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Impact of Temperature Changes on Groundwater Levels and Irrigation Costs in a Groundwater-dependent Agricultural Region in Northwest Bangladesh

Golam Saleh Ahmed Salem
Department of Environmental Studies, Tohoku University, Japan

So Kazama
Department of Civil Engineering, Tohoku University, Japan

Shamsuddin Shahid
Faculty of Civil Engineering, Universiti Teknologi Malaysia, Malaysia

Nepal C. Dey
Research and Evaluation Division, Bangladesh Rural Advancement Committee, Bangladesh

Abstract/ Executive Summary:

Changes in hydrological processes due to rising temperatures and related effects on the socio-economy and people’s livelihood are major concerns in Bangladesh. A study has been performed to assess the effects of increasing temperature on the groundwater levels and consequent changes in irrigation costs for groundwater-dependent irrigated agriculture in Northwest Bangladesh. A support vector machine (SVM) was used to model the temporal variations in groundwater level from rainfall, evapotranspiration, groundwater abstraction, and agricultural return flow. A multiple linear regression (MLR) model was developed to define the functional relationship between irrigation costs and groundwater levels. The model showed that the average groundwater level during the major irrigation period (January–April) decreased by 0.15–2.01 m due to an increase in temperature of 1–5°C, which increased irrigation costs by 0.05–0.54 thousand Bangladesh Taka (BDT) per hector.

Keywords: Temperature rise; Groundwater level; Irrigation cost; Northwest Bangladesh

Location: Northwest Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Groundwater

Objectives:

The major objective of the present study is to assess the effects of increasing temperature on groundwater levels and consequent changes in irrigation costs in a groundwater-dependent irrigated agriculture region in Northwest Bangladesh. Groundwater is the only source of irrigation in this region. Therefore, a decrease in the groundwater table due to rising temperatures may seriously affect the agro-based economy in the region.

Methodology:

The study area in Northwest Bangladesh (latitude: 24.07°N to 24.43°N; longitude: 88.17°E to 88.58°E) is a part of the Ganges River basin. The topography of the study area is extremely flat with some upland in the northwest. The surface geology of the area consists of sedimentary formations of alluvial sand, silt and clay of riverine origin (Shahid et al., 2015; Sattar et al., 2016). High-Yield Variety Boro rice is the major crop grown in the groundwater-based irrigation system and the lifeline of the economy of the area. The maximum depth to the groundwater table in the area is 5–17 m from the land surface during the irrigation season (January–April). The intensively irrigated agriculture in the area effectively contributes to ensuring the food security of Bangladesh. However, because of inappropriate anthropogenic intervention, the groundwater level during the irrigation period continues to decrease. Currently, the groundwater levels in most of the shallow tube-wells, which are widely used for irrigation, are below the suction lift capacity during the peak irrigation period.

Data and sources Bi-monthly data on groundwater levels (the depth to groundwater table from the land surface) recorded at 10 observation wells across the study area during 1991–2009 were obtained from the Bangladesh Water Development Board (BWDB). Daily rainfall and air temperature at 2 meters above the ground surface, which were recorded at Rajshahi station in the study area between 1961–2010, were obtained from the Bangladesh Meteorological Department (BMD). Data related to the irrigation cost, irrigation area, and groundwater level in 116 irrigated paddy fields were obtained from the Bangladesh Rural Advancement Committee (BRAC) Research Centre.

The steps to estimate the effect of increasing temperature on the groundwater level and irrigation cost were as follows: 1. A support vector machine (SVM) model was calibrated and validated to simulate the monthly average depth to groundwater level from the monthly total of rainfall, evapotranspiration, groundwater withdrawal, and irrigation return flow. 2. The calibrated SVM model was used to simulate the changes in depth to groundwater level due to changes in temperature. 3. A multiple linear regression (MLR) model was developed to simulate the irrigation cost from the depth of groundwater level and irrigated area. 4. The MLR model was used to estimate the changes in irrigation cost that result from the changes in the depth of groundwater level due to temperature rise. In the present study, the actual crop evapotranspiration was obtained by multiplying the crop coefficient with the reference evapotranspiration value, which was estimated using the modified Penman formula (Doorenbos and Pruitt, 1977). The crop coefficient values for different growing stages of rice, provided by FAO, were used for this purpose (Brouwer and Heibloen, 1986). Since groundwater is the only source of irrigation in the study area, the monthly amount of groundwater abstraction was considered equal to the net irrigation water required for a paddy field. The irrigation requirement in a paddy field was calculated using the FAO-56 model (Brouwer and Heibloen, 1986):

Source of Information: Hydrological Research Letters 11(1), 85–91 (2017)

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

This paper assesses the effects of increasing temperature on groundwater levels and irrigation costs in a groundwater-dependent irrigated region in Northwest Bangladesh. The results show that the average groundwater level during the major irrigation period (January-April) decreased by 0.15– 2.01 m because of an increase in temperature of 1–5°C, which increased irrigation costs by 0.05–0.54 thousand BDT ha–1. The findings of the study are expected to be helpful for adaptation studies and the adoption of necessary mitigation measures.

Knowledge Management: Journal