Hydrologic and water quality modeling: Spatial and temporal considerations

Hydrologic and water quality models are used to help manage water resources by investigating the effects of climate, land use, land management, and water management on water resources. Water-related issues are investigated over a range of scales, i.e., the extent and resolution of the spatial and temporal contexts, which can vary spatially from point to watershed and temporally from seconds to centuries. In addition, models' formulations may place scale restrictions on their use. In 2012, ASABE published a collection of 22 articles on the calibration, validation, and use of 25 hydrologic and water quality models. Each article detailed the process to follow and the issues that could arise during calibration or application of a specific model. The objective of this article is to synthesize those articles with regard to common spatial and temporal scale principles that should guide selecting, parameterizing, and calibrating a hydrologic model. This article describes how the spatio-temporal extent and resolution of a model application should relate to the modeling objectives, the processes simulated, the parameterization and calibration process, data available for parameterization and calibration, and interpretation of results. Overall, the intended scale of the model should match the scale of the processes that need to be simulated given the modeling objectives, the scale of input and calibration data should be compatible with the scale of the model and with the objectives of the study, and the model should be calibrated at the scale at which the results will be analyzed and interpreted.