The synoptic climate controls on hydrology in the upper reaches of the Peace River Basin. Part Ⅱ: Snow ablation

摘要

The timing and rate of spring snowmelt in the upper reaches of the Peace River Basin control the development of large upstream spring flood waves and subsequent downstream ice-jam flooding events. Given that snowmelt is controlled by atmospheric processes, this study identified the mid-tropospheric circulation patterns that control the timing and rate of the snowmelt season on a critical tributary of the Peace River Basin. Results showed that the date of spring snowmelt initiation in the upper Peace has become significantly earlier over the study period (1963-1996). This was explained by a significant increasing (decreasing) trend in the occurrence of mid-tropospheric ridging (troughing and zonal flow) patterns, which are associated with above (below) average mean daily temperatures and available melt energy at Grande Prairie. Further analysis revealed that variances in the timing and rate of melt at Grande Prairie could be explained by variances in the local synoptic regime. Examination of the broad-scale atmospheric controls identified that the variances in the occurrence of the synoptic patterns could be explained by variances in the Pacific/North American teleconnection pattern. Although El Nino events were associated with average synoptic and snow ablation conditions, La Nina events were found to significantly impact the March synoptic regime over western Canada, and subsequently, the melt timing at Grande Prairie.