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Northwest China has undergone notable alterations in climate and vegetation growth in recent decades. Nevertheless, uncertainties persist concerning the response of different vegetation types to climate change and the underlying mechanisms. This study utilized the Normalized Difference Vegetation Index (NDVI) and three sets of meteorological data to investigate the interannual variations in the association between vegetation and climate (specifically precipitation and temperature) from 1982 to 2015. Several conclusions were drawn. (1) R NDVI-GP (relationship between Growing Season NDVI and precipitation) decreased significantly across all vegetation, while R NDVI-GT (relationship between Growing Season NDVI and temperature) showed an insignificant increase. (2) Trends of R NDVI-GP and R NDVI-GT exhibited great variations across various types of vegetation, with forests displaying notable downward trends in both indices. The grassland exhibited a declining trend in R NDVI-GP but an insignificant increase in R NDVI-GT , while no significant temporal changes in R NDVI-GP or R NDVI-GT were observed in the barren land. (3) The fluctuations in R NDVI-GP and R NDVI-GT closely aligned with variations in drought conditions. Specifically, in regions characterized by VPD (vapor pressure deficit) trends less than 0.02 hpa/yr, which are predominantly grasslands, a rise in SWV (soil water volume) tended to cause a reduction in R NDVI-GP but an increase in R NDVI-GT. However, a more negative trend in SWV was associated with a more negative trend in both R NDVI-GP and R NDVI-GT when the VPD trend exceeded 0.02 hPa/yr, primarily in forests. Our results underscore the variability in the relationship between climate change and vegetation across different vegetation types, as well as the role of drought in modulating these associations., (© 2024. The Author(s).)

Clarifying the spatiotemporal variation of crop irrigation water requirement (IWR) under the background of climate change is an essential basis for water resource management, determining the irrigation quota and adjusting the planting structure. Using 61 years of climate data from 205 stations in Northwest China, this study investigated the spatiotemporal variations of climatic factors and IWR during the growth period of five main grain crops (spring wheat, winter wheat, spring maize, summer maize, and rice) and explored the dominant climatic driving factors of IWR variation. Results showed that (1) the IWR of grain crops showed distinct differences. Rice was the highest water consumption crop (mean of 753.78 mm), and summer maize was the lowest (mean of 452.90 mm). (2) The variation trends and average values of IWR of different grain crops have spatial heterogeneity across Northwest China. For most crops, high values and increasing trends of IWR were mainly located in eastern Xinjiang, western Gansu, and western Inner Mongolia. (3) T max (maximum temperature), T min (minimum temperature), and P eff (effective precipitation) showed an increasing trend during the growth period of each grain crop, while U 10 (wind speed at 10 m height), SD (solar radiation), and RH (relative humidity) presented decreasing trends. (4) SD, T max , and U 10 promoted the increase of grain crops' IWR, while P eff and RH inhibited it. The impacts of climatic factors on the grain crop IWR differed among different regions. P eff was the most influential factor to the IWR of all grain crops in most areas. Therefore, under the premise of a significant increase in T and uncertain precipitation mode in the future, it is urgent to take effective water-saving measures according to the irrigation needs of the region. To cope with the adverse impact of climate change on the sustainable development of agriculture in the northwest dry area, to ensure regional and national food security., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Changes in land management and climate alter vegetation dynamics; however, the factors driving vegetation changes remain elusive at multiple spatiotemporal levels. Here, we assess the drivers of changes in greenness from 2000 to 2015 in Northwest China (NW China). We used multiple stepwise linear regression (MSLR), redundancy analysis (RDA), and 12 other models to quantify the impacts of precipitation and temperature metrics, gross domestic product (GDP), population, and grazing intensity on the normalized difference vegetation index (NDVI) at three administrative levels (county, town, and village), four temporal levels (yearly, May, July, and September), two vegetation types (woodland and grassland), and at annual precipitation gradients of <200, 200-400, and >400 mm. The results suggest that NW China underwent vegetation greening from 2000 to 2015. Precipitation and temperature were the most influential factors contributing to the NDVI change. Population was the main determinant of NDVI under the precipitation gradient of <200 mm, and the effect of GDP on NDVI was moderate. On the temporal scale, annual precipitation, precipitation before the previous year, and precipitation in the current year determined the NDVI in May, July, and September, respectively, for both woodland and grassland. At multiple scales, climate change was the primary driver of vegetation change in NW China, rather than human disturbance. These findings expand our understanding on drivers of NDVI at multiple levels over a long period. Measures to manage decreasing vegetation coverage may be more effective and could be implemented sooner based on predicted climate change in drylands worldwide., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Comprehending the characteristics and causes of vegetation coverage in history is of practical significance for studying ecological and environmental changes. As a typical region of the semi-arid and semi-humid climatic zone in northwest China, the upper reaches of the Weihe River have relatively fragile ecological environment. Based on tree-ring width chronologies, the vegetation coverage represented by the normalized difference vegetation index was reconstructed from 1630 to 2006 using a regression model. There were 64 years with high vegetation coverage and 56 years with low vegetation coverage over the past 377 years. At low frequencies, the coverage was relatively higher in the 1650s and from the 1880s to 1890s, while the coverage was lower in the 1720s and from the 1760s to 1770s. While precipitation and temperature had positive and negative influences on the changes of vegetation coverage, respectively, during the past several centuries, the agricultural cultivation played an important role on coverage changes. Along with the land reclamation expansion in history, the forest cover gradually declined, and vegetation coverage decreased. The vegetation coverage was lower when there were more arable lands reclaimed from woodlands. Regardless of the land reclamation policy during the historical period or the current conversion project of cropland to forest, they affected the vegetation coverage by influencing cover ranges of woodland and farmland., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Though temperature over the past three decades has shown an asynchronous warming trend between daytime and nighttime, the response of vegetation activity to such non-uniform warming is still not very clear. In this study, the least squares linear trend analysis and geographic information system spatial analysis were conducted to analyze the spatiotemporal patterns of the daytime and nighttime warming based on the daily temperature data from 1982 to 2015 in Northwest China. The normalized difference vegetation index (NDVI) from Global Inventory Monitoring and Modeling System and vegetation type data were used to investigate the responses of vegetation activity to the daytime and nighttime warming using the partial correlation analysis. Our results suggested that (1) there was a very significant increasing trend in both daytime and nighttime temperatures in Northwest China from 1982 to 2015; night temperatures increased about 1.2 times faster than daytime temperatures, showing diurnal asymmetric warming; (2) the responses of vegetation activity to daytime and nighttime warming in Northwest China showed a distinct spatial pattern; the change in night temperatures had a more significant (positive in most regions) effect on vegetation; (3) various types of vegetation responded differently to asymmetric daytime and nighttime warming. Grassland NDVI, broad-leaved, and coniferous forest NDVI significantly responded to daytime warming. Shrub NDVI and desert NDVI significantly responded to night warming. These findings can deepen the understanding of the effects of the daytime and nighttime warming on vegetation activities in arid regions in the context of the current asymmetric warming.

