Temporal and spatial distribution characteristics and causes analysis of seasonal drought in hilly area of central Sichuan

Abstract: In order to reduce the influence of seasonal drought on agricultural production in Sichuan Province, the standard precipitation index (SPI) was selected to describe drought characteristics based on monthly precipitation data from eight sites in the hilly area of central Sichuan during 1960－2011. Mann Kendall rank correlation and the morlet wavelet method were applied to analyze the spatial and temporal distribution characteristics of seasonal drought, and the correlation analysis method was used to explore the causes of drought and propose drought prevention measures in the hilly area of central Sichuan. Results indicate that: moderate drought, severe drought, and extreme drought in the hilly area of central Sichuan, which influence this area seriously, mainly concentrated in winter and spring; Moderate drought mainly occurred in Spring (moderate drought frequency -17.3%), while severe and extreme drought mainly occurred in winter (severe and extreme drought frequency -11.5%). During the last 52 years, the SPI of each site increased in June and decreased from September to November, especially in Yibin, SPI were decreased significantly（=0.05） in August and September, which may aggravate drought frequency and the category of hot-drought and autumn drought. Hurst of Spring SPI changes between 0.51(Suining) to 0.72 (Bazhong); Summer Hurst changes from 0.44 (Luzhou) to 0.72 (Daxian); Autumn Hurst varies from 0.49 (Neijiang) to 0.74 (Langzhong); Winter Hurst varies from 0.65 (Luzhou) to 0.81 (Langzhong); Almost all Hurst indexes of seasonal SPI in the region are greater than 0.5, which refers to good persistence on seasonal SPI, thus SPI features during nearly 52 years can be a reference for further drought research in this region. June scales (winter and spring) SPI value shows a cycle of 5, 11, and 28a, in which the strongest shock (11a) was the first cycle, 28a was the second cycle, and 5a was the third cycle. Actual drought conditions were consistent with change process of 11a scale wavelet real part. Drought frequency of drought category differs from regions; Moderate drought in spring and summer are mainly distributed in the central and northeastern sections of the hilly area of central Sichuan, such as Daxian and Gaoping. Otherwise, moderate drought in autumn and winter is mainly distributed in the southwestern part of the region, such as Neijiang. Severe and extreme seasonal drought always occurs in Suining and Yibin. Therefore, Suining and Yibin are the most important region for drought prevention. Correlation analysis was used to analyze relevance between monthly scale SPI and each meteorological factor (precipitation concentration degree was described by the ratio of daily maximum precipitation and monthly rainfall; temperature change with extreme maximum temperature and the average temperature difference to describe), which indicates that SPI was significant negatively correlated with precipitation concentration and sunshine hours (α=0.01), so precipitation concentration and sunshine hours are main factors affecting the drought of the hilly area of central Sichuan. Rainwater harvesting and utilization technology is an effective measure for improving rainwater use efficiency and preventing seasonal drought. This paper provides a reference for Sichuan drought mitigation.