At the moment, population and income growth are the big drivers, with random weather shocks causing more problems today than they would have in the past. (dotearth.blogs.nytimes.com)
I rounded up a few pretty pieces, all of which are on sale, to get through the next two months of random weather patterns. (modernensemble.com)
Add to that the variety of the different continents with random weather events that can impact your stats, such as the heavy rain in Primordia or the sandstorms in Oblivia. (mygameslounge.com)