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Recent precipitation decrease across the western Greenland ice sheet percolation zone

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is
of critical interest in the context of future sea level rise. Increased
melting in the GrIS percolation zone due to atmospheric warming over the
past several decades has led to increased mass loss at lower elevations.
Previous studies have hypothesized that this warming is accompanied by a
precipitation increase, as would be expected from the Clausius–Clapeyron
relationship, compensating for some of the melt-induced mass loss throughout
the western GrIS. This study tests that hypothesis by calculating snow
accumulation rates and trends across the western GrIS percolation zone,
providing new accumulation rate estimates in regions with sparse in situ data or
data that do not span the recent accelerating surface melt. We present
accumulation records from sixteen 22–32 m long firn cores and 4436 km of
ground-penetrating radar, covering the past 20–60 years of accumulation,
collected across the western GrIS percolation zone as part of the Greenland
Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends
from both radar and firn cores, as well as commonly used regional climate
models, show decreasing accumulation rates of 2.4±1.5 % a−1
over the 1996–2016 period, which we attribute to shifting storm tracks
related to stronger atmospheric summer blocking over Greenland. Changes in
atmospheric circulation over the past 20 years, specifically anomalously
strong summertime blocking, have reduced GrIS surface mass balance through
both an increase in surface melting and a decrease in accumulation rates.
