Search Results (43)

The Axi gold deposit, which is located in the Tulasu Basin of the West Tianshan orogenic belt in Northwest China, features vein-type ore bodies hosted in radial structural fractures formed due to volcanic activity. The deposit experienced three distinct mineralization stages: Stage I, characterized by the microcrystalline quartz–pyrite crust; Stage II, characterized by quartz–sulfide–native gold veins; and Stage III, characterized by quartz–carbonate veins. Fluid inclusion studies have identified four types of inclusions: pure vapor, vapor-rich, liquid-rich, and pure liquid. The number of vapor-rich inclusions decreases when moving from Stage I to Stage III, whereas the number of liquid-rich inclusions increases. The fluid temperature gradually decreases from 178–225 °C in Stage I to 151–193 °C in Stage II and further to 123–161 °C in Stage III, whereas the fluid salinity decreases slightly from 2.1%–5.1% wt.% NaCl eqv to 1.4%–4.6% wt.% NaCl eqv and finally to 0.5%–3.7% wt.% NaCl eqv. As suggested by the results of the oxygen, hydrogen, and carbon isotope analyses, the ore-forming fluids were primarily meteoric water. Sulfur isotopic compositions indicate a single deep mantle source. The lead isotopic compositions closely resemble those of Dahalajunshan Formation volcanic rocks, indicating that these rocks were the primary source of the ore-forming material. In addition, gold mineralization formed in a Devonian–Early Carboniferous volcanic arc environment. Element enrichment was mainly caused by the circulation of heated meteoric water through the volcanic strata, while fluid boiling and water–rock interactions were the main mechanisms driving element precipitation. The integrated model developed in this study underscores the intricate interplay between volcanic processes and meteoric fluids during the formation of the Axi gold deposit, offering a robust framework for an understanding of the formation processes and enhancing the predictive exploration models in analogous geological settings. Full article

The “West-to-East Gas Transmission” project has accelerated economic development in Xinjiang and the central-western regions along the pipeline. However, as the pipeline traverses multiple cities and counties in the Tianshan region, it has significantly impacted the local ecology, necessitating a comprehensive assessment. This study employs the Sensitivity-Resilience-Pressure (SRP) model to construct an ecological vulnerability assessment system for the Tianshan region, aiming to analyze changes in ecological vulnerability and evaluate the environmental impact of the “West-to-East Gas Transmission” project. The results indicate that, spatially, ecological vulnerability in the Tianshan region increases progressively from northwest to southeast. Temporally, from 2000 to 2010, the mean Ecological Vulnerability Index (EVI) exhibited a decreasing trend, with values of 0.476, 0.464, and 0.462, primarily shifting to lower vulnerability levels. From 2010 to 2020, the EVI showed an increasing trend, with values of 0.462, 0.466, and 0.468, predominantly transitioning from heavy to very heavy vulnerability. The key influencing factors of ecological vulnerability in the Tianshan region, ranked by importance, are NDVI, NPP, land use type, annual precipitation, and aridity. Furthermore, the “West-to-East Gas Transmission” project consists of three main pipelines (Lines 1, 2, and 3), for which buffer zone analyses were conducted at radii of 1 km, 3 km, and 5 km. The results indicate that ecological vulnerability patterns remained consistent across different buffer zone sizes, and larger buffer radii were associated with lower mean EVI values along the pipeline. After pipeline construction, the mean EVI along Line 1 decreased from 0.566 to 0.550, while the EVI along Line 2 remained nearly unchanged. In contrast, the mean EVI along Line 3 increased from 0.434 to 0.447. Regarding changes in ecological vulnerability levels, along Line 1, the area of improvement (18.83%) exceeded the area of deterioration (1.09%), primarily due to the high proportion of very heavy vulnerability zones (>80%), which are more likely to transition to lower vulnerability levels. Along Line 2, ecological vulnerability remained relatively stable, indicating minimal environmental impact. However, along Line 3, the improvement area (3.81%) was significantly smaller than the deterioration area (20.52%), suggesting that construction of Line 3 had a more pronounced ecological impact, leading to greater degradation of the ecological vulnerability along its route. Full article

