This study presents a comprehensive remote sensing analysis of rainfall
patterns and selected hydropower reservoir water extent in two tropical monsoon
countries, Vietnam and Sri Lanka. The aim is to understand the relationship
between remotely sensed rainfall data and the dynamic changes (monthly) in
reservoir water extent. The analysis utilizes high-resolution optical imagery
and Sentinel-1 Synthetic Aperture Radar (SAR) data to observe and monitor water
bodies during different weather conditions, especially during the monsoon
season. The average annual rainfall for both countries is determined, and
spatiotemporal variations in monthly average rainfall are examined at regional
and reservoir basin levels using the Climate Hazards Group InfraRed
Precipitation with Station (CHIRPS) dataset from 1981 to 2022. Water extents
are derived for selected reservoirs using Sentinel-1 SAR Ground Range Detected
(GRD) images in Vietnam and Sri Lanka from 2017 to 2022. The images are
pre-processed and corrected using terrain correction and refined Lee filter. An
automated thresholding algorithm, OTSU, distinguishes water and land, taking
advantage of both VV and VH polarization data. The connected pixel count
threshold is applied to enhance result accuracy. The results indicate a clear
relationship between rainfall patterns and reservoir water extent, with
increased precipitation during the monsoon season leading to higher water
extents in the later months. This study contributes to understanding how
rainfall variability impacts reservoir water resources in tropical monsoon
regions. The preliminary findings can inform water resource management
strategies and support these countries' decision-making processes related to
hydropower generation, flood management, and irrigation.

这项研究通过遥感分析在两个热带季风国家 —— 越南和斯里兰卡的降雨模式和水库水域范围之间的关系，揭示了降雨格局与水库水域范围动态变化之间的明确关联，对深入了解降雨变异性如何影响热带季风地区的水资源，提供了支持水资源管理策略和决策流程的初步发现。

利用 Google Earth Engine (GEE) 分析选定的水电站水域的降雨和水域变化：以斯里兰卡和越南两个热带国家为例的案例研究

Analysis of Rainfall Variability and Water Extent of Selected Hydropower  Reservoir Using Google Earth Engine (GEE): A Case Study from Two Tropical  Countries, Sri Lanka and Vietnam