Towards a complete description of the hydrologic cycle: Large scale simulations with parallel, 
integrated models
 
Reed Maxwell, Department of Geology and Geological Engineering and International Groundwater 
Modeling Center, Colorado School of Mines, Golden CO, USA
rmaxwell@mines.edu

Integrated hydrologic models are growing in application and show significant promise in 
unraveling connections between the surface, subsurface, land-surface and lower atmospheric 
systems.  Recent advances in numerical methods, coupled formulation and computing power have all 
enabled new levels of high resolution integrated simulation not previously feasible.  Here I will 
discuss some recent applications of an integrated groundwater surface water hydrologic model with 
coupled land surface and atmospheric processes.  Using a computationally powerful, integrated 
model we can address questions related to the propagation of uncertainty in nonlinear systems, 
the nature of scaling over large extents, and feedbacks for both hydrology and water quality in 
ways not possible with standard hydrology tools.  I will demonstrate a number of applications 
including several large-scale watersheds in North and South America modeled at high resolution.  
Details will include techniques for model setup and initialization, in addition to results that 
focus on understanding fluxes, particularly from mountain-block systems, feedbacks and systems 
dynamics.  Additional anthropogenic complications such as the effects of pumping, irrigation and 
urbanization will be discussed and a path forward for integrated simulations of the hydrologic 
cycle will be presented.