SPEI-based drought trend analysis and statistical forecasting in Nalgonda district, Telangana

Abstract

This study assessed drought variability in Nalgonda district using monthly Standardized Precipitation Evapotranspiration Index (SPEI) data for the period 1981-2024. The annual SPEI series exhibited high interannual variability, with severe drought years identified in 1987, 1995, 2002, 2015 and 2022. A major challenge of the study was capturing long-term drought trends under high climatic variability and limited district-level forecasting studies. Trend analysis was carried out using the Mann-Kendall (M-K) test and Sen’s slope (SS) estimator. The annual SPEI showed a weak negative slope (−0.0031), indicating a slight increase in drought tendency over time. Monthly analysis revealed a significant increasing drought trend in June and July, while April showed a significant decreasing trend. Seasonal analysis indicated a decreasing trend during the pre-monsoon period and an increasing trend during the southwest monsoon season. For drought forecasting, ARIMA modeling identified ARIMA (2,0,1) as the best-fit model, with residual diagnostics confirming the absence of autocorrelation and good model performance (RMSE = 0.5228). The study contributes to improved understanding of drought dynamics at the district scale and demonstrates that ARIMA models can effectively support short-term drought forecasting for climate-sensitive regions like Nalgonda.