COMPARISONS OF MODELED AND OBSERVED CLIMATE FOR IMPACT ASSESSMENTS

Comparisons between observed and modelled values of surface temperatur e, surface precipitation and 500 hPa height for the current climate we re made for the southeast United States. Daily values and analyses per tinent to impact assessment, were emphasized. For the model, the time- independent 10-year series of values developed by the Geophysical Flui d Dynamics Laboratory general circulation model were used. Observation s were drawn from records for various stations and decades within the model grid-cell. Cumulative frequency distributions of temperature ind icated both more clustering close to the mean and greater extremes for the model. The model reproduced the seasonal cycle of day-to-day temp erature variability, but introduced a phase shift of about four months . One result was an apparent overabundance of hot spells in the model results. For precipitation the model indicated twice as many raindays as were observed, about the same number of days when precipitation exc eeded 5 mm, and fewer days with amounts exceeding 10 mm, effectively d ecreasing the probability of heavy precipitation while enhancing annua l totals. In winter the model appeared to represent the results from a n aggregation of stations within the grid-cell, but in summer it was c loser to individual station results. The model reproduced the seasonal cycle in the height and standard deviation of the 500 hPa surface, wi th a damped amplitude in both cases.