Northwest China is much more sensitive to climate warming, and the climate has varied rapidly from warm and drought to warm and humid conditions. In addition, due to the complex terrain of Northwest China, the methods and parameterization schemes of different CMIP6 models, these models are mostly applied to arid areas in Northwest China or Central Asia, lacking climate data for plateau areas and eastern Lanzhou, specifically in filtering CMIP6 models and evaluating applicable models. In this paper, 34 CMIP6 climate models are used to evaluate and forecast future trends in Northwest China under the SSP126, SSP245 and SSP585 scenarios in the short, medium and long term. CMIP6 models of temperature and precipitation are identified by applying the interannual variability skill score (IVS) between CN05.1 datasets and historical CMIP6 models, which are suitable for Northwest China. Then, we assess the characteristics, warming and wetting deviations, and uncertainties in the prediction of climatic change according to CMIP6 models over Northwest China. The results show that CMIP6 models in precipitation and temperature applicable to Northwest China are AWI‐CM‐1‐1‐MR, BCC‐CSM2‐MR, FGOALS‐g3, INM‐CM4‐8, INM‐CM5‐0 and MRI‐ESM2‐0. The multi‐model ensemble mean (MMEM) has better capability than individual CMIP6 models in precipitation and temperature prediction. Spatiotemporal climatic change over Northwest China shows overall warming and wetting trends. The IVS provides the ability to estimate CMIP6 model simulation performance both temporally and spatially. The temperature simulation is quite good in the Tarim Basin and Hexi Corridor region, and the precipitation simulation is quite good in the plateau region, Altai Mountains, Tianshan Mountains and Hexi Corridor region. Cold and wet deviations occur in Northwest China due to the topography and few stations, which are common reasons. The main sources of uncertainties in temperature prediction during this century are model uncertainty (before the 2090s) and scenario variability (after the 2090s), and model uncertainty in precipitation for CMIP6 becomes the main source of uncertainty. [ABSTRACT FROM AUTHOR]

Water conservation is an important ecosystem service, which is crucial to the fragile ecological environment and serious soil erosion in Northwest China. However, water conservation has been affected by climate change and human disturbance, and its future spatial and temporal changes are still unclear. This study employed the Integrated Valuation of Ecosystem Services and Trade‐offs (InVEST) model to assess the water conservation capacity of Northwest China between 1990 and 2020. Subsequently, the Patch‐generating Land Use Simulation (PLUS) model and the NASA Earth Exchange Global Daily Downscaled Projections (NEX‐GDDP‐CMIP6) were integrated to examine changes in water conservation from 2030 to 2050. The water conservation quantity in Northwest China had a fluctuating growth tendency between 1990 and 2020, with an average of 816.61 × 108 m3. The water conservation capacity's regional distribution pattern shows a steady increase from northwest to southeast. Northwest China's forest land had the greatest water conservation capacity between 1990 and 2020, at 66 mm, while the water land had the lowest, at 1.46 mm. The water conservation capacity in the 2030–2050 future scenario is less than that in 2020 when the regional distribution pattern is comparable to 2020. Natural development scenario (ND) in 2030 has the lowest water conservation capacity (13.41 mm) under ssp1‐2.6 precipitation scenario, whereas in 2050, the highest water conservation capacity (17.47 mm) is found in same scenario. The ecological protection scenario (EP) has the greatest water retention capacity (18.15 mm in 2040) and the lowest (14.38 mm in 2050) in the ssp5‐8.5 scenario. Our research can help restore and rebuild Northwest China's natural ecosystem and offer a theoretical foundation for the protection of ecological environment and the rational utilization of water resources in the region. [ABSTRACT FROM AUTHOR]

Northwest China (WTL) is an essential ecological barrier zone of China, an important node of the "Silk Road Economic Belt," and a crucial bearing area for China's execution of the "One Road and One Belt" and "Going Global" strategies. However, its ecology is exceedingly fragile and particularly vulnerable to climate change and human interference. This study explored the spatiotemporal evolution characteristics of vegetation in WTL using NDVI data and investigated its drive mechanisms by geodetector, partial correlation analysis, and residual trend analysis methods. As well as forecasting the trend for vegetation changes. The findings demonstrated that (1) the change in NDVI manifested an overall improvement trend and the distribution in space of NDVI rose from the center to the periphery. 57.07% of the area had a sparse cover of vegetation (NDVI between 0 and 0.2). In addition, about 49% of regions had deterioration tendencies, which were mainly aggregated in HX, QCXDB, QCXDN, and the eastern of QCXQN and QCXXB. (2) The NDVI's shifting trend was unsustainability, and the region of uncertain future accounted for 57.45% of the total, with apparent unsustainability features. (3) The key parameters influencing NDVI spatial distribution were Pre (precipitation), vegetation type, land use type, and soil type. The interaction between two factors enhanced the influence of any single element, which appeared as bivariate and nonlinear enhancements. (4) Both climate variations and human activities have been recognized as key variables affecting NDVI growth. NDVI variance in 73.02% of areas was influenced by the combined effects of climate variations and human activities. However, human activities were the most influential element in NDVI growth, with the relative contributions of 80.28% (19.72% of which was caused by climate variations). These results can be conducive to deepening insights into the local vegetation status, identifying the mechanisms driving vegetation change, and providing scientific recommendations for WTL's ecosystem restoration measures based on actual situations. [ABSTRACT FROM AUTHOR]

Abstract Projection of future dry‐wet evolution is essential for making long‐term regional climate adaptation strategies. In this study, the projection of regional dry‐wet evolution is conducted with a careful consideration on uncertainty attribution. The Evaporative Stress Index (ESI) is adopted due to its physical mechanisms for taking evaporative demand into account. A three‐dimensional framework is constructed for quantifying the range of uncertainty of the ESI in which six Global Climate Models (GCMs) in Coupled Model Intercomparison Project 6 (CMIP6), three latest Shared Socioeconomic Pathway (SSP) scenarios, and six Potential Evapotranspiration Models (PETMs) are used. The framework provides 108 different ESI simulations for two future periods: 2041–2070 (mid‐future) and 2071–2100 (far‐future). An agglomerative‐hierarchical clustering method and the Analysis of Variance methodology are employed to evaluate the relative contribution of each uncertainty source. The region of Northwest China is used as a case to illustrate the effectiveness of the proposed framework. The results indicate that most of the parts in Northwest China would experience dry mitigation in both mid‐future and far‐future periods. Projected ESI by PM[CO2] model and ACCESS‐ESM1‐5 suggestes a higher tendency for dry mitigation. Hierarchical clustering analysis of the 108 sets of ESI predictions indicate that most clusters are dominated by GCM forcing, and one cluster is dominated by the SSP1‐2.6 scenario. Furthermore, GCM‐related uncertainty′s relative contribution to the total projection uncertainty is the greatest, with an average value of 49.98% in the far future (i.e., 2071–2100 s). Although the contribution of SSP uncertainty is smaller (21.68%−28.43%), it increases in far‐future over mid‐future. The case study indicates that the large scale ensemble prediction of ESI and its uncertainty analysis provide a more comprehensive data set on climate change and help water managers to gain in‐depth understanding of future trends of drought projections.

