Final answer:
Several factors such as sediments, land reclamation from lakes, groundwater pumping, and sea-level rise due to climate change have contributed to parts of Tokyo being below sea level.
Step-by-step explanation:
About 10% of Tokyo, which consists of 30% of the population, is below sea level due to several factors:
- A. Was built on soft, wet sediments: Tokyo was originally established on an area with soft and wet sediments which can compact over time, leading to subsidence and making the land more vulnerable to sea-level rise.
- B. City planners drained lakes to build homes: In the process of urban development, city planners have at times drained lakes and wetlands to create space for housing and other infrastructure. This can result in the city expanding into areas that are more prone to flooding and sinking.
- C. Pumping groundwater to supply the city has caused subsidence: The extraction of groundwater for the city's water supply has led to ground subsidence. When groundwater is pumped out, the land above can sink as the support provided by the water is reduced.
- D. Sea level has risen: While sea level rise due to climate change is a global issue, it directly impacts low-lying coastal cities like Tokyo by exacerbating flooding and submergence of land. The rise in sea level is caused by a combination of melting ice caps and glaciers and thermal expansion of seawater as it warms.
Adaptation strategies such as the creation or conservation of wetlands may help protect against flooding and storm surges.