RHESSys -

A hydro-ecological model

 

                                                                   Tecate River Sub Basin - ArcView 3.3 animated Digital Elevation Model

To successfully manage water resources within a watershed, an understanding of the relationships between the physical and biological processes is required. One way in which managers can better understand the physical processes of surface water flow through a watershed is through the application of a model. One such model is the RHESSys (Regional Hydro-ecological Simulation System) model.

Description of modeling - What exactly is modeling?
Before we describe the various components of the RHESSys environmental model, it would be beneficial to first gain an understanding of what exactly the term ‘modeling’ refers to and how it is useful to us.
Modeling is a way of simplifying the real world to enable us to solve problems. A model itself is a representation of how a process occurs in the real world. Models are around you constantly in everyday life, for example, a street directory is a model of a city’s roads, a diagram is a model of how something is made, and even a calendar is a model of a year. These models allow us to answer such questions as ‘What is the shortest route?’, ‘How do I put this together?’, ‘How long until my birthday?’ (Australian Academy of Science 2003).
The basis of modeling lies in mathematics, and the science of modeling is perhaps as old as the discipline of mathematics itself. An example of how ancient civilizations used modeling can be described by the use of geometry by Egyptians to model and divide up their farmland. More recently, in the 1600s, Isaac Newton developed calculus, which is a way of mathematically describing moving objects. He used equations to accurately model the motion of the planets - one of the greatest scientific achievements of all time. Today, mathematics is still the basis of modeling, however we use sophisticated computer models to help us solve more complex problems quickly. As an example, we use computer models to help predict the weather on a daily basis, or simulate climate change (Australian Academy of Science 2003).

What makes a good model?
The aim of a model is to simplify the problem, however you usually have to reach a balance between simplicity and accuracy. For instance, it is not feasible - cost, time or space - wise,  to use a model that takes years to implement. On the other hand, a model that is too simple may not give us enough information and so may not be very useful in helping us make predictions or understand a system better. Good models must include the most significant factors of the process and describe the most important features of a problem, and may omit factors of minor importance (Australian Academy of Science 2003).

Uses and benefits of modeling in the environmental field: Description of RHESSys
In environmental studies, modeling has endless applications and has proved invaluable in our understanding of environmental processes. They allow us to simulate processes that are too large or complex to run experiments out in the field again and again. Examples of processes that have been modeled include plant growth, water and air pollution, global warming and population growth. One application where modeling is especially useful is the prediction of water movement around a watershed, known as hydrological modeling. As populations have grown and water resources become more scarce, competition among water resource users has increased, particularly in the semi-arid environment of Southern California. As a result, water resource managers have been required to have a better understanding of  how water moves around a watershed so that resources can be managed more effectively and ultimately conserved. Models that predict the flow of water around a watershed can aid decision makers in their long-term planning of water resources. One such model is the RHESSys (Regional Hydro-Ecologic Simulation System) model and the following page describes how it works and possible applications. Next >>>>

Links to information about environmental models:
http://www.shodor.org/master/environmental/

References:

Australian Academy of Science 2003: http://www.science.org.au/nova/016/016box02.htm