Streamflow Pattern Variations Resulting from Future Climate Change in Middle Tianshan Mountains Region in China

In arid and semi-arid regions of North West china, glacier-melt, seasonal snowmelt and rainfall are the primary sources of flow in the rivers that originate from alpine areas. Spring and summer peak flow resulting from snowmelt and rainfall, respectively, are the main characteristics of streamflow pattern. Because of the damages caused by the spring and summer peak flow, a better understanding of the streamflow pattern variation under future climate warming is crucial. To analyze the variation of streamflow pattern under climate warming, the Kaidu River and the Manasi River watersheds in northern and southern slopes of Middle Tianshan Mountains, located in Xinjiang were selected as study areas. These watersheds receive water from water sources in different proportions. A modified hydrological model was forced with metrological data from CIMP5 data set and the streamflow in Kaidu and Manasi River watersheds were simulated. The results indicate that one-peak-flow pattern is projected to turn to the two-peak-flow pattern in the Manasi River watershed in the future. The two-peak flow pattern will continue in the Kaidu River watershed, but the dominant peak flow will shift from summer to spring in future. This study provides useful information for water resources managers to take different actions to reduce damages caused by spring and summer peak flow under future climate warming

Lake dynamics in Central Asia in the past 30 years

Water is a key resource in arid Central Asia (CA) and is heavily affected by climate change and human activities. Temperature across the region has increased drastically especially in the mountain region while precipitation change is less homogeneous. The increased temperature has caused increased melting of glacier and snow which has a large contribution to the runoff in rivers. Human activities such as agriculture irrigation and reservoir management also affect water availability. In the Soviet era, agriculture in CA expanded continuously and large amount of water was extracted from rivers for irrigation. This has caused the catastrophic decline of the Aral Sea. In the post-Soviet era, countries in CA have reorganized their agriculture structure to be self-sufficient. It is important to understand how these changes affect water availability in CA especially under climate change. This dissertation uses lakes as proxy indicators of water availability and assesses how climate and human activities have affected lakes in CA. Seventeen lakes located in three former Soviet republics and western China from seven basins are examined using remote sensing and hydrologic modeling to estimate their changes in area, water level and volume. Agriculture area changes in these basins from seven countries are also examined using remote sensing. It is found that 1) lakes located in the mountains have generally expanded due to the melting glaciers and snow; 2) lakes located in the lowlands have remained relatively stable due to the relative stability of agriculture area; 3) reservoirs exhibit different seasonal patterns due to their major function as power generation reservoirs release water during the winter while irrigation reservoirs release water during the summer; 4) agriculture area in the former Soviet Central Asia republics is highly dependent on precipitation due to the lack of efficient irrigation infrastructure while agriculture in China has continuously expanded due to the adoption of drip irrigation and groundwater extraction. In conclusion, climate is the more dominant factor affecting water availability especially in the mountains causing the lakes to expand while agriculture irrigation has offset some of the surplus in the lowlands causing the lakes to remain relatively stable

Assessment of climate change in Central Asia from 1980 to 2100 using the Koppen-Geiger climate classification

The accelerated global warming and heterogeneous change in precipitation have been resulting in climate system shifts, which plays a key role in the stability of ecosystem and social economic development. Central Asia is account 80% of the temperate desert, characterized by fragile ecosystem; however, it has experienced the fastest warming in recent decades and projected warming in future. The Koppen-Geiger climate classification is a useful tool to assess the potential impacts of climate change on regional ecosystem. The spatial shift and temporal evolution of each climatic zone based on Koppen-Geiger climate classification are analyzed in historical and future period under different scenarios (RCP2.6, RCP4.5 and RCP8.5), high risk regions that might experience more frequent climatic zone shifts are delimited in this study, which could provide the useful information for developing mitigate strategies in coping with the warming threat. The hotter and dryer subtypes of arid climatic zone and warmer subtypes of temperate climatic zone expanded their coverage in Central Asia, corresponding to the tundra climatic, cooler subtype of arid and temperate climatic zone contracted. Based on a method defining the climate-sensitivity, high risk regions are mainly distributed in northern Kazakhstan and Tianshan Mountains region

