Is there a turning-point towards improved water and ecological security at the arid Tarim River Basin?

The arid Tarim River Basin, situated in the Eurasia hinterland, serves as the heart of China’s Silk Road Economic Belt. It covers an area of 1.02 million km² and is surrounded by the Tienshan Mountains to the north, the Kunlun Mountains to the south and the Pamir to the west. During the past few decades, the contradiction between economic growth and environmental protection is particularly evident. For example, the desert riparian forest vegetation has declined along the lower reaches of the Tarim River.

Under global warming, the climate has experienced significant warming and moistening trend during 1961–2018, and the most dramatic increase has occurred since the mid-1980s. The increased precipitation and temperature and the resulted hydrological and ecological changes lead to a hot debate about the “warm–wet” trend. This study systematically investigated the climate change and their impact on hydrological and ecological processes. The temperature increased at a rate of 0.224 ℃ per decade and an evident jump was detected in 1998. For precipitation, about 72.3% meteorological stations experienced significant increase, with an average increasing rate of 7.47 mm per decade. The changes in climatic factors contribute to the changes in the accumulation and ablation of snow and glaciers, which resulted in changes in hydrological processes. The total lake area in the Tarim River has expanded at a rate of 23.79 km² per year during 2012–2021. More specially, the lake area of Ayakum Lake (located near the northern boundary of the Tibetan Plateau) has increased by 50% since 1990, with an increment of 111.61 km² during 1990–2000 and 401.4 km² during2000–2020. The runoffs of the headwaters (i.e., Kaidu River, Aksu River, Yarkant River and Hotan River) of the Tarim River have also increased by a rate of 2.06×10⁸m³, 2.11×10⁸m³, 1.12×10⁸m³ and 2.56×10⁸m³ per decade, respectively.

However, the changes in ecological systems don’t reflect the wetter trend in the Tarim Basin. The negative effects of climate change on the region’s vulnerable ecology have intensified. The snowfall fraction experienced an overall declining trend, increasing at a rate of 0.6% per decade prior to the mid-1990s, followed by a downward trend at a rate of 0.5% per decade. Potential evaporation decreased at a rate of 41.66mm/10a per decade prior to the mid-1990s, and inversed to increase at a rate of 56.68 mm per decade. Prior to 1998, the normalized difference vegetation index (NDVI) of natural vegetation exhibited an increasing trend at a rate of 0.012 per decade, but from 1999 onwards, the NDVI started decreasing at a rate of 0.005 per decade. The bare soil areas of the Taklamakan Desert boundaries expanded by 7.8 % since 1990. Excessive water use, including unrestrained overpumping of groundwater, causes the loss of groundwater.

This study sheds light on the debate of changes in climate and ecological security under global warming in the endoreic Tarim River Basin. However, more efforts should be made on the continuity of these changes, which is crucial for local development and water and ecological security along the Silk Road.