Fast increases in urban sewage inputs to rivers of Indonesia

We present estimates for nitrogen (N) and phosphorus (P) sewage inputs to 19 Indonesian rivers for 1970–2050. Future trends are based on the four scenarios of the Millennium Ecosystem Assessment. Our results indicate a rapid increase in N and P pollution from sewage over time. In 1970, N and P inputs to rivers were low because not many households were connected to sewage systems discharging to rivers. Sewage connection is increasing over time. As a result, N and P inputs to rivers increase. We calculate that between 2000 and 2050 the N and P inputs increase with a factor of 17–40, depending on the scenario. Important determinants of future N and P sewage inputs are population, economic growth, urbanization, sewage systems development and wastewater treatment. Our calculations are based on an improved model for N and P inputs to rivers, indicating that previous estimates underestimated these inputs considerably.