| Global climate warming is an irrefragable fact. It has resulted in many environmental problems, which consequently have caused various direct and indirect impacts on human health. Among the impacts of climate warming, effect on the outbreak and spread of infectious diseases is one of the severest. Therefore, it is necessary to quicken up the research work in this field, which is undoubtedly very important to prevent and control the diseases, to improve healthy level, and to accelerate the development of human society. In this thesis, Gansu province is chosen as the study area which has complex landforms and multiple climate types. For the first time, we mainly analyze the characteristics of climate change in recent 30 years and the spatial-temporal distribution of infections in recent 20 years, and study the influences of weather situations and climate change on the incidences of infections after systematically collecting and ordering the data of 6 kinds of main infections (bacillary dysentery, Hepatitis A, epidemic encephalitis, epidemic hemorrhagic fever, measles, epidemic cerebrospinal meningitis) from 88 counties of whole Gansu Province during 1951 to 2005. Then, by using the GIS method, the influences of urbanization on the incidences of infections are discussed. At last, forecasting models for the main infections are set up by using the methods of statistics and artificial neural network (ANN). We get some new results, which are summed up as follows:(1) In recent 30 years, the average temperature in Gansu province has been increasing. It rises about 1.10℃and the rising rate is from 0.2℃/10a to 0.8℃/10a. Climate warming in Gansu province is more evident in winter and summer than in other seasons. In Gansu region, the average temperature and the lowest temperature in the Longnan Humid Area rise the fastest with 0.545℃/10a and 0.560℃/10a respectively. Precipitation in Gansu province takes on a declining trend and has great seasonal difference. Precipitation in the flood season of summer decreases the most obviously. It has been keeping decrease since 1970s, which is the main reason of resulting in the decrease of annual precipitation. It can be seen that climate of Gansu province is warming and drying.(2) Bacillary dysentery, Hepatitis A and measles occur in the whole Gansu province, while epidemic encephalitis, epidemic hemorrhagic fever and epidemic cerebrospinal meningitis are parochial infections. The incidences of infections have great differences in different areas. The highest incidence of bacillary dysentery is in Akesai County with 569.62 per 100,000. The highest incidence of Hepatitis A is 198.9 per 100,000 located in Zhouqu County of Gannan Tibetan Autonomous Prefecture. The highest incidence of measles is in Jiayuguan city with 121.94 per 100,000. Among the 18 Counties where epidemic encephalitis occurs, the highest incidence is in Chengxian County with 2.108 per 100,000. Among the 15 Counties where cases of epidemic hemorrhagic fever are found, the highest incidence of is in Hezuo County of Gannan Tibetan Autonomous Prefecture and the value is 9.021 per 100,000. Of the 22 Counties where epidemic cerebrospinal meningitis appears, the highest incidence is in Xiahe County of Gannan Tibetan Autonomous Prefecture with 6.321 per 100,000.(3) The infections mentioned above have evident seasonal climax. Among them, bacillary dysentery and epidemic encephalitis mainly occur from July to September. Hepatitis A is mainly in August, September and October. Epidemic hemorrhagic fever mainly happens from October to December and in February. Measles is mainly from March to May. Epidemic cerebrospinal meningitis mainly occurs from February to April. There are good correlations at lag=0 and lag=l between the monthly cases of infections and monthly average values of meteorological elements. Among them, significant positive correlations are found between bacillary dysentery, epidemic encephalitis and monthly average temperature, the monthly average highest temperature, the monthly average lowest temperature and monthly precipitation, but negative correlation between the two diseases and air pressure. While, significant negative correlations are found between Hepatitis A, epidemic cerebrospinal meningitis and monthly average temperature, the monthly average highest temperature, the monthly average lowest temperature monthly average humidity and monthly precipitation, but positive correlation between the two diseases and air pressure. The correlations between measles and the meteorological elements are not significant as other infections, but there is a good positive correlation between measles and wind speed. The above results show that meteorological elements play a very important role in the occurrence and spread of infections.(4) The urbanization causes great population density, which can influence the spread processes of some infections. For example, the incidence of measles increases with the level of urbanization in the cities, while decreases in the suburbs. The incidences of bacillary dysentery and Hepatitis A decrease in both cities and suburbs with the level of urbanization. On the one hand, this relates to the spreading way of infections themselves, on the other hand, it reflects some adverse influences of urbanization on diseases prevention and control when urbanization promotes economic development and improves the standard of living.(5) The multiple linear models, multiple non-linear models and artificial neural network models (ANN) for forecasting bacillary dysentery and measles are set up for different climatic regions. Relatively, the tested effects of non-linear models are better than that of the linear models, while that of ANN models are much better than the non-linear models. This indicates that it is absolutely feasible to forecast the incidences of diseases by using the method of artificial neural network.
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