Critical Role of Irrigation Efficiency for Cropland Expansion in Western China Arid Agroecosystems

The rapid expansion of desert croplands in the Tarim River Basin, which depend heavily on irrigation with meltwater, has coincided with increases in snow and glacier melt in the high mountains of Asia during the past decades. Meanwhile, there have been intensive investments in modern irrigation technology aimed at enhancing water use efficiency. The importance of meltwater in mountain front agroecosystems has been widely acknowledged, but it is not clear how important this meltwater versus increased irrigation efficiency (IRE) has been for the rapid cropland expansion in the Tarim River Basin. Here we investigate changes in water supply and demand of the meltwater-irrigated cropland bordering the Taklamakan Desert based on multiple remotely sensed and ground-based observation datasets, and we evaluate the contributions of improved IRE to cropland expansion. We find that cropland has increased by 58% between 1990 and 2015. Net streamflow to the region increased by +10% over the same period, but the rate of increase was slower after 2000. This deceleration contrasts with the growing irrigation demand (IRD) imposed by dramatic cropland expansion. At the same time, IRE increased by 73% from 1990 to 2015, providing 18.5 billion m(3) irrigation water savings, which offset the increased IRD. With the adoption of more efficient irrigation, crop water stress due to continuous agricultural expansion in the Tarim River Basin declined significantly, making the dependence of agricultural production on runoff from glacier and snow meltwater less than would otherwise be expected.