Accurate representation of river networks and land surface heterogeneity is crucial for improving the performance of continental-to-global hydrologic and land surface models (LSMs). Traditional approaches rely on either coarse-resolution grids, which may oversimplify complex terrain and limit the accurate representation of key processes, or computationally demanding full-domain high-resolution meshes. This study introduces a novel framework for generating Hydrologic Refined Meshes (HRMs) that seamlessly integrates crucial land surface features, including river networks, watershed boundaries, and lake boundaries, into the mesh generation process within the Model for Prediction Across Scales (MPAS) architecture.
@article{liao2026unstructured,title={An Unstructured {Voronoi} Mesh Framework for Large-Scale Hydrologic and Land Surface Models},author={Liao, Chang and Engwirda, Darren and Xu, Donghui and Zhou, Tian and Tan, Zeli and Leung, L. Ruby},journal={Journal of Advances in Modeling Earth Systems},year={2026},note={Accepted},}
Earth system models are advancing toward kilometer-scale resolution to capture local climate impacts and extremes. High-resolution land and river modeling depends on multiple factors, including mesh, surface datasets, and atmospheric forcing. We evaluated five Energy Exascale Earth System Model land and river configurations over the Mid-Atlantic region using structured versus variable-resolution unstructured meshes, two surface datasets, and three atmospheric forcings.
@article{li2026systematic,title={Systematic Evaluation of Atmospheric Forcing, Surface Datasets, and Mesh Effects on Kilometer-Scale Land Surface and River Modeling},author={Li, Lingcheng and Bisht, Gautam and Xu, Donghui and Hao, Dalei and Liao, Chang and Feng, Dongyu and Leung, L. Ruby},journal={Journal of Hydrology},volume={635},pages={135500},year={2026},doi={10.1016/j.jhydrol.2026.135500},}
Soil moisture regulates plant water supply and drought sensitivity in tropical forests, yet its vertical and topographic variation remains poorly characterized. We combined high-frequency time-domain reflectometry measurements from 5 to 100 cm across plateau, slope, and valley landforms at the Zona Florestal 2 research site north of Manaus, Central Amazonia, to quantify how soil moisture memory, timing of responses to rainfall, dry-down rates, and soil-water depletion vary across contrasting landforms.
@article{negronjuarez2026influence,title={Influence of Plateau, Slope, and Valley on Soil Hydrology During the Dry Season in a {Central Amazon} Old-Growth Forest},author={Negron-Juarez, Robinson and Wright, C. and Ferreira, S. and Hirai, K. and Kobayashi, M. and Warren, J. M. and Oliveira, R. and Liao, Chang and Leung, L. Ruby and de Souza, C. A. S. and Chambers, J. Q. and Lima, A. and Higuchi, N.},journal={Vadose Zone Journal},volume={25},pages={e70095},year={2026},doi={10.1002/vzj2.70095},}
Riverine dissolved organic carbon (DOC), primarily sourced from soil organic carbon (SOC), plays a crucial role in regional and global carbon cycles. We introduce ELM-MOSART-DOC, a DOC module integrated into the riverine component of the Energy Exascale Earth System Model (E3SM)—the Model for Scale Adaptive River Transport (MOSART), simulating DOC transport and transformation across headwater streams and river networks.
@article{li2026elmmosartdoc,title={{ELM-MOSART-DOC}: A Large-Scale Riverine Dissolved Organic Carbon Model and Its Application Over the {United States}},author={Li, Lingcheng and Li, Hong-Yi and Abeshu, G. and Yang, X. and Tang, J. and Tan, Zeli and Liao, Chang and Leung, L. Ruby},journal={Journal of Advances in Modeling Earth Systems},volume={18},pages={e2025MS005307},year={2026},doi={10.1029/2025MS005307},}
Compound riverine and coastal flooding is usually driven by complex interactions among meteorological, hydrological, and ocean extremes. We evaluate compound uncertainties arising from two-way land-river-ocean coupling in E3SM and track cascading meteorological and hydrological uncertainties through ensemble simulations over the Delaware River basin and estuary during Hurricane Irene (2011).