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Located in the interior of Eurasia and to the north of the Qinghai–Tibet Plateau, the Northwest China experiences severe drought conditions as moist air from the ocean is unable to travel the long distance and penetrate the region's mountain barriers. These special geo-climatic conditions result in Northwest China being highly sensitive to climate change. In this study, the characteristics of the response of the normalized difference vegetation index (NDVI) to the trend towards a warmer and wetter climate in Northern China from 1982 to 2019 were investigated. The results show that there were significant differences between these trends for the periods 1982–2000 and 2000–2019, with overall precipitation decreasing before 2000 but increasing afterwards. After 2000, the rate of temperature increase also slowed down, whereas the NDVI increased at an obviously faster rate. Compared with the period 1982–2000, during the period 2000–2019, the NDVI was more affected by precipitation than by the temperature. The results of a normalized linear regression also show that, for most vegetation types, the temperature played a more dominant role during the period 1982–2000, whereas precipitation had a more significant effect on the NDVI during the period 2000–2019. However, it was also found that, throughout the study period, the precipitation had a greater impact on forest NDVI and the temperature had a greater impact on the NDVI in areas of bare land. In addition, the results show that the strength of the relationship between the NDVI and climate in northwest China changed over time, with the relationship between NDVI and precipitation tending to become stronger and the relationship between NDVI and temperature tending to become weaker. The results will provide a new understanding of the relationship between vegetation and climate in northwest China and help to better cope with the risks brought by climate change. [ABSTRACT FROM AUTHOR]

Agricultural irrigation water in Northwest China accounts for more than 80% of total local water consumption, which is 1.23 times that of China. However, Northwest China is the most water-scarce place in China. Water scarcity in restricts crop growth and production. Reference crop evapotranspiration (ET0) is important for agricultural water management. Understanding the reason for ET0 change is helpful to provide a basis for rational planning of agricultural irrigation systems to conserve water. This study investigated the temporal and spatial variation characteristics of ET0 at 181 meteorological stations in Northwest China from 2000 to 2019. And the sensitive factors and dominant factors affecting ET0 change were quantitatively identified based on sensitivity analysis and contribution rate evaluation. Results showed that (1) a significant increase in maximum and minimum temperature (Tmax and Tmin), a significant decrease in sunshine duration (SD) and relative humidity (RH), and a slight increase in wind speed at 10 m height (U10) were observed. (2) Annual ET0 had an insignificant increasing trend. Spring and autumn ET0 contributed greatly to the growth of annual ET0, especially in March, May, September, October, and November. ET0 in HH (Yellow River Basin area) had decreased at annual scale, while other subregions were the opposite trend. Significant differences in monthly and seasonal changes in the spatial distribution of ET0. (3) U10 was the dominating contribution factor related to annual ET0 variability, followed by Tmin, RH, Tmax, and SD. In seasonal time scale, Tmin, SD, U10, and RH were the most dominant factors in spring, summer, autumn, and winter respectively. (4) Spatial distribution for contribution rates of various meteorological factors showed significant diversity among various subregions. The positive contribution of U10 was the major cause of the increase in ET0 in semi-arid grassland area (BGH), the southwest of "Qice line" (QCXXN), and the southeast of "Qice line" (QCXDN); the significant increase in Tmin contributed most in Qaidam Basin (CDM), Hexi inland river basin (HX), the northeast of "Qice line" (QCXDB), and the northwest of "Qice line" (QCXXB), while the contribution of decreasing SD offsets the positive effects of other factors, leading to the decrease in ET0 in HH. Our work illustrates that water management measures should be different at different spatial and temporal scales. The effect of U10 can be offset by covering, to reduce evaporation and maintain water in BGH, QCXXN, and QCXDN. And high-temperature resistant varieties are planted to adapt to temperature growth in CDM, HX, QCXDB, and QCXXB. Agricultural water management strategies should be formulated and selected according to local conditions. [ABSTRACT FROM AUTHOR]

Crop production potential (CPP) is profoundly affected by the change in climate factors (e.g., precipitation, temperature, and solar radiation) brought about by climate change, which ultimately affects the quantity and yield of crops. In China, arid and semi-arid regions are mainly located in the western regions and occupy around 59% of the land area. In order to identify the most important climatic factors restricting the increase in CPP and planting systems in the arid and semi-arid regions of northwest China, the changes in climate factors, CPP, and their correlation and planting systems were analyzed based on a representative semi-arid location, Dingxi, of Gansu province, from 1989 to 2019. The results showed that the temperature and precipitation increased by 0.89 °C and 26.61 mm, respectively, whereas solar radiation decreased by 5–6 d. The standard CPP of five crops (wheat, corn, potato, Chinese herbal medicines, and vegetables) increased by 655.09 kg/ha (1.09-fold), and precipitation played a more important role in improving CPP than other climate factors. Although there were positive correlations between the standard CPP and the five crops' actual yields, no significant relationships were observed. The total cultivation area of the five crops showed a 215.55 × 103 ha (1.75-fold) increase with a 8.91-, 2.33-, 8.73- and 3.10-fold increase for corn, potato, Chinese herbal medicines, and vegetables, respectively, plus a 2.58-fold decrease for wheat. The agricultural ecosystem's adaptability presented an obvious increase, especially from 2013 to 2019, although the agricultural natural environment factor maintained a low level. These findings provide scientific and technological support for the adjustment of planting structure, optimization of agricultural arrangement and development of water-saving agriculture in arid and semi-arid regions of northwest China. [ABSTRACT FROM AUTHOR]

The Asian summer monsoon (ASM) margin of northwest China is a critical region for studying Asian monsoon variability during the Holocene. However, the pattern of precipitation variations and migration of the ASM northern boundary in arid regions during the Holocene remains unclear. In this study, we analyzed oxygen isotopes of 70 calcareous root tube (CRT) samples from the desert hinterlands in the ASM margin of northwest China, including the Badain Jaran, Tengger, Ulan Buh, and Kubuqi deserts. The CRT samples were analyzed to reconstruct millennial‐scale precipitation variation patterns during the Holocene and further explored the location of the ASM northwestern boundary during the middle Holocene. Our results demonstrated that the δ18O values of CRTs during the late Holocene (4.0–1.0 cal kyr BP) were all less negative than those during the middle Holocene (8.0–4.0 cal kyr BP), which revealed that the precipitation decreased from the middle Holocene to the late Holocene. Moreover, an increase in δ18O values from the southeast to northwest revealed that the precipitation decreased. We argued that the Holocene millennial‐scale precipitation changes in this region were influenced by the migrations in the ASM northern boundary. During the middle Holocene, due to the strong summer solar radiation and reduced ice sheets, the ASM northern boundary in the arid region advanced by at least 250 km to the northwest, which resulted in increased precipitation. During the late Holocene, the ASM northern boundary retreated southeastward, resulting in decreased precipitation. Plain Language Summary: The pattern of precipitation variations remains controversial in the Asian summer monsoon (ASM) margin of northwest China. Especially in the desert hinterlands, sedimentary records are scarce. Therefore, it is difficult to accurately determine the spatial distribution of precipitation in the ASM margin of northwest China, and further discuss the migration in the ASM northern boundary during the Holocene. In this study, we attempt to analyze the oxygen isotopes of pedogenic carbonates within calcareous root tube (CRT) samples from deserts in this region to reconstruct the millennial‐scale precipitation variations during the Holocene. Our results showed that precipitation decreased from the middle Holocene (8.0–4.0 cal kyr BP) to the late Holocene (4.0–1.0 cal kyr BP) and decreased from southeast to northwest in this region. Moreover, precipitation was influenced by migrations in the ASM northern boundary in the ASM margin of northwest China. During the middle Holocene, due to strong summer solar radiation and reduced ice sheets, the ASM northern boundary in the arid region advanced by at least 250 km to the northwest, which resulted in an increase of precipitation in this region. During the late Holocene, the ASM northern boundary retreated southeastward, resulting in decreased precipitation. Key Points: Holocene millennial‐scale precipitation variations of deserts in the Asian summer monsoon margin of northwest China were reconstructedPrecipitation decreased from the middle Holocene to the late Holocene and accompanied by decreasing from southeast to northwestDuring the middle Holocene, the Asian summer monsoon northern boundary in the arid region advanced by at least 250 km to the northwest [ABSTRACT FROM AUTHOR]

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Northwest China is one of the most arid regions in the world and has experienced intriguing climate warming and humidification. Nonetheless, future climate conditions in Northwest China still remain uncertain. In this study, we applied an ensemble of the 12 latest model simulations of the Coupled Model Intercomparison Project Phase 6 (CMIP6) to assess future drought conditions until 2099 in Northwest China, as inferred from the Palmer Drought Severity Index (PDSI). Future drought conditions were projected under three climate change scenarios through the combination of shared socioeconomic pathways (SSPs) and representative concentration pathways (RCPs), namely, SSP126 (SSP1 + RCP2.6, a green development pathway), SSP245 (SSP2 + RCP4.5, an intermediate development pathway), and SSP585 (SSP5 + RCP8.5, a high development pathway). For 2015–2099, drought severity showed no trend under SSP126, in contrast, for the SSP245 and SSP585 scenarios, a rapid increase during 2015–2099 was observed, especially under SSP585. We also found that the drought frequency in Northwest China under SSP585 was generally lower than that under SSP126 and SSP245, although the drought duration under SSP585 tended to be longer. These findings suggest the green development pathway in drought mitigation and adaptation strategies in Northwest China, an arid and agricultural region along the Silk Road.

