Satellite monitoring of River Amu Darya oases during 2003-2020 based on irrigation cooling effect

Abstract

The Amu Darya River, with an average annual outflow of 62 km3, is the largest river in Central Asia. Its runoff is almost completely diverted to cropland irrigation, which has led to the catastrophic Aral Sea degradation. Interannual variability in River Amu Darya outflow, insufficient technical equipment of the regional hydrological monitoring system and contradictions in the economic interests of the regional countries make it difficult to organize effective water use in this transboundary river basin. One of the existing river's basin problems is the deficit of objective information about the irrigated cropland state. The list of satellite products that characterize the irrigation agriculture state in Amu Darya River oases can be expanded by the Land Surface Temperature (LST). Irrigation of arable land leads to its cooling - irrigation cooling effect (ICE). The ICE value can act as a parameter that characterizes the water availability of agricultural oases. The product LST FEWS NET (May - September) with ten days renew was used to monitor ICE values for the oasis's territories in the Amu Darya River basin during 2003-2020. Three oases have been considered: Merv (Murghab), Tejen and Khorezm. The first two oases are watered mainly by the Karakum Canal, which originates in the middle reaches of the Amu Darya River. The Khorezm oasis is located in the lower river's reaches. Analysis of the average ICE values for the oasis in the period June - July for the seasons 2003-2020 has shown that there is a close coherence between the regimes of the Merv and Tejen oases. Pearson's correlation coefficient was 0.76. At the same time, the coherence of states between the Khorezm oasis of the lower course of the Amu Darya River and the oases of the middle course is quite low, the Pearson correlation coefficient is 0.34. This indicates the inefficiency of the international mechanisms of water distribution of river runoff. We see that natural seasonal fluctuations in the Amu Darya River outflow do not lead to coherent changes in the ice values in all the oases under consideration. Diagnostics of the coherent level between the oasis state of the middle and lower reaches of the Amu Darya River using correlation analysis in floating time windows (8, 10, 12, 14 years) showed no progress in the international water allocation system during 2003-2020.