The purpose of this article is to consider the importance of Hydrological Data during an extreme event. In this paper we will consider the subject matter with regard to real time systems used to:

• Protect people and property (mitigate flooding).
• Provide public warning.

Referenced will be the “Kuala Lumpur SMART Tunnel Flood Detection and Stormwater Management System”. Designed and installed by an Australian led team in 2007, this world leading system is fully dependent on “accurate” and “reliable” hydrological data pre, during and post extreme events. We will focus on “during”.