西藏扎布耶盐湖30.0 ka B P以来水位与古降水量变化

扎布耶湖9级大型沙砾堤记录了约30．0ka B P以来水位退缩历史，与北部拉果错、南部塔若错的垭口沉积记录了3个湖泊最后分离的时间。本文应用数字地面高程模型(DEM)，计算了扎布耶各级沙堤对应湖面期的湖水面积、体积与含盐量；分析了扎布耶与拉果错、塔若错的分-合历程，计算了各时期汇流盆地总面积；参考湖泊、冰川、孢粉、天文学等多学科关于古温度、辐射平衡的结论，得出了较为可信的计算参数。在此基础上，应用根据西藏实际情况得出的辐射平衡和水面蒸发、陆面蒸发计算模型，代入封闭盆地水量平衡方程，得出了较Kutzbach水-能方程更可靠的降雨量-水域面积／流域面积比的非线性方程，计算出泛湖期(9级沙堤，40．0～28．0ka B P)该区降雨量567 mm／a，盛冰阶时降至350mm／a以下，冰期后增至402mm／a，随后逐步下降直至约Ⅰ-1级阶地时(海拔4421m，3．53ka B P)为280mm／a(约为现代的两倍)。通过定量恢复该区30．0ka B P以来降水量变化，为认识西藏高原湖泊演化和古环境、古季风演化提供了定量依据。

Precipitation Fluctuation since 30.0 ka B P at Chabyer Caka, Western Tibet

The 9 steps of large-sized sand banks at Chabyer Caka of western Tibet plateau have recorded the lake level fluctuations since 30 ka B P. The sediments in the mountain valley river pass have provided us with information about the departure history of Chabyer Caka from north Laggor Co and south Taro Co lakes. Using DEM in GIS, the authors computed the area, volume and salinity of the paleolake and the area of the lake basin corresponding to each period of sand banks. Other researchers' study of lake sediments, glacier and flora also provide us with possible conditions of temperature and insolation during the past 30 ka. Using the above parameters and based on the hydrological balance equation of the drainage basin, the authors developed a more credible models than the Kutzbach hydrological-energy balance model by introducing a more accurate calculating model of the land evaporation, with the purpose of exploring the relationship between the rainfall and the lake area. The model yields a precipitation estimate of 567 mm/yr for Late Pleistocene (40-28 ka B P), and 350 mm/yr for Last Glacial Maximum. The precipitation rose to 402 mm/yr after LGM, and dropped to 280 mm/yr at about 3.53 ka B P. By reconstruction of past rainfall since Late Pleistocene we can understand the pale-o-environment and monsoon evolution in Tibetan plateau quantitatively.