Beneath the asphalt
Air and water. That’s what Madrid needs in particular. But not only freshwater, it requires seawater injected below the aquifers too in order to create a chemical gradient which drives water into those places .
Besides, and this is a global problem, as the surface of the earth is filled with urban concentrations, covering hundreds, thousands of squared meters, the larger the concentration of population is , the more of urbanized area vertically built usually, which implies an overload localized in certain points of the world, such as Japan for instance.
The problem is not only the weight of the huge vertical structures of skyscrapers, that will weigh a lot, there’s the traffic also, and there is what lies beneath the asphalt, which stops interacting naturally with the ecosystem.
It’s like having a patch of plastic glued to the skin, after a few hours, it starts to itch, reddens, and if not removed, ends up giving serious problems.
In the case of large cities, water, for example, is channelled, so that the thin layer that varies between twenty centimetres to five meters, where naturally the roots of plants, herbaceous, shrubs, and trees settle, that thin layer stops being naturally flooded when it rains. Rainwater becomes artificially collected through pipes, conduits that for we humans, make things more comfortable to us in order to walk or drive peacefully through the cities.
What I would do would be to open gaps every ten or twenty meters to break sidewalks and asphalt so that at least, in what is already built, trough those breaches on the streets that thin layer of the substrate, which is where living beings can live, would be watered naturally in harmony with the rhythms of the planet.
I would do the same although more extensively on surface, with respect to the oxygenation of the land, perhaps the medium-term solution is to put bricks lattice grids of some building material that can withstand traffic loads (which I would restrict to residents, public transport, disabled people, loading and unloading, and emergencies within a three miles radius from the centre of large cities, if not more), and that can give the hardness and uniformity appropriate to be used on large urban areas at no more than thirty kilometres per hour (approximately 20 miles per hour), or forty kilometres per hour on motorways. Instead of putting bumps, Berliners cushions, or mushrooms as people colloquially call those elements which are put on roads in order to oblige us to lower speed whilst driving.
But, as fast action is needed, because if not, things will be irremediable, first, divert and restrict traffic in those areas that are already moving, and open ditches that come in contact with the layer where life develops naturally into the substrate, and fill them with gravel so that roads can continue serving to be run upon without too many problems, providing “expansion joints” and thus providing natural irrigation through rainwater when it rains.
And also, do subsoil thermographies, and add salt to areas where there is an increase in temperature in order to create a chemical gradient in those points which are higher in salinity, in those areas where heat cannot be refrigerated by other means, and while a better solution is to come, avoiding so the fragmentation of the bedrock when rain water becomes ice increasing its volume and breaking the soil .