Below are the major changes between MSMA (2000) and MSMA (2011):
1. In MSMA (2011), the formula for computing the IDF data has changed from a polynomial based formula in MSMA (2000) to an empirical equation.
2. The storm intensities have changed due to the changes in the formula used.
3. In MSMA (2000), the data used were up to about 1983 or 1990. For instance, the data used for the Federal Territory was only up to 1983 in MSMA (2000). However, in MSMA (2011), the data used were more up-to-date.
4. In MSMA (2000), the IDF data were available only for 35 major urban centers. In MSMA (2011), however, this has been increased to 135 major urban centers in Malaysia.
5. In MSMA (2000) the IDF formula is applicable for storm duration of 30 minutes to 6 hours, whereas in MSMA (2011), the formula is applicable between 5 min and 72 hours. In MSMA (2000), for duration of less than 30 minutes, a short duration formula is required.
6. In MSMA (2000) the storm A.R.I is available for 2 to 100 years, whereas in MSMA (2011), it is available for 2 to 100 years, plus 0.5 to 12 months.
7. IDF curves were plotted in Annex 3 of MSMA (2011) for the 135 major urban centers for A.R.I. from 2 to 100 years and duration of 5 min to 72 hours.
8. However, these were not provided for A.R.I of between 0.5 to 12 months.
9. In MSMA (2000) the whole of Kuala Lumpur is represented by one IDF curve. But in MSMA (2011), it involves 14 stations covering different parts of Kuala Lumpur. The same is noted for all states. For example, in Selangor there are now ten stations.
10. MSMA (2011) covers the IDF data of 12 states and federal territory in Peninsular Malaysia. Sabah and Sarawak are not covered. In MSMA (2000), the two East Malaysian states are covered.
11. The magnitude of changes in the design storm is covered in the Case Study (Quek, 2013a).