Exposure Index for Maize yield vulnerability Modelling for Nigeria

Exposure capture factors which could be manifested in the magnitude and intensity of long-term changes in climate (Intergovernmental Panel on Climate Change, 2007) and in this context factors with impact on agricultural production. Temperature and rainfall were used to capture the extent to which Maize is exposed to climate change. Data was sourced from the Centre for Environmental Data Analysis (CRU TS release 4), with data extracted for 1941 - 2015. The data were processed within R (Version 3.4.2), within this environment the mean (temperature and rainfall) for northern and southern parts of the country were computed. The growing season for Maize in the north spans from May to September while in the south it starts from March and ends in August (FAO, 2018). Furthermore, long (1941 – 2015) and short (1961 – 2015) term averages for the respective growing season were computed for each of the regions. Following the computation of the long and short-term averages, exposure was computed as the ratio of the long-term to the short-term averages. With exposure index for rainfall and temperature computed separately, the two were added to get the combined exposure index. A high value indicates high exposure to climate variability. In this dataset, the exposure index is presented in raster format (Geotiff) to allow for easy processing across GIS software. In addition, the boundaries of the northern and the southern regions were also included as shapefiles.本数据集所涉及的暴露捕获因子，可体现在气候变化长期变化的幅度与强度（政府间气候变化专门委员会，Intergovernmental Panel on Climate Change，2007），以及此语境下对农业生产产生影响的各类因子范畴内。本研究选取气温与降水量，用以表征玉米受气候变化影响的暴露程度。数据源自环境数据分析中心（Centre for Environmental Data Analysis）发布的CRU TS 第4版数据集，提取时段为1941年至2015年。数据处理采用R语言（Version 3.4.2）完成，在此环境中分别计算了该国南北区域的气温与降水量均值。该国北部玉米生长期为5月至9月，南部则为3月至8月（粮食及农业组织，Food and Agriculture Organization of the United Nations, FAO，2018）。此外，针对两个区域分别计算了对应生长期的长期（1941-2015年）与短期（1961-2015年）气候均值。在得到长期与短期气候均值后，以长期均值与短期均值的比值计算得到暴露指数（exposure index）。分别计算降水量与气温对应的暴露指数后，将二者相加得到综合暴露指数。指数值越高，代表受气候变率影响的暴露程度越高。 本数据集将综合暴露指数以栅格格式（Geotiff）存储，以便在各类地理信息系统（Geographic Information System, GIS）软件中便捷处理。此外，数据集还附带了南北区域的边界shapefiles文件。