Determining Normal Rainfall--Comparison of the Two Different Methods Used By USDA.

When water table data are reported for wetland studies, the rainfall during the period of measurement must be analyzed to determine if the results were made during a normal, wetter than normal, or drier than normal period. Water table measurements made during periods of normal rainfall are believed to represent long-term trends. The USDA-NRCS currently has two different methods that are used to assess normal rainfall, but no attempt has been made to determine if they provide equivalent results. This study compares 1) monthly normal rainfall determined as that within plus or minus one standard deviation of the average of a 30 year record to 2) the range determined by the 30^th and 70^th percentiles as shown on the WETS data tables. Comparisons will be made for 20 locations across the U.S. Results of the study will have impact on development of hydric soil field indicators for wetlands assessments, as well as for determining soil moisture regimes.