Modelling hydrological responses to climate change in a data-scarce semiarid basin in the Tianshan Mountains

The Tianshan Mountains, known as the Water tower of Central Asia, are an essential freshwater source for downstream rivers, residents, irrigation agriculture and ecosystems in Central Asia. Climate in this semiarid region has changed from warm-dry to warm-wet in the last decades. Water resources are highly sensitive to climate change, and their availability is expected to become more unstable in the future. However, hydrological processes in glacierized basins are poorly known due to data scarcity and complex snow and glacier melt dynamics. It is therefore particularly important to improve our understanding of climate change and its impacts on hydrological regimes in dry, glacierized mountain regions such as the Tianshan Mountains. Emphasizing the research gaps related to the scarcity of observational data and lack of understanding of climate variability and hydrological regimes, the aim of this thesis is to model hydrological responses to climate change in a data-scarce glacierized basin in the Tianshan Mountains to better understand mountain hydrology. Spatio-temporal changes of climate change, climate extremes, hydrological and cryosphere were summarized based on data analysis and literature review. ..

Variability of the precipitation and moisture sources of the Tianshan Mountains, Central Asia

Das Tianshan-Gebirge, als „Wasserturm“ Zentralasiens, hat entscheidenden Einfluss auf die Wasserressourcen der Region. Untersuchungen von 1950 bis 2016 zeigen, dass der Jahresniederschlag in den meisten Teilen des Gebirges zunahm, außer im westlichen Tianshan, wo er abnahm. Es gibt hoch- und niedrigfrequente Schwankungen im Niederschlag mit 3-, 6-, 12- und 27-jährigen Quasiperioden. Auf Dekadenskala gab es zwei Trockenperioden (1950–1962, 1973–1984) und zwei Feuchtperioden (1962–1972, 1985–2016). Seit 2004 ist eine kontinuierliche Feuchtezunahme zu verzeichnen. Zusammenhänge wurden zwischen Zirkulationsmustern und dem Niederschlag identifiziert. Das East Atlantic-West Russia (EATL/WRUS)-Muster korreliert positiv mit dem Winter-Niederschlag. Das Scandinavia (SCAND)-Muster beeinflusst den Sommerniederschlag. Das Silk Road-Muster (SRP) war im Zeitraum 1964-1984 relevant. Die Feuchtigkeitsquellen für den Tianshan-Niederschlag stammen zu 93,2% von kontinentalen Quellen und nur begrenzt aus dem Ozean. Zentralasien ist die Hauptfeuchtequelle für das Gebirge. Im westlichen Tianshan kommt die Feuchtigkeit hauptsächlich von Zentralasien von April bis Oktober und von Westasien von November bis März. Im östlichen Tianshan tragen Ost- und Südasien sowie Sibirien konstant zur Feuchtigkeit im Sommer bei. Der Beitrag der Feuchtigkeit aus dem Nordatlantik zum Sommerniederschlag im nördlichen, zentralen und östlichen Tianshan zeigt einen abnehmenden Trend, obwohl dieser Beitrag ohnehin begrenzt ist. In Monaten mit extremem Winterniederschlag stammt die größte Zunahme der Feuchtigkeit im westlichen Tianshan aus Westasien, während Europa einen wichtigen Beitrag zu den extremen Winterniederschlägen im nördlichen Tianshan leistet. Im östlichen Tianshan ist die Feuchtigkeitszufuhr aus Ost- und Südasien sowie aus Sibirien während der extremen Niederschlagsmonate sowohl im Winter als auch im Sommer erhöht.The Tianshan Mountains, the "water tower" of Central Asia, are crucial water sources. Precipitation variability and water vapor transport impact water distribution. The study assessed 1950-2016 precipitation using Mann-Kendall tests and EEMD on GPCC data. Multi-timescale precipitation variations were analyzed with NCEP/NCAR reanalysis, and moisture sources during 1979–2017 with ERA–Interim data. Most of Tianshan had increasing annual precipitation, except Western Tianshan, which experienced a downtrend. Precipitation exhibited 3- and 6-year cycles and 12- and 27-year cycles. On the decadal scale, two dry and two wet periods occurred, with continuous humidification since 2004. A significant positive correlation was found between East Atlantic-West Russia EATL/WRUS circulation pattern and winter precipitation. SCAND influenced Tianshan's summer precipitation, with a wet period after 1988 due to enhanced water vapor flux. SCAND and EAP strengthened water vapor fluxes to Tianshan. SRP impacted Tianshan's summer precipitation during 1964–1984. About 93.2% of Tianshan's moisture comes from continental sources. Central Asia dominates moisture supply. Western Tianshan receives moisture mainly from Central Asia (April to October) and Western Asia (November to March). Almost 13.0% of Eastern Tianshan's summer moisture originates from East and South Asia and Siberia, with steady contributions. Moisture from the North Atlantic Ocean to summer precipitation in Northern, Central, and Eastern Tianshan shows a decreasing trend, but limited overall contribution. Extreme winter precipitation in Western Tianshan is linked to moisture from West Asia. Europe significantly contributes to extreme winter precipitation in Northern Tianshan. Eastern Tianshan sees enhanced moisture from East and South Asia and Siberia during extreme precipitation months in winter and summer

