Snowpack indicator

Key message Early accumulation of snowpack can decrease runoff and ground water recharge during the winter months Lack on snowmelt can increase possibilities for drought during the spring and early summer E.g. In Finland snowpack accumulation is from 10 to 30 % of yearly precipitation The warming climate is predicted to increase variation in the snowpack 26.12.2018

Relevance of the indicator Snowpack is an essential part of water cycle in the northern parts of Europe and in the mountains Snowpack is an indicator of drought risk Not sufficient by itself ! Snowpack can be used to predict the drought risk during the coming spring and summer together with other drought indicators Human abstraction plays no role in the snowpack indicator 26.12.2018

The indicator Static snowpack indicator: sSN = period of return of the annual maximum snowpack water equivalent in mm in water (=kg/m2 of snow) provides information of the relative volume of the snowpack in the catchment in a given year, indicating possible drought used for awareness raising and post evaluation of occurred droughts Dynamic snowpack indicator:  (not tested yet) dSN = period of return of the daily snowpack water equivalent in mm in water (=kg/m2 of snow) provides information of the relative volume of the snowpack in the catchment on a daily basis, indicating drought risks especially in spring and early summer used for forecasting future drought risks and for management purposes Normal level More than normal Much more than normal Less than normal Much less than normal 10 % One year on 10 10 years dry 25 % One year on 4 4 years dry 75 % 3 years on 4 4 years wet 90 % 9 years on 10 10 years wet Quantiles (statistical frequency of the levels for the same day/year)

River Paimionjoki pilot

Experiences Not sufficient indicator of drought by itself Small snowpack doesn’t always mean risk of drought during the spring if winter has been warm, the precipitation is not entirely accumulated into snowpack Instead it may be stored in other natural and artificial storages (e.g. lakes, soil moisture) ensuring adequate runoff during spring and early summer Not quite good indicator in small catchments with low proportion of lakes The runoff from snow melt is rapid and the snowpack is quickly discharged downstream/ocean Works better in bigger catchments ? Needs to be tested.. Gives essential additional information when used hand in hand with other drought indicators May explain some illogical results of other indicators Needs to be tested together with other indicators Nevertheless, very useful indicator of spring floods