Quantitative analysis of lake area variations and the influence factors from 1971 to 2004 in the Nam Co basin of the Tibetan Plateau

Abstract

By using remote sensing and GIS technologies, spatial analysis and statistic analysis, we calculated the water area and volume variations of the Nam Co Lake from 1971−2004, and discussed their influence factors from the viewpoints of climatic change and water balance. Data source in this study includes bathymetric data of the lake, aerial surveyed topographic maps of 1970, remote sensing images of 1991 and 2004 in the lake catchment, meteorological data from 17 stations within 1971−2004 in the adjacent area of the lake catchment. The results showed that the lake area expanded from 1920 km 2 to 2015 km 2 during 1971 to 2004 with the mean annual increasing rate (MAIR) of 2.81 km 2 a −1 , and the lake volume augmented from 783.23×10 8 m 3 to 863.77×10 8 m 3 with the MAIR of 2.37×10 8 m 3 . Moreover, the MAIR of the lake area and volume are both higher during 1992 to 2004 (4.01 km 2 a −1 and 3.61×10 8 m 3 a −1 ) than those during 1971 to 1991 (2.06 km 2 a −1 and 1.60×10 8 m 3 a −1 ). Analyses of meteorological data indicated that the continue rising of air temperature conduced more glacier melting water. This part of water supply, together with the increasing precipitation and the descending evaporation, contributed to the enlargement of Nam Co Lake. The roughly water balance analyses of lake water volume implied that, in two study periods (1971−1991 and 1992−2004), the precipitation supplies (direct precipitations on the lake area and stream flow derived from precipitations) accounted for 63% and 61.92% of the whole supplies, while the glacier melting water supplies occupied only 8.55% and 11.48%, respectively. This showed that precipitations were main water supplies of the Nam Co Lake. However, for the reason of lake water increasing, the increased amount from precipitations accounted for 46.67% of total increased water supplies, while the increased amount from glacier melting water reached 52.86% of total increased water supplies. The ratio of lake evaporation and lake volume augment showed that 95.71% of total increased water supplies contributed to the augment of lake volume. Therefore, the increased glacier melting water accounted for about 50.6% of augment of the lake volume, which suggested that the increased glacier melting water was the main reason for the quickly enlargement of the Nam Co lake under the continuous temperature rising.Tibetan Plateau, Nam Co Lake, lake area variation, remote sensing, water balance Citation:Zhu L P, Xie M P, Wu Y H. Quantitative analysis of lake area variations and the influence factors from 1971

The spatial distribution and sedimentary processes of organic matter in surface sediments of Nam Co, Central Tibetan Plateau

“…Most of these rivers flow only a very short distance from the source to the lake and have a low river discharge. During 1971-2004, the lake water area increased from 1920 km 2 [27] to 2015 km 2 [28] owing to increased melting of glacial water supplies of the lake catchment.…”

Turbulent flux observations and modelling over a shallow lake and a wet grassland in the Nam Co basin, Tibetan Plateau

“…This lake area has been subject to changes in the last decades; the reasons are not well understood due to lack of observational data ). Although Huang et al (2008) report a general decrease of lake volume in QinghaiTibet Plateau, the Nam Co lake area has been increasing (Liu et al 2010;Wu and Zhu 2008;Zhu et al 2010). They attribute this change to increasing precipitation as well as thawing permafrost and glacial melt due to rising mean annual temperatures, nevertheless the relative contribution of the balance components, especially the role of evaporation, is discussed controversially.…”

Recent changes in wetlands on the Tibetan Plateau: A review

“…(b) Inter-annual characteristics: for example, the area and the water volume increased at rates of 2.06 km 2 /a and 1.60×10 8 m 3 /a, respectively, between 1971 and 1991, whereas the area and the water volume increased at rates of 4.01 km 2 /a and 3.61×10 8 m 3 /a, respectively, between 1992 and 2004 (Zhu et al, 2010).…”