Accurately simulating precipitation characteristics in complex terrain is a notorious problem in global climate models. Increasing model resolution, which also increases topographic resolution, seems to be one of the easiest ways to improve model hydrometeorology. Higher resolution is relatively easy to implement, but computationally costly to run. The number of grid cells increases exponentially and the number of time steps increases roughly linearly with increasing resolution, which requires more computer time and data storage, transfer, and processing. Improved representation of meteorological and hydrologic processes in complex terrain would be expected with higher resolution; however this hypothesis remains to be rigorously tested at practical regional model resolutions.

Are the higher-resolution simulations in fact better, or do they only look better? To address these questions, 25km and 10km Weather research and Forecasting (WRF) model runs are compared to Tropical Rainfall Measuring Missions (TRMM) observations. The North American Monsoon is used as a case study. The 10km WRF runs are conducted with 25km and 10km terrain to discern the effect of model resolution from terrain resolution. The spatial and temporal realism of simulated precipitation is assessed using TRMM data.