Exploring MERIT Hydro : Global Hydrogeography Rasters in ProRaster

MERIT Hydro is a set of six global scale hydrogeography rasters prepared by the Global Hydrology Group at The University of Tokyo. The group is headed by Dai Yamazaki.

In this series of three videos, I show you how to acquire the data, and I describe how I processed it to convert the TIFF files to merged MRR files. I use ProRaster to render three of the rasters and demonstrate some more advanced features of ProRaster including opacity modulation. Finally, I use the rasters to examine the Hawkesbury-Nepean River system and the Northern Rivers region in NSW around Lismore to find explanations in the data for the floods that have occurred in those regions in 2022.

I download the Upstream Drainage Area, River Channel Width, and Height Above Nearest Drainage rasters. I use a Join raster processing operation to merge the 1150 TIFF files in each raster collection into a single MRR. In all cases, I use data conditioning to remove unwanted data. I employ either decimal precision restriction or storage as integers using translation and scaling to reduce the information content, improve compression, and produce smaller MRR rasters.

The hydrogeographic work is based on the MERIT DEM and other datasets. I have described how to obtain this MRR format raster here and compared the quality of this DEM to other global DEMS here.

I use ProRaster to visualise the three rasters. In the second video, you can learn how to see raster histograms in ProRaster, when to use the Stable Equal Area transform, how to enable and set up opacity modulation, how to adjust hill-shading parameters, and more.

In the third video, I use ProRaster to take a closer look at the hydrogeography data in the Hawkesbury- Nepean River system and in the Northern Rivers region of NSW and the town of Lismore.

Rendering the Upstream Drainage Area, River Channel Width, and Height Above Nearest Drainage rasters in the context of imagery and terrain helps you to identify choke points in the rivers, quantify the catchment area, and map regions that are likely to be subject to riverine flooding.

The Global Hydrodynamics Lab can be visited here:

The MERIT Hydro datasets can be downloaded from here: