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

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.

Graph Theory Applications in Advanced Geospatial Research

Geospatial sciences include a wide range of applications, from environmental monitoring transportation to infrastructure planning, as well as location-based analysis and services. Graph theory algorithms in mathematics have emerged as indispensable tools in these domains due to their capability to model and analyse spatial relationships efficiently. This technical report explores the applications of graph theory algorithms in geospatial sciences, highlighting their role in network analysis, spatial connectivity, geographic information systems, and various other spatial problem-solving scenarios. It provides a comprehensive idea about the key concepts and algorithms of graph theory that assist the modelling processes. The report provides insights into the practical significance of graph theory in addressing real-world geospatial challenges and opportunities. It lists the extensive research, innovative technologies and methodologies implemented in this field.