The Comoro River flows through the western side of the city, while the Bemorl and Benmauc Rivers  join together in the East. The Maloa river lies between these. The Maucau river flows through Tibar, while the Akanunu and Mota Kiik rivers flow through Hera. The Comoro is the largest, with a drainage basin extending  inland to a point where the mountains are  high. The water level within these rivers differs greatly between the dry and wet seasons. Parts of the city are considered to face drought hazards and flooding risk from rivers, issues related to climate change. Within the main city of Dili (although not in Hera or Tibar), rivers have reinforced to contain a once in 25 year flood. Small-scale flooding occurs in a minority of houses a few times each year, and reports of land subsidence are found throughout the city. The Maloa river is the most commonly flooded. Landslides have previously caused damage and loss of life. The area is thought to face earthquake and tsunami risks, although no major events have occurred. Air pollution is considered an increasing issue, with contributors including forest fires, wood-fuelled cooking, and vehicles.