Systems and modular devices for roof or ground-level stormwater management are disclosed. A modular stormwater management device includes a water retention mat structured to absorb stormwater, a rigid frame structured to support the water retention mat, and a perforated surface structured to permit drainage of the stormwater from the water retention mat through the perforated surface. A modular stormwater management system includes a plurality of modular stormwater management devices, each of the modular stormwater management devices including a water retention mat structured to absorb stormwater, a rigid frame structured to support the water retention mat, and a perforated surface structured to permit drainage of the stormwater from the water retention mat through the perforated surface.