Analysis of Regional Changes in Geodetic Mass Balance for All Caucasus Glaciers over the Past Two Decades

Glaciers and snow in the Caucasus are major sources of runoff for populated places in many parts of this mountain region. These glaciers have shown a continuous area decrease; however, the magnitude of mass balance changes at the regional scale need to be further investigated. Here, we analyzed regional changes in surface elevation (or thickness) and geodetic mass balance for 1861 glaciers (1186.1 +/- 53.3 km(2)) between 2000 and 2019 from recently published dataset and outlines of the Caucasus glacier inventory. We used a debris-covered glacier dataset to compare the changes between debris-free and debris-covered glaciers. We also used 30 m resolution ASTER GDEM (2011) to determine topographic details, such as aspect, slope, and elevation distribution of glaciers. Results indicate that the mean rate of glacier mass loss has accelerated from 0.42 +/- 0.61 m of water equivalent per year (m w.e. a(-1)) over 2000-2010, to 0.64 +/- 0.66 m w.e. a(-1) over 2010-2019. This was 0.53 +/- 0.38 m w.e. a(-1) in 2000-2019. Mass loss rates differ between the western, central, and eastern Greater Caucasus, indicating the highest mean annual mass loss in the western section (0.65 +/- 0.43 m w.e. a(-1)) in 2000-2019 and much lower in the central (0.48 +/- 0.35 m w.e. a(-1)) and eastern (0.38 +/- 0.37 m w.e. a(-1)) sections. No difference was found between the northern and southern slopes over the last twenty years corresponding 0.53 +/- 0.38 m w.e. a(-1). The observed decrease in mean annual geodetic mass balance is higher on debris-covered glaciers (0.66 +/- 0.17 m w.e. a(-1)) than those on debris-free glaciers (0.49 +/- 0.15 m w.e. a(-1)) between 2000 and 2019. Thickness change values in 2010-2019 were 1.5 times more negative (0.75 +/- 0.70 m a(-1)) than those in 2000-2010 (0.50 +/- 0.67 m a(-1)) in the entire region, suggesting an acceleration of ice thinning starting in 2010. A significant positive trend of May-September air temperatures at two selected meteorological stations (Terskol and Mestia) along with a negative trend of October-April precipitation might be responsible for the negative mass balances and thinning for all Caucasus glaciers over the study period. These results provide insight into the change processes of regional glaciers, which is key information to improve glaciological and hydrological projections in the Caucasus region.