1. What is HexWatershed?

1.1. Overview

HexWatershed is a mesh independent flow direction model for hydrological models.

1.2. 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:

• It cannot represent adjacency uniformly;

• It leads to the “island effect” and the diagonal travel path issue in D8 scheme;

• It cannot provide a spherical coverage without significant spatial distortion;

• It cannot be coupled with other unstructured mesh-based models such as the oceanic models.

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.