Pakistan is predominantly arid, with low rainfall and humidity and high solar radiation over much of the country. Most of its regions receive less than 200 millimetres of rain per year except the northern mountains which receive more than 500 millimetres annually. The rainfall distribution varies widely; in the Sindh and Punjab provinces, 60 per cent of rainfall occurs during the monsoon season, commencing in late June to early September, while over Baluchistan and the northern mountains most rain falls between October to March (FAO, 1987).