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.
Global warming accelerates the water cycle worldwide, and directly affects hydrological changes and may cause changes in water availability. The Tianshan Mountains, known as “water tower of Central Asia”, is situated in the Eurasia hinterland. It serves as the main water source and ecological barrier in Central Asia. Most rives originated from the Tianshan Mountains are recharged with rainfall, glacier melt and snow meltwater. The hydrological processes in the Tianshan Mountains are strongly affected by changes in temperature and precipitation, as well as changes in the snow and glaciers. Increases in temperature have important consequences for the hydrological cycle, particularly in areas dominated by glacier and snow melt.This study systematically investigated precipitation and temperature changes and their impacts on glaciers, snow cover and hydrological processes in the Tianshan Mountains using station observations, remote sensing data and reanalysis data. In a warming climate, precipitation is more likely to occur as rainfall rather than snowfall. Temperature-induced precipitation shifted from snow to rain since mid-1990s, with S/P experiencing an overall declining trend at a rate of 0.5%/decade. In addition, an overall increase in extreme precipitation was detected, as reflected in 25 indices. The number of consecutive dry days decreased from 87.02 to 69.35 while the number of consecutive wet days increased from 3.89 to 4.61. Changes in extreme precipitation frequency were shown to increase with event rareness. For R95p, the observed changes in frequency are 34.46%, but these jump to 96.58% for R99p.  By creating a long-term, high-quality, daily snow cover extent (HMASCE) product (1982–2019, spatial resolution of 5 km), the spatial and temporal variability in snow metrics (snow cover area and snow cover phenology) has investigated. Snow cover in the Tian Shan region showed a slight increase during this period, mainly in West Tianshan (0.66% a-1), Hissar Alay (0.64% a-1), and East Tianshan (0.24% a-1).Approximately 97.52% of glaciers in the Tianshan Mountains showed a retreating trend. For the northern TianShan Mountains,  total area and volume of glaciers exhibited negative trends, decreased by 456.43 km2 (16.08%) and 26.14 km3 (16.38%), respectively, from 1990 to 2015. The reduction in the glacier area exhibited an accelerating trend, with a decreasing rate of 0.60% a-1 before 2000, but of 0.71% a-1 after 2000. River runoff responds in a complex way to changes in climate and cryosphere. For example, the runoffs of the Kaidu River and the Aksu River, located in the south flank of the Tianshan Mountains, have increased by 27.4% and 14.4%, respectively, during 1960 to 2021. The total water storage in the Tianshan Mountains also experienced a significant decreasing trend with a rate of 12.12 mm a-1 during 2020~2021..This study sheds light on current and future changes in water cycle under global warming in the Tianshan Mountains. More efforts should be made on the interpretation of impacts and mechanisms of these changes on runoff, which is a key factor that controls the amount and seasonality of freshwater resources for domestic and agricultural needs.
Abstract. Results from ten global climate change models are synthesized to investigate changes in extremes, defined as wettest and driest deciles in precipitation, soil moisture and runoff based on each model's historical twentieth century simulated climatology. Under a moderate warming scenario, regional increases in drought frequency are found with little increase in floods. For more severe warming, both drought and flood become much more prevalent, with nearly the entire globe significantly affected. Soil moisture changes tend toward drying while runoff trends toward flood. To determine how different sectors of society dependent the on various components of the surface water cycle may be affected, changes in monthly means and interannual variability are compared to data sets of crop distribution and river basin boundaries. For precipitation, changes in interannual variability can be important even when there is little change in the long-term mean. Over 20% of the globe is projected to experience a combination of reduced precipitation and increased variability under severe warming. There are large differences in the vulnerability of different types of crops, depending on their spatial distributions. Increases in soil moisture variability are again found to be a threat even where soil moisture is not projected to decrease. The combination of increased variability and greater annual discharge over many basins portends increased risk of river flooding, although a number of basins are projected to suffer surface water shortages.
Abstract The arid region of Northwest China (ARNC) has experienced a significantly higher warming rate than the global average and exhibits pronounced seasonal asymmetry, which has important implications for the region’s water-dependent systems. To understand the spatiotemporal patterns and driving mechanisms of seasonal asymmetric warming in the ARNC, we investigated seasonal changes in temperature rise and their underlying causes based on station and reanalysis data. We found that the dominant season of temperature increase shifted from winter to spring. The contribution of spring warming to the total temperature increase rose from −5%–7% to 58%–59%, while the contribution of winter warming decreased from 60%–75% to −4%–9%. However, the mechanisms underlying spring warming and winter cooling differ. An increase in solar radiation caused by a decrease in cloud cover ( R = −0.64) was the main reason for spring warming, while a strengthening Siberian High primarily drove winter cooling.
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