• Based on trends and mechanisms that can be seen in the past years.
  
• More reliable for shorter-terms and well-defined areas.
  
• Use of Scenario is good for comparative purposes and when there is a significant uncertainty about the future.
  
• External Scenario – dependent on factors which cannot be controlled.
  
• Policy Scenario – user can influence in a significant way.

• External Scenario have been used to estimate the future population, GDP, traffic etc. for land use and transport planning.

• Computer modeling is commonly used to forecast environmental implications but before deciding whether to use it or designing the types of computer modeling, the following points should be noted:

- The level of details required by the SEA should be carefully considered at an early stage as sophisticated models are usually time consuming and expensive but may not be meaningful for SEA in all cases.
- Even though sophisticated models are available, special attention should be paid on whether credible information is available as input assumptions.
- Margin of error of the model should be compared with that of the assumptions adopted.
- Time available for conducting computer modeling should be assessed as even though very accurate results are produced, it would be useless if decisions have been made.

• To deal with the uncertainty and to avoid unexpected environmental impacts, strategic environmental monitoring & audit should be developed as part of SEA to check the change of assumptions and follow up on the implementations of environmental mitigations that are necessary to avoid major problems.

• Examples are SEA for TDSR [more...], CTS-3, RDS-2, HK2030, etc.
  

• Future goal is set.

• Steps required to achieve this future goal.
  

• Used in HK2030 together with the Forecast approach.

• In addition to the development pressure (such as population growth), the SEA also looked at the likely environmental targets in 30 years time and the possible trend or direction.

• Measures required to achieve these future “targets” are also investigated and those related to land use planning are recommended to be incorporated in the strategic land use planning framework.