Lord Krishna ascended to His Divine abode at the end of dwapara yuga and immediately kali yuga started. Just after he left the earth planet, a catastrophic rain, storm and sea deluge, that lasted for seven days, totally drowned and destroyed the town of Dwarika ( His Royal Kingdom). This catastrophe was also recorded in Babylonia’s ancient town known as "Ur" (which was mythologized in the West as Noah’s flood) and in the ancient Mayan records. Both dates are identical.