HMS-PrePro: An Automated GIS Toolbox for Extracting Cloud-based Data, Delineating Watersheds, and Calculating Hydrological Parameters

HMS-PrePro is an ArcGIS preprocessing tool that was designed to improve GIS-based watershed modeling. The tool rapidly creates a basin model and estimates hydrological parameters for any watershed in the world by connecting the user to Esri’s Living Atlas of the World and automating spatial analysis steps.

When the user specifies a watershed boundary, HMS-PrePro connects to ArcGIS REST API Servers and uses the watershed location as a common denominator to link distinct spatial datasets for the area of interest. Authoritative datasets are extracted from Living Atlas servers and downloaded to the user’s computer for further processing. Common datasets required for standard hydrological modeling are obtained, including land cover, terrain elevation, and hydrological soils data. Instead of requiring the user to search a plethora of websites, each with unique formats, and then download, extract, and process the data locally, HMS-PrePro automates these steps within a matter of minutes. The data is stored and managed locally in a format that is amenable to typical hydrological modeling.

The tool then performs a series of spatial analysis steps to delineate the watershed by linking with the Arc Hydro Toolbar and the Hydrology Toolset in ArcGIS ArcMap. The program manipulates the digital elevation model (DEM) and performs terrain processing steps for delineating the watershed boundary into catchments, reaches, and longest flow paths. The DEM processing in HMS-PrePro follow the standard steps used by Arc Hydro, including:

Fill Sinks, Flow Direction, Flow Accumulation, Stream Definition, Stream Segmentation, Catchment Grid Delineation, Catchment Polygon Processing, Drainage Line Processing, and Longest Flow Path (see Arc Hydro Tutorial)

With the datasets downloaded and the DEM processed, the tool then assigns a unique hydrological identifier to each watershed element for connecting common features. The aforementioned steps are executed in succession when the user runs the HMS-PrePro GetData script tool. Runtimes vary depending on the size of the watershed, computing capability, internet speed, and user-specified stream definition threshold (see Arc Hydro Tutorial); however, observed execution times are generally between 3 – 5 minutes.

The user may then run the HMS-PrePro Preprocess Basin script tool to estimate a variety of common hydrological parameters using the downloaded datasets. Execution times for this script tool are generally less than one minute. Hydrological methods supported by HMS-PrePro include:

Canopy Method, SCS Curve Number Lag Method, TR-55 Lag Method, SCS Curve Number Loss Method, Green and Ampt Loss Method, Lag Routing, Muskingum-Cunge Routing, SCS Unit Hydrograph, Clark Unit Hydrograph, Snyder Lag Method
(see HEC-HMS User’s Manual)

Parameters are estimated using a series of spatial analysis steps and appended to the local Catchment and Reach shapefiles. An output text file is then created in the format necessary to be automatically read by the U.S. Army Corps of Engineers HEC-HMS hydrological software for creating a Basin Model, which describes the physical properties of the watershed system prior to calibrating and applying atmospheric conditions. While the output text file is specific to HEC-HMS, the tool’s functionalities of creating a comprehensive hydrological basin model using web-based datasets and parameter estimates may be used to streamline initialization steps for a variety of hydrological applications. Data downloading, processing, and spatial analysis are common steps, that are typically lengthy and tedious, for preparing a watershed model from GIS datasets, irrespective of the final simulation software used to route the rainfall into runoff hydrographs.

The tool’s conceptual framework was originally presented in a 2016 ArcUser Article as a novel way to improve hydrological modeling by connecting the user with authoritative, seamless, cloud-based datasets, such as those hosted in Esri’s Living Atlas of the World. At that time, the tool was not operational for public use but was rather a proposed concept for improving existing hydrological techniques. HMS-PrePro was deployed as a public software in 2020 with the publication of the article “GIS preprocessing for rapid initialization of HEC-HMS hydrological basin models using we-based data services” in Environmental Modelling & Software (here).


The tool may be downloaded from GitHub at: HMS-PrePro is currently verified for ArcMap Version 10.7. The GitHub site contains a User’s Guide for tool execution and a Technical Appendix, which includes additional details regarding the hydrological methodologies available in HMS-PrePro.

HMS-PrePro was developed through an NSF-GRFP Fellowship at the University of Texas Center for Water and the Environment, Grant No. 2013162199. The tool was authored by Cyndi Castro under supervision of Dr. David Maidment.

The toolbox code is open source, meaning that end-users may use and modify the Python scripting to fit their unique needs at no cost. However, the author requests that any helpful modifications are released back to GitHub to benefit the GIS and hydrological community.

When publishing results using HMS-PrePro, users should cite:

Castro, C. V., & Maidment, D. R. (2020). HMS-PrePro: A GIS preprocessing tool for rapid initialization of HEC-HMS basin models. Environmental Modelling & Software, 104732.


Cyndi V. Castro, P.E.

Cyndi Castro is a PhD Candidate at the University of Houston who specializes in watershed modeling, geospatial analysis, environmental risk assessment, resiliency, and socio-hydrology. As a licensed Professional Engineer, Ms. Castro has over 8 years’ experience in private and municipal consulting. She has worked for AECOM, an international design firm that is consistently ranked as #1 by Engineering News-Record (ENR), and a smaller, Texas-based civil engineering firm. She has also provided consulting services for the City of Houston’s Public Works Department and Mayoral Offices of Recovery & Resiliency. Ms. Castro obtained her bachelor’s degree from Texas A&M University and her master’s from the University of Texas. She has received two National Science Foundation (NSF) fellowships for her graduate research (NSF-GRFP and NSF-INTERN). In her spare time, Ms. Castro has partnered with over a dozen NGO organizations to improve water planning worldwide.

About the author

Project Manager for the ArcGIS Living Atlas of the World Environment Team

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