Can the Canadian drought code predict low soil moisture anomalies in the mineral soil? An analysis of 15years of soil moisture data from three forest ecosystems in Eastern Canada

The Canadian Drought Code (CDC) is an empirical soil-drying model adapted to high-latitude forests and commonly used by Canadian fire managers and researchers to predict the water content of the organic soil layer. Better knowledge of the capacity of the CDC to predict the effect of droughts on the water content of the mineral soil could improve our capacity to predict the future response of Canadian boreal forests to future changes in drought frequency and intensity. We tested the capacity of the CDC to predict mineral soil water content (SWC) and droughts against long-term (14-16years) daily mineral SWC data from time domain reflectometry probes in multiple stations within three forest ecosystems of Eastern Canada respectively dominated by sugar maple, balsam fir and black spruce. Droughts were defined as SWC values lower than one standard deviation from their historical mean. The drought intensity and frequency of each growing season were computed as the sum of daily SWC departures from normal and the sum of days of drought, respectively. Our results show that the CDC is a reliable predictor of mineral SWC (r=0.6-0.8), drought frequency (r=0.5-0.9) and intensity (r=0.7-0.9) for high-latitude forest ecosystems of Eastern Canada. Lower correlations were due to the poor accuracy of the model at predicting mild droughts at the sugar maple stand due to the SWC values close to the drought threshold. We detected a higher susceptibility to droughts at the black spruce stand due to a 1-month-earlier occurrence of severe droughts. Copyright (c) 2015 John Wiley & Sons, Ltd.