HYDROCLIMATOLOGY OF CONTINENTAL WATERSHEDS .1. TEMPORAL ANALYSES

The linkage between meteorology/climate and hydrology of temperate lat itude catchments on daily to decade time scales is studied. Detailed h ydrology is provided by a hydrologic catchment model, adapted from the operational streamflow forecast model of the National Weather Service River Forecast System. The model is tuned to respond to observed dail y precipitation and potential evaporation input. Results from the Bird Creek basin with outlet near Sperry, Oklahoma, and from the Boone Riv er basin with outlet at Webster City, Iowa, indicate that the model qu ite accurately simulates the observed daily discharge over 40 years at each of the two 2000-km(2) basins. Daily cross-correlations between o bserved and simulated basin outflows were better than 0.8 for both bas ins over a 40-year historical period. Soil moisture variability over a period of four decades is studied, and an assessment of temporal and spatial (as related to the separation distance of the two basins) scal es present in the estimated soil moisture record is made. Negative soi l. water anomalies have larger magnitudes than positive anomalies, and comparison of the simulated soil water records of the two basins indi cates spatial scales of variability that in several cases are as long as the interbasin distance. The temporal scales of soil water content are considerably longer than those of the forcing atmospheric variable s for all seasons and both basins. Timescales of upper and total soil water content anomalies are typically 1 and 3 months, respectively. Li nkage between the hydrologic components and both local and regional-to -hemispheric atmospheric variability is studied, both for atmosphere f orcing hydrology and hydrology forcing atmosphere. For both basins, cr osscorrelation analysis shows that local precipitation strongly forces soil water in the upper soil layers with a 10-day lag. There is no ev idence of soil water feedback to local precipitation. However, signifi cant cross-correlation values are obtained for upper soil water leadin g daily maximum temperature with 5-10 day lags, especially during peri ods of extremely high or low soil water content. Complementary results of a spatial hydroclimatic analysis are presented in a companion pape r (Cayan and Georgakakos, this issue).