Drought characteristics in Songnen Plain with SPI calculated by optimal probability function

Songnen Plain is an important region for grain production. Precipitation data from 21 weather stations in Songnen Plain from 1961 to 2015 were examined, standardized precipitation index by optimal fitting was used to construct drought index. Spatial-temporal drought characteristics were analyzed for drought frequency, duration and occurring-station ratios. Songnen Plain was found to show a significant wetting tendency in winter ( P = 0.002) and spring ( P = 0.039), with corresponding drought frequency of 26% and 29.7% respectively, indicating a heavy drought. Whilst arid tendency and drought frequency of 22.2% was found in summer and autumn, no heavy drought was indicated. Although a total of 7 drought events lasting more than 7 months in 54 a were found on an annual scale, much higher than duration of other drought events, a wetting trend was indicated. Drought frequency was found to increase from southwest to northeast on annual and seasonal scales. High-frequency arid regions in winter were mainly found distributed in Tailai, Mingshui and Fuyu and surrounding areas, showing a sporadic distribution pattern. High-frequency arid regions in spring and summer were mainly found concentrated in northeastern part of Songnen Plain. High-frequency arid area in spring was found to be larger than high-frequency arid area in summer. In autumn it was found mainly concentrated in northwest and central part of Songnen Plain, mainly distributed in Fuyu, Qiqihar and Anda. Although drought severity of Songnen Plain has declined, station proportion of drought was found to be greater than 50% and area affected by drought has expanded. This work will provide some guidance for drought and mitigation, and for protection of food security in Songnen Plain.