The southern slope of the Tianshan Mountains features complex terrain and an arid climate, yet paradoxically experiences frequent extreme precipitation events (EPEs), which pose significant challenges for weather forecasting. This study investigates an EPE that occurred from 20 to 21 August 2019 using multi-source data to examine circulation patterns, mesoscale characteristics, moisture dynamics, and energy-instability mechanisms. The results reveal distinct spatiotemporal variability in precipitation, prompting a two-stage analytical framework: stage 1 (western plains), dominated by localized convective cells, and stage 2 (northeastern mountains), characterized by orographically enhanced precipitation clusters. The event was associated with a “two ridges and one trough” circulation pattern at 500 hPa and a dual-core structure of the South Asian high at 200 hPa. Dynamic forcing stemmed from cyclonic convergence, vertical wind shear, low-level convergence lines, water vapor (WV) transport, and jet-induced upper-level divergence. A stronger vorticity, divergence, and vertical velocity in stage 1 resulted in more intense precipitation. The thermodynamic analysis showed enhanced low-level cold advection in the plains before the event. Sounding data revealed increases in precipitable water and convective available potential energy (CAPE) in both stages. WV tracing showed vertical differences in moisture sources: at 3000 m, ~70% originated from Central Asia via the Caspian and Black Seas; at 5000 m, source and path differences emerged between stages. In stage 1, specific humidity along each vapor track was higher than in stage 2 during the EPE, with a 12 h pre-event enhancement. Both stages featured rapid convective cloud growth, with decreases in total black body temperature (TBB) associated with precipitation intensification. During stage 1, the EPE center aligned with a large TBB gradient at the edge of a cold cloud zone, where vigorous convection occurred. In contrast to typical northern events, which are linked to colder cloud tops and vigorous convection, the afternoon EPE in stage 2 formed near cloud edges with lesser negative TBB values. These findings advance the understanding of multi-scale extreme precipitation mechanisms in arid mountains, aiding improved forecasting in complex terrains. Full article

The Tianshan Mountains are located in the hinterland of the Eurasian continent, spanning east to west across China, Kazakhstan, Kyrgyzstan, and Uzbekistan. As the primary water source for Central Asia’s arid regions, the Tianshan mountain system is pivotal for regional water security and is highly sensitive to the nuances of climate change. Utilizing ERA5 precipitation datasets alongside 24 atmospheric circulation indices, this study delves into the variances in Tianshan’s precipitation patterns and their correlation with large-scale atmospheric circulation within the timeframe of 1981 to 2020. We observe a seasonally driven dichotomy, with the mountains exhibiting increasing moisture during the spring, summer, and autumn months, contrasted by drier conditions in winter. There is a pronounced spatial variability; the western and northern reaches exhibit more pronounced increases in precipitation compared to their eastern and southern counterparts. Influences on Tianshan’s precipitation patterns are multifaceted, with significant factors including the North Pacific Pattern (NP), Trans-Niño Index (TNI), Tropical Northern Atlantic Index (TNA*), Extreme Eastern Tropical Pacific SST (Niño 1+2*), North Tropical Atlantic SST Index (NTA), Central Tropical Pacific SST (Niño 4*), Tripole Index for the Interdecadal Pacific Oscillation [TPI(IPO)], and the Western Hemisphere Warm Pool (WHWP*). Notably, NP and TNI emerge as the predominant factors driving the upsurge in precipitation. The study further reveals a lagged response of precipitation to atmospheric circulatory patterns, underpinning complex correlations and resonance cycles of varying magnitudes. Our findings offer valuable insights for forecasting precipitation trends in mountainous terrains amidst the ongoing shifts in global climate conditions. Full article

