What is a Model
A
model is a simplified representation of the real world
There are two types of models
·
Conceptual
·
Mathematical
Conceptual Models
What are they?
·
Qualitative, usually based on graphs
·
Represent important system:
·
components
·
processes
·
linkages
·
Interactions
When should they be used?
·
As an initial step –
·
For hypothesis testing
·
For mathematical model development
·
As a framework –
·
For future monitoring, research, and management
actions at a site
·
Design field sampling and monitoring programs
·
Ensure that all important system attributes are
measured
·
Determine causes of environmental problems
·
Identify system linkages and possible cause and effect
relationships
·
Identify potential conflicts among management
objectives
·
Anticipate the full range of possible system responses
to management actions
·
Including potential negative effects
Mathematical Models
What are they?
·
Mathematical equations that translate
a conceptual understanding of a system or process into quantitative terms (Reckhow and Chapra 1983)
How are they used?
·
Diagnosis
·
E.g., What is the cause of
reduced water clarity in a lake?
·
Prediction
·
E.g., How long will it take
for lake water quality to improve, once controls are in place?
Categories of Mathematical Models
Type 

Empirical Based on data analysis 
Mechanistic Mathematical descriptions based on
theory 
Time Factor 

Static or steadystate Timeindependent 
Dynamic Describe or predict system behavior
over time 
Treatment of Data Uncertainty and
Variability 

Deterministic Do not address data variability 
Stochastic Address variability/uncertainty 
When should you not use a model?
·
If you do not understand the problem
or system well enough to express it in
concise, quantitative terms
·
If the model has not been tested and
verified for situations and conditions similar to your resource
It is important to understand model:
·
Structure
·
Assumptions
·
Limitations