Doing It Yourself: An In-House Approach to Gauge Adjusted Radar Rainfall

Gauge-adjusted radar rainfall (GARR) is tremendously useful when rainfall events are needed for computer model simulations. It allows the users to have a more accurate picture of the rainfall patterns in areas not covered by rain gauges. Most municipalities and companies view this information as a service or a process to be performed by someone else because of its seemingly daunting nature. Rainfall datasets are purchased from any of several vendors who provide quality-checked, spatially organized, and gauge adjusted rainfall datasets based on measurements from NOAA's NEXRAD radar network. This NEXRAD data is available to the public free of charge, so companies are providing a processing service, not the data itself. The purpose of this paper is to demonstrate that the same work these providers do can be performed in-house using programs that engineers and hydrologic modelers typically already have available. Since the same NEXRAD data is used that the companies would be using, the final product can be comparable to what is provided for sale.The benefits of doing the work in-house are that it can provide better accuracy and allow more control over the information, removing the “black box” effect. Local rain data can be used that might not be available to vendors. In-house processes can also provide a finer temporal distribution at daily rain gauges. Depending on the scope of the work, the work may also be able to be done faster than by a data provider. This paper and presentation will show users how to create GARR datasets in-house, potentially leading to rainfall datasets with increased accuracy, lower costs, and shorter turn-around time.A description of the process will come from the work that was done for the hydrologic model for the Reedy River in upstate South Carolina and to support sewer flow monitoring efforts pursuant to Virginia DEQ Special Order of Consent work in a city in southeast Virginia. This phase of both projects has been completed and the results are being used in other phases with satisfactory results. This in-house work has been performed to assist with other completed projects as well.