A major cause of the growing violence in Yemen is a worsening water shortage. This is largely due to a growing population and more land being used to grow the narcotic plant Khat (which now accounts for about 37 percent of water used). About 90 percent of the water use is for agriculture, which is still the mainstay of the economy. There is big money in Khat, mainly because most of it is smuggled into Saudi Arabia. Khat, along with recreational drugs and alcohol, is illegal in Saudi Arabia and the border patrol has become more effective. As a result, smuggling activity has decreased over fifty percent.
While hard drugs and booze can be brought in via other routes (Iraq being a favorite), the narcotic leaf Khat, cannot. Khat is grown in Yemen, and delivered quickly to Saudi customers each day. Khat must be relatively fresh, or else it loses its effect. So other forms of smuggling will not be very effective, because they take too much time. Khat gives you more of a buzz than caffeine or nicotine, but less than stronger drugs. It is addictive.
Khat has created another problem, the importation of powerful, and often forbidden, insecticides, to facilitate the growing of more Khat. Since the Khat leaves are chewed, using too much, or too poisonous (to humans) insecticide makes the users sick. Many Khat growers are more concerned with producing more Khat, than they are in injuring their customers. So the Yemeni government is struggling to keep illegal insecticides out of the country, if only to prevent Yemeni Khat users from getting sick. Just as Colombia and Afghanistan were thrown into chaos by major drug gangs (producing cocaine and heroin, respectively) Yemen is being brought low by Khat.