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Showing posts from March, 2020

Watershed Delineation On A Hexagonal Mesh Grid: Part B

This is the second part of a study, the first part can be accessed from Here.
So we decided to use the ISEA alike grid, a hexagon mesh grid to address these issues.

(The figures are high resolution, you might need to zoom in to view.)

What follows is something I should have learned if my major was hydrology. Even though we have been using ArcSWAT, ArcHydro many times, we seldom really looked into the algorithms because they are mostly straight forward.

But when we decided to try this on a different mesh grid, a lot of details start to emerge, and through which we also learned a lot.
The overall workflow is pretty simple: But because the grid is different, we made several improvements. First,  we need a new index system, and we need to rebuild the neighbor information.

We also need to do the depression filling, here we used the priority flooding method. This method is pretty impressive in this application. Without getting into details, this is how it works:

After this, we are able to c…

Watershed Delineation On A Hexagonal Mesh Grid: Part A

One of our recent publications is "Watershed Delineation On A Hexagonal Mesh Grid" published on Environmental Modeling and Software (link).
Here I want to provide some behind the scene details of this study.

(The figures are high resolution, you might need to zoom in to view.)

First, I'd like to introduce the motivation of this work. Many of us including me have done lots of watershed/catchment hydrology modeling. For example, one of my recent publications is a three-dimensional carbon-water cycle modeling work (link), which uses lots of watershed hydrology algorithms.
In principle, watershed hydrology should be applied to large spatial domain, even global scale. But why no one is doing it?  I will use the popular USDA SWAT model as an example. Why no one is setting up a SWAT model globally? 
There are several reasons we cannot use SWAT at global scale: We cannot produce a global DEM with a desired map projection. SWAT model relies on stream network, which depends on DEM.…