Evaluating Cost-Effectiveness of Rainwater Harvesting for Irrigation in Arid Climate of Gujarat, India

Abstract

Small reservoirs have proved as successful rainwater harvesting systems in semi-arid regions; however, their dependability in arid regions is not tested. This study aimed at evaluating cost-effectiveness of small reservoir used for supplying irrigation water to wheat and mustard crops in an arid region of India by employing three performance indicators, i.e., benefit-cost (B-C) ratio, net present value (NPV) and internal rate of return (IRR). In addition, sensitivity analysis of the variables influencing the economics of the reservoirs is also carried out. The actual water requirements for wheat and mustard crops over their entire life span of 110 and 95 days, respectively, are computed as 319 and 227 mm, respectively, in comparison to existing practice of excessively irrigating the crops. Fixed cost, i.e., cost of construction of the reservoir is estimated as Rs. 1,033,349, for a total storage capacity of 29,184.5 m3, whereas, the running cost, i.e., cost of cultivation for wheat and mustard, is worked out to be Rs. 41,800 and 31,100 per ha, respectively. The net benefit of Rs. 28,901 and 38,835 per ha, respectively for wheat and mustard crops clearly indicated that mustard is 34% economical over the wheat. The optimistic, pessimistic, and average unit costs of harvested rainwater over a 30-year period is calculated as Rs. 1.51, 3.03, and 2.27 m−3, respectively, which suggests that a small reservoir is a viable option for rainwater management in the arid regions. This finding is further supported from the optimum values of B-C ratio (1.01), NPV (Rs. 10,093), and IRR (10.12%). This study considered a scenario of demand-based efficient irrigation supplies with improved values of the B-C ratio (2.18), NPV (Rs. 1,330,558), and IRR (24%). Furthermore, sensitivity analysis revealed that the grain yield is the most significant variable affecting the cost-effectiveness of the reservoir system, which needs to be carefully monitored and enhanced in order to further increase reservoir dependability in arid regions. Finally, the findings of this study are very useful for planners and decision-makers to formulate appropriate strategies for managing scarce rainwater in the study area as well as in other arid climate regions of the world.