The Effects of Lake Level and Area Changes of Poyang Lake on the Local Weather

Abstract

Poyang Lake is the largest freshwater lake in China and is characterized by significant intra-annual variation, with higher water levels and area in the wet season compared to the dry season. However, the effects of the seasonal variation in Poyang Lake on the local weather are still not well-recognized. With the help of the weather research and forecasting (WRF) model, we designed one control experiment (CTL) using the default Poyang Lake level and area data and two sensitivity experiments, EXPT1 and EXPT2, the former representing the higher lake level and the greater area of Poyang Lake in the wet season and the latter representing the lower lake level and the smaller area of Poyang Lake in the dry season, to assess how these changes affect the local weather. The results of EXPT1 show that, as the lake’s level and area increase, the latent heat flux (LH), the sensible heat flux (SH), and the land surface temperature (LST) in the lake area decrease compared to those of the CTL. Meanwhile, the planetary boundary layer height (PBL), the convective available potential energy (CAPE), the wind speed, and the vapor flux over the lake decrease as well, indicating increased atmospheric stratification stability and resulting in a domain-averaged decline in precipitation of −22.3 mm. However, the low lake level and less area in EXPT2 show increasing SH, LST, PBL, and wind speed, and decreasing LH and CAPE compared to those of the CTL. The increasing SH and weakened atmospheric stratification stability in EXPT2 cause a significantly higher wind speed over the eastern part of the lake. As a result, more water vapor is transported to the east side of the lake by westerly upper winds, leading to a decreasing precipitation on the western side of the lake and a slightly increasing precipitation on the eastern side, resulting ultimately in a domain-averaged decline in precipitation of −23.8 mm in the simulation of the low level and less area of Poyang Lake. Although the LH and CAPE decline both in EXPT1 and EXPT2, the main cause is the higher water thermal capacity and lower lake-surface temperature with more lake water for EXPT1 and the lower evaporation with less lake water for EXPT2. Overall, a deeper and larger Poyang Lake will reduce the local temperature, inhibit water evaporation from the lake surface, and make the near-surface atmosphere more stable, resulting in restrained local precipitation. A shrinking lake level and area will raise the local temperature and the instability of the near-surface atmosphere but reduce water vapor and enlarge local wind and circulation, resulting in declining precipitation and a changing fall zone.