Post-Soviet changes in cropping practices in the irrigated drylands of the Aral Sea basin

Abstract

Water withdrawals for irrigated crop production constitute the largest source of freshwater consumption on Earth. Monitoring the dynamics of irrigated crop cultivation is crucial for tracking crop water consumption, particularly in water-scarce areas. We analyzed changes in water-dependent crop cultivation for 650 000 km2 of Central Asian drylands, including the entire basin of the Amu Darya river, once the largest tributary to the Aral Sea before large-scale irrigation projects grossly reduced the amount of water reaching the river delta. We used Landsat time series to map overall cropland extent, dry season cropping, and cropping frequency in irrigated croplands annually from 1987 to 2019. We scrutinized the emblematic change processes of six localities to discern the underlying causes of these changes. Our unbiased area estimates reveal that between 1988 and 2019, irrigated dry season cropping declined by 1.34 million hectares (Mha), while wet season and double cropping increased by 0.64 Mha and 0.83 Mha, respectively. These results show that the overall extent of cropland in the region remained stable, while higher cropping frequency increased harvested area. The observed changes’ overall effect on water resource use remains elusive: Following the collapse of the Soviet Union, declining dry season cultivation reduced crop water demand while, more recently, increasing cropping frequency raised water consumption. Our analysis provides the first fine-scale analysis of post-Soviet changes in cropping practices of the irrigated areas of Central Asia. Our maps are openly available and can support future assessments of land-system trajectories and, coupled with evapotranspiration estimates, changes in crop water consumption.

Focus on the future of water-limited agricultural landscapes

“…However, climatic changes have spurred new shifts that challenge both currently irrigated and traditionally dryland systems' capacity to cope with growing scarcity of water supplies. This is evident in practices such as the increased emphasis on wet season cropping in the Aral Sea basin (Rufin et al 2022), or the redesign of viable cropping strategies prompted by irrigation retirement in the Great Plains region of the US (Núñez et al 2022). In areas where agriculture depends heavily on irrigation, looming cutbacks in water availability underscore the need to understand how the transition from irrigated to non-irrigated systems will play out, along with its economic and environmental implications.…”

Correlation analysis between the Aral Sea shrinkage and the Amu Darya River

“…As the largest inland terminal lake in arid Central Asia, the Aral Sea plays a key role in the ecological environment and water resource utilisation. However, along with population growth, the rapid expansion of croplands in the middle and upper reaches of the Amu Darya River and Syr Darya River (Rufin et al, 2022), which represent the main water sources of the Aral Sea, has significantly decreased the incoming water to the lake basin. In addition, over the past 100 years, glacial recession and an increase in evapotranspiration caused by global warming have exacerbated the severity of this problem in Central Asia (Wang et al, 2020).…”

“…For instance, research conducted by Huang et al (2022) and Zhang et al (2022), who analysed glacier changes over the past century, showed that the inland lakes in Central Asia decreased, while the higher-altitude alpine lakes increased significantly along with glacier meltwater, stressing the importance of human activities in the lake area reduction of the Aral Sea. Rufin et al (2022) reported that croplands increased from 4.400×10 4 km 2 in 1987 to 5.200×10 4 km 2 in 2017, with more than a 200% increase in double-cropping irrigation lands, followed by a rapid urban expansion and sharp rise in water consumption in the last 20 years (Yan and Li, 2023), contributing to the problem. A comparative analysis of climatic and anthropogenic factors by Yang et al (2020a) concluded that anthropogenic factors were the main cause of the reduction in the lake area.…”