Scottish snow cover dependence on the North Atlantic Oscillation index

Michael Spencer,Richard Essery

doi:10.2166/nh.2016.085

Abstract

Forecasting seasonal snow cover is useful for planning resources and mitigating natural hazards. We present a link between the North Atlantic Oscillation (NAO) index and days of snow cover in Scotland between winters beginning from 1875 to 2013. Using broad (5 km resolution), national scale data sets like UK Climate Projections 2009 (UKCP09) to extract nationwide patterns, we support these findings using hillslope scale data from the Snow Survey of Great Britain (SSGB). Currently collected snow cover data are considered using remotely sensed satellite observations, from moderate-resolution imaging spectroradiometer; but the results are inconclusive due to cloud. The strongest correlations between the NAO index and snow cover are found in eastern and southern Scotland; these results are supported by both SSGB and UKCP09 data. Correlations between NAO index and snow cover are negative with the strongest relationships found for elevations below 750 m. Four SSGB sites (two in eastern Scotland, two in southern Scotland) were modelled linearly with resulting slopes between −6 and −16 days of snow cover per NAO index integer value. This is the first time the relationship between NAO index and snow cover duration has been quantified and mapped in Scotland.

Highlights

Snow is important in Scotland for water resources, e.g., the largest instrument-measured flow in Scotland’s largest catchment, the River Tay, was partly caused by snowmelt (Black & Anderson )
Spatial variability of snow cover is a big challenge and is difficult to observe and quantify. This is typified by the contrasting results of UK Climate Projections 2009 (UKCP09) snow and MODIS data correlations
We have overcome this by using disparate snow cover data sets, encompassing anecdotal type data (Bonacina index), interpolated ground observed data (UKCP09), the Snow Survey of Great Britain (SSGB) and satellite observations (MODIS)

Summary

Introduction

Snow is important in Scotland for water resources, e.g., the largest instrument-measured flow in Scotland’s largest catchment, the River Tay, was partly caused by snowmelt (Black & Anderson ). The North Atlantic Oscillation (NAO) index is the normalised pressure difference between the Icelandic low and. The NAO index could indicate the duration of snow cover as colder weather means a greater chance of snow and its persistence, but this signal may be confused by positive NAO phases bringing increased precipitation

Results

Discussion

Conclusion