Abstract:  Climate change has become an indisputable fact. According to the fifth report of the Intergovernmental Panel on Climate Change (IPCC), the global average temperature has increased by 0.85 ℃ in the past 100 years. Warming as the main feature of climate change has had a series of important impacts on cropping system and quality layout. Its concrete performance is as follows: crop planting boundaries moved to north and expanded to high altitude, crop variety layout and crop planting structure changed obviously, and multi-cropping indices increased significantly. Relevant researches revealed that annual and seasonal average temperature showed a roughly upward trend in paddy region of Guangxi. In addition, growth period and agricultural climate resources allocation pattern changed obviously in these areas. Layout of double cropping rice is sensitive to the change of agricultural resources. However, the impacts of climate change on the planting layout of double cropping rice in Guangxi was seldom discussed. In order to reveal the change characteristics of layout of double cropping rice under the background of climate change, meteorological data from Guangxi Meteorological Bureau and geographic data from National Geomatics Center of China were utilized in the study. Four climatic factors were selected as the key factors which affected the layout of rice planting .They were safe days of growth period of double cropping rice, active integrated temperature (≥10℃) during safe growth period, total sunshine hours during the period of daily average temperature above 10℃ in a year and annual average temperature respectively. In this paper they were abbreviated to D, AT, SH and T. Based on the daily temperature and sunshine hours of 91 meteorological stations in Guangxi from 1960 to 2019, changing trend of four key climatic factors were analyzed. The study period was divided into two phases, namely first 30 years (P1:1960-1989) and last 30 years (P2:1990-2019). The equal weight principle was used to evaluate and score each key climatic factor in the two phases. According to the total scores of four key climatic factors, double cropping rice planting zones were divided into four climatic suitable regions in Guangxi, namely regions of single cropping and ratooning rice (S+R), regions of early and medium maturing double cropping rice (E+M), regions of medium and late maturing double cropping rice (M+L) and regions of late maturing double cropping rice (L+L). Different combination patterns of double cropping rice mentioned above were determined by their demands for agricultural climatic resources. Generally speaking, demand of single cropping and ratooning rice for heat resources was small. It mainly distributed in the high altitude areas of north and west of Guangxi, while the late maturing double cropping rice distributed in south areas involved Youjiang river valley of Guangxi because of the great demand for heat resources and longer safe growth season. Early and middle maturing double cropping rice and middle and late maturing double cropping rice mainly distributed in the central areas of Guangxi. Their demands for agricultural climatic resources were between S+R and L+L. In the end, the spatial distribution characteristics and changing rules of different combination patterns of double cropping rice were analyzed in two phases. The results revealed that safe days of growth period of double cropping rice increased significantly in the north and west of Guangxi. Active integrated temperature(≥10℃) and annual average temperature increased significantly, while the total sunshine hours during the period of daily average temperature above 10℃ in a year decreased significantly in most study areas. The heat resources increased towards to the north and high altitude, while sunshine hours decreased from the north to the south. Comparing with the first 30 years (P1:1960-1989), climatic suitable areas of single cropping and ratooning rice and medium and late maturing double cropping rice increased by 2.1 and 4.2 percent point, while those of early and middle maturing double cropping rice and late maturing double cropping rice decreased by 3.6 and 2.7 percent point in the last 30 years (P2:1990-2019). The significantly changing areas mainly distributed in Yangshuo and Lipu regions of Guilin, the surrounding regions of Hezhou, Mashan and Longan regions of Nanning. The purpose of this research is to provide a scientific reference to make full use of the sunlight and heat resources under background of climate change and to optimize planting layout of double cropping rice in Guangxi.

Key words:  Climate change, Rice, Planting regionalization, Guangxi