There are some ephemeral streams on the Iranian coast south of Bushehr, but virtually no fresh water flows into the gulf on its south-west side. Large quantities of fine dust are, however, blown into the sea by predominant north-west winds from the desert areas of the surrounding lands. The Persian Gulf has a notoriously bad climate. Temperatures are high, though winters may be quite cool at the north-western extremities. The sparse rainfall occurs mainly as sharp down pours between November and April and is heavier in the north-east.
Humidity is high.
The little cloud cover is more prevalent in winter than in summer. Thunderstorms and fog are rare, but dust storms and haze occur frequently in summer. Until the discovery of oil in Iran in 1908, the Persian Gulf area was important mainly for fishing, pearling, the building of dhows , sailcloth making, camel breeding, reed mat making, date cultivating, and the production of other minor products, such as red ochre from the islands in the south. Today these traditional industries have declined, and the economy of the region is dominated by the production of oil. The Persian Gulf and the surrounding countries produce approximately 31 per cent of the world's total oil production and have 63 per cent of the world's proven reserves.