Natural Hazards in a Changing World: A Case for Ecosystem-Based Management

<div><p>Communities worldwide are increasingly affected by natural hazards such as floods, droughts, wildfires and storm-waves. However, the causes of these increases remain underexplored, often attributed to climate changes or changes in the patterns of human exposure. This paper aims to quantify the effect of climate change, as well as land cover change, on a suite of natural hazards. Changes to four natural hazards (floods, droughts, wildfires and storm-waves) were investigated through scenario-based models using land cover and climate change drivers as inputs. Findings showed that human-induced land cover changes are likely to increase natural hazards, in some cases quite substantially. Of the drivers explored, the uncontrolled spread of invasive alien trees was estimated to halve the monthly flows experienced during extremely dry periods, and also to double fire intensities. Changes to plantation forestry management shifted the 1∶100 year flood event to a 1∶80 year return period in the most extreme scenario. Severe 1∶100 year storm-waves were estimated to occur on an annual basis with only modest human-induced coastal hardening, predominantly from removal of coastal foredunes and infrastructure development. This study suggests that through appropriate land use management (e.g. clearing invasive alien trees, re-vegetating clear-felled forests, and restoring coastal foredunes), it would be possible to reduce the impacts of natural hazards to a large degree. It also highlights the value of intact and well-managed landscapes and their role in reducing the probabilities and impacts of extreme climate events.</p></div

Wave run-up elevations for various storm-wave return intervals for different scenarios of beach slope and climate change.

<p>Simulations used here are for a typical sandy beach location in Eden (Tergniet, near Mossel Bay), which is prone to storm-wave damage. Return periods were based on the simulated wave run-up elevations for a south-south westerly swell, and spring high tide levels. The numbers prefixing the annotated description of each scenario provides a reference to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095942#pone-0095942-t001" target="_blank">Table 1</a>, which describes each scenario in more detail.</p

Flood return intervals for different scenarios of land cover and climate change.

<p>The numbers prefixing the annotated description of each scenario provides a reference to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095942#pone-0095942-t001" target="_blank">Table 1</a>, which describes each scenario in more detail. The changes in the values for each return interval illustrate the potential changes in the likelihood of extreme flow events under the different scenarios. For example, the return period of a flood with a daily flow of 150 mm (similar to the May 1981 flood in this area) would decrease from a baseline of more than 100 years to 70 years under future climate (scenario 5).</p

Flow duration curve for different scenarios of land cover and climate change.

<p>This shows the cumulative proportion of the months where a flow exceeded a given discharge for the different scenarios. The numbers prefixing the annotated description of each scenario provides a reference to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095942#pone-0095942-t001" target="_blank">Table 1</a>, which describes each scenario in more detail. Extreme low flows were defined as those with >90% exceedance, which were used in this study to represent severe drought conditions. A log-normal probability curve was used to allow the low and high flow ends of the plot to be more clearly displayed.</p

The location of the hazard model study areas within Eden.

<p>The inset showing the location of Eden in South Africa.</p