The urbanization effect (UE) on local or regional climate is a prominent research topic in the research field of urban climates. However, there is little research on the UE of Urumqi, a typical arid region city, concerning various climatic factors and their spatio–temporal characteristics. This study quantitatively investigates the UE of Urumqi on multiple climatic factors in summer based on a decade-long period of WRF–UCM (Weather Research and Forecasting model coupled with the Urban Canopy Model) simulation data. The findings reveal that the UE of Urumqi has resulted in a reduction in the diurnal temperature range (DTR) within the urban area by causing an increase in night-time minimum temperatures, with the maximum decrease reaching −2.5 °C. Additionally, the UE has also led to a decrease in the water vapor mixing ratio (WVMR) and relative humidity (RH) at 2 m, with the maximum reductions being 0.45 g kg⁻¹ and −6.5%, respectively. Furthermore, the UE of Urumqi has led to an increase in planetary boundary layer height (PBLH), with a more pronounced effect in the central part of the city than in its surroundings, reaching a maximum increase of over 750 m at 19:00 Local Solar Time (LST, i.e., UTC + 6). The UE has also resulted in an increase in precipitation in the northern part of the city by up to 7.5 mm while inhibiting precipitation in the southern part by more than 6 mm. Moreover, the UE of Urumqi has enhanced precipitation both upstream and downstream of the city, with a maximum increase of 7.9 mm. The UE of Urumqi has also suppressed precipitation during summer mornings while enhancing it in summer afternoons. The UE has exerted certain influences on the aforementioned climatic factors, with the UE varying across different directions for each factor. Except for precipitation and PBLH, the UE on the remaining factors exhibit a greater magnitude in the northern region compared to the southern region of Urumqi. Full article

Western Tianshan National Nature Reserve in Xinjiang, China stands out for its uniqueness and high biodiversity, including lichens. This study aims to characterize lichen diversity and compare distribution patterns of different life forms, substratum affinities and photobiont types. Surveys were conducted from June to August 2024 using stratified sampling methods at elevation ranging from 1100 m to 3400 m in the study area. Morphological, anatomical and chemical studies revealed 173 lichen species from 24 families and 58 genera, of which 100 species were identified as crustose, 46 as foliose and 27 as fruticose. Among the different habitat groups, strictly saxicolous lichens were dominant with 89 species, followed by corticolous lichens with 44 species and terricolous lichens with 40 species. The total species richness of lichens has a bimodal pattern: one peak appears at a low altitude (1701–2000 m) and the other at a high altitude (2901–3200 m). Among the three substratum categories studied, the species richness of terricolous lichens showed a unimodal relationship with elevation, and the saxicolous lichen had a bimodal pattern. The species richness of corticolous lichens was highest at lower and medium elevations and decreased at higher elevations. With respect to photobiont type, the species richness of cyanolichens showed a unimodal relationship with elevation. Maximum richness occurred at 2700 m, contrary to the chlorolichens, which had a bimodal pattern. Species richness of all three growth forms of lichens showed a bimodal pattern related to elevation. Among the three morphological types, crustose and foliose species richness had their highest values of 38 and 19, respectively, at 1701–2000 m, and fruticose lichens peaked with a maximum of 13 species at 2301–2600 m. The species richness of crustose lichens is lowest between altitudes 2300 and 2600 m, while the lowest species richness of fruticose and foliose lichens occurs at 2001–2300 m and elevations above 2900 m. Full article

