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[AHW24-05] Quantifying Historical Water Consumption Components in the Aral Sea Basin Using a Terrestrial Water Circulation Model
Keywords:The Aral Sea, Endorheic basin lake, Land surface model, Irrigation water demand, Human impact
The Aral Sea has significantly shrunk due to large-scale irrigation development since the latter half of the 20th century. The increase in water consumption was not only due to water absorbed by crops but also included other factors such as irrigation inefficiencies and withdrawals outside the basin. Quantifying these water consumption components is essential for reproducing and predicting changes in the lake. Therefore, Touge et al. (2024) developed a terrestrial water circulation model for the entire basin, coupled with an endorheic lake budget model. The objectives were: (i) to establish a physical framework that represents changes in the endorheic lake in response to the basin’s water balance, and (ii) to quantify water consumption components. In this presentation, we will introduce the model structure and the results related to (ii).
The model consists of 3 key components: vertical water and heat balance for each grid using land surface model, basin water balance assessment, and endorheic lake budget model to estimate changes in lake surface area. The analysis was conducted at a 1 km resolution for 1961-2010. The high spatial resolution is expected to improve the accuracy of long-term glacier melt estimates and seasonal snowmelt variations in mountainous areas, which are crucial for this region (Sadyrov et al., 2024). The model is a valuable tool for assessing climate change impacts, particularly in relation to irrigation water demand, water management, and drought.
The land surface model SiBUC was used to capture various land cover types, including irrigated areas and water bodies, which were critical to this study. The irrigation scheme was calibrated using in-situ soil moisture measurements (Touge et al. 2015), while the distribution of irrigated areas was derived from the MIRCA2000. ISIMIP3a data were utilized and further adjusted to align with reported long-term land cover changes. Since SiBUC does not directly model irrigation efficiency, efficiency rates were estimated based on the values reported by Aus der Beek et al. (2011).
Water withdrawals outside the basin were estimated using historical records, with diversion to the Karakum Canal inferred from reported values for 1995 and changes in irrigated area along the canal. Assuming a constant withdrawals ratio for 1995, past withdrawal trends were reconstructed. In addition, historical surface water area estimates from Landsat imagery were estimated for sink lakes such as Lake Sarygamysh, aligning with observed changes in the lake.
Long-term trends in water consumption components across the Aral Sea basin were analyzed (Fig. 1, Touge et al. 2024). Between 2001 and 2010, the estimated annual water consumption components were: irrigation water demand (39.0 Gt/yr), losses due to irrigation inefficiencies (26.3 Gt/yr), withdrawals to the Karakum Canal (9.4 Gt/yr), and drainage into Lake Sarygamysh (6.5 Gt/yr). These figures directly point to the scale of water loss in the basin, especially given that total evaporation from the Aral Sea during this period was less than 30 Gt/yr. The results show the critical role of irrigation inefficiencies and inter-basin water transfers in accelerating the decline of the Aral Sea.
Reference:
Aus der Beek et al., 2011. Modelling the impact of Global Change on the hydrological system of the Aral Sea basin. Physics and Chemistry of the Earth, 36, 684–695.
Sadyrov et al., 2024. Modelling runoff components and hydrological processes in glaciated catchments of the inner Tien-Shan, Kyrgyzstan. Frontiers in Earth Science, 11, 1306476.
Touge et al. 2015. Developing a Water Circulation Model in the Aral Sea Basin based on in situ Measurements on Irrigated Farms. Journal of Arid Land Studies 25, 133–136.
Touge et al. 2024. Reproduction of Historical Water Balance in the Aral Sea Basin: the Physically-Based Framework to Quantify Water Consumption Components in Endorheic Lake. Journal of Hydrology, 640, 131711.
The model consists of 3 key components: vertical water and heat balance for each grid using land surface model, basin water balance assessment, and endorheic lake budget model to estimate changes in lake surface area. The analysis was conducted at a 1 km resolution for 1961-2010. The high spatial resolution is expected to improve the accuracy of long-term glacier melt estimates and seasonal snowmelt variations in mountainous areas, which are crucial for this region (Sadyrov et al., 2024). The model is a valuable tool for assessing climate change impacts, particularly in relation to irrigation water demand, water management, and drought.
The land surface model SiBUC was used to capture various land cover types, including irrigated areas and water bodies, which were critical to this study. The irrigation scheme was calibrated using in-situ soil moisture measurements (Touge et al. 2015), while the distribution of irrigated areas was derived from the MIRCA2000. ISIMIP3a data were utilized and further adjusted to align with reported long-term land cover changes. Since SiBUC does not directly model irrigation efficiency, efficiency rates were estimated based on the values reported by Aus der Beek et al. (2011).
Water withdrawals outside the basin were estimated using historical records, with diversion to the Karakum Canal inferred from reported values for 1995 and changes in irrigated area along the canal. Assuming a constant withdrawals ratio for 1995, past withdrawal trends were reconstructed. In addition, historical surface water area estimates from Landsat imagery were estimated for sink lakes such as Lake Sarygamysh, aligning with observed changes in the lake.
Long-term trends in water consumption components across the Aral Sea basin were analyzed (Fig. 1, Touge et al. 2024). Between 2001 and 2010, the estimated annual water consumption components were: irrigation water demand (39.0 Gt/yr), losses due to irrigation inefficiencies (26.3 Gt/yr), withdrawals to the Karakum Canal (9.4 Gt/yr), and drainage into Lake Sarygamysh (6.5 Gt/yr). These figures directly point to the scale of water loss in the basin, especially given that total evaporation from the Aral Sea during this period was less than 30 Gt/yr. The results show the critical role of irrigation inefficiencies and inter-basin water transfers in accelerating the decline of the Aral Sea.
Reference:
Aus der Beek et al., 2011. Modelling the impact of Global Change on the hydrological system of the Aral Sea basin. Physics and Chemistry of the Earth, 36, 684–695.
Sadyrov et al., 2024. Modelling runoff components and hydrological processes in glaciated catchments of the inner Tien-Shan, Kyrgyzstan. Frontiers in Earth Science, 11, 1306476.
Touge et al. 2015. Developing a Water Circulation Model in the Aral Sea Basin based on in situ Measurements on Irrigated Farms. Journal of Arid Land Studies 25, 133–136.
Touge et al. 2024. Reproduction of Historical Water Balance in the Aral Sea Basin: the Physically-Based Framework to Quantify Water Consumption Components in Endorheic Lake. Journal of Hydrology, 640, 131711.