Standardize Storage Index (SSI)

  SSI_W3RA_2003_2021.mat includes: SSI_G derived from W3RA deep-soil + Groundwater storage changes

                                   SSI_S derived from W3RA surface (top) soil water storage changes
                             
   SSI_MCMC_2003_2021.mat includes: SSI_G derived from MCMC-DA deep-soil + Groundwater storage changes

                                    SSI_S derived from MCMC-DA surface (top) soil water storage changes
   All data are 2D matrixes (T*P), where T is the length of time series, P is the number of spatial grid points covers only continental regions. 
   Landmask_50km.mat and Lat_Lon_50km.mat can be used to have a 360*720 grid of SSIs over the globe.