Emergy-based study on eco-economic system of arid and semi-arid region: a case of Gansu province, China

: Taking Gansu province as a model case, this study provides an integrated analysis on the eco-economic system of arid and semi-arid region based on emergy synthesis theory. Through calculating the values of renewable emergy flow, non-renewable resources, imported emergy, exported emergy, waste emergy, and total emergy during the period of 1978-2007, the performance of Gansu eco-economic system was analyzed. The results indicated that the renewable emergy flow within the province basically remained steady state which was estimated at 2.99x10(22) solar emjoules (sej) from 1978 to 2007. The imported emergy and exported emergy were estimated at 3.75x10(17) sej and 2.99x10(20) sej in 1978 and increased to 1.07x10(22) sej and 1.44x10(22) sej respectively in 2007. The nonrenewable emergy flow was estimated at 1.62x10(22) sej and increased to 1.85x10(23) sej, with annual growth rate of 8.7%, while the estimated total emergy was 4.58x10(22) sej in 1978 and increased to 2.11x10(23) sej in 2007, with annual growth rate of 5.41%. Our results indicate a deteriorate situation between economic development and environmental protection in the region. The rapid economic growth in the past thirty years was based on a great consumption of nonrenewable resource and caused continuous decrease in the capacity of sustainable development. The environmental loading ratio was 0.53 in 1978, increased to 6.06 in 2007, indicating a rapid degradation of the regional environment quality. We calculated that the actual population was 1.53 times the renewable resource population in 1978, increased to 7.06 times in 2007. During the period of 1978-2007, the emergy rose from 2.45x10(15) sej/(capita.a) to 8.07x10(15) sej/(capita.a). Our analysis revealed that the emergy density presented a trend of gradual increase, and then the emergy currency ratio in Gansu decreased from 7.08x10(13) sej/Chinese Yuan to 7.82x10(12) sej/Chinese Yuan.