Spatio-Temporal Trend of Dry Spells in Western Undulating Zone (WUZ) of Odisha Using Modified Mann-Kendall Test

Abstract

Rainfall variability and short-term dry spells critically influence agricultural productivity in rainfed regions such as the Western Undulating Zone (WUZ) of Odisha. With over 75% of annual rainfall concentrated in the monsoon months, any deviation in rainfall distribution can lead to moisture stress, crop yield loss, and heightened vulnerability to drought. This study presents a comprehensive trend analysis of dry spells across Kalahandi and Nuapada districts using 30 years (1995–2024) of daily rainfall data. Two indicators were used: consecutive dry days (CDD), and consecutive dry weeks (CDW). Dry spell events of varying durations were extracted for each block, and the Modified Mann–Kendall (MMK) test was applied to detect monotonic trends. Results reveal a strong spatial heterogeneity. In Kalahandi district, several blocks exhibited significant increasing trends in medium and long dry spells. Karlamunda showed the highest concentration of increasing trends across multiple durations (11-, 12-, 13-, 14-, and 15-day spells), followed by Bhawanipatna, Jaipatna and Junagarh. This indicates escalating drought risk and potential intensification of rainfall breaks within the crop-growing season. CDW analysis also confirmed increasing week-scale moisture stress in Karlamunda. Conversely, Nuapada district presented an opposite pattern, with multiple blocks Boden, Nuapada, Komna, and Sinapali, showing decreasing trends in both daily and weekly dry spell frequencies. These reductions suggest a gradual improvement in rainfall stability, although localized vulnerabilities persist, especially in Khariar and certain short-duration dry spells. The findings suggests to prioritize high-risk blocks for water resource allocation, contingency crop planning, and investment in irrigation infrastructure, ensuring agricultural resilience in Western Undulating Zone.