@article{feng2025disentangling,title={Disentangling Atmospheric, Hydrological, and Coupling Uncertainties in Compound Flood Modeling Within a Coupled Earth System Model},author={Feng, Dongyu and Tan, Zeli and Engwirda, Darren and Wolfe, J. D. and Xu, Donghui and Liao, Chang and Bisht, Gautam and Benedict, J. J. and Zhou, Tian and Deb, M. and Li, Hong-Yi and Leung, L. Ruby},journal={Natural Hazards and Earth System Sciences},volume={25},pages={3619--3639},year={2025},doi={10.5194/nhess-25-3619-2025},}
Discrete Global Grid systems (DGGs) are emerging spatial data structures widely used to organize geospatial datasets across scales. This study pioneers the development of new flow routing datasets using Icosahedral Snyder Equal Area (ISEA) DGGs and a novel mesh-independent flow direction model for the tropical Amazon River Basin and the Arctic Yukon River Basin.
@article{liao2025dggs,title={Discrete Global Grid System-Based Flow Routing Datasets in the {Amazon} and {Yukon} Basins},author={Liao, Chang and Engwirda, Darren and Cooper, Matthew G. and Li, M. and Fang, Y.},journal={Earth System Science Data},year={2025},doi={10.5194/essd-2023-398},}
We propose a generic formula that directly connects SOC concentration with DOC concentration in headwater streams and derive a high-resolution DOC transformation rate map over the contiguous U.S. using machine learning and catchment-scale attributes.
@article{li2025deriving,title={Deriving a Transformation Rate Map of Dissolved Organic Carbon over the Contiguous {U.S.}},author={Li, Lingcheng and Li, Hong-Yi and Abeshu, G. and Tang, J. and Leung, L. Ruby and Liao, Chang and Tan, Zeli and Tian, H. and Thornton, Peter and Yang, X.},journal={Earth System Science Data},year={2025},doi={10.5194/essd-2024-43},}
Lateral groundwater flow (LGF) is an important hydrologic process in controlling water table dynamics. In this study, we developed a hillslope-based lateral groundwater flow model based on Darcy’s equation and coupled it to the land component (ELM) and river component (MOSART) of the Energy Exascale Earth System Model (E3SM).
@article{liao2025representing,title={Representing Lateral Groundwater Flow From Land to River in Earth System Models},author={Liao, Chang and Leung, L. Ruby and Fang, Yilin and Tesfa, Teklu and Negron-Juarez, Robinson},journal={Geoscientific Model Development},volume={18},number={14},pages={4601--4624},year={2025},doi={10.5194/gmd-18-4601-2025},}
Both lateral surface and subsurface water flow affect soil moisture dynamics. Here we use a 3-D ecosystem model that considers both land surface and subsurface hydrologic processes to simulate soil moisture, which is then used to drive a 1-D vertical soil thermal model to simulate soil moisture effects on soil thermal dynamics in central Alaska.
@article{liu2025changes,title={Changes in Soil Water Content and Lateral Flow Exert Large Effects on Soil Thermal Dynamics Across {Alaskan} Landscapes},author={Liu, X. and Zhuang, Qianlai and Liao, Chang and Jorgenson, M. T.},journal={Environmental Research Letters},volume={20},pages={024021},year={2025},doi={10.1088/1748-9326/adaa05},}
Flow routing is a fundamental process of Earth System Models’ river components. This study extends the river component of the Energy Exascale Earth System Model (E3SM) to unstructured Voronoi meshes and evaluates the model’s performance in simulating river discharge and water depth across Arctic, temperate, and tropical watersheds.
