Land use land cover change (LULCC) have emerged as important concerns in the context of environmental and resource conservation, especially where the pace of development is fast as in the Lower Turag River Basin in Bangladesh. The expansion of urban areas typically results in drastic changes in vegetation cover, thereby having a profound impact on local ecosystems, agriculture and water resources. It is worth mentioning the changes in the extent and pattern of urbanization and the quantity and quality of the agricultural land that is consumed as the population expands. Land is needed to fulfill this need by converting agricultural lands into urban forms. In addition, problems of water source disruption and bio-diversity loss are not an exception to this issue; thus, general food insecurity endangers ecological balance [1] . From 1989 to 2009, agricultural land use in areas close to Dhaka decreased significantly due to urban encroachment and improved transportation networks [2] . Rural-urban migration, especially, caused the growth of the Dhaka Metropolitan Development Planning area at an average annual rate of 3.84% between 1981 and 2011 [3] .

The Lower Turag River Basin primarily occurs in the highly productive agricultural zone and has experienced significant urbanization within the past twenty years. Various factors may lead to the transformation of rural areas, such as population, economic, and infrastructural development. Such dynamics of land use/land cover changes (LUCC) have implications for other hydrologic, nutrient, and general ecosystem status in the region [4] [5] . Research has revealed that urbanization has characteristic effects on runoff, sediment transportation, and water quality deterioration if the ratio of urban land extends beyond some benchmarks [6] [7] . To mitigate the challenges of unplanned urbanization, effective monitoring and management of land use changes is necessary [8] . The lack of adequate development planning has led to vulnerabilities in peri-urban areas [9] . Measuring the agricultural land consumption and population growth rates is important to determine the spatial pattern of land conversion [10] . A study reveals the decadal change of LULC, showing a 22.1% increase in built-up areas where agricultural land and green space have reduced significantly by utilizing remote sensing data [11] . Moreover, the use of remote sensing devices and Geographic Information System (GIS) have made it easier for the researchers to assess these changes.

It is appreciable that using Google Earth Engine (GEE) tools, temporal land cover dynamics can be determined and consequences of urbanization on agricultural land and water quality can be analyzed [5] [12] . Again, SDG Indicator 11.3.1 evaluates the balance between urban land consumption and population growth, providing a framework to assess sustainable urbanization. A ratio greater than 1 indicates disproportionate land consumption relative to population growth, often linked to inefficient land use practices. Integrating Land Consumption Rate (LCR) and Population Growth Rate (PGR) can be helpful to analyze the land use efficiency which provides a framework that can be applied to Dhaka to assess urban growth sustainability [13] . This study intends to identify and measure land cover conversion by Urban Expansion in the Lower Turag River Basin between the years 2000 and 2020, with particular emphasis on arable land consumption per head of the growing population, which will be conducted up to 2030 based on the next census. Identifying these dynamics will better inform sustainable land management practices and policy decisions that balance urban development with agricultural needs and environmental conservation.

Turag River of Bangladesh is a tide-influenced River passing through west-north and north of Dhaka City [14] . The Turag River originates from the Bangshi River [15] which originates from the foot of the madhupur tract. Turag is also the upper tributary of the Buriganga River [15] . Buriganga merges with the Shitlakya River near Narayanganj district. The Turag flows through Gazipur district and joins the Buriganga at Mirpur in Dhaka district. The Tongi Khal links the Turag with the Balu River [16] . The entire regime of the Turag is almost a semi-funnel-shaped basin, and its catchment is located on the central and southern parts of the Madhupur tract, which flows from north to south within the basin [17] . The lower Turag River Basin area includes 11 Unions with 88 Mauzas and 42 Wards having 199 Mauzas from 2 districts (Dhaka and Gazipur).

The Digital Elevation Model (DEM) of the Lower Turag River Basin shows that the basin’s highest elevation is 55 meters and is located primarily in the southwestern and northern parts. The lowest elevation, which is −16, is concentrated in the central region, which has the main course of the river, according to SRTM DEM data.

