Water usage trends under intensive groundwater-irrigated agricultural development in a changing climate ? Evidence from Bangladesh

Comprehensive information on the past trend of local-level water usage of the cultivated crops is important for agricultural planning and forecasting water needs. This vital information is however deficient for the North-West (NW) region of Bangladesh. We estimated actual crop evapotranspiration (ET), total and crop-usable effective rainfalls (TER and ER, respectively) and irrigation requirement (IR) of 8 major crops and 8 cropping patterns over historical period (1985?2015) by using SWBcropwat model and trends of these water parameters by using MAKESENS tool for the 16 districts of the region. ET of the Rabi crops and cropping patterns revealed significant (p ? 0.05) decreasing trends in all districts, the average decrease being 13?31% in different districts. ER decreased significantly for most dry season crops in 4 districts. TER was often greater than ER for Kharif crops, which could not fully utilize TER always because of its non-uniform temporal distributions. IR showed significantly decreasing trend for the Rabi crops in 11 districts and increasing trend for the Kharif crops in 5 districts. Although ET and IR decreased in most cases, their total volumetric quantities showed significantly increasing trends due to expanded irrigated area in 16 districts over time; IR increased by 27?186% in different districts. Because of water scarcity and prospective economic benefit, farmers have been spontaneously adjusting crop selection ? shifting from higher-water demanding crops to lower water-demanding crop-cultivation ? during the last two decades. Our information would guide planning the agriculture of the NW region by selecting appropriate crops based on sustainable limit of groundwater resources. The employed methodology can evaluate crop suitability periodically for adjustment in any area.

Automated summary

Comprehensive information on the past trend of local-level water usage of cultivated crops is important for agricultural planning. However, such information is lacking for the North-West region of Bangladesh. The study found significant decreasing trends in ET for Rabi crops and cropping patterns in all districts, as well as an increase in total volumetric quantities of water due to expanded irrigated area over time.