<P> Other problems include flooding, which results from increased impervious surfaces for roads and parking; increased temperatures from heat islands, which leads to a significantly increased risk of mortality in elderly populations; </P> <P> At the same time, the urban cores of these and nearly all other major cities in the United States, Western Europe, and Japan that did not annex new territory experienced the related phenomena of falling household size and, particularly in the U.S., "white flight", sustaining population losses . This trend has slowed somewhat in recent years, as more people have regained an interest in urban living . </P> <P> Due to the larger area consumed by sprawling suburbs compared to urban neighborhoods, more farmland and wildlife habitats are displaced per resident . As forest cover is cleared and covered with impervious surfaces (concrete and asphalt) in the suburbs, rainfall is less effectively absorbed into the groundwater aquifers . This threatens both the quality and quantity of water supplies . Sprawl increases water pollution as rain water picks up gasoline, motor oil, heavy metals, and other pollutants in runoff from parking lots and roads . </P> <P> Gordon & Richardson have argued that the conversion of agricultural land to urban use is not a problem due to the increasing efficiency of agricultural production; they argue that aggregate agricultural production is still more than sufficient to meet global food needs despite the expansion of urban land use . </P>

Which characteristic would have the greatest effect on what is known as suburban sprawl