Current Trends in Upper Water Layer Temperature in Coastal Zones of Baikal

Аннотация

Based on the data from 17 meteorological stations, we have analysed the characteristics of the temperature change within the surface water layer (0.2–0.5 m) in the coastal zone of Lake Baikal. It was determined that during 1970–2016, the average temperature trend in May–September was increasing from Southern Baikal to Central and Northern Baikal due to a combination of physical– geographical features (heat from the sun, orography of the coastal mountains and underwater slopes, wind conditions, and water dynamics) in the lake basin. It was established that the low value of the trend in Southern Baikal is due to a relatively poor protection of its water area by the Primorskii Ridge (approximately 800 m high) from strong winds of the western quarter. It was found that an increased wind activity causes a more pronounced wind–wave mixing in the upper layers as well as more frequent upwellings/downwellings which also involve the waters from the deeper layers in the exchange with the upper water layers. In the Central Baikal basin, the influence of the water mass on the atmospheric circulation in the surface layer is the most obvious. Its consequence implies high atmospheric transparency and decreased cloudiness over the lake leading to an increase in incident solar radiation in the upper water layers. The high temperature trends, compared to the other parts of Baikal, correspond to the Northern Baikal basin best protected from the strong westerly winds by the Baikalskii Ridge (up to 2500 m high). Over the past two decades (1994–2016), the trend of warming of the surface water layer has decreased significantly, along with an increase in the warming rate of Central and Southern Baikal. Using data of deep–water temperature monitoring in Southern Baikal, we estimated the spatial scales of the identical response of the surface temperature and the lake water column to climate change.