The Spring Maize Drought Index in Northeast China Based on Meteorological Drought Index

Drought is the main disaster which influences spring maize over Northeast China, and spring maize yields are often affected by large regional and sustainable drought seriously. The decreasing effects can be described with meteorological drought index or agriculture drought index. Using the soil relative moisture data and county spring maize yield, as well as meteorological drought index SWAP (standardized weighted average of precipitation), a new spring maize drought index (I_MD) is proposed, which can reflect the decreasing maize yield induced by drought. Using soil moisture data, the spring maize drought limit is firstly researched based on SWAP. Results show in different stages of spring maze growth, SWAP thresholds are different, which are -0.9 for sowing and seeding stage, -1.0 for seeding and elongating stage, -1.2 for elongating and flowering stage, and -0.7 for flowering and maturity of spring maize. In other words, the growth of spring maize can be influenced when SWAP is moderate drought. A new spring maize drought index is researched based SWAP and SWAP limits. And results also show there is a good relationship between spring maize drought index and the provincial crop area affected by drought, especially in drought years. The coefficient between spring maize drought index and the provincial crop area affected by drought is 0.69 in Liaoning, and 0.73 in Jilin, as well as 0.64 in Heilongjiang, which indicates the new spring maize drought index can indicate actual maize drought. Finally, the classification of drought is divided using the county spring maize yields. The drought grades are defined according to the corresponding decrease of spring maize yield, light drought for (3%, 5% decrease, moderate drought for (5%, 10% decrease, severe drought for (10%, 20% decrease, and extreme drought when the spring maize yield decrease is more than 20%. As a result, when light drought, moderate drought, severe drought and extreme drought happens, the spring maize drought index range is (3.2, 4.2, (4.2, 6.7, (6.7, 11.7, and above 11.7. The research could provide effective method for drought prevention and disaster reduction.