'Indian El Niño' behind east Africa flooding

Irregularity known as Indian Ocean dipole bringing weather extremes across region

Twenty years ago in 1999 a new weather pattern was described for the first time. Now it has shifted up a gear and is causing devastation across east Africa.

The Indian Ocean dipole, sometimes called the Indian El Nino, is an irregular oscillation in which the surface temperature of the sea is alternatively greater in the ocean's west and its east. The positive phase, when it is warmer in the west, sees more rain in the west and greater chance of drought in the east. These are reversed in a negative phase.