The NCDC monthly precipitation index is computed as a simple average of the monthly precipitation at several stations within a climate division. The influences of the discontinuities in records used by NCDC are quantified for the central climate division of Oklahoma. An improvement of the calculation method is proposed. The number of stations used is fixed and the missing monthly data values are filled. The monthly averages of the absolute values of the differences between the two indices vary from 6 % (May) to 13 % (August) of the mean monthly precipitation and from 9 % (November) to 24 % (August) of their mean temporal variations. These values demonstrate that the discontinuities in station records of the NCDC divisional precipitation index can be relevant and that research results on regional precipitation variability should be interpreted with consideration of the approximation errors introduced.
Regional precipitation index, temporal variability, U.S. Great Plains.
Frederic Rossel, GRL-ARS-USDA, 7207 West Cheyenne Street,
El Reno, OK 73036,