Hazard specific knowledge gaps and recommendations

Recommendation: Work towards the development of integrated damage-assessment methods that strive to reflect the interplay of possible coinciding natural hazards.

4.2.2 Droughts

The compilation of methods that assess the direct cost of droughts revealed that most of the available studies are ex-post analyses that are based on self- and media reports. Since these are prone to biases, current drought damage estimations show a large uncertainty. At the same time, hardly any methods are available for the ex-ante analysis of drought damages. However, the few studies that is available show that droughts can cause substantial damages not only to agricultural production but also to infrastructure and buildings, navigation, or power production.

Even though drought-induced soil subsidence causes substantial structural damage to buildings and infrastructure, this aspect has been hardly addressed by the current literature. Most of the studies examining drought damages focus on the agricultural sector, so far.

Recommendation: Given the projected increase in frequency and intensity of droughts, e.g. in the Mediterranean basin, the development of such ex-ante evaluation approaches is therefore important. The development of ex-ante models is also needed to examine the development of drought damages over time and to evaluate various drought damage mitigation strategies. Given the large damage associated with drought-induced soil subsidence, future research should es-pecially focus on structural drought damages assessments.

Other studies assess drought damages by comparing production output during drought years with production output during non-drought years. Also this approach implies considerable uncer-tainties, because a decline in production can have other reasons that are external to drought events. In addition, following this approach, no differentiation can be made between direct and indirect damages. It cannot be established whether production output is reduced during a drought year due to direct damages to crops and life stock or due to indirect effects spreading through the economy. Such a distinction might be useful, though, with respect to the prioritization of mitigation and adaptation strategies. In addition, the methods currently applied are unable to take the dynamics of drought damages over time into account.

Recommendation: More sophisticated drought damage models that are based on assessments of losses to economic flows should be developed. These could significantly improve current cost assessments.

So far, there are no drought damage models, according to our knowledge, that take drought mit-igation measures into account. As a result, the damage reducing effect of drought mitmit-igation measures is largely unknown. This significantly hampers the evaluation and choice among dif-ferent adaptation strategies. This is e.g. the case in terms of drought damages to buildings due to drought-related soil subsidence. Against the background that existing studies suggest that damage amounts caused by this phenomenon are comparable with other large scale natural disasters, such as floods, this should be further investigated.

Recommendation: Future model development should strive to capture the effect of drought miti-gation measures. Existing data bases on drought-induced soil subsidence to different types of building could provide a basis for this future work.

4.2.3 Coastal Hazards

A major drawback of current methods to assess directs costs of coastal hazards are the lack of specific damage functions. Across Europe, damage functions that were derived and constructed for the assessment of riverine flooding are commonly applied to assess potential damages from coastal flooding. This is problematic, given the different damaging processes that can be ob-served for riverine and coastal flooding. It can be expected that flood forces and thus resulting damages are considerably higher for coastal flooding, as it has been demonstrated by studies from the US.

These findings exemplify the need to derive and develop separate damage functions and as-sessment methods for storm surges also in the European context, given the different damage causing process of riverine and coastal flooding and the expected rise in sea-levels.

Recommendation: Given the expected effects of global warming on sea-levels and the associ-ated increase in the risk of coastal flooding, specific damage functions should be derived and applied for the assessment of coastal flooding. Alternatively, future research could address the question to what extent damage functions for riverine flooding can be transferred to coastal are-as in order to derive adjustment factors. In line with the recommendation provided by FEMA for the US, standard depth damage functions should not be applied if high flow velocities and wave forces can be expected (Nadal et al., 2010).

4.2.4 Alpine Hazards

Especially in the context of Alpine hazards, there is a risk of cascading and coinciding natural hazards that can show very different damaging processes. However, no methods are currently available that take this into account.

Often, standard depth damage functions are applied also for flood events in Alpine areas. This is problematic, because floods in mountainous regions can show very different hazard characteris-tics, e.g. in terms of flow velocities. Following from this, different and more severe damaging processes can be expected that are not captured by applying standard depth-damage functions.

Recommendation: Especially in the context of Alpine hazards, it seems important to work to-wards integrative damage assessments methods that are able to capture potentially coinciding events. In line with the recommendation provided by FEMA for the US, standard depth damage functions should not be applied if high flow velocities, ice or debris induced damage or erosion can be expected (Nadal et al., 2010).