Spatiotemporal characteristics of future changes in precipitation and temperature in Central Asia

The arid and semi-arid areas in Central Asia have scarce water resources and fragile ecosystems that are especially sensitive and vulnerable to climate change. Reliable information regarding future projections of change in climate is crucial for long-term planning of water resources management and structural adjustment of agriculture in this region. However, the low-density meteorological observation network brings great challenges for investigating the effects of climate variations. In this study, variations of precipitation and temperature in Central Asia were examined by a combination of gridded climate dataset of the Climate Research Unit and the latest general circulation models (GCMs) under a representative concentration pathway 4.5. Three downscaling methods, Delta, Advanced Delta, and Bayesian model averaging (BMA) methods, translate the coarse GCMs to local climatic variations for the period 2021-2060 relative to 1965-2004. Major results suggested that the Advanced Delta and BMA methods outperformed the Delta method in precipitation downscaling. Projected precipitation exhibited a general increasing trend at a rate of 4.63 mm/decade for entire Central Asia with strong spatiotemporal heterogeneity. While a declining trend was observed in the southwestern and central parts of Central Asia in summer. The projected temperature was revealed an obvious ascending at 0.37 degrees C/decade, while the warming rate accelerated in higher latitude and mountainous areas. [Correction added on 03 December 2018, after first online publication: The preceding statement has been corrected in this version.] The surface land coverage had significant effects on the variations of precipitation and temperature, respectively. The driven factors of local climate were suggested by analysing the relationships between climate variations and large-scale atmospheric circulation fields anomalies. The findings of this study aims to provide useful information to improve our understanding for future climate change and benefit local decision makers

Using SPOT-VGT NDVI as a successive ecological indicator for understanding the environmental implications in the Tarim River Basin, China