@article{liao2025evaluation,title={Evaluation of Flow Routing on the Unstructured {Voronoi} Meshes in Earth System Modeling},author={Liao, Chang and Xu, Donghui and Cooper, Matthew G. and Zhou, Tian and Engwirda, Darren and Bisht, Gautam and Li, Hong-Yi and Li, Lingcheng and Feng, Dongyu and Leung, L. Ruby},journal={Journal of Advances in Modeling Earth Systems},year={2025},}
Projections of terrestrial climate feedbacks from Earth System Models depend on simulated carbon and water dynamics of vegetation. Here, we discuss how models simulate plant hydraulic processes and identify opportunities to improve confidence in model outputs, focusing on vegetation physiology, hydrodynamics, and groundwater flow models.
@article{dukes2025improving,title={Improving the Representation of Plant Water Stress and Water Use in Earth System Models},author={Dukes, J. S. and Xu, C. and Liao, Chang and Novick, K. A. and Phillips, R. P. and Beverly, D. P. and Fang, Yilin and Jacobs, E. M. and McAdam, S. A. M. and Paudel, I. and Rimer, I. M. and Robbins, Z. J.},journal={New Phytologist},year={2025},doi={10.1111/nph.70687},}
Coastal wetlands play an important role in global water and biogeochemical cycles. To investigate the structural uncertainty of coastal wetland eco-geomorphology models, we developed a multi-algorithm model framework within a single hydrodynamics model and tested it across two saltmarsh wetlands and one mangrove wetland.
@article{tan2024multialgorithm,title={A Multi-Algorithm Approach for Modeling Coastal Wetland Ecogeomorphology},author={Tan, Zeli and Leung, L. Ruby and Liao, Chang and Carniello, Luca and Rodriguez, Jose F. and Saco, Patricia M. and Sandi Rojas, Steven and Megonigal, J. Patrick and Bailey, Vanessa L.},journal={Frontiers in Earth Science},volume={12},pages={1421265},year={2024},doi={10.3389/feart.2024.1421265},}
Coastal zone compound flooding can be caused by interactive fluvial and oceanic processes. In this study, we present a novel multi-scale coupling framework within E3SM, integrating atmosphere and land with interactively coupled river and ocean models on variable-resolution meshes near coastlines.
@article{feng2024simulation,title={Simulation of Compound Flooding Using River-Ocean Two-Way Coupled {E3SM} Ensemble on Variable-Resolution Meshes},author={Feng, Dongyu and Tan, Zeli and Engwirda, Darren and Wolfe, J. D. and Xu, Donghui and Liao, Chang and Leung, L. Ruby},journal={Journal of Advances in Modeling Earth Systems},volume={16},number={6},pages={e2023MS004054},year={2024},doi={10.1029/2023MS004054},}
Streamflow variability plays a crucial role in shaping ecosystem dynamics. In this study, we performed experiments with the land and river components of E3SM over the Pantanal region to disentangle hydrological and hydraulic controls on streamflow variability and propose a two-step joint calibration procedure.
@article{xu2024disentangling,title={Disentangling the Hydrological and Hydraulic Controls on Streamflow Variability in {E3SM V2} -- A Case Study in the {Pantanal} Region},author={Xu, Donghui and Bisht, Gautam and Tan, Zeli and Liao, Chang and Zhou, Tian and Li, Hong-Yi and Leung, L. Ruby},journal={Geoscientific Model Development},volume={17},pages={1197--1215},year={2024},doi={10.5194/gmd-17-1197-2024},}
Accurately representing river networks in spatially distributed hydrologic models is sensitive to model resolution. We developed a topological relationship-based river network representation method using graph theory algorithms to simplify vector networks and reconstruct conceptual river networks across structured and unstructured meshes.
