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1. chinaXiv:202106.00010 [pdf]

Potential responses of vegetation to atmospheric aerosols in arid and semi-arid regions of Asia

JIAO Linlin; WANG Xunming; CAI Diwen; HUA Ting
Subjects: Geosciences >> Geography

Changes in atmospheric aerosols have profound effects on ecosystem productivity, vegetation growth and activity by directly and indirectly influencing climate and environment conditions. However, few studies have focused on the effects of atmospheric aerosols on vegetation growth and activity in the vulnerable arid and semi-arid regions, which are also the source areas of aerosols. Using the datasets of aerosol optical depth (AOD), normalized difference vegetation index (NDVI) and multiple climatic variables including photosynthetically active radiation (PAR), surface solar radiation (SSR), surface air temperature (TEM) and total precipitation (PRE), we analyzed the potential responses of vegetation activity to atmospheric aerosols and their associated climatic factors in arid and semi-arid regions of Asia from 2005 to 2015. Our results suggested that areas with decreasing growing-season NDVI were mainly observed in regions with relatively sparse vegetation coverage, while AOD tended to increase as NDVI decreased in these regions. Upon further analysis, we found that aerosols might exert a negative influence on vegetation activity by reducing SSR, PAR and TEM, as well as suppressing PRE in most arid and semi-arid regions of Asia. Moreover, the responses of atmospheric aerosols on vegetation activity varied among different growing stages. At the early growing stage, higher concentration of aerosol was accompanied with suppressed vegetation growth by enhancing cooling effects and reducing SSR and PAR. At the middle growing stage, aerosols tended to alter microphysical properties of clouds with suppressed PRE, thereby restricting vegetation growth. At the late growing stage, aerosols exerted significantly positive influences on vegetation activity by increasing SSR, PAR and TEM in regions with high anthropogenic aerosols. Overall, at different growing stages, aerosols could influence vegetation activity by changing different climatic factors including SSR, PAR, TEM and PRE in arid and semi-arid regions of Asia. This study not only clarifies the impacts of aerosols on vegetation activity in source areas, but also explains the roles of aerosols in climate.

submitted time 2021-06-04 From cooperative journals:《Journal of Arid Land》 Hits2851Downloads464 Comment 0

2. chinaXiv:202106.00015 [pdf]

Spatiotemporal analysis of drought variability based on the standardized precipitation evapotranspiration index in the Koshi River Basin, Nepal

Nirmal M DAHAL; XIONG Donghong; Nilhari NEUPANE; Belayneh YIGEZ; ZHANG Baojun; YUAN Yong; Saroj KOIRALA; LIU Lin; FANG Yiping
Subjects: Geosciences >> Geography

Drought is an inevitable condition with negative impacts in the agricultural and climatic sectors, especially in developing countries. This study attempts to examine the spatial and temporal characteristics of drought and its trends in the Koshi River Basin (KRB) in Nepal, using the standardized precipitation evapotranspiration index (SPEI) over the period from 1987 to 2017. The Mann-Kendall test was used to explore the trends of the SPEI values. The study illustrated the increasing annual and seasonal drought trends in the KRB over the study period. Spatially, the hill region of the KRB showed substantial increasing drought trends at the annual and seasonal scales, especially in summer and winter. The mountain region also showed a significant increasing drought trend in winter. The drought characteristic analysis indicated that the maximum duration, intensity, and severity of drought events were observed in the KRB after 2000. The Terai region presented the highest drought frequency and intensity, while the hill region presented the longest maximum drought duration. Moreover, the spatial extent of drought showed a significant increasing trend in the hill region at the monthly (drought station proportion of 7.6%/10a in August), seasonal (drought station proportion of 7.2%/10a in summer), and annual (drought station proportion of 6.7%/10a) scales. The findings of this study can assist local governments, planners, and project implementers in understanding drought and developing appropriate mitigation strategies to cope with its impacts.

submitted time 2021-06-04 From cooperative journals:《Journal of Arid Land》 Hits932Downloads174 Comment 0

3. chinaXiv:202105.00010 [pdf]

Characteristics and hazards of different snow avalanche types in a continental snow climate region in the Central Tianshan Mountains

HAO Jiansheng; Richard MIND'JE; LIU Yang; HUANG Farong; ZHOU Hao; LI Lanhai
Subjects: Geosciences >> Geography