This study aims to explore the temporal and spatial evolution of rainfall concentration against the global climate change in the Northwest region of China. Mann-Kendall trend test and change-point detection were carried out on a series of monthly raster rainfall data in the Northwest region from 1960 to 2017. Morlet wavelet was also used to analyze the periodic change in rainfall concentration. Moreover, a hotspot analysis was made on the spatial distribution and aggregation characteristics of rainfall concentration. A cross-wavelet analysis was used to explore the relationship between atmospheric circulation factors and rainfall concentration, thereby determining the influence of landform distribution on rainfall concentration. The results showed that: 1) The average rainfall concentration presented a decreasing trend in the Northwest region and the three sub-regions (subarea 1 which is in the west of “Qice Line”, subarea 2 which is between “Yangguan Line” and “Qice Line”, and subarea 3 which is between “Hu Line” and “Yangguan Line”) from 1960 to 2017, where there were significant change-points (P<0.05). Specifically, the average rainfall concentration in subarea 1 showed a significant downward trend (P<0.05). The significant change-points in rainfall concentration of the entire study area were mainly concentrated in the 1980s, 1990s, and 2010s (P<0.05). Furthermore, the maximum multi-year average rainfall concentration was distributed in subarea 2. There was also uneven rainfall distribution during the year, indicating obvious seasonal changes. Some areas were abnormally concentrated or continued to decrease, thereby flatting the distribution of rainfall over the year in the future. 2) The average rainfall concentration varied greatly in the entire study area. Specifically, the three sub-regions from 1960 to 2017 presented a main cycle of about 40 a, and a secondary cycle of about 24 a. The overall cycle changes of rainfall concentration in the entire study area and three sub-regions remained the same, indicating no obvious difference. 3) There were cold and hot spots in the spatial distribution of rainfall concentration from 1960 to 2017. The rainfall concentration in cold spots showed a significant decreasing trend (P<0.05), while continued to decrease in the future. The rainfall concentration in hotspots presented an insignificant decreasing trend (P>0.05). The interannual variation was higher than that in cold spots. 4) North Atlantic Oscillation (NAO) and Pacific Decade Oscillation Index (PDO) presented a strong influence on the changes in rainfall concentration, where different atmospheric circulation factors had different effects on rainfall concentration. At the same time, the distribution difference of landform in Northwest China has a certain impact on the change of rainfall concentration. The rainfall concentration in the high mountainous landforms is the highest, with an average of 28.55. Consequently, much more attention can be paid to the influence of abnormal factors of atmospheric circulation on rainfall concentration, especially the distribution of rainfall in arid and semi-arid regions over the year. The findings can provide scientific support to ecological and environmental protection, as well as the response to water resources in the Northwest region. [ABSTRACT FROM AUTHOR]

Over the past two decades, environmental studies in research on prehistoric China have been gaining popularity and importance. For Northwest China in particular, climate change, especially the so-called ~4.2k BP event has been seen as the main reason for an alleged collapse of Late Neolithic societies and a transition to pastoral-heavy economies and mobile lifeways. Yet, these explanatory models tend to rely on limited archaeological and environmental data and non-contemporaneous historical data, resulting in simplistic causal relationships between environmental changes and social response. This paper re-evaluates the Incipient Bronze Age in China's Northwestern region, discussing evidence for climate change and its exact dates, as well as textual and archaeological evidence. We argue that the old narratives perpetuating the image of a dichotomy between Steppe and Sown are inaccurate, while large-scale models of region-wide subsistence change in response to climate cooling tend to disregard local developments and group-specific responses as well as chronological issues. Focusing on the Xindian and Siwa archaeological phenomena, this paper provides a view into sub-regional responses to this climate event, warning against simplistic broad-brush reconstructions and calling for both a return to archaeological fundamentals and large-scale intensive fieldwork and interdisciplinary studies involving archaeologists, paleobotanists, zooarchaeologists, isotope specialists, and climate scientists. [ABSTRACT FROM AUTHOR]

In the Asian monsoon margin of Northwest China, the impact factors for variations in the aridity and humidity of the summer climate are complex and unclear. In this study, we selected the Alashan Plateau, located in the mid‐latitude arid zone and the Asian monsoon margin of Northwest China, as the study area. Changes in the aridity index K (a proxy for the arid–humid variations in the summer climate of the Alashan Plateau) were calculated for the period 1960–2010 using meteorological data. Relationships among the aridity index K, changes in the intensity of atmospheric circulations, and local precipitation and evaporation in summer are discussed. The results indicated that the arid–humid variations in the summer climate in different regions of Alashan Plateau exhibit significant spatial differences. The summer climate became more humid during 1960–1968 and 1988–1995 and arid in 1996–2010 with different trends, but exhibited asynchronous changes during other periods. Hence, the arid–humid variations in the summer climate exhibited significant spatial differences in the Alashan Plateau. These variations were mainly affected by East Asian summer monsoon in the eastern Alashan Plateau, local precipitation and evaporation in the central and northwestern Alashan Plateau, and atmospheric circulations and evaporation in the southwestern Alashan Plateau. The increase in the monsoon precipitation is not the only factor that affected arid–humid variations in the summer climate over the entire Alashan Plateau, therefore, other non‐circulation factors, such as local precipitation and evaporation, should also be considered. The study provides new evidence on how to understand the mechanisms driving global and regional climate change. [ABSTRACT FROM AUTHOR]

Climate change and human activities are affecting the ecological health of rivers and the economic value of its ecosystem services. Taking water quantity as the intermediate variable, we proposed a quantitative calculation method for the impact of climate change and human activities on the economic value produced by the ecosystem service functions of rivers. The framework mainly consists of three steps: firstly, we quantitatively determined the changes in the amount of water coming from rivers due to climate change and human activities; secondly, combining the theory of resource and environmental economics to calculate the economic value generated by ecological service functions of rivers; finally, we quantitatively identified and analyzed the impact of climate change and human activities on the economic value produced by the ecosystem service functions of rivers. Taking Baoji section of Weihe River (BSWR) as an example, we quantitatively analyzed and calculated the impact of climate change and human activities on the economic value produced by ecosystem service functions of rivers. The main conclusions of this paper are as follows: in recent 52 years, the economic value produced by the ecosystem service functions of rivers decreased by 3.57 billion yuan due to the climate change and human activities; the total economic value has been reduced by an average of 68 million yuan per year. This useful work can not only reveal the impact of climate change and human activities on the economic value of ecosystem services of rivers but also can provide an important basis for the reasonable management model of water resource of ecosystem of rivers watershed. [ABSTRACT FROM AUTHOR]

