| 1. The climate change in Sichuan showed its unique characteristics due to its special geographic position and topography, though the general change was consistent with the global and national changes. The annual mean temperature, annual mean maximum air temperature, annual mean minimum air temperature and high temperature days increased during1961-2007. There was a warming trend in all seasons, and the temperature in winter and autumn increased more significantly than spring and summer. The increase of temperature was the greatest in Northwest Sichuan Plateau and relatively smaller in Sichuan basin. The annual precipitation declined continuously at a rate of20mm every ten years averagely, caused by the decreasing rainfall in summer and autumn, though the precipitation in spring did not change much and there was more rainfall in winter. The comparison of the precipitation between regions showed a great decrease of precipitation in Sichuan basin, and an increase in Northwest Sichuan Plateau and the mountainous area of Southwest Sichuan.2. The water resources were decreased due to the declined total precipitation. The extreme events, like rainstorm and continuous rainless days, became more common, and the occurrence of moderate and heavy rain was less frequent in the past over forty years. These caused the low water use efficiency, aggravated water and soil loss, and the poor soil fertility. The seasonal agricultural drought was more serious than in the past. The warming trend led to higher field evapotranspiration, less snow cover at plateau and mountain tops, low water levels and the lack of irrigation water. Water deficit became more severe; therefore, drought will become a serious threat to agricultural production.3. In this study, daily precipitation, air temperature, sunshine hours, relative humidity, wind speed and water vapor pressure, from1959to2008were collected from149meteorological stations in Sichuan province and used to calculate the relative moisture index (M). The author analyzed the spatial distribution of drought frequency and intensity in Sichuan at annual and seasonal time scale, and addressed the annual variation of drought intensity and distribution in the recent50years. The results showed that, drought frequency at annual time scale was high in the west, and low in the east, exhibiting pronounced zonation patterns in Southwest China. The areas with high incidence of drought mainly located at the western Sichuan plateau, the mountainous area in Southwestern Sichuan, the middle basin, and parts of the southern basin. In these areas, drought intensity was mainly moderate or severe. The areas with low incidence of drought included Dazhou, Luzhou, Yibin, Leshan, Meishan and Yaan, and it was mainly mild drought in these areas. Over the past50years, drought was less severe, apart from the recent10years. The variation of drought frequency was significant between seasons. Drought happened most frequently in winter, followed by spring, autumn and summer. Winter drought was the most severe among the four seasons, followed by spring drought, autumn drought and summer drought. Spring and winter drought was less severe but the region was widened. Summer drought was more serious both in density and spatial distribution. Autumn drought showed similar trend to spring drought, and it was more severe in the recent10years. A few samples were taken to test the drought classification method used in this study, and the results showed that the method was suitable in Sichuan province.4. A drought monitoring model for corn was developed based on water budget. The results showed that the maize drought occurred in high frequency between jointing stage and milk ripe stage, and it happened most widely in this period. Sichuan basin was divided into three arid areas, and the south of Daba mountains, Fu river and Tuo river basin had the highest drought frequency, generally over50%, through the whole growth season of corn.5. The ago-ecological areas in Sichuan were divided into eight ago-ecological zones according to temperature, altitude, dryness, topography and geographic characteristics. For each agro-ecological zone, analysis were done to compare the precipitation satisfied degree, precipitation satisfied degree guarantee index, yield reduction rate related to precipitation requirements, risk index of yield reduction rate, rainfall use efficiency and economic efficiency of precipitation at the typical station for the common cropping patterns. The results showed that,(1) the precipitation satisfied degree and precipitation satisfied degree guarantee index varied greatly among regions, and they were lowest in Panzhihua, and highest in Yaan.(2) The averaged yield reduction rates related to precipitation requirements varied with regions, cropping patterns, crop species and crop growth stages, significantly. It was lowest in Yaan,23%, and highest in Panxi, over50%. And it was around30-40%in other regions. For different cropping patterns, the yield reduction rates of dry triple cropping pattern with wheat-maize-Chinese trumpet creeper were lower than that of the rotation pattern with wheat-rice. The reduction rates of winter wheat, winter rape and autumn sowing potato were generally higher than that of rice, maize, cotton, sweet potato and soybean. It was higher before and after flowering for winter wheat, winter rape and autumn sowing potato, but was lower at the late growth stage for each crop.(3) Based on the natural precipitation, Panzhihua, Xichang, Pingwu, Suining and Bazhong encountered the highest risk of drought, but the risk index of yield reduction rate for the dry triple cropping pattern with wheat-maize-Chinese trumpet creeper was relatively lower. Due to excessive precipitation in Yaan, the waterloddging was more severe; therefore, the rotation pattern with wheat-rice was slightly superior to the dry triple cropping pattern with wheat-maize-Chinese trumpet creeper.(4) It showed a consistent rule in the comparison of rainfall use efficiency and economic efficiency of precipitation at all stations. The double cropping pattern with wheat (rape or potato)-rice was the most suitable in these regions, followed by the dry triple cropping pattern with wheat (rape)-maize-Chinese trumpet creeper (soybean).(5) Considering the risk of drought and flood, rainfall use efficiency, economic efficiency of precipitation and topography factors, the double cropping rotation pattern with wheat (rape or potato)-rice was advised in well-irrigated croplands, while dry triple cropping pattern with wheat (rape)-maize-Chinese trumpet creeper (soybean) was recommended for the dry lands with poor irrigation.6. Based on the information of maize yield, phonological period, related weather data, and the requirements of drought risk transfer technical service, such as agricultural insurance premium rate, four models (those of climatic drought risk, crop drought risk, yield loss risk, and drought resistant capability) applicable for the assessment of maize drought risk in Sichuan Basin and the corresponding index systems were established. The Sichuan Basin was divided into three regions, with high, medium and low maize drought risk, respectively. The region with high risk was mainly in the most areas of northwest basin, the middle basin, and parts of the south basin of Sichuan, the region with medium risk was in the north basin and some parts of the south basin, and the region with low risk was in the northeast and southwest basin, and parts of the southeast basin. |
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