Disaster warnings can be fast, but how can we also ensure their accuracy and credibility, ask Rohan Samarajiva and Nalaka Gunawardene.
The challenge with disaster warnings is to make the best possible decisions quickly using imperfect information. With lives and livelihoods at stake, there is much pressure to get it right. But one can't be timely and totally accurate at the same time.
Only governments can balance these factors. No other entity can take on the responsibilities and attendant liabilities of issuing public warnings that may result in mass evacuations.
Timely decisions taken on the basis of the best available evidence require clear protocols within government. But often, turf wars and the lack of a clear demarcation of authority between different actors slow decision-making.
Now, social media are making this delicate balance even harder. To remain effective in the always-connected and chattering global village, disaster managers have to rethink their strategies for engaging with people at risk.
Tight warning window
Rapid onset disasters such as tsunamis or flash floods only allow a very tight window from detection to impact. Others, such as cyclones and floods, may come within a few hours or days of detection.
For those who must respond to potential hazards, it is a race against time. The errors that can occur in detection and rapid decision-making fall into two categories.
First is a missed alarm, when telltale signs are ignored, or those with access to data about a looming disaster simply fail to connect the dots.
Second is a false alarm, when those responsible err on the side of caution. In recent years, several tsunami warnings have caused unwarranted panic in the Indian Ocean region.
The devastating event on 26 December 2004, which hit a dozen countries with minimal or no public warning, is a scenario unlikely to be repeated: much has been done to improve detection, assessment and dissemination.
And since a tsunami warning centre was established in the Pacific in 1949, it has never failed to warn about damaging tsunamis but there have been some expensive evacuations that turned out to be unnecessary.
We must now guard against 'cry-wolf syndrome'. Too many false alarms and evacuation orders can erode public trust, a vital element in disaster response.
ICTs add to complexity
The proliferation of information and communication technologies (ICTs) adds a new dimension to disaster warnings. Having many information sources, dissemination channels and access devices is certainly better than few or none. However, the resulting cacophony makes it difficult to achieve a coherent and coordinated response.
This happened on 11 April 2012, for example, when an 8.6-magnitude quake occurred beneath the ocean floor 610 kilometres southwest of Banda Aceh, Indonesia.
Indian Ocean countries reacted differently. Several issued quick warnings and some also ordered coastal evacuation. Thai authorities shut down Phuket International Airport, while Chennai port in southern India was closed for a few hours.
In the end, the quake did not generate a tsunami, but it triggered plenty of chaos. In Sri Lanka, for example, coastal bus and train services were stopped, electricity was shut down and public offices were abruptly closed.
Some journalists and activists tweeted for several hours, providing ground-level updates as well as relaying news from international wire services.  In contrast, state agencies mandated to issue warnings relied on faxes and phone interviews with broadcast channels.
The controlled release of information is no longer an option for any government. In the age of social media and 24/7 news channels, many people will learn of distant hazards independently of official sources.
Humanitarian groups are now increasingly using Twitter, blogs and video-sharing platforms such as YouTube. Government disaster managers should join these conversations.
Unless governments communicate in a timely and authoritative manner, the vacuum will be filled by multiple voices some of which may cause panic and confusion.
The ideal scenario would be for the non-governmental voices to complement and amplify the public warnings issued by governments.
Ensuring clarity, engendering trust
Regardless of the medium, frequency and accuracy with which alerts are communicated, unclear language can also be a problem. Disaster professionals use precise terms such as watch, which means standby for more updates, and warning, which means take action. But even experienced journalists sometimes mix these up.
Discussions are under way among disaster-response managers in the Indian and Pacific oceans on how to use terms that are less open to misinterpretation.
In the meantime, the accuracy of warnings and how decision-makers respond to them needs to be improved. Public trust is the lubricant that helps move the wheels of law and order in the right direction. It takes time and effort to build, but can be lost quickly.
In November 2007, as tropical Cyclone Sidr approached southern Bangladesh, many communities ignored early warnings, and more than 1,000 people died needlessly.  A false tsunami alert and evacuation two months earlier had eroded their trust in the country's well-established early warning system.
Communicating in real time is now within reach of at least a third of humanity, who are connected to the web. Our challenge is to harness that power to maintain public trust and outrun fear and panic.
Rohan Samarajiva was a former telecommunications regulator in Sri Lanka and heads the regional think-tank LIRNEasia, which has been active in disaster risk reduction since its inception. Science writer Nalaka Gunawardene has covered disasters for 20 years and co-edited Communicating Disasters: An Asia Pacific Resource Book in 2007.
 Gunawardene, N. Nurturing Public Trust in Times of Crisis: Reflections on April 11 Tsunami Warning (Groundviews, 26 April 2012