A Study on the Evolution Characteristics of Qinghai Lake Ice in Recent 40 Years Based on an Analytical Model

Abstract

Lakes widely distribute in the Qinghai-Xizang Plateau， and most of them are seasonally frozen lakes.Under the background of global warming， lake ice thickness and phenology are changing significantly， which has a profound impact on regional climate evolution.However， the evolution characteristics of ice thickness and phenology on the climatological scale are not well understood at present.Therefore， in this paper， the lake ice thickness and phenological evolution characteristics of Qinghai Lake during 1979 -2017 were studied by using the field lake ice observation data from Qinghai Lake Xiashe Hydrology Station， MODIS Lake ice coverage dataset， meteorological observation data from Gangcha Meteorological Station and CMFD， combined with a quasi-steady state model of lake ice.The results show that the simulated average ice thickness is 0.31 m， which is close to the measured value of Xiashe Hydrology Station.The error in modelling breaking-up end is only 0.07 days， and the errors of the freezing-up start and the ice duration are 5.60 days and 5.67 days， respectively.The simulated maximum ice thickness decreases from 1979 to 2017 is in good agreement with the observed trend， that is， the ice thickness decreases by 0.003 m per year.In the freezing periods from 1979 to 2017， the freezing-up start of Qinghai Lake is delayed （0.23 d·a-1）， the breaking-up end is advanced （0.32 d·a-1）， and the length of the ice duration is shortened （1.02 d·a-1）， especially in the 1980s （2.2 d·a-1）.During the freezing periods of Qinghai Lake from 1979 to 2017 （from December to April of the following year）， the downward longwave radiation and air temperature （both of which showed an increasing trend） have a significant negative correlation with the average ice thickness and the maximum ice thickness， while the downward shortwave radiation （which showed a decreasing trend） has a significant positive correlation with the maximum ice thickness and the average ice thickness.The detrending sensitivity test shows that： downward longwave radiation， air temperature， downward shortwave radiation and specific humidity are the main driving factors of mean ice thickness and maximum ice thickness variability in Qinghai Lake from 1979 to 2017， contributing 42.08%， 40.93%， -36.99% and 17.45% to mean ice thickness variability， and 44.48%， 44.68%， -34.77% and 19.92% to maximum ice thickness variability， respectively.All the meteorological driving factors contribute 83.40% and 87.01% to the two factors.It can be seen that the maximum ice thickness variability of Qinghai Lake is more susceptible to the influence of meteorological conditions than the average ice thickness variability.The results of this study provide an understanding of the long-term evolution trend of lake ice in the cryosphere， and provide a reference for the study of other lakes in the Tibetan Plateau in the cold season.

Keywords

• qinghai lake
• quasi-steady model
• lake ice thickness
• ice phenology