In urban areas, increasing drought damages vegetation. Most species of grass are not able to stand prolonged periods of drought. Trees and bushes can become seriously or irreparably damaged by prolonged periods of drought. In order to limit these effects on urban green, irrigation is required. This comes at the expense of the already scarce fresh water supply in times of drought.
The interspersed planting of trees in public green areas provides shade for the lower plants preventing excessive evaporation and cooler spots for city dwellers to sit. The trees themselves have deeper roots and are able to provide for their own water supply. Certain tree species are able to stand drought better than others.
Drought-resistant plants are more suitable for bridging longer periods of drought, as they have a greater capacity to absorb water in urban areas and/or have a relatively low level of evaporation. Although all climate scenarios show an average increase in winter temperatures, vegetation in the Netherlands needs to be frost-resistant. Mediterranean vegetation can not readily be planted.
The degree to which groundwater extraction occurs depends on the type of vegetation. In general a tree, for example, usually draws water from an area as large as three times the diameter of the crown.
In cases of problems with building foundations and a low groundwater level, removing a large tree and replacing it with a drought-tolerant tree can be very effective.
Removing a large tree also has disadvantages: the effects of shade are lost, the cooling effect from evaporation disappears and it reduces the biodiversity.
Examples of drought-resistant trees are: Catalpa, Eastern Redbud, Hawthorn, American Elm and Callery Pear. In general it is true that because of their deep roots trees are not that adversely affected by a low water table and can often survive relatively easily during dry spells. Trees suffer more from flooding; they can survive for only a short time. [Bennink, 2010]
See chapter Heat.