Successful ecosystem management requires knowledge of the many interacting processes, both biological and physical in an environment and the ability to predict the consequences of different management choices. Because of the complexity of these processes, the large time periods they act over and the large spatial scales involved, most attempts require computer models. As part of SNEP, we developed an ecosystem simulation model that can be used to provide an accurate hydrologic assessment for use at watershed scales. Hydrologic processes are influenced by climate, topography, soil type and structure, and vegetation. Because these factors vary continuously in the landscape and interact together, it is difficult to predict the impacts of changes in any of their properties within the watershed without a simulating tool. The model integrates various sources of information allowing prediction of hydrologic responses at high time and space resolutions. Because of this ability, it can be used to simulate and test the impact of different management practices for explicit conditions in the watershed.

The model, Simulator of Processes on Landscapes Surface-Subsurface Hydrology (SPLASH) is coupled with a geographic information system that provides an easy way to manipulate large arrays of distributed data. This structure allows the model to be run at any grid cell resolution and for any time interval. Thus, by changing the inputs and running the program, we can visualize and analyze their effects on the outputs, spatially and temporally. Finally, this model can be considered as a management tool to predict the impact of landscape transformations like forest fires, logging, grazing or other activities on the hydrologic budget. Because the model can simulate the effects of complex interactive phenomena, it may improve our understanding of hydrologic processes in mountainous areas. The recent floods and the droughts of the past two decades demonstrate the importance of this research. A better understanding of regional hydrologic processes is needed if we are to predict how land management interacts with the climate system so that realistic strategies can be developed for balancing the demand for urban and agricultural water use. While the model is still in a testing and implementation phase, some scenarios that might be considered for use with the model are climate processes, wildfire impacts, forest logging, or other extractive management choices. During the SNEP, the model was tested on the Camp Creek watershed, a subbasin of the Cosumnes River drainage. This catchment is a mid-elevation west slope Sierra Nevada watershed that was also used for Bruce McGurk's application of the USGS Modular Modeling System. We obtained weather data for a full water year, digital topographic, soils and vegetation maps to use in driving the eco-hydrologic model.

Related SNEP chapter:
Ustin, S. L., W. W. Wallender, L. Costick, R. Lobato, S. N. Martens, J. Pinzon, and Q. Xiao. Modeling terrestrial and aquatic ecosystem responses to hydrologic regime in a California watershed. Vol. 3, chapter 6, pp. 275-307.