The total area of the Turag River is about 631 km². The Lower Turag River basin is considered southward from the Kodda Bridge, Tangail, and ends at the point where Turag meets the Buriganga River, covering a total area of approximately 252 square kilometers ( Figure 1 ).

SRTM DEM data was used to produce the map of the Lower Turag Basin area. By using satellite imageries from Landsat 5 and Landsat 8 on the GEE platform, LULC maps in JavaScript have been produced. Google Earth Engine (GEE) is a cloud-based geospatial analysis platform that enables efficient processing of large-scale satellite data. It is particularly effective for tracking land cover changes over time due to its integration of multi-temporal and multi-resolution datasets. To assess the statistical significance of those produced maps, Kappa Accuracy and Overall Accuracy, taking 70% for training samples and 30% for testing samples, were calculated ( Figure 2 ).

Following the formula provided by UN Habitat to calculate SDG Indicator 11.3.1, Agricultural Land Consumption Rate to Population Growth Rate (ALCRPGR) across Turag River Bassin has been calculated for the period of 2000-2010 and 2010-2020 ( Figure 3 ) and agricultural land transforming pattern has been observed at 1 km² gridded map for the respective years in ArcMap 10.8.

Equation (1) is Land Consumption Rate, i.e.

$\text{LCR}=\frac{V_{\text{present}}-V_{\text{past}}}{V_{\text{past}}}\ast \frac{1}{\left(t\right)}$ (1)

where:

V_present is total built-up area in the current year;

V_past is total built-up area in the past year;

t is the number of years between V_present and V_past (or length in years of the period considered.

Equation (2) is Population Growth rate, i.e.

$\text{PGR}=\frac{\text{LN}\left({\text{Pop}}_{t+n}/{\text{Pop}}_t\right)}{\left(y\right)}$ (2)

where:

LN is the natural logarithm value;

Pop_t is the total population within the urban area/city in the past/initial year;

Pop_t+n is the total population within the urban area/city in the current/final year;

y is the number of years between the two measurement periods.

Equation (3) is

$\text{LCRPGR}/\text{LUE}=\left(\frac{\text{Land}\text{Consumption}\text{rate}}{\text{Population}\text{growth}\text{rate}}\right)$ (3)

The overall formula can be summarized as:

$\text{LCRPGR}=\left(\frac{V_{\text{present}}-V_{\text{past}}}{V_{\text{past}}}\ast \frac{1}{T}\right)/\left(\frac{\text{LN}\left(\frac{{\text{Pop}}_{t+n}}{{\text{Pop}}_t}\right)}{y}\right)$ [18]

This study shows the land use and land cover dynamics over two decades, which will continue up to 2030, based on the next census. By leveraging Google Earth Engine and SDG metrics, it is evident that the study indicates a clear decline in agricultural land as urban expansion continues to consume cultivated areas in the Lower Turag River Basin. The agricultural land consumption rate demonstrates that cropland is being lost at a significant rate relative to population growth. The spatial analysis further reveals that the areas closest to urban centers and along the riverbanks have been the most affected by this conversion. The findings highlight the need for strategic planning and policy interventions to protect the remaining agricultural land from further encroachment. Without such measures, the region risks losing vital farmland, which could have serious consequences for local food security and environmental sustainability. This study emphasizes the urgent need to balance urban development with agricultural preservation to ensure a sustainable future for the Lower Turag River Basin.

The authors are grateful to Rezaul Roni, Associate Professor, Department of Geography and Environment, Jahangirnagar University, for providing the necessary infrastructure and facilities. The authors acknowledge the Bangladesh Bureau of Statistics for providing census data. We are also thankful to MD. Ashikur Rahman Rahat, Postgraduate Researcher, Department of Geography and Environment, Jahangirnagar University, for helping with data integration throughout the study.