If I build a concrete surface on a 1km x 1km area and painted it black, will I create convection (updraft from ground)?
In principle: yes. But i won't give exact numbers for a mere km², though i'd expect a skilled paraglider under optimal atmopsheric conditions to be able to make some use of it ;-)

Actually, gliders use industrialized areas exactly because of this, a low albedo created by asphalt, concrete, dense construction/building.

How high and strong the resulting thermal convection will be depends on the weather, atmospheric layering, solar irradiation, wind, cloud cover, temperature and moisture. The ability of the ground to store heat (e.g. street canyons, or heat strored in the air of a high grown cornfield) also influences the triggering of convection. In some cases a rising thermal is visualized by a dust devil. 

Thermal convection can be calculated/estimated and predicted from atmospheric soundings, instrumented weather balloons to measure the state of the atmopshere from ground to tropopause. The results are visualized in Skew-T or Stüve diagrams.

Reading and interpreting them is an art. But they can tell when the trigger temperature for thermals will be reached, how high they go, if there will be clouds and at which level their base is, etc.

Side effects of this are called urban heat islands or generally heat islands due to low albedo ground. They can cause local low pressure due to the rising air over the hotter ground, which can result in showers or even thunderstorms in the evening/afternoon.

Quite obviously, these effects can also be triggered by naturally occurring differences in ground albedo and plant cover. They are a driving force for local weather phenomena.