Historical 12 month Standardized Precipitation Evapotranspiration Index across Canada

Persistent, large-area droughts are among Canada’s costliest natural disasters, having major impacts on sectors such as agriculture, industry, forestry, recreation, human health and society, and ecosystems. This dataset provides 50 km gridded, 12-month Standardized Precipitation Evapotranspiration Index (SPEI) values across land regions of Canada. Over southern areas of the country (south of 60°N) data are from 1900-2011 while in northern areas, the time period is shorter (approximately 1950-2011). The SPEI is a commonly used drought index, which evaluates the deviation of moisture deficit calculated as the difference between precipitation and potential evapotranspiration, the latter determined by temperature. It can be calculated on a variety of temporal scales (e.g., 1, 3, 12, 24 months). The values are standardized with negative SPEI representing drier than normal conditions and positive values corresponding to wetter than normal conditions. The SPEI are calculated using precipitation and temperature input from the Canadian gridded (CANGRD) dataset. For each grid point, the data consist of consecutive monthly values that represent the SPEI values for the previous 12 months. At present, these data have been used to characterize historical drought and excessive wet periods over the Oldman and Swift Current Creek watersheds in the southern Prairies, and the Athabasca River Basin in north-central Alberta.