Crop Evapotranspiration Study On Evolution Rule And Forecast Model In Chaoyang Area

Crop water requirement is the fundamental basis of water resources development and irrigation project planning, design, management. By reference crop evapotranspiration to estimate crop water requirements is an important method recommended by FAO. Therefore, accurate prediction of reference crop evapotranspiration, to improve the efficiency of agricultural water in the region, determine a reasonable scale irrigation, to develop scientific irrigation system and to achieve sustainable agricultural development and sustainable use of water resources are very important significance.Using monthly meteorologic data of seven weather stations (Chaoyang station, Yebaishou station, Jianping station, Beipiao station, Yangshan station, Lingyuan station, Kazuo station) in Chaoyang area during 1967 and 2006, the following contents are studied in this thesis:The use of climate trend rate, the cumulative anomaly and statistical methods, inter-annual variation and monthly variations of meteorological elements were analyzed in Chaoyang region. The results show that the highest, lowest, average temperature of seven stations showed a significant upward trend over the past 40 years, Sunshine, wind speed, relative humidity and evaporation showed a significant downward trend; in annual rainfall did not change significantly. From the point of the season, process of change is consistent with the annual change.Daily reference crop evapotranspiration in Chaoyang area during 1967 and 2006 was calculated by the penman-montieth formula, and its annual variation and monthly variation were analyzed, the results show that ETo was significantly declined trend over the past 40 years. From the point of the season, most of the stations showed a significant downward trend, only individual sites did not change significantly. Monthly analysis shows that the trend during the year of ETo is a single peak in Chaoyang area. The maximum value of ETo occurs in May, the minimum value occurs in January, various stands change situation has the uniformity. ETo presents the tendency which in the space elevates gradually from west to east.The main meteorological factors affected ETo by the correlation analysis and statistical tests.The results show that sunshine, wind speed, evaporation and relative humidity are the main meteorological factors of ETo long-term trend of changes in Chaoyang area. From the point of the season, wind speed and evaporation for spring, autumn ETo major effect factor, temperature, wind speed for summer ETo major effect factor, wind speed for winter ETo major effect factor. Has established Genetic algorithm-based projection pursuit regression model (RAGA-PPR), Projection Pursuit based on PartialLeast-Squares Regression model (PLSPP) and Stationary Time Series-Projection Pursuit Combined model (STS-PPR) using monthly ETo datas over the past 40 years. Application results show:three prediction models of ETo reached higher prediction accuracy. RAGA-PPR forecasting model prediction accuracy is the highest, However, the predictors of the need to need to extract the correlation coefficient is relatively large, and require more years of data the prediction accuracy will be higher; PLSPP model in the sample point are few and the variable are many of conditions can also be modeled, the model is simple, the stability is good, the serviceability is stronger, and the traditional projection pursuit regression model compared to higher accuracy; STS-PPR model in meteorological factor flaw situation, Apply the steady time series forecast model to predict the relevant meteorological factors of ETo, then RAGA-PPR forecasting model to predict reference crop evapotranspiration, ETo of forecast obtained the high precision. Thus causes projection pursuit regression model to obtain a more widespread application.