“…A drought is temporally slow, which suggests monitoring processes [18], while in a flood that extends over a certain area, pictures can be used as a base for modelling or as ground data, e.g., modelling the flood extent in order to find elements at risk [35,39,45]. Finally, an earthquake, tsunami, fire, storm or volcanic eruption can occur suddenly, and therefore, it is necessary to have up-to-date data about hazard-prone or previously-affected areas to be adequately prepared and to conduct mitigation activities [15,41,43,44]. These examples show the diverse options that exist for the selection of tools and data types, as well as the tasks that the crowd is asked to perform.…”