Although it promotes national economic development, urbanization causes regional ecosystems to suffer from disturbances and impacts that cannot be completely avoided. Ecosystems urgently need to improve their resilience; however, existing studies lack an analysis of the interaction between urbanization and ecological resilience. In this study, the interaction between urbanization and ecological resilience is investigated, taking the urban agglomeration on the north slope of Tianshan Mountain (UANST) as a study area and using the entropy value method to construct an urbanization evaluation system. Based on land use change data, an ecological resilience evaluation model is constructed using the InVSET model, the landscape pattern index, and the unit area value equivalent factor method. The degree of coupling and coordination of the interaction coupling between urbanization and ecological resilience are measured for the years 1990–2020, and their internal action mechanisms are analyzed. The results show that (1) with the development of urbanization, ecological resilience shows a decreasing and then increasing double “U”-shaped change characteristic. (2) The coupling degree of urbanization and ecological resilience in the UANST increased from 0.6888 to 0.9485, and the coordination degree increased from 0.3367 to 0.4410. (3) There are three types of coupling coordination: basic coordination, basic dysfunction, and serious dysfunction. Basic coordination is mainly distributed in the central part of the urban agglomeration, and basic dysfunction and serious dysfunction are mainly concentrated on the east and west sides; the overall trend is to shift from dysfunction to coordination. (4) Economic urbanization plays a driving role, and population urbanization, spatial urbanization, and social urbanization have an inhibitory role in the degree of coupling coordination; base quality and structural stability have a driving role in the degree of coupling coordination, while ecological services have an inhibitory role; and the population density, the proportion of built-up area to the total land area of the city, and the value of ecosystem services have a stronger influence on the level of coupling coordination. Full article

Statistical characteristics of atmospheric circulation patterns (ACPs) and associated diurnal variation characteristics (DVCs) of precipitation in summer (June–August) from 2015 to 2019 over the complex terrain in northern Xinjiang (NX), northwestern arid region of China, were investigated based on NCEP FNL reanalysis data and Weather Research and Forecasting model simulation data from Nanjing University (WRF-NJU). The results show that six different ACPs (Type 1–6) were identified based on the Simulated ANealing and Diversified RAndomization (SANDRA), exhibiting significant differences in major-influencing synoptic systems and basic meteorological environments. Types 5, 3, and 2 were the most prevalent three patterns, accounting for 21.6%, 19.7%, and 17.7%, respectively. Type 5 mainly occurred in June and July, while Types 3 and 2 mainly occurred in August and July, respectively. From the perspective of DVCs, Type 1 reached its peak at midnight, while Type 5 was most frequent in the afternoon and morning. The overall DVCs of hourly precipitation intensity and frequency demonstrated a unimodal structure, with a peak occurring at around 16 Local Solar Time (LST). Basic meteorological elements in various terrain regions exhibit significant diurnal variation, with marked differences between mountainous and basin areas under different ACPs. In Types 3 and 6, meteorological elements significantly influence precipitation enhancement by promoting the convergence and uplift of low-level wind fields and maintaining high relative humidity (RH). The Altay Mountains region and Western Mountainous regions experience dominant westerly winds under these conditions, while the Junggar Basin and Ili River Valley regions benefit from counterclockwise water vapor transport associated with the Iranian Subtropical High in Type 6, which increases RH. Collectively, these factors facilitate the formation and development of precipitation. Full article

Rapid population growth and subsequent urbanization pose significant challenges of water shortage in arid regions. As an important area along the One Belt and One Road line, the Northern Slope of Tianshan Mountains (NSTM) has suffered from water shortages owing to rapid urbanization in recent decades. To conserve water resources and protect the ecosystem, understanding the temporal and spatial variations of the domestic water consumption, availability, and its influencing factors is essential. According to water resource regionalization and its characteristics in NSTM, it was divided into three sections, namely the west section, the middle section, and the east section. In addition, this work characterized the temporal and spatial variation of domestic water consumption in NSTM with a focus on the understanding of the influence of urbanization on domestic water consumption from 1990 to 2020 based on three sections. The results showed that during this period of time, construction land use increased by 2256 km² corresponding to the population increase of 158.58 × 10⁴. Subsequently, the total domestic water consumption increased from 7.55 × 10⁷ m³ in 1990 to 2.60 × 10⁸ m³ in 2020. The eastern section demonstrated steady growth, while the western and middle sections experienced larger fluctuations in domestic water consumption. Urbanization has been identified as a significant factor influencing the shift in domestic water consumption. This study offers a scientific foundation for the sustainable management of water resources in arid areas. Full article

