**5. Conclusions**

Being an increasingly dangerous environmental hazard, flash floods are intensively investigated worldwide. Information on floods in remote areas is accumulating. Probably related to climate change, flash floods are also becoming a common phenomenon in the mountainous and hilly region of Southern Transdanubia. At least 433 settlements are located and 700,000 inhabitants live in areas potentially affected by flash floods – although the return period of severe inundations is likely to exceed 100 years for most localities. Unfortunately, new developments often ignore this potential hazards and during prolonged dry periods agricultural cultivation frequently extends over floodplains. However, a flood of long return time may cause economic losses of millions of Euros. The investigations in Southwest-Hungary helped to identify areas where, despite the available long-term

Today numerical models are widely applied tools to simulate the areal extent of inundations and flooding along a watercourse (i.e during riverine floods) (Gaume et al., 2004). They are also suitable for flood simulation in urban environments, where the proportion of permeable surfaces are limited and impervious paved surfaces are widespread (e.g. Xia et al., 2011). Numerical modelling is particularly suitable for the analyses of risk scenarios, such as dam breaching, and also capable of the exact localization and parameterization of the elements of the channel and drainage systems (e.g. bridges, levees and culverts) and

The prediction of flood occurrence is the ultimate goal of modelling. Prediction models are classified into two categories: real-time direct forecasting (similar to weather forecasting – e.g. Doswell III, 1996, 1998) and flowchart-type modelling or scenario building (similar to climate change prediction). The models of the first type of forecasting do not seem useful in flash flood prediction in our case since no appropriate monitoring system exists in the study area. Applying the second approach scenarios or flowcharts can be designed for the most endangered catchments in the region (e.g. Alkema, 2003). Flowchart-type modelling takes advantage of the results of the aforementioned rapid screening analysis and risk assessment. The most probable environmental change scenarios are generated with preselected boundary conditions. The boundary conditions incorporated in the model include soil moisture content, relief, surface storage, canopy cover, cumulative rainfall and rainfall intensity. To validate the suitability of this model type we need to verify it with hindcast modelling, i.e. we perform simulation backward in time to see whether it reconstructs the

For a flowchart analysis data on preceding rainfall events have to be collected to see whether the previous rainfall event was followed by flood warning. Precipitation data originates from meteorological data usually with a 3-hour lead time. These rainfall prediction schemes determine whether a heavy convective, or a prolonged and relatively low-intensity rainfall is expected. All the scenarios in a flow chart model contain a unique code. An analytical software investigates the resemblance of the present scenario to all the predetermined scenarios and finally selects the most adequate output scenario. Finally, it

Being an increasingly dangerous environmental hazard, flash floods are intensively investigated worldwide. Information on floods in remote areas is accumulating. Probably related to climate change, flash floods are also becoming a common phenomenon in the mountainous and hilly region of Southern Transdanubia. At least 433 settlements are located and 700,000 inhabitants live in areas potentially affected by flash floods – although the return period of severe inundations is likely to exceed 100 years for most localities. Unfortunately, new developments often ignore this potential hazards and during prolonged dry periods agricultural cultivation frequently extends over floodplains. However, a flood of long return time may cause economic losses of millions of Euros. The investigations in Southwest-Hungary helped to identify areas where, despite the available long-term

supports the decision of authorities on issuing a flood warning or not.

even appropriate for the 3D representation of these structures.

**4. Potential prediction models** 

observed event.

**5. Conclusions** 

statistics, settlements, residential areas and farmlands are potentially affected by flooding and serious damage from floods can be predicted. The choice of methodological approaches to the topic is rapidly broadening. The combination of rapid screening methods, GIS-based risk assessment with numerical hydrological modelling and the flowchart analysis of probable scenarios opens new vistas in this research field.
