The decline in water level that occurred in Lake Toba, North Sumatra lately has become an important issue for the local government and the community around the lake. Climate factors also have a great impact especially when the extreme conditions ENSO and IOD occurred. The purpose of this research is to look at the relationship between rainfall and the ENSO and IOD through the changing of Lake Toba’s water surface level and area. Monitoring of the dynamics of the water surface level and area of Lake Toba can be analyzed through remote sensing by using Landsat imagery to be more effective and efficient. Then the image is processed by using the MNDWI (Modified Normalized Difference Water Index) method to separate water bodies from the land. Retrieval of Landsat imagery was taken in the range of 2008 - 2017, then selected years when the conditions of ENSO and IOD occurred. The results showed in 2008, which was the La-Nina year followed by a positive IOD, the surface area of water decreased to 4.45 km² from the average area, but in 2015 when the El-Nino phase followed by positive IOD the water surface area increased to 4.7 km² from the average area. ENSO and IOD did not have much influence on rainfall in the Lake Toba region but slightly affected the water surface level and area of Lake Toba.

近日，北苏门答腊多巴湖出现的水位下降已成为当地政府和湖周围社区关注的重要问题。气候因素也有很大的影响，特别是当极端条件ENSO和IOD发生时。本研究的目的是通过多巴湖水面水位和面积的变化来研究降雨与 ENSO 和 IOD 之间的关系。多巴湖水面和面积的动态监测可以通过遥感分析利用 Landsat 影像更加有效和高效。然后使用 MNDWI（修正归一化差异水指数）方法对图像进行处理，将水体与陆地分离。Landsat 图像的检索是在 2008 - 2017 年期间进行的，然后选择发生ENSO和IOD条件的年份。结果显示，2008 年是拉尼娜年，随后 IOD 为正，水面面积减少到 4.45 km²平均面积，但在 2015 年厄尔尼诺阶段随后 IOD 为正时，水面面积从平均面积增加到 4.7 km ²。ENSO和IOD对多巴湖地区的降雨量影响不大，但对多巴湖的水面水位和面积影响较小。