Snow avalanches are a common natural hazard in many countries with seasonally snow-covered mountains. The avalanche hazard varies with snow avalanche type in different snow climate regions and at different times. The ability to understand the characteristics of avalanche activity and hazards of different snow avalanche types is a prerequisite for improving avalanche disaster management in the mid-altitude region of the Central Tianshan Mountains. In this study, we collected data related to avalanche, snowpack, and meteorology during four snow seasons (from 2015 to 2019), and analysed the characteristics and hazards of different types of avalanches. The snow climate of the mid-altitude region of the Central Tianshan Mountains was examined using a snow climate classification scheme, and the results showed that the mountain range has a continental snow climate. To quantify the hazards of different types of avalanches and describe their situation over time in the continental snow climate region, this study used the avalanche hazard degree to assess the hazards of four types of avalanches, i.e., full-depth dry snow avalanches, full-depth wet snow avalanches, surface-layer dry snow avalanches, and surface-layer wet snow avalanches. The results indicated that surface-layer dry snow avalanches were characterized by large sizes and high release frequencies, which made them having the highest avalanche hazard degree in the Central Tianshan Mountains with a continental snow climate. The overall avalanche hazard showed a single peak pattern over time during the snow season, and the greatest hazard occurred in the second half of February when the snowpack was deep and the temperature increased. This study can help the disaster and emergency management departments rationally arrange avalanche relief resources and develop avalanche prevention strategies.

submitted time 2021-04-30 From cooperative journals:《Journal of Arid Land》 Hits581Downloads142 Comment 0

4. chinaXiv:202104.00093 [pdf]

Soil bacterial characteristics between surface and subsurface soils along a precipitation gradient in the Alxa Desert, China

TENG, Zeyu; XIAO, Shengchun; CHEN, Xiaohong; HAN, Chao
Subjects: Geosciences >> Geography

Bacteria in desert soil have unique phylogeny and important ecological functions, and their responses to changes in precipitation need further attention. However, relevant studies have mainly focused on the surface soil, and studies on the responses of bacteria at different soil depths to variations in precipitation are rare. Thus, we used 16S rDNA high-throughput sequencing to investigate the changes in soil bacterial distribution along a mean annual precipitation gradient (50–150 mm) in the Alxa Desert, China, and compared the variation characteristics in the surface soil layer (0–10 cm) and subsurface soil layer (10–20 cm). Results showed that soil bacterial communities significantly changed along the precipitation gradient in both soil layers. However, the subsurface soil layer could support bacterial communities with higher diversity and closer internal relationships but more internal competition than the surface soil layer. Additionally, compared with the surface soil layer, variations in diversity and co-occurrence patterns in the subsurface soil layer were more in line with the changes in the mean annual precipitation, while bacterial community structure was less variable in the subsurface soil layer. Compared with the mean annual precipitation, soil moisture had little influence on the structure and diversity of soil bacterial community but had a high correlation with intercommunity connectivity. Therefore, soil moisture might play a complex role in mediating environmental conditions and soil bacterial community characteristics. Due to the different responses of surface and subsurface soil bacteria to the changes in precipitation, it is necessary to distinguish different soil layers when predicting the trends in desert soil bacterial conditions associated with precipitation, and prediction of subsurface soil bacteria may be more accurate.

submitted time 2021-04-22 From cooperative journals:《Journal of Arid Land》 Hits554Downloads164 Comment 0

5. chinaXiv:202104.00095 [pdf]

Glacier mass balance in High Mountain Asia inferred from a GRACE release-6 gravity solution for the period 2002–2016

XIANG, Longwei; WANG, Hansheng; JIANG, Liming; SHEN, Qiang; STEFFEN, Holger ; LI, Zhen
Subjects: Geosciences >> Geography

