Remote Sensing-Based Spatiotemporal Assessment of Agricultural Drought in Ampara District, Sri Lanka using Google Earth Engine

Abstract

Agricultural drought is a significant environmental problem affecting the yield, water resources, and human health, particularly in climate-sensitive regions. This study analyses the spatio-temporal changes of agricultural drought in Ampara District, Sri Lanka, using remote sensing indices in the Google Earth Engine (GEE) platform. Remote sensing indicators such as the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) were used to derive the Vegetation Condition Index (VCI) and Temperature Condition Index (TCI) to calculate the Vegetation Health Index (VHI), which is the major indicator of agricultural drought. The Standardized Precipitation Index (SPI) and Precipitation Condition Index (PCI) were used to measure meteorological drought. The analysis was conducted for the period 2016–2025, and the drought conditions display considerable spatial and temporal variability. There is an overall increase in Land Surface Temperature (LST) and a decrease in vegetation health, particularly since 2020, with large areas under moderate to extreme drought conditions. The VHI showed a consistent increase in the area under extreme drought conditions. Conversely, the area under no-drought conditions declined over the study period. Meteorological indices (SPI and PCI) indicate variable precipitation patterns and frequent moisture deficits, which have an impact on vegetation. The significant positive correlation (R²=0.96-0.99) between VHI and SPI confirms the effect of rainfall on vegetation. This research reveals the Ampara District to be facing an emerging agricultural drought largely due to increased temperatures and highly variable rainfall. This study demonstrates the potential of combining remote sensing and cloud-based geospatial analysis for effective drought monitoring, supporting informed decision-making for sustainable drought management and agricultural development.

SAARC J. Agric., 24(1): 249-269 (2026)