Long-term Trend Analysis of Agrometeorological Variables and their Influence on Sugarcane Productivity in North Coastal Andhra Pradesh, India (1991–2024)

Abstract

Agrometeorological variables such as temperature, rainfall, sunshine hours, and evaporation strongly influence sugarcane growth and productivity. Long-term changes in these variables can affect crop performance and agricultural planning. This study examines trends in key agrometeorological factors and their relationship with sugarcane yield in North Coastal Andhra Pradesh. This longitudinal study analysed 34 consecutive years (1991–2024) of daily records from a single agrometeorological observatory - the Regional Agricultural Research Station (RARS), Anakapalle, Visakhapatnam District, North Coastal Andhra Pradesh (17.6913°N, 83.0039°E) - to characterize long-term trends in eight meteorological variables: maximum temperature (Tmax), minimum temperature (Tmin), mean temperature (Tmean), diurnal temperature range (DTR), total annual rainfall, rainy days, sunshine hours, and pan evaporation, and to assess their relationships with sugarcane (Saccharum officinarum L., cv. 87 A 298) cane yield. The complete daily record comprised 12,054 observations recorded using standardised IMO-compliant instruments. The non-parametric Mann–Kendall (MK) trend test with Hamed–Rao autocorrelation correction and Sen's slope estimator were applied to annual time series; where lag-1 autocorrelation exceeded |r₁| > 0.10, the Hamed–Rao modified MK test replaced the standard test. Autocorrelation analysis revealed significant positive lag-1 serial correlations in sunshine hours (r₁ = 0.635), pan evaporation (r₁ = 0.764), Tmin (r₁ = 0.783), and Tmean (r₁ = 0.711), necessitating the modified test for these variables. After autocorrelation correction, no statistically significant trends were detected in any temperature or rainfall variable (all p > 0.25). Highly significant declining trends were confirmed in both mean annual sunshine hours (MK Z = −4.92, Sen's slope = −0.062 h day⁻¹ yr⁻¹, p < 0.001, cumulative decline: 2.04 h day⁻¹, 26.8% from 1991) and mean annual pan evaporation (MK Z = −4.91, Sen's slope = −0.030 mm day⁻¹ yr⁻¹, p < 0.001, cumulative decline: 0.99 mm day⁻¹, 19.9% from 1991) - both trends remaining highly significant even after conservative autocorrelation correction. The concurrent decline in sunshine hours and pan evaporation under stable temperatures constitutes evidence of the 'evaporation paradox' driven by declining surface solar irradiance. Exploratory Pearson correlation analysis between annual weather variables and four years of observed sugarcane cane yields (2021–2024, n = 4) identified heat stress days (r = −0.610) and DTR (r = −0.645) as the most agronomically coherent associations; all yield correlations were statistically non-significant owing to the small sample size and should be interpreted as hypothesis-generating only.