We provide estimates of glacier mass changes in the High Mountain Asia (HMA) area from April 2002 to August 2016 by employing a new version of gravity solutions of the Gravity Recovery and Climate Experiment (GRACE) twin-satellite mission. We found a total mass loss trend of the HMA glaciers at a rate of –22.17 (±1.96) Gt/a. The largest mass loss rates of –7.02 (±0.94) and –6.73 (±0.78) Gt/a are found for the glaciers in Nyainqentanglha Mountains and Eastern Himalayas, respectively. Although most glaciers in the HMA area show a mass loss, we find a small glacier mass gain of 1.19 (±0.55) and 0.77 (±0.37) Gt/a in Karakoram Mountains and West Kunlun Mountains, respectively. There is also a nearly zero mass balance in Pamirs. Our estimates of glacier mass change trends confirm previous results from the analysis of altimetry data of the ICESat (Ice, Cloud and Land Elevation) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) DEM (Digital Elevation Model) satellites in most of the selected glacier areas. However, they largely differ to previous GRACE-based studies which we attribute to our different post-processing techniques of the newer GRACE data. In addition, we explicitly show regional mass change features for both the interannual glacier mass changes and the 14-a averaged seasonal glacier mass changes. These changes can be explained in parts by total net precipitation (net snowfall and net rainfall) and net snowfall, but mostly by total net radiation energy when compared to data from the ERA5-Land meteorological reanalysis. Moreover, nearly all the non-trend interannual mass changes and most seasonal mass changes can be explained by the total net radiation energy data. The mass loss trends could be partly related to a heat effect due to increased net rainfall in Tianshan Mountains, Qilian Mountains, Nyainqentanglha Mountains and Eastern Himalayas. Our new results for the glacier mass change in this study could help improve the understanding of glacier variation in the HMA area and contribute to the study of global change. They could also serve the utilization of water resources there and in neighboring areas.

submitted time 2021-04-22 From cooperative journals:《Journal of Arid Land》 Hits641Downloads201 Comment 0

6. chinaXiv:202101.00072 [pdf]

How precipitation and grazing influence the ecological functions of drought-prone grasslands on the northern slopes of the Tianshan Mountains, China?

HUANG Xiaotao; LUO Geping; CHEN Chunbo; PENG Jian; ZHANG Chujie; ZHOU Huakun; YAO Buqing; MA Zhen; XI Xiaoyan
Subjects: Geosciences >> Geography

Drought-prone grasslands provide a critical resource for the millions of people who are dependent on livestock for food security. However, this ecosystem is potentially vulnerable to climate change (e.g., precipitation) and human activity (e.g., grazing). Despite this, the influences of precipitation and grazing on ecological functions of drought-prone grasslands in the Tianshan Mountains remain relatively unexplored. Therefore, we conducted a systematic field investigation and a clipping experiment (simulating different intensities of grazing) in a drought-prone grassland on the northern slopes of the Tianshan Mountains in China to examine the influences of precipitation and grazing on aboveground biomass (AGB), soil volumetric water content (SVWC), and precipitation use efficiency (PUE) during the period of 2014–2017. We obtained the meteorological and SVWC data using an HL20 Bowen ratio system and a PR2 soil profile hydrometer, respectively. We found that AGB was clearly affected by both the amount and seasonal pattern of precipitation, and that PUE may be relatively low in years with either low or excessive precipitation. The PUE values were generally higher in the rapid growing season (April–July) than in the entire growing season (April–October). Overall, moderate grazing can promote plant growth under water stress conditions. The SVWC value was higher in the clipped plots than in the unclipped plots in the rapid growing season (April–July), but it was lower in the clipped plots than in the unclipped plots in the slow growing season (August–October). Our findings can enhance the understanding of the ecological effects of precipitation and grazing in drought-prone grasslands and provide data that will support the effective local grassland management.

submitted time 2021-01-22 From cooperative journals:《Journal of Arid Land》 Hits858Downloads501 Comment 0

7. chinaXiv:202101.00074 [pdf]

Long-term variations in runoff of the Syr Darya River Basin under climate change and human activities

Subjects: Geosciences >> Geography

In this study, we analyzed the hydrological and meteorological data from the Syr Darya River Basin during the period of 1930–2015 to investigate variations in river runoff and the impacts of climate change and human activities on river runoff. The Syr Darya River, which is supplied by snow and glacier meltwater upstream, is an important freshwater source for Central Asia, as nearly half of the population is concentrated in this area. River runoff in this arid region is sensitive to climate change and human activities. Therefore, estimation of the climatic and hydrological changes and the quantification of the impacts of climate change and human activities on river runoff are of great concern and important for regional water resources management. The long-term trends of hydrological time series from the selected 11 hydrological stations in the Syr Darya River Basin were examined by non-parametric methods, including the Pettitt change point test and Mann-Kendall trend tests. It was found that 8 out of 11 hydrological stations showed significant downward trends in river runoff. Change of river runoff variations occurred in the year around 1960. Moreover, during the study period (1930–2015), annual mean temperature, annual precipitation, and annual potential evapotranspiration in the river basin increased substantially. We employed hydrological sensitivity method to evaluate the impacts of climate change and human activities on river runoff based on precipitation and potential evapotranspiration. It was estimated that human activities accounted for over 82.6%–98.7% of the reduction in river runoff, mainly owing to water withdrawal for irrigation purpose. The observed variations in river runoff can subsequently lead to adverse ecological consequences from an ecological and regional water resources management perspective.

