Inundation scenarios for flood damage evaluation in polder areas

We present an approach for flood damage simulations through the creation of a comparatively large number of inundation scenarios for a polder area, using a high-resolution digital elevation model. In particular, the method could be used for detailed scenario studies of the impact of future socioeconomic and climatic developments on flood risks. The approach is applied to a case-study area in the south of the Netherlands along the river Meuse. The advantage of our approach is that a large number of potential flood events can be created relatively fast without hydrodynamical calculations, and that it can be applied to high-resolution elevation models and for large areas. The large number of flood scenarios and the high horizontal resolution reduces at least part of the uncertainties encountered in flood loss modelling. The approach with a low horizontal-resolution (100-m) for loss modelling results in an overestimation of losses by up to 22% for high density urban areas, and underestimation of 100% for infrastructure, compared to the high-resolution (25-m). Loss modelling at 5-m horizontal resolution shows that aggregate losses may be overestimated by some 4.3%, compared to the 25-m resolution. The generation of a large variety of inundation scenarios provides a basis for constructing loss probability curves. The calculated range and expected values of damages compare reasonably well with earlier independent estimates

Detecting the long-term impacts from climate variability and increasing water consumption on runoff in the Krishna river basin (India)

Variations in climate, land-use and water consumption can have profound effects on river runoff. There is an increasing demand to study these factors at the regional to river basin-scale since these effects will particularly affect water resources management at this level. This paper presents a method that can help to differentiate between the effects of man-made hydrological developments and climate variability at the basin scale. We show and explain the relation between climate, water consumption and changes in runoff for the Krishna river basin in central India. Runoff under climate variability and increasing water consumption for irrigation and hydropower is simulated for the last 100 years using the STREAM water balance model. Runoff under climate variability is shown to vary only by about 14–34 mm (6–15%). It appears that reservoir construction after 1960 and increasing water consumption has caused a persistent decrease in annual runoff of up to approximately 123 mm (61%). Variation in runoff under natural climate variability only would have decreased over the period under study, but we estimate that increasing water consumption causes about two thirds of the current runoff variability

Approaches to analyse and model changes in impacts:reply to discussions of “How to improve attribution of changes in drought and flood impacts”^*

We thank the authors, Brunella Bonaccorso and Karsten Arnbjerg-Nielsen for their constructive contributions to the discussion about the attribution of changes in drought and flood impacts. We appreciate that they support our opinion, but in particular their additional new ideas on how to better understand changes in impacts. It is great that they challenge us to think a step further on how to foster the collection of long time series of data and how to use these to model and project changes. Here, we elaborate on the possibility to collect time series of data on hazard, exposure, vulnerability and impacts and how these could be used to improve e.g. socio-hydrological models for the development of future risk scenarios.</p