High-resolution and long-term land surface analysis in the Aral Sea basin

Abstract

Starting in the 1940s, the Soviet Union conducted a large-scale irrigation policy in the Aral Sea basin. As a result, the Aral Sea shrank drastically and it became 1/10 size of original area. Since the collapse of the Soviet Union, there has been no concerted effort among the independent countries to deal with water resources, and sloppy water management is still practiced. It is essential to provide scientific evidence to achieve sustainable water resource management in the basin as soon as possible.

In this study, the land surface model (SiBUC^A)) of the Aral Sea basin was improved by increasing the spatial resolution of the analysis and by using newly available data, referring to the analysis methodology of Touge^B). We increased the spatial resolution of the analysis by 20 times higher comparing to the analysis conducted by Touge. By doing this, we can capture the topography and land use in more detail, and the analysis results of various hydrological quantities can be improved. This is particularly effective to calculate with high accuracy by capturing the elevational characteristics of mountainous areas without averaging its elevation in an analysis mesh. In addition, new forcing data and Aral Sea bathymetry data were used in parallel to improve the analysis. The specific analysis outline is as follows. We analyzed the Aral Sea basin using the land surface model SiBUC^A) for a period of 50 years from 1961 to 2010 with a spatial resolution of 30 seconds. The Aral Sea shrinkage and the increase of irrigated area, which are remarkable area changes in the analysis period, were considered, referring to the methodology of Touge. We prepared Land use data with different irrigated area fraction for each year, and did coupling of the results of SiBUC to the dynamic change of the Aral Sea area for each year. The GSWP3^C) was newly used as the forcing data for the calculation of land surface processes.

As a result, the overestimation of runoff in the water balance of the Aral Sea catchment, which was an issue in the Touge’s paper, was improved. The water balance of the Aral Sea was analyzed with good accuracy, and the Aral Sea area was successfully reproduced considering its depth. In addition, we succeeded to visualize land use change and climate change in the watershed, and also, by comparing the results between 30sec resolution and 5min resolution, we found some usefulness of high-resolution analysis.