Spatio-temporal characteristics of drought at different maize growth stages in Sichuan Province as determined by water budget index

Maize, as a major grain crop in Sichuan, has contributed significantly to total grain production in the province. Sichuan Province has a complex topography and various landforms where droughts have posed serious threat to crop production. Drought is therefore a critical factor that has limited the development, growth and yield formation of maize in Sichuan. It has frequently occurred with an increasing severity in the spring and summer, and has caused the unstable yearly maize production. This paper analyzed spatio-temporal distribution of drought at different maize growth stages in order to lay the scientific basis for relevant departmental development of agricultural production programs and disaster prevention and mitigation strategies which would guide insurance agencies in formulating agricultural insurance premium rates. Daily meteorological data, collected from 144 stations in main corn production regions in Sichuan during 1970-2010, were used to calculate water budget index as an indicator for drought during corn growth season. Spatio-temporal variations in drought frequency and drought risk distribution were analyzed for each corn growth stage in 6 six main production regions (hilly area of southern basin, hilly area of central basin, plain and hill areas of western basin, mountain area around basin, equal ridge-valley region of eastern basin and mountain area of southwest Sichuan) of Sichuan Province. The results showed that since the late 1990s, drought frequency had increased in most corn production regions. The changes in drought frequency with time, however, varied from region to region. With the exception of the eastern basin, station-based mean drought frequency during maize jointing to milk-ripening stage increased across the regions. Also station-based mean drought frequency during maize milk-ripening to maturity stage increased in the southern and western basins and the basin edge. For the entire maize cultivation region in Sichuan, mild to strong drought was more prevalent than severe drought. While mild drought was most common in the hilly area of the southern basin, strong drought was prevalent in the shallow hilly area of the central basin. More severe droughts were less frequent in the low hilly areas of the western basin and in the paralleled ridge valley areas of the eastern basin. Severe drought was most frequent in the hilly areas of the southern basin of Sichuan. The risk of drought was high in the central basin and across most of the eastern basin and parts of the southern basin during corn growth season. Between jointing and milking stage, the risk of drought was high in the northern basin and across most of the central basin. From milk to maturity, there was high risk of drought during corn growth season in the north and southeast of the basin and parts of the central basin.