Extending across three major plateaus, namely the Qinghai-Tibetan Plateau, the Inner Mongolia-Xinjiang Plateau and the Loess Plateau, Northwest China has the complex terrain and spatio-temporal climate variations, and is affected by the interactions among different circulation systems, such as the summer monsoon, the westerlies and the plateau monsoon. The understanding of the climate variability, as well as its characteristics and evolution mechanisms in this area has been limited so far. In this paper, the precipitation characteristics and mechanisms in the eastern and western parts of Northwest China during the flood season are compared and analyzed based on the data from 192 national meteorological observational sites in Northwest China in 1961–2016. The results show that, divided by the northern boundary of the East Asian summer monsoon, there are huge differences in the precipitation variation characteristics between the eastern and western parts. The inter-annual variations, inter-decadal variations and total trends in the two parts all show a significant seesaw phenomenon. Moreover, it is found that the seesaw phenomenon of precipitation variation is closely related to the opposite variation between the East Asian summer monsoon index (MI) and the westerly circulation index (WI). In addition, the inverse variations on different time scales are only related to the contributions of precipitation at specific grades. Besides, in the two matching patterns of precipitation in the seesaw phenomenon, the middle and high latitudes are occupied by the "high-low-high" wave trains in the precipitation increases in the east of Northwest China (ENWC) and decreases in the west of Northwest China (WNWC) pattern, meaning precipitation increases in ENWC and decreases in WNWC. Whereas the opposite "low-high-low" wave trains at 500 hPa height are observed in the middle and high latitudes in the WH-EA pattern at 500 hPa height, meaning precipitation increases in WNWC and decreases in ENWC. Thus, the atmosphere circulation situation with two wave train types can support both the precipitation seesaw phenomenon and the opposite variation between MI and WI. Moreover, the seesaw phenomenon is shown to be related to the separate or joint effects of the South Asian High, ENSO and the plateau heating on the common but opposite effect on the summer monsoon and the westerlies, in which the South Asian High probably plays a more critical role. This study could deepen the scientific understanding of precipitation mechanisms and improve the weather forecast technology in Northwest China during the flood season. [ABSTRACT FROM AUTHOR]

The arid/semiarid region of Northwest China (NWC, north to 35°N, and west to 100°E in China) experienced significant wetting after the late 1980s. We used both the summer precipitation and standardized precipitation indices (precipitation index [PI] and standardized precipitation index) to reexamine the regime shift. Consistent with the rainfall, the drought condition represented by the standardized precipitation index was significantly alleviated over most areas of NWC during P2 (1989–2016) than that during P1 (1961–1988). Along with the increased rainfall over the NWC, significant changes also occur in the interannual variation‐related circulation. The Ural High (UH) was found to be closely related with the interdecadal change during the late 1980s. The NWC PI‐related wave propagation from the UH weakened after the late 1980s. The persistent tropical Indian Ocean sea surface temperature (SST) from the preceding winter to the summer were also found to influence the NWC PI through modulating the South Asian High during P1. However, during P2, the ENSO signals in the preceding winter, which can be memorized by the Indian Ocean SST in the spring and propagate to the Indo‐Pacific SST in the summer, can influence the NWC PI. The wave train pattern in the convection from the Maritime Continent to NWC and northwestern Europe seems to be a key bridge. The UH seems to be independent of the above SST‐forced atmospheric circulations. The SST signals of the preceding winter can provide useful information for the summer drought prediction in NWC. Key Points: The summer drought over Northwest China (NWC)‐related atmospheric circulation show significant changes at the late 1980sThe Ural High's impact on the atmospheric circulation over NWC becomes much weaker during P2 (1989‐2016) than that during P1 (1961‐1988)The key SST regions related with the NWC drought shifted from the tropical Indian Ocean during P1 to the Indo‐Pacific region during P2 [ABSTRACT FROM AUTHOR]

Past geological and climatic changes have promoted shifts in both intraspecific differentiation and distribution ranges for many desert plants, though little is known about the effects of these changes specifically on spring ephemerals in Northwest China. In the present study, we aimed to survey the population structure and phylogeographic history of an endemic spring ephemeral species, Ixiolirion songaricum P. Yan in Northwest China. We sequenced the nITS and two ptDNA fragments (psbB-psbH and ycf6-psbM) for 265 individuals from 15 populations across the entire range. Eight nITS ribotypes and eleven plastid chlorotypes were identified, with three of them dominant. A significant phylogeographic structure was detected for the species in which two larger, distinct phylogeographic lineages were identified. A high proportion of the total genetic variation existed between populations and between the two lineages. The species had undergone a sudden range expansion in the late Quaternary, which might have been driven by an interglacial warm, humid climate following the largest Pleistocene glaciation period in Northwest China. The ecological niche modeling suggested the species experienced continuous shrinkage of potential range since the last interglacial, which is distinct from other desert plants. Overall, our results indicated that climate change associated with the Quaternary greatly promoted differentiation of I. songaricum. The shift in population distribution was likely driven by increasing aridity in Xinjiang during the Quaternary. [ABSTRACT FROM AUTHOR]

Abstract In the arid Hexi Corridor of northwest China, vegetation cover plays a pivotal role in sustaining the unique terrestrial ecosystem. In this paper, vegetation changes during growth season from April to October were investigated through examining the trends in the Normalized Difference Vegetation Index (NDVI) across the Hexi region. Based on the GMMIS NDVI 3g.v1 dataset, NDVI trend and its dependency on elevation and land cover were analyzed for the period 1982–2015 according to multiple statistical tests. Results showed that NDVI exhibited a significantly increasing trend in ∼70% of the vegetated area, in contrast with a negative trend only in 2.85%. The resulting distinct groups with respect to decreasing, increasing and no trends presented significant differences in elevation and land cover composition, and the correlation between elevation, land cover and NDVI trend magnitude was subjected to precipitation and temperature change. The elevation and grassland cover were found to mainly account for variations in NDVI trend, and increase in elevation and various types of land cover excluding impervious and bare land would facilitate the trend magnitude. The dependency of NDVI trend on elevation and land cover was very vulnerable to increasing air temperature, which triggered an improvement in the vegetable activity to adapt to climate change, especially grass and forest. The contribution of crop and shrub to NDVI change was sensitive to precipitation trend change, but the crop was primarily influenced by human activities. The identified patterns of vegetation change would help to gain insights into the adapting mechanism of the fragile ecosystems in arid areas to changing environmental conditions. Graphical abstract Image 1 Highlights • A significantly increasing trend in NDVI was detected at 70% of the vegetated area. • The NDVI trend was strongly related to characteristics of elevation and land cover. • Significant variations in elevation and grass land imply the NDVI trend dependency. • The NDVI trend dependent on elevation and land cover is subject to climate change. • Effect of precipitation or temperature change was distinguished on the land cover. [ABSTRACT FROM AUTHOR]

In the hinterland of the desert, valuable archives of paleoenvironmental evolution are scarce. Calcareous root tubes (CRTs) have a strong potential for reconstructing paleoenvironmental conditions. It is still unclear, however, whether chemical elements in the CRTs can provide insights into paleoenvironmental conditions. In this study, the major- and trace-element composition of 32 CRT samples from the Alashan Desert were analyzed by X-ray fluorescence spectrometry. Results showed that the elemental composition and content change were controlled by the parent material and climatic conditions at the time of CRT formation. Ca, Mg, and Sr were significantly affected by climate, whereas the enrichment of P is likely related to the growth of plants. Higher (lower) Mg/Ca and Sr/Ca ratios corresponded to higher (lower) effective moisture and a higher (lower) Mg/Sr ratio indicated a higher (lower) temperature during the middle Holocene (8–5 cal ka BP). The reconstruction results for effective moisture were consistent with those in the Asian monsoon margin of northwestern China, which were caused by higher monsoon precipitation and lower evaporation. Therefore, chemical elements in the CRTs can reflect changes in paleo-effective moisture and paleotemperature at a millennial resolution in this area. [ABSTRACT FROM AUTHOR]