@article{liao2023topological,title={Topological Relationship-Based Flow Direction Modeling: Mesh-Independent River Networks Representation},author={Liao, Chang and Zhou, Tian and Xu, Donghui and Cooper, Matthew G. and Engwirda, Darren and Li, Hong-Yi and Leung, L. Ruby},journal={Journal of Advances in Modeling Earth Systems},volume={15},number={3},pages={e2022MS003089},year={2023},doi={10.1029/2022MS003089},}
PyFlowline is an open-source Python package that generates mesh-independent river networks. With PyFlowline, hydrologic modelers can generate conceptual river networks at various spatial resolutions for both structured and unstructured computational meshes.
@article{liao2023pyflowline,title={{PyFlowline}: A Mesh-Independent River Network Generator for Hydrologic Models},author={Liao, Chang and Cooper, Matthew G. and Xu, Donghui and Zhou, Tian and Bisht, Gautam and Leung, L. Ruby},journal={Journal of Open Source Software},volume={8},number={91},pages={5446},year={2023},doi={10.21105/joss.05446},}
This follow-up study presents a novel DEM processing approach for flow direction modeling consisting of a topological relationship-based hybrid breaching-filling stream burning method and a modified depression removal method for rivers and hillslopes across arbitrary mesh systems.
@article{liao2023streamburning,title={Topological Relationship-Based Flow Direction Modeling: Stream Burning and Depression Filling},author={Liao, Chang and Zhou, Tian and Xu, Donghui and Tan, Zeli and Bisht, Gautam and Cooper, Matthew G. and Engwirda, Darren and Li, Hong-Yi and Leung, L. Ruby},journal={Journal of Advances in Modeling Earth Systems},volume={15},number={7},pages={e2022MS003487},year={2023},doi={10.1029/2022MS003487},}
2022
HESSD
Investigating Coastal Backwater Effects and Flooding in the Coastal Zone Using a Global River Transport Model on an Unstructured Mesh
Using two mid-Atlantic river basins as a testbed, we simulate backwater effects comprehensively using the MOSART river transport model within E3SM configured on regionally-refined unstructured meshes to understand backwater drivers, storm surge interaction, and long-term variations.
@article{feng2022investigating,title={Investigating Coastal Backwater Effects and Flooding in the Coastal Zone Using a Global River Transport Model on an Unstructured Mesh},author={Feng, Dongyu and Tan, Zeli and Engwirda, Darren and Liao, Chang and Xu, Donghui and Bisht, Gautam and Zhou, Tian and Li, Hong-Yi and Leung, L. Ruby},journal={Hydrology and Earth System Sciences Discussions},year={2022},doi={10.5194/hess-2022-251},}
We calibrated 11 runoff-relevant parameters in the Energy Exascale Earth System Model (E3SM) Land Model (ELM) using a surrogate-assisted Bayesian framework based on polynomial chaos expansions and Bayesian compressed sensing, significantly improving model performance.
@article{xu2022using,title={Using a Surrogate-Assisted {Bayesian} Framework to Calibrate the Runoff-Generation Scheme in the {Energy Exascale Earth System Model (E3SM) v1}},author={Xu, Donghui and Bisht, Gautam and Sargsyan, K. and Liao, Chang and Leung, L. Ruby},journal={Geoscientific Model Development},volume={15},pages={5021--5043},year={2022},doi={10.5194/gmd-15-5021-2022},}
Watershed delineation and flow direction representation are the foundations of streamflow routing in hydrologic modeling. In this study, we explored approaches such as spatial resampling and hybrid breaching-filling stream burning techniques to improve watershed delineation using HexWatershed in the Columbia River basin.
@article{liao2021advances,title={Advances in Hexagon Mesh Based Flow Direction Modeling},author={Liao, Chang and Zhou, Tian and Xu, Donghui and Barnes, Richard and Bisht, Gautam and Li, Hong-Yi and Tan, Zeli and Tesfa, Teklu and Duan, Zhuoran and Engwirda, Darren and Leung, L. Ruby},journal={Advances in Water Resources},volume={160},pages={104099},year={2022},doi={10.1016/j.advwatres.2021.104099},}
2021
IMR
Unified Laguerre Power Meshes for Coupled Earth System Modelling
We describe a unified approach in which Earth system model components (ocean, atmosphere, ice, land, river) are represented on a common multi-scale unstructured mesh conforming to complex coastline and river network features using restricted Laguerre Power tessellations.