Raindrop size distribution (DSD) has an essential effect on rainfall kinetic energy estimation (RKEE) and dual-polarization radar quantitative precipitation estimation (QPE); DSD is a key factor for establishing a dual-polarization radar QPE scheme and RKEE scheme, particularly in mountainous areas. To improve the understanding of seasonal DSD-based RKEE, dual-polarization radar QPE, and the impact of rainfall types and classification methods, we investigated RKEE schemes and dual-polarimetric radar QPE algorithms across seasons and rainfall types based on two classic classification methods (BR09 and BR03) and DSD data from a disdrometer in the Tianshan Mountains during 2020–2022. Two RKEE schemes were established: the rainfall kinetic energy flux–rain rate (KE_time–R) and the rainfall kinetic energy content–mass-weighted mean diameter (KE_mm–D_m). Both showed seasonal variation, whether it was stratiform rainfall or convective rainfall, under BR03 and BR09. Both schemes had excellent performance, especially the KE_mm–D_m relationship across seasons and rainfall types. In addition, four QPE schemes for dual-polarimetric radar—R(K_dp), R(Z_h), R(K_dp,Z_dr), and R(Z_h,Z_dr)—were established, and exhibited characteristics that varied with season and rainfall type. Overall, the performance of the single-parameter algorithms was inferior to that of the double-parameter algorithms, and the performance of the R(Z_h) algorithm was inferior to that of the R(K_dp) algorithm. The results of this study show that it is necessary to consider different rainfall types and seasons, as well as classification methods of rainfall types, when applying RKEE and dual-polarization radar QPE. In this process, choosing a suitable estimator—KE_time(R), KE_mm(D_m), R(K_dp), R(Z_h), R(K_dp,Z_dr), or R(Z_h,Z_dr)—is key to improving the accuracy of estimating the rainfall KE and R. Full article

Urumqi is located in the arid region of northwestern China, known for being one of the most delicate ecological environments and an area susceptible to climate change. The urbanization of Urumqi has progressed rapidly, yet there is a lack of research on the urbanization effect (UE) in Urumqi in terms of the regional climate. This study investigates the UE of Urumqi (urban built-up area) on the regional thermal environment and its mechanisms for the first time, based on the WRF (Weather Research and Forecasting) model (combined with the Urban Canopy Model, UCM) simulation data of 10 consecutive years (2012–2021). The results show that the UE on surface temperature (Ts) and air temperature at 2 m (T2m) is strong (weak) during the night (daytime) in all seasons, and the UE on these is largest (smallest) in spring (winter). In addition, the maximum UE on both Ts and T2m is present over southern Urumqi in winter, whereas the maximum UE is identified over the northern Urumqi in other seasons. The maximum UE on Ts occurred in northwestern Urumqi at 18 LST (Local Standard Time, i.e., UTC+6) in autumn (reaching 5.2 °C), and the maximum UE on T2m occurred in northern Urumqi at 4 LST in summer (reaching 2.6 °C). Urbanization showed a weak cooling effect during daytime in summer and winter, reflecting the unique characteristics of the UE in arid regions, which are different from those in humid regions. The maximum cooling of Ts occurred in northern Urumqi at 11 LST in summer (reaching −0.4 °C), while that of T2m occurred at 10 LST in northern and northwestern Urumqi in winter (reaching −0.25 °C), and the cooling effect lasted for a longer period of time in summer than in winter. The UE of Urumqi causes the increase of Ts mainly through the influence of net short-wave radiation and geothermal flux and causes the increase of T2m through the influence of sensible heat flux and net long-wave radiation. The UE on the land surface energy balance in Urumqi can be used to explain the seasonal variation and spatial differences of the UEs on the regional thermal environment and the underlying mechanism. Full article

