Recent studies have emphasized the importance and severity of cascading effects in the occurrence of crises. Critical infrastructures depict an important part of decision making during crises. A blackout in one infrastructure system could be propagated to other infrastructure systems, e.g. a power blackout could lead to severe consequences in the interconnected water grid or mobile phone grid. Infrastructures and supply grids are highly interconnected and therefore damages caused by natural hazardous events (heavy storm, volcano eruption, flood) can propagate across different systems. A damage propagation from a supply grid element to another, both within the same grid or across different grids, is called a cascading effect. These cascading effects are complex and could lead to damages in human, environmental, technical or economic systems which were not originally caused by the natural hazard. In addition, damaged critical infrastructure in crises can lead to cascading effects aggravating the crisis impact for humans, the economy and the environment.
In Snowball, the understanding of cascading effects especially beyond system borders will be increased by the use of a computer simulation, where different influences on supply grids are analyzed. The computer simulation focusses on the power grid, the water grid, the mobile phone grid as well as human behavior during crises. For instance, damages and outages in the power grid can propagate to the water and mobile phone grid and lead to cascading effects. Human behavior can either aggravate or mitigate these effects. With the help of a computer simulation, vulnerability and resilience measures for the considered grids having regard to human behavior are built. The simulation aims at a better understanding of the influence of human behavior, decisions and reactions on cascading effects and of damages and damage propagation between different grid types in certain scenarios. The knowledge about damage propagations can support decision making to reduce the crisis impact, increase the preparation and the situational awareness in crises, identifying vulnerabilities of grids and increasing their resilience.
The overall target of the damage propagation models is to understand the role of cascading effects in resilience of grids. This target is reached by the development of the computer simulation tool CaESAR (Cascading Effect Simulation in urban Areas to assess and increase Resilience) by Fraunhofer EMI. A general overview over the components of CaESAR is given in Figure 1. CaESAR receives as input a predefined crisis with georeferenced grid models. It combines power grids, water grids and mobile phone grids in one model and interconnects them. Based on this combined model, a time-dependent computer simulation is started, where the damage model computes the damage probability depending from the crisis event in each grid, e.g. the probability for a power pole break down during a storm event. Afterwards, the damage propagation model computes the probability for a propagation within each grid (by using external simulators) and across grid borders using the models of CaESAR including the time condition (e.g. water pumps with battery supply could work a time t without electricity). The results of damage propagation models and the influence of agents to the damages are combined as consequences of damages. Based on these damages, the next simulation iteration starts. The results of the computer simulation are processed by vulnerability and resilience assessment for identifying weak points of the grids including damage propagation across grid borders and providing suggestions for mitigation.