3.4 Relationship between lake level changes and precipitation variations
Since the late 1990s, the expansion of Tibetan lakes has been mainly affected by regional climate changes such as increased water vapor content, potential evaporation reduction and significantly enhanced air convection. (Yang et al. 2014; Yang et al. 2011; Lei et al. 2017; Lu et al. 2015). Therefore, with the acceleration of climate warming and humidification, precipitation could be also gradually increase (Yang et al. 2014), which supports the observation of the rapid lake expansion in the TP.
As shown in Fig. 3 and supplementary materials (Fig. S1), the trends of lake level changes since 1990 are generally consistent with previous studies. Our findings reveal that the drastic water level jumps in Tibetan lakes since 2016, has been a result of continued precipitation increase after a relatively drier period from 2012 to 2016. This suggests that precipitation remains to be a first-order driver of Tibetan lake dynamics. It was found that the drastic increase of lake level in 2017-2018 was consistent with the increase of precipitation in the near past several years, so the monthly precipitation data in recent years was selected and compared with the lake level. According to the study, the monthly precipitation and the lake water level during the period 2013-2018 were selected to study the influence of specific monthly precipitation on the lake water level. The most prominent feature was the good correspondence between lake level increase and the summer precipitation. In addition, we can find that the decrease of water level in individual years (e.g. 2015) corresponded to less summer precipitation. The amplitude of wet season lake level increases showed a good relationship with precipitation amount. For example, the drastic lake level rises in 2017 and 2018 in the TP corresponded to high precipitation. This suggests that the excessive precipitation during the wet season of 2017 and 2018 played a crucial role in the recent lake level increase. Overall, precipitation appears to play a more dominant role than temperature (and its induced glacier/permafrost melting). This was implied by the fact warming-induced melting did not reverse the slow-down or hiatus of lake expansion before 2016 (when precipitation was less), and it would have to be the precipitation increase again that eventually triggered another round of lake level increase. More details on other lakes and meteorological stations can be found in the Supplement (Fig. S2).