R codes used to process gridded SPI dataset.
Three codes are included:
- calculate mean SPI by decade (output = raster grids of mean SPI by decade)
- calculate frequency by decade (output = raster grids of drought frequency by decade)
- spatially average pixels by island to create statewide & island time series (output = time series .txt file for each island and for the entire state of Hawaii)
All codes use 250 m gridded SPI dataset from 1920-2012, which was calculated for 10 SPI time periods from 1-month up to 60-months using the Hawaii statewide monthly rainfall maps developed by Frazier et al. 2016. SPI grids generated by Matthew Lucas, UH Manoa, Honolulu, HI - m p lucas @ hawaii .edu.