What do century-long rainfall trends reveal about climate change in Bihar’s Makhana-growing wetland districts?

Abstract

This study investigates the spatio-temporal variability and long-term trends in rainfall across the major Makhana-growing wetland districts of Bihar, India, using data spanning from 1901 to 2022. To detect trends in seasonal and annual rainfall, statistical methods such as the Mann-Kendall (MK) test, trend-free pre-whitened MK (TFPW-MK) test, Sen’s slope estimator, and simple linear regression (SLR) were employed. Innovative Trend Analysis (ITA) was applied as a complementary graphical method to enhance interpretation of trend behavior. Change-point detection was conducted using Pettitt’s and the cumulative sum (CUSUM) tests at 1%, 5%, and 10% significance levels. The analysis revealed predominantly negative trends in annual and monsoon rainfall across most districts, except for Supaul, which exhibited a statistically significant increasing trend. Sen’s slope estimates indicated spatial heterogeneity in trend magnitudes, with the most pronounced decline observed in Araria. Change-point analysis identified significant temporal shifts, particularly in monsoon rainfall, which strongly influenced annual totals. ITA effectively corroborated the results of the statistical tests, offering a nuanced visual understanding of trend patterns. The integrated use of statistical and graphical approaches provides a comprehensive assessment of rainfall dynamics, with implications for climate-resilient agricultural planning and water resource management in Bihar’s wetland agro-ecosystems.