One approach to understanding the regional impacts of climate change is to use a hierarchy of linked numerical models (i.e., a general circulation model [GCM] driving a regional climate model [RegCM], which in turn drives a hydrologic model). This approach has been under development within the Susquehanna River Basin (SRB) Experiment (SRBEX) group at Penn State. The long-range plans are to study the response of the SRB to a sequence of storms, the annual cycle, El Niņo-Southern Oscillation forcing, and increased atmospheric greenhouse-gas concentrations.
The SRBEX suite of models includes the GENESIS GCM, the Penn State-NCAR mesoscale model (MM5) which has been modified to act as a RegCM, and the Hydrologic Model System (HMS). As a first step to long-term modeling, the SRBEX group is studying the problems associated with those simulations by using the modified MM5 to simulate a sequence of storms (during a period of approximately one month), and the HMS to simulate the SRB hydrologic response, and then comparing with the observed precipitation fields and hydrograph. For these particular applications MM5 is driven by observations, instead of by GENESIS output, to study the effect that the resolution of the initial and lateral boundary conditions has on the simulated precipitation fields. Also, MM5 uses different nested-domain configurations (i.e., four domains with 108-36-12-4 km grid increments, versus three domains with 108-36-12 km grid increments) to assess the effect the MM5 resolution has on the simulated precipitation fields and, as a result, on the simulated hydrograph. The results from these simulations will be presented, including a discussion of the problems associated with them.