Comparative Analysis of Hydro-Climatic Variability in High-Arid and Low-Arid Regions of Karnataka's Semi-Arid Landscapes

Semi-arid regions are often classified as a single climatic category in regional planning, yet such categorization tends to obscure the underlying heterogeneity. This study compares hydro-climatic variability between the High-Arid districts of Vijayapura, Bagalakote, and Raichur and the Low-Arid/Semi-Humid districts of Belagavi and Dharwad, all within Karnataka's twelve-district semi-arid belt, using a 25-year rainfall and temperature record (2000-2024) and the De Martonne Aridity Index (DMAI). We tested trend significance with the Mann-Kendall test and Sen's slope estimator, consistent with standard climatological practice. The High-Arid zone records mean annual rainfall of just 576.4-678.6 mm against a Low-Arid/Semi-Humid mean of 1,093.2-1,611.1 mm - nearly a three-fold gap - while running 2-3 °C warmer on average, with Raichur showing the only statistically significant warming trend in the comparison (+0.031 °C/year, p = 0.040). Mean DMAI confirms the divide numerically: 17.08-18.58 (Arid) in the High-Arid zone against 35.00-53.12 (Semi-Humid to Humid) in the Low-Arid zone. Yet the Low-Arid zone is not risk-free - it shows the highest rainfall variability in the dataset (coefficient of variation up to 28.7%) and the only statistically significant rainfall trend in either zone, a sharp rise in Belagavi (+32.8 mm/year, p = 0.023) driven by increasingly extreme wet years, including 2,617 mm in 2019. Read together, the results argue against a uniform semi-arid management template: The High-Arid zone needs drought-proofing and moisture conservation, while the Low-Arid/Semi-Humid zone needs drainage and flood-resilience planning, even though both sit inside the same nominal climatic belt.