Urban sprawl can inhibit convection and decrease rainfall over an Amazonian city during a squall line type phenomenon

Abstract

Numerical sensitivity experiments were carried out to evaluate the impact of urban sprawl in Manaus on a squall line (SL) event. Four scenarios were considered: non-urban, current urban area, three times and six times the current urban area. It was seen the urban growth produces an immediate change in the latent heat flux due to the replacement of forest cover by urban cover and increases temperatures on a local and regional scale. Firstly, temperature and sensible heat flux were enhanced over and to the west of the city due to urban cover presence's itself. Moreover, far from the city, the field temperature pattern was also modified. Over the city, thermic anomaly is transported to upper levels of the lower atmosphere, which reduces the thermal gradient between the layers and creates an environment that weakens the convection. Also, thermic anomaly is advected to the west of the city, which contributes to the weakening of the thermal gradient through the western city's border, as well as the convective intensification over inhomogeneous surface. Together, these effects are responsible for inhibits the approach and the maintenance of the SL, as well as for a reduction in cloud cover and in accumulated rainfall.