Vertical distribution of annual water temperature maxima in the southern coastal zone of Lake Baikal

Abstract

It is frequently observed that an extreme event, such as a temperature maximum, has a greater impact on a lake ecosystem than changes in average conditions. For the first time, we examine the vertical variability of annual water temperature maxima (AWTM) and dates of their occurrence based on in-situ measurements of water temperature with discreteness of 15 minutes for a stable stratification period over eleven years (since 2005 to 2016 except 2009) in the southern coastal zone of Lake Baikal with a bottom depth of 545 m. The estimated statistical characteristics clearly distinguish various features of the vertical distribution of AWTM. There are significant time shifts (about 86 days) between the uppermost horizon (about 15 m) and the lowest 300 m horizon. The average maximum annual temperatures (15 °C) decrease from the upper horizon to a temperature of 4 °C at 300 m depth. To quantify changes in the annual maximum water temperature, the empirical functions were constructed to estimate relationships between AWTM, dates of their occurrence and depth. These dependencies are not linear and verified by independent data. They have fairly high coefficients of determination.