Methods to evaluate normal rainfall for short-term wetland hydrology assessment

Abstract

Identifying sites meeting wetland hydrology requirements is simple when long-term (> 10 years) records are available. Because such data are rare, we hypothesized that a single-year of hydrology data could be used to reach the same conclusion as with long-term data, if the data were obtained during a period of normal or below normal rainfall. Long-term (40–45 years) water-table and rainfall data were obtained for two sites in North Carolina (with modeling), and one site in Minnesota (direct measurements). Single-year wetland hydrology assessments were made using two-rainfall assessment procedures recommended by the U.S. Army Corps of Engineers for their Wetland Hydrology Technical Standard, and two other rainfall assessment methods that were modifications of those procedures. Percentages of years meeting wetland-hydrology conditions during normal or drier than normal periods were identified for each plot with each rainfall assessment method. Although the wetland hydrology criterion was met in over 90% of the years across all plots using the long-term records, the four assessment techniques predicted the criterion was met in 41–81% of the years. Based on our results, we recommend that either the Direct Antecedent Rainfall Evaluation Method, or its modified version, be used for wetland hydrology assessment.