Comparison of the SPI and ESPI on predicting drought conditions and streamflow in Canada
One drought index that is becoming a standard tool for assessing drought is the Standardized Precipitation Index (SPI), which is based solely on precipitation variability. However, the Standardized Precipitation and Evaporative Index (SPEI) takes into account the effect of temperature on drought. In Canada this could be an important element in understanding the effect of increasing temperatures on drought. This study compares the SPI and SPEI in different climate zones in Canada in order to determine which one better represents past drought conditions. The study also introduced artificial warming to determine whether one index was better at representing drought conditions under anticipated increased temperature scenarios. Both indices were also assessed in terms of how they represent monthly stream flows in selected prairie river systems.
There was no significant difference in how the indices represented past drought conditions however the SPEI was better at capturing the effect of increasing temperatures on droughts based on the artificial warming models. The SPEI was able to only partially represent streamflow conditions. The correlations between SPEI and streamflow varied with the season, showing stronger correlations during the summer and autumn months and weaker correlations during the winter and spring. Statistically significant correlations were observed for 6, 9 and 12 month temporal scales however the correlations weakened at temporal scales higher than 12 months.