Israel has ordered its military to fortify critical military installations against missile and rocket attack. This would mean a lot more underground (or partially so) storage facilities. Last year the military was ordered to disperse its stocks of supplies, equipment and spare parts to a larger number of (better protected) locations. Apparently, it was later determined that putting more stuff in bunkers was also necessary. This fortification program will begin next year.
All this is old news for Israeli civilians. Fourteen years ago, Israel decided to upgrade its civil defense arrangements. As part of that effort, they passed a law mandating that new houses have at least one "bomb proof" safe room, to be used as a shelter during rocket attacks. But most builders have ignored the law. It's expensive. To add such a room to existing houses costs about $25,000 per home. But many Israelis have designated one room in the house as the "safe room", and perhaps reinforced it a bit, and stored emergency supplies there. But the danger is growing, and for the last five years Israel has accelerated the upgrading of defenses against rocket and missile attack.
In addition to rockets fired by Hamas and Hezbollah, there is also concern that Syria would fire larger, and longer range, rockets armed with explosive or chemical warheads. Hamas has several thousand, mostly short (under 20 kilometers range) rockets stockpiled, while Hezbollah up in Lebanon is believed to have 40,000 rockets stored and ready to fire near the Israeli border. But Hamas, Hezbollah and Syria also have over a 1,500 larger rockets that can reach anywhere in Israel.
Syria has underground storage and launch facilities for its arsenal of over a thousand SCUD missiles. Armed with half ton high explosive or cluster bomb warheads, the missiles have ranges of 500-700 kilometers. Syria also has some 90 older Russian Frog-7 missiles (70 kilometer range, half ton warhead) and 210 more modern Russian SS-21 missiles (120 kilometer range, half ton warhead) operating with mobile launchers. There are also 60 mobile SCUD launchers. The Syrians have a large network of camouflaged launching sites for the mobile launchers. Iran and North Korea have helped Syria build underground SCUD manufacturing and maintenance facilities. The Syrian missiles are meant to hit Israeli airfields, missile launching sites and nuclear weapons sites, as well as population centers. Syria hopes to do enough damage with a missile strike to cripple Israeli combat capability.
Currently, the Israelis estimate that there would be as many as 3,300 Israeli casualties (including up to 200 dead) if Syria tried to use its long range missiles and explosive warheads against Israel. If the Syrians used chemical warheads, Israeli casualties could be as high as 16,000. Over 200,000 Israelis would be left homeless, and it's believed about a 100,000 would seek to leave the country.