Temporal and spatial scales of climatic variability and implications for water resource systems in the United States

This study demonstrates the importance of temporal and spatial scales of climatic variability to the issue of global climatic changes and their regional hydrological impacts.;To facilitate climatic impact assessment and examination of the importance of time scale in hydrological modeling, I develop a water balance model which simulates continuous monthly hydrological budgets based on daily or monthly data of precipitation and temperature.;Based on the water balance model, the sensitivity of water balance estimates to time scale and the hydrological impacts of changes in storm clustering are examined. The difference between daily- and monthly-derived runoff correlates well with the amount of storm clustering within a month. Water balance modeling based on hypothetical storm scenarios shows that annual moisture surplus tends to increase with an increase in storm clustering.;Annual peak discharge data in the contiguous U.S. indicate that the dependence of annual peak flood seasonality and magnitude on drainage scale varies greatly among different climates. Annual peak flood seasonality exhibits strong dependence on drainage area in cold humid regions. In warm southern states, however, drainage area has little effect on annual peak flood seasonality. This study reveals a gradual shift in the timing of annual peak floods from the spring toward the winter in the northern Pacific coastal region.;Annual peak flood magnitude is strongly related to drainage area under different climatic regimes. However, in arid and semi-arid regions annual peak discharges are highly variable and increase slowly with an increase in drainage scale.;There is a change in record-high stream discharges in the Upper Midwest. Record-high discharges generated from small watersheds ;Among the various forms of subtle changes in precipitation regime, spatially extensive in the Upper Midwest, is a systematic increase in the number of rain days and a corresponding decrease in the average daily rainfall amount. These changes in precipitation regime may have important impacts on runoff, soil moisture, and sedimentation.