Yemen is not currently a failed state, but it is experiencing huge political and economic problems that can have a direct impact on U.S. interests in the region. It has a rapidly expanding population with a resource base that is limited and already leaves much of the current population in poverty. The government obtains around a third of its budget revenue from sales of its limited and declining oil stocks, which most economists state will be exhausted by 2017. Yemen has critical water shortages aggravated by the use of extensive amounts of water and agricultural land for production of the shrub qat, which is chewed for stimulant and other effects but has no nutritional value. All of these problems are especially difficult to address because the central government has only limited capacity to extend its influence into tribal areas beyond the capital and major cities. Adding to these difficulties, Yemen is also facing a variety of interrelated national security problems that have strained the limited resources of the government, military, and security forces. In Sa'ada province in Yemen's northern mountainous region, there has been an intermittent rebellion by Houthi tribesmen who accuse the government of discrimination and other actions against their Zaydi Shi'ite religious sect. In southern Yemen, a powerful independence movement has developed which is mostly nonviolent but is also deeply angry and increasingly confrontational.