Changes in land use/land cover and net primary productivity in the transboundary Ili-Balkhash basin of Central Asia, 1995-2015

Using remotely sensed data, we documented changes in land use/land cover (LULC) from 1995 to 2015 and net primary productivity (NPP) from 2000 to 2014 in Central Asia's 415,048 km(2) Ili-Balkhash Basin (IBB). This basin, which is shared by China and Kazakhstan, is in the midst of significant socioeconomic transformation due to the collapse of the Soviet Union, the emergence of Kazakhstan, and the economic rise of China. Grazing land covered 82.4% of the IBB in 1995; water bodies and bare land were the only other LULC categories occupying more than 3% of the basin's area. Changes in LULC were most evident on the Chinese side of the border, where crop production areas increased and grazing areas decreased between 1995 and 2015. The area of irrigated cropland in China grew by nearly 30%, primarily in the upper Tekes River valley and along the Ili River near the border with Kazakhstan. In contrast, the irrigated lands in Kazakhstan shifted geographically during this period, but the extent did not change. Expansion of wetlands and permanent water bodies, which occupied 2.1 to 2.9% and 4.6 to 4.7%, respectively, of the IBB in 1995 and 2015, was associated with accretion of Lake Balkhash and Kapchagai Reservoir in Kazakhstan and the construction of new reservoirs in China. NPP of the basin approached 700 g C m(-2)/year in a few areas but was generally less than half this level and characterized by a declining trend except in highly productive irrigated areas of dense, stable vegetation. NPP decreases of more than -10 g C m(-2)/year were apparent in mountainous and upland areas, as well as broad band of grassland and cropland in Kazakhstan. Areas surrounding Lake Balkhash were characterized by unstable to moderately stable, often sparse vegetation.