Urban areas are at increased risk of both flooding and groundwater loss due to concrete and buildings which prevent rain and melted snow from being absorbed back into the groundwater supply. Surface water is freely moving water in rivers - and gutters - or in standing pools and lakes - or puddles. Surface water seeps into ground water that is in underground areas connected by porous rock or caves. Other types of groundwater are completely enclosed and are considered nonrenewable sources of water when they are tapped with wells.
The water that is used for daily human needs, agricultural or industrial needs can rapidly deplete ground water supplies when rainwater, wastewater, and agricultural runoff isn't returned to the water cycle of evaporation from surface water returning to surface and ground water from the atmosphere in the form of rain or snow.
Simple solutions can help within urban environments if they are included in planning and building or rebuilding phases of construction. Planters and mini gardens in parking lots or on rooftops help absorb rain either into the ground water cycle or at least into a planter where it can slowly evaporate back into the atmosphere instead of flooding the urban sewer system in severe storms or if large amounts of snow melt rapidly. Parking lot and other sidewalk or patio construction can also include more areas of water porous tile or gravel that allows water to be absorbed into the ground rather than adding to puddles and overflowing gutters.
The additional benefit of more trees and flowerbeds is a mental health benefit and direct reduction of carbon dioxide (CO2) as the plants use CO2 and release oxygen (O2) into the atmosphere.
For more information about increasing groundwater and reducing flood risk with urban planting and porous construction techniques see:
"To Tackle Runoff, Cities Turn to Green Initiatives," Yale E360, E360.yale.edu.
"Grass and trees in urban areas help reduce flood risk," Science for Environment Policy, European Commission.
Rainwater can also be collected in urban areas and stored for later use: "Examples of Rainwater Collection and Utilisation Around the World," United Nations Environment Programme, Division of Technology, Industry, and Economics, ec.europa.eu.pdf.
In warm areas tropical ferns provide oxygen throughout the year, and a place for rain to be absorbed into the ground.
Disclaimer: Opinions are my own and the information is provided for educational purposes within the guidelines of fair use.