In order to deepen the knowledge of the seasonal variation in total cloud cover (TCC) in Xinjiang, China (XJ), a typical arid region, and to broaden the understanding of the seasonal variation in cloud type (CLT) in the region, we used TCC and CLT datasets from the latest generation of the geostationary satellite Fengyun 4A (FY-4A) from 2018 to 2022 to investigate the seasonal variation characteristics of TCC and CLT in XJ. Meanwhile, to verify the accuracy of TCC from FY-4A, ground observation (GROB) TCC datasets from 105 national meteorological stations (NMSs) in XJ and TCC datasets from ERA5 during the same period were used. In addition, the correlation between TCC from FY-4A and meteorological factors from ERA5 was also analyzed in this study. The TCC from FY-4A, GROB, and ERA5 can all well reflect the significant seasonal variation in TCC in XJ, with the highest (lowest) mean TCC and a distribution pattern of high in the southwest (northwest) and low in the northeast (southeast) in spring (fall) in XJ. Although the mean TCC from FY-4A in all four seasons was lower than that from GROB, the two were comparable in spring (44.09% and 47.32%) and summer (42.88% and 43.17%), while there was a significant difference between the two in fall (27.86% and 40.19%) and winter (30.58% and 46.93%) for 105 NMSs in XJ. The TCC from FY-4A was lower (higher) than that from GROB in spring and summer at most NMSs in northern (southern) XJ, while the TCC from FY-4A was lower than that from GROB for the vast majority of NMSs in fall and winter, especially in northern XJ. The seasonal variation in the spatial distribution of different CLTs (clear, water-type, supercooled-type, mixed-type, ice-type, cirrus-type, and overlap-type) from FY-4A exhibited diverse variation characteristics. Water-type (supercooled-water-type) had a high-frequency center of over 30% in the Tarim Basin (Kunlun Mountains) during summer. Mixed-type (ice-type and cirrus-type) had the highest frequency in winter (spring), while overlap-type had the highest frequency in summer. The correlation between TCC and water vapor conditions (total column vertically integrated water vapor, specific humidity at 250 hPa, 500 hPa, and 700 hPa) was positive in XJ. Full article

This study proposes a novel approach to estimate canopy density in Picea Schrenkiana var. Tianschanica forest sub-compartments by integrating optical and radar satellite data. This effort is aimed at enhancing methodologies for forest resource surveys and monitoring, particularly vital for the sustainable development of semi-arid mountainous areas with fragile ecological environments. The study area is the West Tianshan Mountain Nature Reserve in Xinjiang, which is characterized by its unique dominant tree species, Picea Schrenkiana. A total of 411 characteristic factors were extracted from Gaofen-2 (GF-2) sub-meter optical satellite imagery, Gaofen-3 (GF-3) multi-polarization synthetic aperture radar satellite imagery, and digital elevation model (DEM) data. Consequently, 17 characteristic parameters were selected based on their correlation with canopy density data to construct an estimation model. Three distinct models were developed, including a multiple stepwise regression model (a linear approach), a Back Propagation (BP) neural network model (a neural network-based method), and a Cubist model (a decision tree-based technique). The results indicate that combining optical and radar image characteristics significantly enhances accuracy, with an Average Absolute Percentage Precision (AAPP) value improvement in estimation accuracy from 76.50% (with optical image) and 78.50% (with radar image) to 78.66% (with both). Of the three models, the BP neural network model achieved the highest overall accuracy (79.19%). At the sub-component scale, the BP neural network model demonstrated superior accuracy in low canopy density estimation (75.37%), whereas the Cubist model, leveraging radar image characteristics, excelled in medium density estimations (87.46%). Notably, the integrated Cubist model combining optical and radar data achieved the highest accuracy for high canopy density estimation (89.17%). This study highlights the effectiveness of integrating optical and radar data for precise canopy density assessment, contributing significantly to ecological resource monitoring methodologies and environmental assessments. Full article

