Changing occurrence of crop water surplus or deficit and the impact of irrigation: An analysis highlighting consequences for rice production in Bangladesh

Disentangling the impacts of water deficit and lack of irrigation infrastructure on critical food supplies such as rice in countries like Bangladesh remains a challenge. In this paper, we explore this challenge using North Bengal as a case study site over 1979–2018. We characterise crop water surplus/deficit with meteorological and soil moisture data and analyse the coherence of these timeseries with rice production in the study region. We then examine the trends, periodicities and degree of coherence between crop water surplus/deficit, irrigation, and rice production. Our results indicate an almost constant water deficit during winter and maximum water deficits in the pre-monsoon and post-monsoon periods. Critically, crop water surplus shows a significantly decreasing trend since 1979 during the monsoon period. We find that the correlation between crop water surplus/deficit, while strongly correlated with meteorological drought, weakens over time. This is suggestive of the important role that irrigation development has played over this period. Although the severity and frequency of water deficits have increased during the study period, possibly as a result of climate change or variability, rice production has decoupled from this trend and is instead positively correlated with irrigation. Despite this encouraging finding, it is unknown if technological progress will continue and whether there will be sufficient extractable groundwater and surface water to meet increasing irrigation demand in the future. Our finding of a long-term increase in water deficit underscores the likely future challenges in these critical rice growing regions for the people of Bangladesh, should this trend continue. The future sufficient rice production in the region will likely rely on the availability of reliable and affordable fuel or electric power to operate irrigation systems and a proactive and vigilant approach to agricultural water security in a variable and changing climate.