Climatic fluctuations during the Quaternary significantly affect many species in their intraspecific divergence and population structure across northwest China. In order to investigate the impact of climate change on herbaceous plants, we studied Panzerina lanata (Lamiaceae), a widely distributed species. Sequences of two chloroplast DNA (cpDNA) intergenic spacers (trnH-psbA and rpoB-trnC) and a nuclear ribosomal region (nrDNA, ITS) were generated from 27 populations of Panzerina lanata and resulted in the identification of seven chloroplast haplotypes and thirty-two nuclear haplotypes. We applied AMOVA, neutrality test and mismatch distribution analysis to estimate genetic differentiation and demographic characteristics. The divergence times of the seven cpDNA haplotypes were estimated using BEAST. Our results revealed high levels of genetic diversity (cpDNA: Hcp = 0.6691, HT = 0.673; nrDNA: Hnr = 0.5668, HT = 0.577). High level of genetic differentiation (GST D 0.950) among populations was observed in the cpDNA sequences, while the genetic differentiation values (GST D 0.348) were low in nuclear sequences. AMOVA results revealed major genetic variation among the three groups: northern, central, and eastern group. However, the genetic differentiation in ITS data was not found. The species distribution modeling and demographic analysis indicated that P. lanata had not experienced recent range expansion. The occurrence of divergence between seven cpDNA haplotypes, probably during Pleistocene, coincides with aridification and expansion of the desert across northwest China that resulted in species diversification and habitat fragmentation. In addition, we discovered that the deserts and the Helan Mountains acted as effective geographic barriers that promoting the intraspecific diversity of P. lanata. [ABSTRACT FROM AUTHOR]

The dominant modes wintertime precipitation in northwest China (NWC) and the possible causes are investigated during the period 1961–2013 in the inter‐annual timescale, as winter climate condition could greatly affect local economic development and people's lives. The analysis of this study is divided into three parts. First, the spatiotemporal variability of dominant modes wintertime precipitation is described by an empirical orthogonal function (EOF) method. The atmospheric circulation anomalies associated with wintertime precipitation variations are then discussed through regression and composite analysis. Third, the relationships between wintertime precipitation and sea surface temperature (SST) anomalies are investigated. The results indicate that the leading mode (EOF1) shows a uniform sign in the entire region, and the second mode (EOF2) exhibits a zonal‐dipole pattern; they account for 25.6 and 15.7% of the total variance, respectively. The atmospheric circulation anomalies EOF1 closely related to is the Eurasian (EU) teleconnection pattern. Years when a negative phase of EU pattern occurs tend to be rainy with anomalous southerly transporting water vapour from low‐latitudes and profound ascending motion anomalies. Atmospheric circulation anomalies associated with the second mode resemble the Arctic Oscillation (AO) pattern. AO pattern influences EOF2 precipitation variations through the anomalous circulations over Mongolia and western Europe. The sea surface temperature (SST) anomalies related to EOF1 show an El Niño‐Southern Oscillation (ENSO) like pattern, which may modulate the wintertime precipitation mode through the western North Pacific anticyclone. The EOF2 mode has a close relationship with a tripole SST anomaly mode in the North Atlantic Ocean. This SST pattern is likely to influence wintertime precipitation by modulating the North Atlantic Oscillation (NAO). The results of this study could be beneficial for wintertime precipitation prediction and the decrease of economic losses in NWC and may also provide useful references for other areas with similar climatic features such as the central Asia. (a, c) EOF1 and (b, d) EOF2 of inter‐annual wintertime precipitation variations for 1961–2013 in NWC. (a, b) Regression maps on the normalized time series (unit: mm); (c, d) normalized time series. [ABSTRACT FROM AUTHOR]

We investigated drought activity and the relationship between drought and vegetation in Northwest China over the period 1982-2013 using the standardized precipitation evapotranspiration index (SPEI) and the normalized difference vegetation index (NDVI). The indexes were, respectively, calculated from ground-based meteorological data and from remotely sensed satellite data. The spatial and temporal distributions of drought (SPEI) and of vegetation cover (NDVI) were compared using annual trends, and the relationships between these trends were analyzed. The results are: (1) Overall, Northwest China had a drought trend during the study period, although some a few regions show a significant wetness trend; (2) the mean annual NDVI fluctuates, but overall shows an increasing trend, particularly in some mountainous areas that have at least adequate water and vegetation cover, while unused land becomes degraded; (3) most regions show a positive correlation between SPEI and NDVI, although the western parts of the Tarim basin, Qaidam basin, and some regions in the southeastern part of study area show a negative correlation; and (4) the various regions respond differently to global climate change, but in general regions with more vegetation cover show increased vegetation growth, while regions with less vegetation cover are becoming degraded and thus more vulnerable to the adverse effects of climate change. [ABSTRACT FROM AUTHOR]

Previous studies have reported that much of the surface wind speed (SWS) over the mid‐latitudes of the northern hemisphere has declined. However, very few studies have investigated the relatively recent phenomenon of wind recovery. Based on 68 wind data series, this paper examines changes in wind speed in northwest China between 1969 and 2015. In 1992, following a decade of sharply decreasing at a rate of 0.036 m s−1 a−1 (p < .05), the SWS began to significant increase at a rate of 0.004 m s−1 a−1. The specific reasons for this increase are as follows: (a) The decrease in SWS during the pre‐1992 slowdown period is the result of declining wind speeds in spring and summer, whereas increases in wind speed during the post‐1992 recovery period are caused by increased wind in winter. (b) The number of days featuring strongly varying wind speeds has changed. Specifically, the number of days above 2 m s−1 all show a significant decreasing trend from 1969 to 1992, whereas the number of days of 1–3 m s−1 shows a significant upward trend from 1993 to 2015. (c) Stations located between 1,000 and 1,500 m.a.s.l. (meter above sea level) are more sensitive to climate change than those at other altitudes, which shows the biggest decline (increase) trend during wind speed slowdown (recovery) period. These stations could potentially act as climatic indicators to predict future wind speed changes. SWS in northwest China have been affected by changes both in large‐scale atmospheric circulation and in regional warming. Surface pressure gradient variations between high‐ and low‐latitude regions may be important contributors to wind speed changes under asymmetric warming. However, urbanization is only moderately responsible for trend changes in SWS. [ABSTRACT FROM AUTHOR]

In this study, authors investigated both year-to-year variation and long-term changes in precipitation in Northwest China. Based on statistical analysis, anomalous regional rising motion and convergence of moisture flux are identified as the causes of year-to-year variation of precipitation in Northwest China. Aside from the year-to-year variation, long-term changes in these regional circulations also led to a significant enhancement of precipitation in Northwest China after the mid-1980 s. In addition, the changes in these regional circulations are controlled by anomalous eddies in the upper troposphere. The anomalous regional rising motion and the convergence of moisture flux are a result of the anomalous divergence of wind in the upper troposphere and southeasterly wind in the mid to lower troposphere. Both are induced by a negative center of eddy height in the upper troposphere to the west of Northwest China. It is also noted that the year-to-year variation of the negative center is concurrent with the circumglobal teleconnection. On the other hand, the long-term change in the negative center is concurrent with the weakening of midlatitude eddies in the mid-1980 s. [ABSTRACT FROM AUTHOR]