@inproceedings{engwirda2021unified,title={Unified {Laguerre} Power Meshes for Coupled Earth System Modelling},author={Engwirda, Darren and Liao, Chang},booktitle={29th International Meshing Roundtable (IMR)},year={2021},doi={10.5281/zenodo.5558988},}
We developed a watershed delineation model (HexWatershed) based on hexagonal grid spatial discretization to overcome the limitations of Cartesian grids, such as non-uniform adjacency, showing significant advantages for spatially distributed hydrologic simulations.
@article{liao2020watershed,title={Watershed Delineation on a Hexagonal Mesh Grid},author={Liao, Chang and Tesfa, Teklu and Duan, Zhuoran and Leung, L. Ruby},journal={Environmental Modelling \& Software},volume={130},pages={104702},year={2020},doi={10.1016/j.envsoft.2020.104702},}
Building upon a distributed hydrological model and a process-based biogeochemical model, we developed a three-dimensional terrestrial ecosystem model (ECO3D) to elucidate how lateral water flow impacts regional dissolved organic carbon (DOC) dynamics in the Tanana Flats Basin in central Alaska.
@article{liao2019quantifying,title={Quantifying Dissolved Organic Carbon Dynamics Using a Three-Dimensional Terrestrial Ecosystem Model at High Spatial-Temporal Resolutions},author={Liao, Chang and Zhuang, Qianlai and Leung, L. Ruby and Guo, L.},journal={Journal of Advances in Modeling Earth Systems},volume={11},number={12},pages={4489--4512},year={2019},doi={10.1029/2019MS001792},}
This study uses a spatially distributed surface hydrology model (PRMS) calibrated with PEST to investigate the role of snowmelt in stream discharge for the Tanana Flats Basin in interior Alaska, evaluating long-term trends in snow cover and runoff dynamics under warming conditions.
@article{liao2017snowmelt,title={Quantifying the Role of Snowmelt in Stream Discharge in an {Alaskan} Watershed: An Analysis Using a Spatially Distributed Surface Hydrology Model},author={Liao, Chang and Zhuang, Qianlai},journal={Journal of Geophysical Research: Earth Surface},volume={122},number={11},pages={2183--2195},year={2017},doi={10.1002/2017JF004214},}
AAAR
Quantifying the Role of Permafrost Distribution in Groundwater and Surface Water Interactions Using a Three-Dimensional Hydrological Model
This study uses a 36-year regional MODFLOW-USG simulation to investigate groundwater dynamics and surface water interactions considering permafrost distribution and taliks in the Tanana Flats Basin in interior Alaska.
@article{liao2017quantifying,title={Quantifying the Role of Permafrost Distribution in Groundwater and Surface Water Interactions Using a Three-Dimensional Hydrological Model},author={Liao, Chang and Zhuang, Qianlai},journal={Arctic, Antarctic, and Alpine Research},volume={49},number={1},pages={81--100},year={2017},doi={10.1657/AAAR0016-026},}
2015
EI
Reduction of Global Plant Production Due to Droughts From 2001 to 2010: An Analysis With a Process-Based Global Terrestrial Ecosystem Model
Droughts dramatically affect plant production of global terrestrial ecosystems. Here, this study incorporates a drought index into a process-based terrestrial ecosystem model constrained with MODIS GPP data to evaluate global drought impacts from 2001 to 2010.
@article{liao2015reduction,title={Reduction of Global Plant Production Due to Droughts From 2001 to 2010: An Analysis With a Process-Based Global Terrestrial Ecosystem Model},author={Liao, Chang and Zhuang, Qianlai},journal={Earth Interactions},volume={19},number={1},pages={1--21},year={2015},doi={10.1175/EI-D-14-0030.1},}