| Global warming, characterized by climate change, has significant impact on social-economy and agroecology, and has brought broad attention to researchers. Climate change, especially extreme weather and climate events, has negative impact on agriculture and it has also restricted the sustainable Socio-economic development. Rice is one of the three major crops in China. The impact of climate change on rice yields directly affects the food security in China. In this study, climate data from 1961 to 2014 and the rice yield data from 1981 to 2012 in Sichuan were collected. The methods used includes regression analysis and wavelet analysis. Combining the mathematical /statistical method with the spatial interpolation method, the spatial distribution of agricultural climate resources during the growing season of rice in Sichuan province were analyzed. The responses of rice yield to climate change during different growth stages were also discussed. The spatial distribution of heat damages, drought in different rice growth stages and the assessment of rice yield loss risk were discussed. The main conclusions are as follows:(1) From 1961 to 2014, the heat resources during rice growing season in Sichuan province showed a significant increasing trend. The annual average temperature, annual maximum and minimum temperature was higher in the north and lower in the south during the whole growing period and at different growth stages, respectively. The diurnal temperature range (DTR) was higher in the north and south and lower in the central areas. The solar radiation was higher in the south and lower in the north; it also showed a decrease at different growth stages, which was consistent with the whole growing period. The precipitation and effective precipitation at whole growing stage declined. The annual reference crop evapotranspiration (ETo) and water requirement showed a decreasing trend, while the water deficit slightly increased.(2) From 1981 to 2012, the impact of change in temperature, precipitation and solar radiation on rice yield in Sichuan province showed spatial variation. With 1 ℃ increase in growing-season air temperature,1℃ increase in diurnal temperature range,100 mm decrease in precipitation and a 100 MJ·m-2 decrease in radiation, the rice yields in certain areas showed significant difference. From transplanting to maturity stages, the effect of rising average temperature contributed the most to the rice yield, followed by decreasing radiation and declining precipitation. Rising average temperature affected 7.05% of the whole planting area, and the corresponding yield change was from -6.82% to 5.74%. Regarding on rice yield,6.95% of the whole planting area had negative response to rising average temperature. With respect to different growth stages, both the overall and the negative effects of rising DTR on rice yield were largest from transplant to booting stages, which accounted for 10.83% and 10.52% of the whole area, respectively. The combined effects of the four climatic variables caused significant change on rice yield, affecting roughly 47.6% of the whole planting area, with the yield change from -11.77 to 24.55%; meanwhile, roughly 20.3% of the whole planting area showed yield decrease, which was mainly located in the south and west and middle of the Sichuan Basin. Average temperature was the major factor affecting the rice yield; while solar radiation was the major factor contributing to the rice yield decrease.(3) For the heading-flowering stage, the number of stations with total heat damage, mild and medium heat damage increased significantly during the period of 1961 to 2014. For the grain-filling period, the number of stations with heat damage, medium heat damage and severe heat damage increased; while the number of stations with mild heat damage decreased. The frequency of different grades heat damage at the heading-flowering and grain-filling stages showed significant periodicity. For the heading-flowering stage, the frequency of both the mild and medium heat damage was higher in the northeast and lower in the southwest. For the grain-filling period, the frequency of all the mild, medium and severe heat damage was higher in the east and lower in the west and the south of the study region.(4) From 1961 to 2014, the number of stations with total drought, severe and extremely severe drought from booting to heading periods all increased; while the number of mild and medium drought slightly decreased. The number of stations with total drought and mild drought from heading to maturity periods decreased; while the number of medium and severe drought increased. The frequency of different grades drought from booting to heading and from heading to maturity periods showed significant periodicity. The frequency of drought from booting to heading periods was higher in the north and lower in the south. The frequency of total drought, mild and medium drought from heading to maturity periods was all higher in the east and lower in the west of the Sichuan Basin, and that was all higher in the north and lower in the south of the Southwest Sichuan. The drought risk from booting to heading period was higher in the north and lower in the south of the Sichuan Basin, and that was higher in the north and east, and lower in the south of the Southwest Sichuan. The drought risk from heading to mature period was higher in the northeast and lower in the south and west of the Sichuan Basin, and higher in the north and lower in the south of the Southwest Sichuan.(5) From 1961 to 2014, the area with relatively high average yield reduction rate during the year of low harvest was mainly distributed in Mianyang City, Cangxi County in Guangyuan City and Meigu County in Liangshan. The risk probability with the yield reduction rate more than 5% was low in north and south region, and high in middle region. The area with relatively high integrated risk index was mainly distributed in Guangyuan, Luzhou and Yibin, while the area with low integrated risk index was scattered. |
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