The Heihe River basin is one of the important bases for commercial grain production in China. The climate change impacts on crop yield and crop water productivity (CWP) need to be examined for sustainable development of regional agriculture, especially under the pressure of population growth and regional water scarcity. A distributed hydrological model was constructed for the upper-middle reaches of the Heihe River basin on the basis of the Soil and Water Assessment Model (SWAT). The sensitivity ranks of hydrological parameters were evaluated for the runoff and evapotranspiration processes, and then independently calibrated with the observations of three gauging stations (Qilian, Zhamashike, and Yingluoxia stations) and the evapotranspiration data derived by remote-sensing. The study first simulated crop yield and CWP for four typical crop types, namely corn, spring wheat, spring barley, and spring canola-Polish, for the period of 1966–2014 using the SWAT model, calibrated with the crop yield data (during the period of 2005–2014) from Zhangye Statistics Yearbook. The spatial-temporal features of crop yield and CWP were analyzed. A fluctuating growth was found for the 49 year trend of corn, spring wheat, and spring canola-Polish. The spring barley shows a slightly decreasing trend. The high-yield area moved from the west part (Suzhou and Gaotai counties) to the east part (Linze, Ganzhou, and Shandan counties) of the basin for the past 49 years, and the area of high CWP concentrated in the Gaotai and Linze Counties. The responses of CWP to climatic forcing were further studied using wavelet coherence method. It is found that maximum temperature dominated the CWP evolutions, especially at the long-term scales. The corn showed the largest elastic responses to the climatic factors, which may be favorable to improve regional CWP by expanding planting area. In addition, the strategies of regional CWP improvement were discussed based on the results. [ABSTRACT FROM AUTHOR]

Lakes provide valuable water resources for people, life, and socioeconomic development in Northwestern China---a core region of the arid Central Asia where water is seriously deficient. In this study, we report the first investigation of the 30-year changes in all lakes larger than 1 km 2 in Northwestern China and the associated driving forces. We found that the number of lakes increased from 121 to 135, and the total lake area increased from 5495 km 2 to 6445 km 2 in this region. However, increases in lake area occurred mainly in the less populated mountainous areas caused by glacier melting and increase in precipitation. Conversely, lakes in the densely populated regions decreased by 40% since the year of 2000, which was significantly related to the increasing intensity of irrigation. These results not only suggest an ongoing water crisis in Northwest China but also reflect the lake dynamics in arid Central Asia where climate changes and irrigation are occurring prevalently with high intensity. Given the fact that the benefits of glacier melt in Central Asia can be substantially offset by intensive irrigation, we thus call an urgent need for a policy of sustainable water management in this critical region. [ABSTRACT FROM AUTHOR]

In this study, the temporal variations of the standard precipitation index (SPI) were analyzed at different scales in Northwest China (NWC). Discrete wavelet transform (DWT) was used in conjunction with the Mann-Kendall (MK) test in this study. This study also investigated the relationships between original precipitation and different periodic components of SPI series with datasets spanning 55 years (1960-2014). The results showed that with the exception of the annual and summer SPI in the Inner Mongolia Inland Rivers Basin (IMIRB), spring SPI in the Qinghai Lake Rivers Basin (QLRB), and spring SPI in the Central Asia Rivers Basin (CARB), it had an increasing trend in other regions for other time series. In the spring, summer, and autumn series, though the MK trends test in most areas was at the insignificant level, they showed an increasing trend in precipitation. Meanwhile, the SPI series in most subbasins of NWC displayed a turning point in 1980-1990, with the significant increasing levels after 2000. Additionally, there was a significant difference between the trend of the original SPI series and the largest approximations. The annual and seasonal SPI series were composed of the short periodicities, which were less than a decade. The MK value would increase by adding the multiple D components (and approximations), and theMK value of the combined series was in harmony with that of the original series. Additionally, the major trend of the annual SPI in NWC was based on the four kinds of climate indices (e.g., Atlantic Oscillation [AO], North Atlantic Oscillation [NAO], Pacific Decadal Oscillation [PDO], and El Nino-Southern Oscillation index [ENSO/NINO]), especially the ENSO. [ABSTRACT FROM AUTHOR]

The effect of climate variables (temperature and precipitation) on forest spatial distribution is more prominent in dryland high mountains, where forest distribution is inherently very sensitive to and strongly limited by the substantial spatial heterogeneity of site conditions. Thus, a more reliable prediction of forest distribution under changing environment depends upon an understanding of the joint influence of climatic and topographic factors and their thresholds. This study was conducted on Qinghai spruce forests as dominant tree species in the Qilian Mountains of northwest China. The spruce forest distribution was surveyed by remote sensing in Dayekou watershed and by field investigation in a nested smaller watershed. Analyses showed that mean annual air temperature and precipitation, which vary with elevation, are the key climatic factors determining forest distribution, but slope aspect also plays an essential role. The potential core distribution area of denser forests and potential distribution area including sparse forests are between the axes of elevation (2635.5–3302.5 and 2603.4–3325.8 m a.s.l.) and slope aspect (− 74.4–61.2° and − 162.6–147.1° deviated from north). The corresponding threshold of mean annual air temperature at the upper elevation boundary is − 2.59 and − 2.73°C, while the threshold of mean annual precipitation at the lower elevation boundary is 378.1 and 372.3 mm, respectively. Using these thresholds and the elevation gradients of climatic factors, the shifting of elevation boundaries under climate change scenarios can be predicted. However, the forest distribution is also limited by a soil thickness of ≥ 40 cm; and by slope position of lower-, lower- and middle-, and entire-slope within the elevation ranges of < 2800, 2800–2900, and > 2900 m a.s.l., respectively. This study showed that adding geographic factors will greatly improve the prediction of changes in forest distribution area in dryland mountains, in addition to the influence of climatic factors. [ABSTRACT FROM AUTHOR]

Under global warming, drought problems have become increasingly prominent, which has seriously affected the ecological environment's protection and social and economic development at global and regional scales. Ningxia is an arid region in northwest China with serious water problems, and droughts further exacerbate its water security and hinder ecological and socio-economic development. Therefore, this study explored the temporal and spatial distribution characteristics of meteorological and agricultural droughts and their driving factors in Ningxia during 2002–2021 by combining wavelet analysis and grey relational analysis. The main conclusions are as follows: (1) precipitation, soil moisture (SM), and evapotranspiration (ET) in Ningxia increased significantly, while the main meteorological drought events in Ningxia appeared around 2006, 2011, and 2015, and the agricultural drought first became stronger and then weaker; (2) precipitation and ET were correlated with meteorological drought in Ningxia, with a coefficient above 0.8, while the correlation between agricultural drought and precipitation, ET, and gross primary production (GPP) were very significant; and (3) precipitation, ET, and GPP were not all included in the drivers of meteorological drought in Ningxia, whereas agricultural drought had a grey correlation with precipitation, ET, and GPP according to the grey relational analysis. This study is of great significance for revealing the spatiotemporal characteristics and driving factors of drought in Ningxia as well as the early warning and risk management. • Ningxia experienced a state of becoming dry before becoming wet. • The correlation between agricultural drought and meteorological drought in Ningxia is not significant. • Almost all eco-hydrological factors in Ningxia have a large impact on agricultural drought. • Different ecohydrological factors have different impacts on different regions of Ningxia. [ABSTRACT FROM AUTHOR]

