Tuesday, 11 February 2003: 4:45 PM
Regional Hydrological Cycle and Weather and Climate in the Contiguous United States
Hydrological cycle in the Earth-atmosphere system is not only a manifestation of the weather and climate but also a driving force for changes of the climate, particularly when the cycle is disturbed by anthropogenic changes of land surface conditions. Understanding the hydrological cycle and its variability and relation to weather and climate on various time scales will assist us to understand both regional and global climate and how anthropogenic effects may alter the water cycle and current climate. In this study, hydrological cycles for different regions in the United States were analyzed using NCEP-NCAR Reanalysis data of 1948-2000. In addition, the relationship of the hydrological cycle intensity and regional properties of precipitation and temperature were examined. Major results show that in the west coasts and the southeastern United States, the local water recycling ratio has a significant but negative relationship with precipitation processes from intense summer rainfall events to mild and extended light rain episodes, a relationship indicating a weak influence of local water cycling but a dominant role of moisture advection and convergence in the regionís rainfall events. On the contrary, the local water recycle plays a much more important role in precipitation in the western Great Plains and the Mountainous regions of the Rockies. In these in-land regions, a relatively large fraction of the rainfall is attributed to the local water recycle, although net convergence of moisture flux from outside these regions also contributes to the precipitation. These results suggest that land surface changes in the in-land regions could influence the regionís water cycle and precipitation climate more significantly than they could do to local precipitation climate in the coastal areas and adjacent regions. The relation between the hydrological cycle and regional temperature shows that an increase of temperature in the central United States would raise the local water recycling ratio and change the role of the local water recycle in the regionís precipitation climate. Such effect is not shown in the eastern and western coastal regions.