Soil Moisture anomaly index （SMAI） in Dongting Lake watershed

Based on the principle of water balance, the Soil Moisture Anomaly Index (SMAI) can be obtained by calculating the monthly hydrological components and suitable soil precipitation for plant growth through the soil moisture balance law. This index can effectively represent the surplus and deficit of soil moisture on the grid. The specific steps are to generate process values for different grids through the VIC hydrological model of the Dongting Lake watershed, including the actual and possible values of each water balance component. Then, by comparing the monthly average actual and possible values of each component, the climate constant values of each climate component for each month are obtained. From this, the climate suitable precipitation of the Dongting Lake watershed is obtained. Finally, the monthly water anomaly of each grid is obtained by the difference between the actual precipitation and the suitable precipitation. The water anomaly is multiplied by the climate characteristic coefficient of each grid to obtain the soil water anomaly index for each month of the corresponding grid The resolution of the SMAI raster dataset is 0.08333 °, approximately 10km. The spatial reference system is GCSWGS_1984 in NetCDF4 format. At present, the SMAI dataset covers data from the Dongting Lake Basin from 1961 to 2019, divided into four time periods from T1 to T4, which can be used to characterize the monthly average soil moisture status within the four time periods. The four time periods total 48 months, so the SMAI.nc file contains a total of 48 bands. The 1-12 bands correspond to the T1 (1961-1984) period from January to December, the 13-24 bands correspond to the T2 (1985-2003) period from January to December, the 25-36 bands correspond to the T3 (2004-2014) period from January to December, and the 37-48 bands correspond to the T4 (2015-2019) period from January to December. A grid value greater than 0 indicates that the soil moisture in the grid has been in a surplus state for a long time, while a value less than 0 indicates that the soil moisture has been in a deficit state for a long time, which is not conducive to vegetation growth.