Abstract: Temperature and humidity are the most important meteorological elements affecting the epidemics of wheat powdery mildew. Based on the wheat powdery mildew epidemics data in the main wheat production areas in Hebei Province in 1987-2010 and the related meteorological data, and by the methods of composite analysis and rank correlation analysis, the key meteorological factors affecting the wheat powdery mildew epidemics were set up. According to the rule of thumb, the epidemic degree of the powdery mildew was distinguished by the anomaly of temperature and the anomaly of humidity climate at different epidemic stages of the powdery mildew, and the year types and controlling factors of the powdery mildew epidemics were determined. From the validation of historical data, the general accordance ratio was 84%. By using the extrapolated controlling factors values of the powdery mildew epidemics in 2011 and 2012, the forecast accuracy was 100%. When integrated with the climate year types, the forecast accuracy was above 85%. Our results could provide scientific references for the assessment and long-term forecast of wheat powdery mildew epidemics.

Key words: remote sensing, ecological environment quality, principal component analysis, vegetation fraction, hilly and gully region.