GPCC Drought Index Product (GPCC_DI) at 1.0° based on GPCC Monitoring Product: Globally Gridded Drought Index with averaging periods 1,3,6,9,12,24,48 months

Summary: The Global Precipitation Climatology Centre drought index (GPCC_DI) is a combination of the Standardized Precipitation Index (SPI; McKee et al., 1993) in the DWD modification according to Pietzsch et al. (2011) and the Standardized Precipitation Evapotranspiration Index (SPEI) according to Vicento-Serrano et al. (2009). The 'Monitoring Product' (DOI:10.5676/DWD_GPCC/MP_M_V5_100) is used as precipitation input data. For the monthly mean temperature data NOAA's Climate Precdiction Center (CPC) Monthly Global Surface Air Temperature Data Set is utilized (Fan and van den Dool, 2008). The temperature data are applied to calculate the potential evapotranspiration (PET) according to Thornthwaite (1948). Parameters to calculate SPI and SPEI were referenced to 1961-1990. Due to the non-applicability of the gamma distribution for precipitation in arid regions the SPI can not be calculated there. On the other hand the PET can not be computed in cold regions applying the formula from Thornthwaite. Hence the GPCC_DI is calculated as the mean of the SPI and SPEI. If one of these indices can not be computed, the one available is used, yielding an almost global coverage of the GPCC_DI. The GPCC_DI is computed with averaging periods of 1, 3, 6, 9, 12, 24 and 48 months. The GPCC_DI has a spatial resolution of 1.0° latitude by longitude using gridded input data fields at the same resolution. To issue a monthly GPCC_DI product all seven averaging periods are compiled into one netCDF-file. The GPCC_DI based on the GPCC Monitoring Product is availabile for all months since January 2015.