on heavy fuel oil for power generation, and these were supplied by KEDO (the Korean Peninsula Energy Development Organization). About 70% of power generated in the DPRK came from hydropower sources, and the serious winter-spring droughts of 1996 and 1997 (and a breakdown on one of the Yalu River's large hydro turbines) created major shortages throughout the country at that time, severely cutting back railway transportation (which was almost entirely dependent on electric power), which in turn resulted in coal supply shortages to the coal-fueled power stations which supplied the remaining 20% of power in the country. A 2008 study, however, found no variation in children's nutrition between counties that had experienced flooding and those that had not. Failure of the public distribution system North Korea's vulnerability to the floods and famine was exacerbated by the failure of the public distribution system. The regime refused to pursue policies that would have allowed food imports and distribution without discrimination to all regions of the country. During the famine, the urban working class of the cities and towns of the eastern provinces of the country was hit particularly hard. The distribution of food reflected basic principles of stratification of the communist system. Food was distributed to people according to their political standing and their degree of loyalty to the state. The structure is as follows (the World Food Program considers 600 grams of cereal per day to be less than a "survival ration"): However, the extended period of food shortages put a strain on the system, and it spread the amount of available food allocations thinly across the groups, affecting 62% of the population who were entirely reliant on public distribution. The system was feeding only 6% of the population by 1997. Long-term causes The famine was also a result of the culmination of a long series of government decisions that accrued slowly over decades. The attempt to follow a closed-economic model caused the regime to abandon the possibility of engaging in international markets and importing food and instead restrict demand such as carrying out a "Let's eat two meals a day" campaign in 1991. Attempts to increase exports and earn foreign exchange through the Rajin Sonbong free trade zone in 1991 were unsuccessful – it was located in the most isolated part of North Korea and lacked a clear legal foundation for international business. The North Korean government also missed the