Experts attribute this to decades of unplanned development spurred by the IT boom of the 1990s. "We've over-concretised Bengaluru, leaving no space for water to percolate," said civic activist V Ravichandar. “Low-lying areas are built upon, and roads are sometimes lower than drains..Our drainage was designed for 75 mm rainfall/hour, but...we see 120–130 mm/hour, overwhelming the system," he added.