Surface water in the Northern Territory (NT) is controlled mainly by climate.
The NT has humid and arid climatic zones.
The humid zone has all of the following features:
- mean annual rainfall of 600mm to 1700mm
- streamflow of 2 megalitres per hectare each year
- all the streams flow north into the Timor Sea or the Gulf of Carpentaria.
Streamflow shows huge variability - most streams have recorded no flow over the Dry Season months, but maximum monthly stream flows up to 10 times the average during the Wet Season.
The arid zone has all of the following features:
- mean annual rainfall of 100mm to 550mm
- streamflow of 0.2 megalitres per hectare each year
- all streams flow inland and do not drain into the sea.