Many questions that arise with regard to the development of urban areas, require the use of different disciplines. Therefore, the project URBEM (Urban Energy and Mobility System) deals with the holistic view of possible changes in urban areas and their effects. URBEM was founded as doctoral programme at the TU Wien in cooperation with the Wiener Stadtwerken. The aim of the project is the development of an interactive environment to analyse scenarios to a sustainable, secure supply, affordable and liveable city- on the Example of the city of Vienna. In order to achieve this goal, it requires the collaboration and interaction of many different scientific fields. The basis for the investigations are three developed URBEM scenarios, which describe the possible future paths of change. The analysis of the effects on the thermal energy supply by political, social, economic and technological changes is an important part of the investigations. As a result, the present thesis deals with the subject of the thermal networks and the gas networks of urban areas. To be able to give answers in an interdisciplinary context, a separate development of calculation methods for the determination of operating parameters of large meshed networks was realised. Considering a district heating network, the modeling of the thermohydraulic behavior in the case of modified boundary conditions is in focus. Therefore, a quasi-steady state hydraulic calculation is combined with a transient thermal calculation. The application of this methodology has the advantage, that the thermal behavior of a district heating network can be simulated very detailed. The analysis of the gas networks should be done with regard to the hydraulic changes considering the compressibility of gases. By using the developed calculation methods, the impact due to the changes, resulting from the defined scenarios, on the primary district heating network and the low-pressure gas network of Vienna should be analysed. Subsequently, the influences of a decentralized feed and the use of thermal storages in the district heating network are investigated. Another question relates to the connection possibilities of urban expansion areas. For this purpose, simulations are carried out by vary the connection to the gas network and the district heating network, taking into account the electrical networks. The comparison between the further developed hydraulic calculation method and the commercial software PSS SINCAL using a test network, shows the numeric advantages of self-development with regard to convergence speed.