Impact of Rainfall Trend on Irrigated Agriculture of Narayanapura Command in a Semi-Arid Region of South India

Water demands have been exacerbated by the uncertainty in rainfall occurrences and distribution due to various factors in a changing climate and growing population. The irrigation sector has the highest water demand, accounting for 85 percent of total water use in Karnataka. Rainfall plays a critical part in meeting irrigation needs. To effectively allocate and manage water resources for command area management, examining rainfall patterns, distribution of rainfall trends, both regional and temporal variations is necessary. Hence, the primary focus of this research is to investigate the impact of rainfall trends on agricultural water requirements for a typical study area in semi-arid region.

To assess the rainfall trend, time-series statistical trend tests called Mann–Kendall (MK) test and the Innovative Trend Analysis (ITA) approach are used to examine the spatio-temporal distributions of long-term rainfall patterns for the Narayanapura command region. The results are then geo-processed to examine the spatial distribution of trends using the isohyetal concept. The findings illustrate the spatial distribution of rainfall trend for the command in a semi-arid region on a monthly, monsoon, and annual basis.

Spatio-temporal analyses from both methodologies indicates the trend in rainfall pattern is decreasing annually and in monsoon months, with a rising trend for pre-monsoon showers. The trend variation pattern also reveals periodic oscillation alignment in the direction of south-west monsoon movement. According to MK test results, monsoon rainfall is anticipated to decrease by 12 percent by 2047, and by 21 percent from ITA results. Further, impact analysis indicates that, for every unit millimeter of rainfall deficit, there would be a 62 Ha-m increase in irrigation water demand.