Urban areas have less vegetation and therefore less evapotranspiration, which reduces moisture in the air (i.e. lower humidity).
Less vegetation also means less interception and, therefore, more precipitation lands on hard, urban surfaces.
The slate, tile, concrete and tarmac used in urban areas are impermeable and so the urban catchment is dominated by surface run-off, particularly in city centres.
Both shallow and deep infiltration is significantly reduced and drains are therefore needed to remove surface water quickly.