The resilience and vulnerability of terrestrial ecosystem in the Tarim River Basin, Xinjiang is critical in sustainable development of the northwest region in China. To learn more about causes of the ecosystem evolution in this wide region, vegetation dynamics can be a surrogate indicator of environmental responses and human perturbations. This paper aims to use the inter-annual and intra-annual coefficient of variation (CoV) derived by the SPOT-VGT Normalized Difference Vegetation Index (NDVI) as an integrated measure of vegetation dynamics to address the environmental implications in response to climate change. To finally pin down the vegetation dynamics, the intra-annual CoV based on monthly NDVI values and the inter-annual CoV based on seasonally accumulated NDVI values were respectively calculated. Such vegetation dynamics can then be associated with precipitation patterns extracted from the Tropical Rainfall Measuring Mission (TRMM) data and irrigation efforts reflecting the cross-linkages between human society and natural systems. Such a remote sensing analysis enables us to explore the complex vegetation dynamics in terms of distribution and evolution of the collective features of heterogeneity over local soil characteristics, climate change impacts, and anthropogenic activities at differing space and time scales. Findings clearly indicate that the vegetation changes had an obvious trend in some high mountainous areas as a result of climate change whereas the vegetation changes in fluvial plains reflected the increasing evidence of human perturbations due to anthropogenic activities. Some possible environmental implications were finally elaborated from those cross-linkages between economic development and resources depletion in the context of sustainable development

Spatiotemporal analysis of vegetation variability and its relationship with climate change in China

This paper investigated spatiotemporal dynamic pattern of vegetation, climate factor, and their complex relationships from seasonal to inter-annual scale in China during the period 1982–1998 through wavelet transform method based on GIMMS data-sets. First, most vegetation canopies demonstrated obvious seasonality, increasing with latitudinal gradient. Second, obvious dynamic trends were observed in both vegetation and climate change, especially the positive trends. Over 70% areas were observed with obvious vegetation greening up, with vegetation degradation principally in the Pearl River Delta, Yangtze River Delta, and desert. Overall warming trend was observed across the whole country (\u3e98% area), stronger in Northern China. Although over half of area (58.2%) obtained increasing rainfall trend, around a quarter of area (24.5%), especially the Central China and most northern portion of China, exhibited significantly negative rainfall trend. Third, significantly positive normalized difference vegetation index (NDVI)–climate relationship was generally observed on the de-noised time series in most vegetated regions, corresponding to their synchronous stronger seasonal pattern. Finally, at inter-annual level, the NDVI–climate relationship differed with climatic regions and their long-term trends: in humid regions, positive coefficients were observed except in regions with vegetation degradation; in arid, semiarid, and semihumid regions, positive relationships would be examined on the condition that increasing rainfall could compensate the increasing water requirement along with increasing temperature. This study provided valuable insights into the long-term vegetation–climate relationship in China with consideration of their spatiotemporal variability and overall trend in the global change process

Concurrent and lagged effects of drought on grassland net primary productivity: a case study in Xinjiang, China

Xinjiang grasslands play a crucial role in regulating the regional carbon cycle and maintaining ecosystem stability, and grassland net primary productivity (NPP) is highly vulnerable to drought. Drought events are frequent in Xinjiang due to the impact of global warming. However, there is a lack of more systematic research results on how Xinjiang grassland NPP responds to drought and how its heterogeneity is characterized. In this study, the CASA (Carnegie Ames Stanford Application) model was used to simulate the 1982–2020 grassland NPP in Xinjiang, and the standardized Precipitation Evapotranspiration Index (SPEI) was calculated using meteorological station data to characterize drought. The spatial and temporal variability of NPP and drought in Xinjiang grasslands from 1982 to 2020 were analyzed by the Sen trend method and the Mann-Kendall test, and the response characteristics of NPP to drought in Xinjiang grasslands were investigated by the correlation analysis method. The results showed that (1) the overall trend of NPP in Xinjiang grassland was increasing, and its value was growing season > summer > spring > autumn. Mild drought occurred most frequently in the growing season and autumn, and moderate drought occurred most frequently in spring. (2) A total of 64.63% of grassland NPP had a mainly concurrent effect on drought, and these grasslands were primarily located in the northern region of Xinjiang. The concurrent effect of drought on NPP was strongest in plain grassland and weakest in alpine subalpine grassland. (3) The lagged effect is mainly in the southern grasslands, the NPP of alpine subalpine meadows, meadows, and alpine subalpine grasslands showed mainly a 1-month time lag effect to drought, and desert grassland NPP showed mainly a 3-month time lag effect to drought. This research can contribute to a reliable theoretical basis for regional sustainable development