submitted time 2021-01-22 From cooperative journals:《Journal of Arid Land》 Hits643Downloads367 Comment 0

8. chinaXiv:202101.00076 [pdf]

Investigation of crop evapotranspiration and irrigation water requirement in the lower Amu Darya River Basin, Central Asia

Durdiev KHAYDAR; CHEN Xi; HUANG Yue; Makhmudov ILKHOM; LIU Tie; Ochege FRIDAY; Abdullaev FARKHOD; Gafforov KHUSEN; Omarakunova GULKAIYR
Subjects: Geosciences >> Geography

High water consumption and inefficient irrigation management in the agriculture sector of the middle and lower reaches of the Amu Darya River Basin (ADRB) have significantly influenced the gradual shrinking of the Aral Sea and its ecosystem. In this study, we investigated the crop water consumption in the growing seasons and the irrigation water requirement for different crop types in the lower ADRB during 2004–2017. We applied the FAO Penman–Monteith method to estimate reference evapotranspiration (ET0) based on daily climatic data collected from four meteorological stations. Crop evapotranspiration (ETc) of specific crop types was calculated by the crop coefficient. Then, we analyzed the net irrigation requirement (NIR) based on the effective precipitation with crop water requirements. The results indicated that the lowest monthly ET0 values in the lower ADRB were found in December (18.2 mm) and January (16.0 mm), and the highest monthly ET0 values were found in June and July, with similar values of 211.6 mm. The annual ETc reached to 887.2, 1002.1, and 492.0 mm for cotton, rice, and wheat, respectively. The average regional NIR ranged from 514.9 to 715.0 mm in the 10 Irrigation System Management Organizations (UISs) in the study area, while the total required irrigation volume for the whole region ranged from 4.2×109 to 11.6×109 m3 during 2004–2017. The percentages of NIR in SIW (surface irrigation water) ranged from 46.4% to 65.2% during the study period, with the exceptions of the drought years of 2008 and 2011, in which there was a significantly less runoff in the Amu Darya River. This study provides an overview for local water authorities to achieve optimal regional water allocation in the study area.

submitted time 2021-01-22 From cooperative journals:《Journal of Arid Land》 Hits686Downloads404 Comment 0

9. chinaXiv:202011.00131 [pdf]

Can climate change influence agricultural GTFP in arid and semi-arid regions of Northwest China?

FENG,Jian; ZHAO,Lingdi; ZHANG,Yibo; SUN,Lingxiao; YU,Xiang; YU,Yang
Subjects: Geosciences >> Geography

