaPOR portal
2. WaPOR Portal navigation
In this video, you will learn:
- How to start using the WaPOR portal
- How to select and display data layers on the portal
You can practice the following steps at https://wapor.apps.fao.org/.
3. Using analysis tools on WaPOR portal
In this video, you will learn how to use the WaPOR portal analysis tool. This tool can be used to:
- extract time-series data of a point
- extract time-series data of an area
- calculate crop water productivity rasters of an area from total biomass water productivity.
Note: When you are saving points or areas into MyWaPOR, they are only saved for that level. For example, points and areas saved in Level 1 (Continental 250m) can only be used for analyses in Level 1 and are not available for use in Levels 2 (National 100m) or Level 3 (Sub-national 30m). This is due to the different geospatial reference systems used for each level.
Common Errors: When using WaPOR 'Area Time Series', if you have the same error as below, try to save the area to MyWaPOR without space in the name. For example, 'myplot' instead of 'my plot'.
4. Downloading WaPOR raster data
In this video, you will learn how to download raster data from the WaPOR portal. With WaPOR portal, you can collect raster data for the whole layer or a small area using 'Area Raster Download' in the analysis tool.
Downloaded raster data need to be corrected with a conversion factor so that pixel values in the raster show physical unit of the variable. You can do this using the' Raster calculator' tool in GIS software (ArcGIS, QGIS, etc.). The next page will provide a tutorial on how to pre-process raster data in QGIS.
5. Pre-processing raster data downloaded from WaPOR portal
In this tutorial, you will learn how to use QGIS to pre-process raster data downloaded from the WaPOR portal, which involves correcting raster values with conversion factors.
Spatial data is often stored in a specific format by the provider. In order to extract information properly, we need to understand the data format and metadata provided with the data we have collected. The first step is to find this information from the WaPOR data catalog, understand how it applies to the data layer.
In the next step, you will need to multiply the value in each pixel by the conversion factor given. For annual and monthly data, the raster data provided is already calculated for the year and month, respectively. This makes the conversion quite simple to calculate. For AETI, for example, the calculation is:
average annual value * 0.1 = mm/year
average monthly value * 0.1 = mm/month
For dekadal data, the given data is an average daily value (mm/day). To convert it to an average value per dekad (mm/dekad), you need to multiply by the number of days in the dekad of analysis. For AETI, for example, the calculation is:
average daily value * 0.1 * number of days in the dekad = mm/dekad
In order to multiply the value in each pixel by the conversion factor, we can use QGIS 'Raster calculator' tool. This video will show you how to do it.
Note: If you do not see 'Processing Toolbox' in QGIS, on the top menu bar, select View>Panels>Processing Toolbox.