Climate change resulted in changes in crop growth duration and planting structure, northward movement of planting region, and more severe plant diseases and insect pests in Northwest China. It caused earlier seeding for spring crop, later seeding for autumn crop, accelerated crop growth, and reduced mortality for winter crop. To adapt to climate change, measures such as optimization of agricultural arrangement, adjustment of planting structure, expansion of thermophilic crops, and development of water-saving agriculture have been taken. Damaging consequences of imbalance between grassland and livestock were enhanced. The deterioration trend of grassland was intensified; both grass quantity and quality declined. With overgrazing, proportions of inferior grass, weeds and poisonous weeds increased in plateau pastoral areas. Returning farmland to grazing, returning grazing to grassland, fence enclosure and artificial grassland construction have been implemented to restore the grassland vegetation, to increase the grassland coverage, to reasonably control the livestock carrying capacity, to prevent overgrazing, to keep balance between grassland and livestock, and to develop the ecological animal husbandry. In Northwest China, because the amount of regional water resources had an overall decreasing trend, there was a continuous expansion in the regional land desertification, and soil erosion was very serious. A series of measures, such as development of artificial precipitation (snow), water resources control, regional water diversion, water storage project and so on, were used effectively to respond to water deficit. It had played a certain role in controlling soil erosion by natural forest protection and returning farmland to forest and grassland. In the early 21st century, noticeable achievements had been made in prevention and control of desertification in Northwest China. The regional ecological environment has been improved obviously, and the desertification trend has shown sign of under control. Citation: Zhao, H.-Y., J.-Q. Guo, C.-J. Zhang, et al., 2014: Climate change impacts and adaptation strategies in Northwest China.Adv. Clim. Change Res.,5(1), doi: 10.3724/SP.J.1248.2014.007.

The temporal dynamics of vegetation biomass are of key importance for evaluating the sustainability of arid and semiarid ecosystems. In these ecosystems, biomass and soil moisture are coupled stochastic variables externally driven, mainly, by the rainfall dynamics. Based on long-term field observations in northwestern (NW) China, we test a recently developed analytical scheme for the description of the leaf biomass dynamics undergoing seasonal cycles with different rainfall characteristics. The probabilistic characterization of such dynamics agrees remarkably well with the field measurements, providing a tool to forecast the changes to be expected in biomass for arid and semiarid ecosystems under climate change conditions. These changes will depend--for each season--on the forecasted rate of rainy days, mean depth of rain in a rainy day, and duration of the season. For the site in NW China, the current scenario of an increase of 10% in rate of rainy days, 10% in mean rain depth in a rainy day, and no change in the season duration leads to forecasted increases in mean leaf biomass near 25% in both seasons. [ABSTRACT FROM AUTHOR]

The solar radiation data are of high importance to the solar energy systems. Conventional methods to obtain the solar radiation data are from weather stations, solar radiation models, commercial software databases, and field measurements. In the present study, a new daily global solar radiation model is proposed, by combining the quadratic function of sunshine fraction and sine function of the day of the year. The solar radiation model calculated data are then compared with China Meteorological Data Sharing System (CMDSS) data, TRNSYS data, and field-measured data in Northwest China climate. It is found that the newly proposed solar radiation model has better performance than the other nine solar radiation models in the literature. The solar radiation model calculated data fit well with the CMDSS annually average data. The TRNSYS data are a bit larger than the CMDSS annually average data in summer half year and a little smaller than those in winter half year. The solar radiation model and the CMDSS annually average data have the best correlation, whereas the TRNSYS data and the fieldmeasured data have the worst correlation. The solar radiation model calculated data have the best correlation with the other three data sources. [ABSTRACT FROM AUTHOR]

The Hexi Corridor of northwestern China was a principal axis of cultural interchange between eastern and western Eurasia during the prehistoric and historic epochs. Neolithic groups began dense settlements in Hexi Corridor after 4300 BP with millet crops and polychrome pottery from north China and bronze from Central Asia around 4000 BP accompanied by wheat, barley, and sheep. The impact of these activities on the environment during the late Neolithic and Bronze Age is not clearly understood. Therefore, we analyzed the Cu concentrations of samples collected within cultural layers of anthropogenic sediments from 17 Late Neolithic and Bronze Age sites located within the Hexi Corridor. The Cu content is reported in view of the archaeological and paleoclimatic research undertaken in the area. Our results enabled us to explore the variety of human impact on the environment before and after the introduction of bronze technology into Hexi Corridor. During 4300-4000 BP, Cu concentrations of the anthropogenic sediments were constrained within natural background values. However, from 4000 to 3400 BP, they increased substantially and far exceeded the natural background. The Cu concentrations then declined and remained above the natural background from 3000 to 2400 BP. Our work suggests that the introduction of copper melting technology led to human alteration of sediments' chemical properties in their surrounding environments in Hexi Corridor since 4000 BP; its intensity was closely related to human settlement density, which was further affected by climate change and livelihood transition in the area during Bronze period. [ABSTRACT FROM AUTHOR]

Based on the precipitation data from 96 weather stations in Northwest China (NWC) during 1960–2013, the Continuous Wavelet Transform (CWT) and the Mann-Kendall (MK) test were applied to analyze the precipitation spatiotemporal variations at different time scales. The relationships between the original precipitation and different periodic components were investigated. The results indicated that the annual precipitation was significantly increasing (P < 0.01) at the rate of 0.55 mm/a in the NWC. In terms of seasonal precipitation, the summer original precipitation significantly increased (P < 0.05) in the Southern Altay Mountain Basin (SAMB), Qaidam Basin (QB), Qiang Tang Plateau Basin (QTPB), Turpan-Hami Basin (THB), Tarim Desert Basin (TDB), Northern Tianshan Mountain Basin (NTMB) and NWC. For the winter original precipitation, except the Inner Mongolia Inland Rivers Basin and Northern Kunlun Mountain Basin, the significant increases (P < 0.05) were detected in the other sub-basins. In terms of monthly precipitation, significant increases were detected in January in the SAMB, NTMB and NWC, and July in the QB, Headstreams of Tarim River Basin (HTRB) and N. Additionally, most of the increasing and decreasing trends began in the mid-1980s or mid-1990s. Moreover, the periodic components were not always similar to the original data with the significant trends. The dominant scale of the original data from the periodic components was different in spatiotemporal distribution. Meanwhile, the relationship between the precipitation and El Niño-Southern Oscillation (ENSO) was different from period to period and from time scale to time scale. This study will help to develop better management measures to account for climate change and the supply/demand of water. [ABSTRACT FROM AUTHOR]

Water resources, which are considerably affected by land use/land cover (LULC) and climate changes, are a key limiting factor in highly vulnerable ecosystems in arid and semi-arid regions. The impacts of LULC and climate changes on water resources must be assessed in these areas. However, conflicting results regarding the effects of LULC and climate changes on runoff have been reported in relatively large basins, such as the Jinghe River basin (JRB), which is a typical catchment (> 45 000 km²) located in a semi-humid and arid transition zone on the central Loess Plateau, northwest China. In this study, we focused on quantifying both the combined and isolated impacts of LULC and climate changes on surface runoff. We hypothesized that under climatic warming and drying conditions, LULC changes, which are primarily caused by intensive human activities such as the Grain for Green Program, will considerably alter runoff in the JRB. The Soil and Water Assessment Tool (SWAT) was adopted to perform simulations. The simulated results indicated that although runoff increased very little between the 1970s and the 2000s due to the combined effects of LULC and climate changes, LULC and climate changes affected surface runoff differently in each decade, e.g., runoff increased with increased precipitation between the 1970s and the 1980s (precipitation contributed to 88% of the runoff increase). Thereafter, runoff decreased and was increasingly influenced by LULC changes, which contributed to 44% of the runoff changes between the 1980s and 1990s and 71% of the runoff changes between the 1990s and 2000s. Our findings revealed that large-scale LULC under the Grain for Green Program has had an important effect on the hydrological cycle since the late 1990s. Additionally, the conflicting findings regarding the effects of LULC and climate changes on runoff in relatively large basins are likely caused by uncertainties in hydrological simulations. [ABSTRACT FROM AUTHOR]