GEOMETRIC CORRECTION OF SHORTWAVE RADIATION MEASUREMENTS OVER COMPLEX TERRAIN FOR USE IN HYDROLOGIC MODELS

Large-scale hydrological modeling is often used to explain complex, multi-variable, heterogeneous environmental processes, driven by water and energy fluxes. Understanding the hydrologic cycle is necessary to interpret a system in constant flux, as well as to accurately and adequately manage our water resources, an increasing concern worldwide. Elaborate physics, needed to describe a triphasic system (snow, vapor and liquid water), creates a demand for computer-assisted models. We generate a model to analyze the re-distribution of solar radiation over complex topographic regions to understand how shortwave radiation interacts with a hydrologic cycle. The model is a function of the geometric characteristics of the terrain, three-dimensional orientation in relation to the sun’s zenith angle and atmospheric properties. The model we propose uses information collected by pyranometers and a Digital Elevation Model (DEM), which calculates how solar irradiance is spatially distributed over the specified domain. This information, coupled with physical hydrological functions, will provide detailed knowledge of watershed runoff and evapotranspiration rates. This is critical to understand the dynamics of water at regional scales, as well as long-term potential impacts of changes in solar radiation to worldwide systems, and the people that those systems serve. This analytical simulation of the distribution of solar energy can be applied to any hydrologic system with the necessary input data, notably to mountain regions characterized by complex topography such as the Rocky Mountain Range. Water resources at the Crown of the Continent, especially at the headwaters of the Colombia and Mississippi rivers, are extremely important for they largely dictate changes in obtainable water for the entire continent. The Bitterroot Mountains of Montana, a headwater range for the Clarkfork-Columbia Rivers, will be used as a test bed for our model. Identifying how these systems operate is imperative to allow the continuing usage of fresh water without depleting our limited supply. This research is significant to understand this multifarious system and will help decipher a broader understanding of the processes involved. Recognizing how to better manage this system is crucial impending an inevitable shortage of fresh water.