The Antecedent Precipitation Tool (APT)
The final "Revised Definition of 'Waters of the United States'" rule was published in the Federal Register on January 18, 2023, and the rule took effect on March 20, 2023. Please visit the Rule Status page for additional information about the status of the rule and litigation. Learn more about the final rule. Consistent with longstanding practice, the agencies will continue to use a variety of tools and resources to implement the final rule, including automated tools like the Antecedent Precipitation Tool, as appropriate.
What is the APT?
The Antecedent Precipitation Tool (APT) is a desktop tool developed by the U.S. Army Corps of Engineers (Corps). The APT is commonly used by the Corps and the U.S. Environmental Protection Agency (“the agencies”) to support decisions as to whether field data collection and other site-specific observations occurred under normal climatic conditions. This tool was originally developed by the Corps to streamline the review of climate data, which supports decision-making related to wetland delineations. The APT facilitates the comparison of antecedent or recent rainfall conditions for a given location to the range of normal rainfall conditions that occurred during the preceding 30 years. In addition to providing a standardized methodology to evaluate normal precipitation conditions (“precipitation normalcy”), the APT can also be used to assess the presence of drought conditions, as well as the approximate dates of the wet and dry seasons for a given location.
Download the APT
The APT can be accessed from the Corps’ APT GitHub repository, where users can also find information about how to download and install the APT on to the user’s desktop. After installing the APT, users can access the APT Help Page which provides step-by-step instructions for running an analysis using the APT. Beginning in June 2023, APT users will need to download and install the latest version (2.0) located on the Corps' APT GitHub repository.
Additional information about the APT
Future updates
On May 28, 2020, the Corps released version 1.0 of the APT available for public use. The Corps will continue to maintain and update the APT as it determines necessary to ensure the continuous effectiveness, accuracy, and reliability of the tool over time. Future improvements, including enhanced capabilities, functionality, or other features to better-facilitate use of the tool, may also be considered.
Once the APT is installed on the user’s desktop, the tool is configured to automatically check for the most up-to-date version available as future updates and improvements are released over time. Updated versions of the tool will be indicated by a change in the version number and date on the on-screen display and in the documentation generated by the tool, and a summary of the updates will be available on the Corps’ APT GitHub repository. Beginning in June 2023, APT users will need to download and install the latest version (2.0) located on the Corps' APT GitHub repository.
Supporting documentation
Additional information on the APT, including step-by-step instructions for running an analysis, an explanation of the resulting output, and a detailed discussion of the tool’s underlying methodology and data sources, is available on the APT Help Page. The APT Help Page can be accessed by clicking the APT Help Button, which is an orange question mark icon located in the top right corner of the APT user interface. Additional support materials may be developed over time to facilitate use of the APT, and those materials will generally be released via the APT Help Page.
Other useful resources
- Antecedent Precipitation Tool (APT) Version 2.0: Technical and User Guide
- Antecedent Precipitation Tool Q&As – Fact Sheet (PDF)
- Additional Information on the Antecedent Precipitation Tool (pdf)
- Report: Evaluation of Climatic and Hydroclimatic Resources to Support the U.S. Army Corps of Engineers Regulatory Program
- Antecedent Precipitation Tool Demonstration - This video provides a demonstration of how to use the tool. Note that although the video mentions the 2020 Navigable Waters Protection Rule, the Navigable Waters Protection Rule is not in effect. Please visit the Rule Status page.
Contact us
For questions or comments regarding the day-to-day use of the APT, please contact EPA at CWAwotus@epa.gov. Any errors or programmatic issues encountered with the APT can be reported by clicking the “Report Issue” button on the APT Help Page or by emailing the Corps directly at APT-Report-Issue@usace.army.mil.