What is "HexWatershed"?

HexWatershed is a hydrologic routing model based on the hexagon/unstructured mesh framework.

Why do we develop HexWatershed?

Spatial discretization is the cornerstone of all spatially-distributed numerical simulations including watershed hydrology. Traditional square grid spatial discretization has several limitations:

  1. It cannot represent adjacency uniformly;

  2. It leads to the "island effect" and the diagonal travel path issue in D8 scheme;

  3. It cannot provide a spherical coverage without significant spatial distortion.

Therefore, we developed a watershed delineation model (HexWatershed) based on the hexagon mesh spatial discretization.

We further improve HexWatershed to fully unstructured mesh-based to support variable-resolution meshes such as the MPAS mesh.

We propose that spatially distributed hydrologic simulations should consider using a hexagon grid spatial discretization.

How we did it?

We basically rewrote all the core watershed delineation algorithms, just on a completely different data structure.

What is the current status of "HexWatershed"?

We are finalizing a few core components in the HexWatershed ecosystem:

  • A special designed resampling tool for HexWatershed will be available soon;

  • HexWatershed is ready for continental and global scale simulation;

  • HexWatershed is supporting MPAS mesh;

  • We are evaluating hydrology simulations using HexWatershed routing maps.


Chang Liao, Tian Zhou, Donghui Xu, Richard Barnes, Gautam Bisht,

Hong-Yi Li, Zeli Tan, Teklu Tesfa, Zhuoran Duan, Darren Engwirda, and L. Ruby Leung. Advances in hexagon mesh based flow direction modeling. Advances in Water Resources (2021).

Liao, C., Tesfa, T., Duan, Z., & Leung, L. R. (2020). Watershed delineation on a hexagonal mesh grid. Environmental Modelling & Software, 104702.