Water Balance Analysis Based on a Quantitative Evapotranspiration Inversion in the Nukus Irrigation Area, Lower Amu River Basin

Zhibin Liu,Xiaohui Pan,Jiabin Peng,Yongchao Duan,Shamshodbek Akmalov,Tie Liu,Wei Xing,Junli Li,Yue Huang,Chenyu Guo

doi:10.3390/rs12142317

Abstract

Human activities are mainly responsible for the Aral Sea crisis, and excessive farmland expansion and unreasonable irrigation regimes are the main manifestations. The conflicting needs of agricultural water consumption and ecological water demand of the Aral Sea are increasingly prominent. However, the quantitative relationship among the water balance elements in the oasis located in the lower reaches of the Amu Darya River Basin and their impact on the retreat of the Aral Sea remain unclear. Therefore, this study focused on the water consumption of the Nukus irrigation area in the delta of the Amu Darya River and analyzed the water balance variations and their impacts on the Aral Sea. The surface energy balance algorithm for land (SEBAL) was employed to retrieve daily and seasonal evapotranspiration (ET) levels from 1992 to 2018, and a water balance equation was established based on the results of a remote sensing evapotranspiration inversion. The results indicated that the actual evapotranspiration (ETa) simulated by the SEBAL model matched the crop evapotranspiration (ETc) calculated by the Penman–Monteith method well, and the correlation coefficients between the two ETa sources were greater than 0.8. The total ETa levels in the growing seasons decreased from 1992 to 2005 and increased from 2005 to 2015, which is consistent with the changes in the cultivated land area and inflows from the Amu Darya River. In 2000, 2005 and 2010, the groundwater recharge volumes into the Aral Sea during the growing season were 6.74×109 m3, 1.56×109 m3 and 8.40×109 m3; respectively; in the dry year of 2012, regional ET exceeded the river inflow, and 2.36×109 m3 of groundwater was extracted to supplement the shortage of irrigation water. There is a significant two-year lag correlation between the groundwater level and the area of the southern Aral Sea. This study can provide useful information for water resources management in the Aral Sea region.

Highlights

The Aral Sea crisis has become a global ecological and social problem and is one of the hotspots in water resources research for Central Asia
The surface energy balance algorithm for land (SEBAL) model was initially developed by Bastiaanssen et al [32]; this model is based on the energy balance equation of the land surface, and the distribution of sensible heat flux is calculated by the cyclic recursive method, while the ETa of a region is obtained by the energy residual method [33]
The results indicate that the R2 and root mean square error (RMSE) values between the ETobservation and ETSEBAL values for water bodies are 0.81 and 1.76, respectively (Figure 3a)

Summary

Introduction

Human activities mainly include unsustainable irrigation methods and the expansion of cultivated land areas around the Amu Darya and Syr Darya River Basins [4,5,6,7], which have led to the overuse and waste of surface water resources and have indirectly affected the Aral Sea. For example, most drainage of the Amu Darya River, which is the largest river in central Asia, is presently controlled and used for irrigation [5]. Due to the construction of water conservation facilities and irrigation systems in the upper reaches, a number of immigrants were attracted to the middle and lower reaches to reclaim land, which caused the irrigation area to continue expanding, and agricultural water conditions were aggravated [8], which influenced the water balance of the Aral Sea by perturbing surface runoff and groundwater recharge [9,10,11,12]. It is important to study the water balance dynamics of the irrigation areas in the Aral Sea Basin when agricultural activities prevailed

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Conclusion