Studies of the hydrological cycle over the US have captured the interest of researchers for many years, yet a consistent description at regional scales has remained an evasive issue as the possibilities and limits of such endeavor only now are beginning to be understood. The GEWEX Continental-scale International Project (GCIP) recognized from an early stage the importance of mesoscale circulations in resolving the water and energy balances, and thus put a special interest into this area of research. As a consequence, by relying in products of mesoscale models, GCIP has significantly advanced the knowledge of the water and energy cycles for the Mississippi basin at subcontinental scales, and their related surface processes.

A systematic effort to compute these budgets from mesoscale regional analyses produced with NCEP’s operational Eta Data Assimilation System has been carried out at the University of Maryland, and currently the archive is about seven years long (1995-2002). This presentation will discuss the resulting regional climatology of the water and energy cycles using these model products combined with diverse observations. Because this is the operational version of the Eta model, its changes throughout the years may have affected the output. These potential effects will be discussed before addressing other variabilities. We will then focus on the effects of higher frequency variability on the water cycle, and seek to assert whether changes from year to year also affect the closure or stability of the moisture budgets. The period includes the 1997/98 ENSO cycle, which provides a glimpse at the longer term variability at the regional mesoscales.

Comparisons to a similar climatology produced from NCEP’s global reanalyses will highlight the fundamental differences between the two datasets, in particular with reference to aspects related to studies of the hydrological cycle.