Twentieth Century Rainfall Trends of Uttarakhand, India: A Spatio-Temporal Analysis

Rainfall is a prime input of the hydrological cycle and therefore its variability analysis plays a key role in designing of engineering structures and crop planning. The increase in uncertainty of rainfall events may affects the water resources which lead to decrease the production in agricultural sector especially in hill region like Uttarakhand. The present study was based on spatio-temporal analysis of rainfall variation in the state of Uttarakhand, India over the 20th century (1901–2000). Sen's slope and Mann-Kendall statistics were used to test the trend in annual and seasonal rainfall pattern, and the maximum decrease in monsoon rainfall was observed in Champawat district (2.16 mm year⁻¹) followed by Bageswar (1.82 mm year⁻¹), and Pithoragarh (1.80 mm year⁻¹). Rainfall in winter and postmonsoon seasons also decreased in all the districts but the changes observed were not significant (p>0.05). Pettitt's test was employed to know the most probable change year for seasonal and annual rainfall trend. After 1986, a significant declining trend over the year was observed in annual, post-monsoon and monsoon rainfall showed at the probability levels of 0.052, 0.085 and 0.059, respectively. Whereas, after 1964, a declining trend during winter rainfall was observed but the change was found to be nonsignificant (p= 0.452). To know the periodicity of rainfall pattern, Wavelet analysis was done and observed an increasing frequency of annual and monsoon extreme rainfall events with stronger periodicity of 2–8 years in the recent decades. These findings will be helpful for the policy makers for optimal water allocation and also for making scientific management strategies for constructions of engineering structures, utilization of rain water for agriculture such as land preparation and sowing, and other uses.