Assessment of drought dynamics in the phalgu river basin, middle ganga plain, based on CHIRPS and MODIS- derived indices

Abstract

Climate change has significantly increased the frequency, intensity, and spatial extent of drought events, highlighting the importance of drought assessment and monitoring studies. Therefore, evaluating drought characteristics such as duration, frequency, and classification within a spatio-temporal framework at the basin scale, using key climatic variables, is essential. The present study examines the spatial and temporal behavior, long-term trends, change-point patterns of drought and vulnerable zones in the Phalgu River Basin, Middle Ganga Plain, India, from 1985–2024. In this work, the Standardized Precipitation Index (SPI), Vegetation Health Index (VHI), Vegetation Condition Index (VCI), and Temperature Condition Index (TCI) were derived from CHIRPS and MODIS datasets and processed in Google Earth Engine (GEE). Among climate teleconnections, IOD (Indian Ocean Dipole) exert stronger control on drought as compared to other ENSO indices. Frequency-based Innovative Trend Analysis (F-ITA), a nonparametric method, was applied to determine the direction and magnitude of drought indices at decadal scales. The results reveal a rising trend in SPI-12, SPI-24, and VCI, while TCI remained nearly stable with a negligible positive trend, and VHI exhibits decreasing tendencies. Using the Pruned Exact Linear Time (PELT) algorithm, change points were identified for TCI in 2010 and 2015, SPI-12 in 1990, SPI-24 in 1991, VCI in 2005 and VHI in 2015 are statistically significant (p-value < 0.05).From the AHP based weighted overlay approach, it was found that northern part of the basin is placed under very high vulnerability zone (17.85%) requiring utmost attention. Mapping Drought vulnerable zones is significant in policy level intervention part of research for people at grassroots level. Assessment of historical drought patterns provides a scientific basis for drought mitigation, sustainable water management, and long-term river basin conservation planning. Although SPI shows a gradual tendency for wetting, TCI indicates stable thermal stress with negligible rise. This suggests that rising temperatures may increasingly constrain vegetation health.