Bochum is the sixth largest and one of the southernmost cities in the Low German dialect area. The terrain of Bochum is characterised by rolling hills that rarely have more than three per cent graduation. Steeper graduation can be found at the Harpener Hellweg near the Berghofer Holz nature reserve 3. The city extends north to south The perimeter of the city limits is There is sedimentary rock of carbon and chalk.
The geological strata can be visited in the former quarry of Klosterbusch in Querenburg and at the Geological Gardens in Wiemelhausen.
The urban area is divided into the river Ruhr catchment in the south and the Emscher catchment in the north.
The Ruhr in combination with upstream reservoirs is also used for drinking water abstraction. The industrial developments in the region since the 19th century were leading to a kind of division of labour between the two river catchments, pumping drinking water from the Ruhr into the municipal supply system and discharging waste water mainly into the Emscher system. The ecological restoration of the Emscher tributaries initiated by the Emschergenossenschaft started with the Internationale Bauausstellung Emscher Park in The south of the city has woods, the best known of which are the Weitmarer Holz [ de ].
These are generally mixed forests of oak and beech. The occurrence of holly gives evidence of Bochum's temperate climate. Extreme temperatures are uncommon. On the other extreme, freezing temperatures are common between mid-November and late March. In some years, however, frosts may occur as late as early May.