There are eight provinces and autonomous regions (Gansu Province, Ningxia Hui Autonomous Region, Xinjiang Uygur Autonomous Region, Inner Mongolia Autonomous Region, Tibet Autonomous Region, Qinghai Province, Shanxi Province, and Shaanxi Province) in Northwest China, most areas of which are located in arid and semi-arid regions (northwest of the 400 mm precipitation line), accounting for 58.74% of the country's land area and sustaining approximately 7.84×106 people. Because of drought conditions and fragile ecology, these regions cannot develop agriculture at the expense of the environment. Given the challenges of global warming, the green total factor productivity (GTFP), taking CO2 emissions as an undesirable output, is an effective index for measuring the sustainability of agricultural development. Agricultural GTFP can be influenced by both internal production factors (labor force, machinery, land, agricultural plastic film, diesel, pesticide, and fertilizer) and external climate factors (temperature, precipitation, and sunshine duration). In this study, we used the Super-slacks-based measure (Super-SBM) model to measure agricultural GTFP during the period 2000–2016 at the regional level. Our results show that the average agricultural GTFP of most provinces and autonomous regions in arid and semi-arid regions underwent a fluctuating increase during the study period (2000–2016), and the fluctuation was caused by the production factors (input and output factors). To improve agricultural GTFP, Shaanxi, Shanxi, and Gansu should reduce agricultural labor force input; Shaanxi, Inner Mongolia, Gansu, and Shanxi should decrease machinery input; Shaanxi, Inner Mongolia, Xinjiang, and Shanxi should reduce fertilizer input; Shaanxi, Xinjiang, Gansu, and Ningxia should reduce diesel input; Xinjiang and Gansu should decrease plastic film input; and Gansu, Shanxi, and Inner Mongolia should cut pesticide input. Desirable output agricultural earnings should be increased in Qinghai and Tibet, and undesirable output (CO2 emissions) should be reduced in Inner Mongolia, Xinjiang, Gansu, and Shaanxi. Agricultural GTFP is influenced not only by internal production factors but also by external climate factors. To determine the influence of climate factors on GTFP in these provinces and autonomous regions, we used a Geographical Detector (Geodetector) model to analyze the influence of climate factors (temperature, precipitation, and sunshine duration) and identify the relationships between different climate factors and GTFP. We found that temperature played a significant role in the spatial heterogeneity of GTFP among provinces and autonomous regions in arid and semi-arid regions. For Xinjiang, Inner Mongolia, and Tibet, a suitable average annual temperature would be in the range of 7°C–9°C; for Gansu, Shanxi, and Ningxia, it would be 11°C–13°C; and for Shaanxi, it would be 15°C–17°C. Stable climatic conditions and more efficient production are prerequisites for the development of sustainable agriculture. Hence, in the agricultural production process, reducing the redundancy of input factors is the best way to reduce CO2 emissions and to maintain temperatures, thereby improving the agricultural GTFP. The significance of this study is that it explores the impact of both internal production factors and external climatic factors on the development of sustainable agriculture in arid and semi-arid regions, identifying an effective way forward for the arid and semi-arid regions of Northwest China.

submitted time 2020-11-25 From cooperative journals:《Journal of Arid Land》 Hits3202Downloads547 Comment 0

10. chinaXiv:202011.00132 [pdf]

Responses of Amygdalus pedunculata Pall. in the sandy and loamy soils to water stress

PEI,Yanwu; HUANG,Laiming; SHAO,Ming'an; ZHANG,Yinglong
Subjects: Geosciences >> Geography

Amygdalus pedunculata Pall. is a major species that is widely planted in afforested soils with different textures in the transitional zone between Mu Us Desert and Loess Plateau, China. However, the responses of A. pedunculata to increasing intensity of water stress in different textural soils are not clear. Here, we conducted a soil column experiment to evaluate the effects of different textures (sandy and loamy) on water consumption, water use efficiency (WUE), biomass accumulation and ecological adaptability of A. pedunculata under increasing water stress, i.e., 90% (±5%) FC (field capacity), 75% (±5%) FC, 60% (±5%) FC, 45% (±5%) FC and 30% (±5%) FC in 2018. A. pedunculata grown in the sandy soil with the lowest (30% FC) and highest (90% FC) water contents had respectively 21.3%–37.0% and 4.4%–20.4% less transpiration than those with other water treatments (45%–75% FC). In contrast, A. pedunculata transpiration in the loamy soil decreased with decreasing water content. The magnitude of decrease in transpiration increased with increasing level of water deficit (45% and 30% FC). Mean daily and cumulative transpirations of the plant were significantly lower in the sandy soil than in the loamy soil under good water condition (90% FC), but the reverse was noted under water deficit treatments (45% and 30% FC). Plant height, stem diameter and total biomass initially increased with decreasing water content from 90% to 75% FC and then declined under severe water deficit conditions (45% and 30% FC) in the sandy soil. However, these plant parameters decreased with decreasing water content in the loamy soil. WUE in the sandy soil was 7.8%–12.3% higher than that in the loamy soil, which initially increased with decreasing water content from 90% to 75% FC and then declined under water deficit conditions (45% and 30% FC). The study showed that plant transpiration, biomass production and WUE responded differentially to increasing intensity of water stress in the sandy and loamy soils. The contrasting responses of A. pedunculata to water stress in different textural soils can guide future revegetation programs in the northern region of Chinese Loess Plateau by considering plant adaptability to varying soil and water conditions.

submitted time 2020-11-25 From cooperative journals:《Journal of Arid Land》 Hits2501Downloads457 Comment 0

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