Variations of oxygen-18 in West Siberian precipitation during the last 50 yr

Abstract

Abstract. Global warming is associated with large increase in surface air temperature and precipitation in Siberia. Here, we apply the isotope-enhanced atmospheric general circulation model ECHAM5-wiso to investigate the variability of δ18O in West Siberian precipitation and the underlying mechanisms during the last fifty years, and to assess the potential of a recently opened monitoring station in Kourovka (57.04° N, 59.55° E) to successfully track large-scale water cycle and climate change in this area. Our model is constrained to atmospheric reanalysis fields to facilitate the comparison with precipitation δ18O from observations. In Russia, annual-mean model surface temperatures agree within ±1.5 °C with climatological data, while the model tends to overestimate precipitation by 10–20 mm month−1. Simulated precipitation δ18O shows a southwest to northeast decreasing pattern. The simulated annual-mean and seasonal δ18O results are in overall good agreement with observations from 15 Russian stations of the Global Network of Isotopes in Precipitation between 1970 and 2009. Annual-mean model results and measurements are highly correlated (r2~0.95) with a root mean square deviation of ±1‰. The model reproduces the seasonal variability of δ18O, which parallels the seasonal cycle of temperature, and the seasonal range from −25‰ in winter to −5‰ in summer. Analysing model results for the extended period 1960–2010, long-term increasing trends in temperature, precipitation and δ18O are detected in western Siberia. During the last 50 yr, winter temperatures have increased by 1.8 °C. Annual-mean precipitation rates have increased by 2–6 mm month−1 50 yr−1. Long-term trends of precipitation δ18O are also positive but at the detection limit (<1‰ 50 yr−1). Regional climate is characterized by strong interannual variability, which in winter is strongly related to the North Atlantic Oscillation. In ECHAM5-wiso, regional temperature is the predominant factor controlling δ18O variations on interannual to decadal time scales with slopes of about 0.5‰ °C−1. Focusing on Kourovka, the simulated evolution of temperature, δ18O and, to a smaller extent, precipitation during the last fifty years is synchronous with model results averaged over entire western Siberia, suggesting that this site will be representative to monitor future isotopic changes this region.