## 5 Discussion
In addition, the environmental information reflected by the grain size of lake sediments in different regions is also different, for example, it can reflect wind intensity and dust transport [75, 76], riverine input [77] and lake water level changes [78]; however, it can be used as a useful indicator for quantitative reconstruction of long-term paleoprecipitation in the region of Lake Ta-Lung-Chi in Tianshan Mountains. The total precipitation from April to September showed a significant downward trend from 1930 to 1975, after which an overall increasing trend began. What caused this change? The study area is located in the mid-latitude zone, which is affected by westerlies, and the change in the North Atlantic Oscillation (NOA) is closely related to westerly intensity [79, 80]. From the Figure 6, it was an interesting phenomenon that the precipitation change in the study region may be affected by the NAO, which showed that there is a certain correspondence between the Monthly North Atlantic Oscillation Index (station-based, December, January, and February) [81, 82] and the precipitation curve reconstructed since 1930 in this study. The North Atlantic Oscillation Index is positively correlated with the westerly wind intensity [83], indicating that more water vapor is brought to the study area with increasing westerly winds, which may result in more precipitation. However, existing studies have shown that the precipitation in Central Asia and NAO have an anti-phased relationship on interannual to multi-centennial time scales [19, 84, 85]. The impact mechanism of the North Atlantic Oscillation on climate change in the Tianshan Mountains and even Central Asia may be different at different time scales, which is worthy of further discussion in the future. From the Figure 6, 1951 years ago, the reconstructed precipitation from April to September are inconsistent with the change from the CRU data, which was mainly because the earliest instrumental records of weather stations of China started at 1951 [86] (Figure 1), and thus the data before 1951 in this region were mainly calculated based on data from weather stations in the western section of the Tian Shan (within Kyrgyzstan, Figure 1). By comparing the data from our study area to data from a  
Figure 6: Comparisons of regional climate change. (**a**) Total precipitation from April to September at the meteorological station (Chonkyzylsu, 42.20\({}^{\circ}\) N 78.19\({}^{\circ}\) E, 1883–1996) located in the western Tian Shan [86]. **(b**) The three-point moving average curve of silty fraction content of 16 to 32 \(\upmu\)m. (**c**) Total precipitation from April to September from cru_ts_4.04 grid-box data for 42.25\({}^{\circ}\) N, 83.25\({}^{\circ}\) E in the region of Lake Ta-Lung-Chi [22]. (**d**) The monthly North Atlantic Oscillation Index (station-based, December, January, and February) [81,82]. (**e**) The total content of clay and fine-silty fraction (0–16 \(\upmu\)m). (**f**) The monthly precipitation in July from CRU TS 4.04 grid-box data for 42.25\({}^{\circ}\) N, 83.25\({}^{\circ}\) E in the region of Lake Ta-Lung-Chi [22]. meteorological station (Chonkyzylsu, 42.20\({}^{\circ}\) N, 78.19\({}^{\circ}\) E; 1883-1996) in the Tian Shan [86], it can be seen that there is a large difference in precipitation between central Tian Shan and the region of Lake Ta-Lung-Chi in western Tian Shan. What is the reason for this difference? The main influencing factor of precipitation is the source of water vapor. The HYSPLIT analysis showed that water vapor sources in the region of Lake Ta-Lung-Chi (42.45\({}^{\circ}\) N, 83.29\({}^{\circ}\) E) from April to September are not only affected by westerlies blowing from west to east, but also in part by winds blowing from east to west (8.33%) and from north to south (20.56%), which infers a local effect to water vapor transmission (Figure 7).