Using Repeat Photography for Hazard and Risk Communication

This document discusses repeat photography (often known as rephotography), in particular its use in communicating hazard and risk to the general public and decision makers. Rephoto consists of combining two photographs taken at exactly the same location and with the same viewpoint at two or more times. This combination of photos (often using a software tool that allows the viewer to switch between the images easily or by showing the newer photo as an insert within the older one) provides the viewer with an understanding of how a location has changed over the period covered by the images (Figure 1). The concept of rephoto has a long history but it has become increasingly used in the past decade with the advent of cheap digital cameras, particularly those on smartphones, and initiatives that allow people to display their photos online to encourage creation, continuation and sharing of rephoto sequences. Burton et al. (2011) summarise the benefits and limitations of repeat photograph (their Table 1) as well as the use of this technique to investigate changes in landscape. Burton et al. (2011) use the approach to study recovery of the area affected by the Katrina hurricane in the state of Mississippi (USA) over a three-year period every six months. The purpose of this repeat photography was not to create images for communication but to calculate metrics showing how 131 locations survey recovered from the impact of the hurricane. In the following section, a brief summary of previous uses of rephoto is provided. In particular, the focus of this summary is the use of rephoto to communicate hazard and risk, particularly in the field of natural hazards. Based on this survey of the literature, the final section of this document provides some guidance about how to undertake rephoto and best practice.