Arid central Asia (ACA) is dominated by mid-latitude westerlies and characterized by a climate optimum (a relatively humid climate that has supported the development of human culture) in clear contrast with the climate of monsoonal Asia during the Holocene. Significantly, whether the onset of the Holocene Climate Optimum (HCO) had an impact on cultural exchanges along the ancient Silk Road remains unknown. In this study, we compared the onset of the HCO in different parts of the vast ACA region by referring to a variety of previously established paleo-moisture/precipitation records. Intriguingly, we found significant differences in the onset of the HCO between the western and eastern parts of ACA. The onset of the HCO in the western part of ACA (i.e., to the west of the Tianshan Mountains) mainly occurred at ~8 ka BP (1 ka = 1000 cal yr BP). In contrast, the onset of the HCO occurred at ~6 ka in northern Xinjiang and even as late as ~5 ka in southern Xinjiang; this is a delay of 2–3 thousand years compared with the western part of ACA. These results likely indicate that the onset of the HCO occurred in a time-transgressive manner in ACA, namely, ‘early in the west but late in the east’. On the other hand, we found that the onset of the HCO in the western part of ACA may have resulted in the inception of wheat planting and the development of agricultural civilization and that the onset of the HCO in northern Xinjiang may have prompted the southward migration of Afanasievo culture after ~5 ka. Additionally, the initiation of the HCO in southern Xinjiang could provide an environmental basis for the spread and planting of wheat and millet in this area after ~4.5 ka. We speculate that the spatial differences in the onset of the HCO in ACA are mainly related to temporal changes in the intensity and position of the mid-latitude westerly jet. Although the increase in insolation and reduction in the global ice volume would have led to an increase in the water vapor feeding the western part of ACA around 8 ka, the climate in the eastern part of ACA (namely, the Xinjiang region) could have only become humid after 6 ka when the westerlies were intensified and became positioned in the south. Moreover, the delayed HCO in southern Xinjiang probably benefited from the stronger westerly winds that appeared around 5 ka, which could have overcome the influence of the tall topography of the Tianshan Mountains. Therefore, in addition to external forcing (i.e., insolation), the ocean–atmospheric teleconnection, the regional topography, and their connection to the climate system are important in determining the spatial differences in the time-transgressive onset of the HCO in ACA. Our findings contribute to understanding the spatio-temporal characteristics of the hydroclimate in regions with complex eco-environmental systems and a diverse history of human activity. Full article

This study investigates, for the first time, the urbanization effect (UE) on local extreme climate events in Urumqi, China, based on 22 indices of climate extremes, which are calculated with daily observation data from 1976 to 2018. These analyses reveal a pronounced nocturnal urban heat island (UHI) effect and a daytime urban cold island (UCI) effect. Due to Urumqi’s arid climate background, the UCI effect is considered a unique feature of the UE, which significantly differs from those in eastern and northern China. The UE on the TR20 index (number of days with minimum daily temperature exceeding 20 °C) reached 5.22 d/10a, indicating that urbanization has led to a fast increase in the number of hot nights in Urumqi. The absolute averaged UE on the indices measuring the frequency of warm events is about twice as large as that on the indices measuring the frequency of cold events, while that on the indices measuring the intensity of warm events is about one third of that on the indices measuring the intensity of cold events. The highest averaged urbanization contributions (UCs) to the extreme warm and cold events are represented by the frequency indices and the intensity indices, respectively, while those contributing to the extreme precipitation events are represented by the duration indices. Moreover, urbanization probably exacerbates the degree of wetting in the overall “warming and wetting” climate trend of the region. These findings can be seen as new evidence to provide scientific basis for further investigation of the UE on climate changes in arid regions. Full article