Oasis Area Research Articles

The impact of increasing land productivity on groundwater dynamics: a case study of an oasis located at the edge of the Gobi Desert

BackgroundIntensification of agricultural systems may result in overexploitation of water resources in arid regions because enhanced productivity of crops is often associated with increased actual evapotranspiration (AET). The aim of this study was to quantify the effect of increased regional AET on the groundwater level in a case study of the oasis located within the Shiyang River Basin near the edge of the Gobi Desert.ResultThe results of the study show that regional AET increased during the period from 1981 to 2010 due to increasing oasis area and air temperature. The water losses due to AET exceeded the water supply from the mountainous discharges of the basin by the end of this period, leading to groundwater overexploitation in the oasis area.ConclusionsThis case study shows the importance of considering the effect of climate change on water losses associated with increasing agricultural production for the sustainable agricultural development of arid regions.

Suitable Scale of an Oasis in Different Scenarios in an Arid Region of China: A Case Study of the Ejina Oasis

The main objective of this work is to calculate the suitable scale of the Ejina Oasis in different scenarios (high-, normal-, and low-flow years), assess the stability of the Ejina Oasis, and, finally, accurately determine if an artificial oasis area and total oasis area need to be reduced or increased. Using the water balance method, we calculated the suitable scale of the artificial Ejina Oasis as 767.80, 624.00, and 451.33 km2 in high-, normal-, and low-flow years, respectively. By utilizing the water-heat balance method combined with an assessment of the present stability of the Ejina Oasis, the results showed that in high-flow years, the suitable scale of the Ejina Oasis is 1174–1762 km2, and the stability index of the current oasis is 0.55. In normal-flow years, the suitable scale of the Ejina Oasis is found to be 915–1373 km2, and the stability index of the current oasis is 0.43. In low-flow years, the suitable scale of the Ejina Oasis is 590–885 km2, and the stability index of the current oasis decreases to 0.27. In order to further improve the stability of oases, it remains necessary to control the scale of oases to cope with water resource shortages that result from water resource instability under climate change. The present study’s findings will enable optimal water-use planning decisions that take social, economic, and ecological issues into account, and provide the foundation for optimal decision-making for regional administrative departments to effectively coordinate regional economic development, farmland protection, environmental protection, and water resource protection.

Migration as one of several adaptation strategies for environmental limitations in Tunisia: evidence from El Faouar

Water scarcity and management of this problem are increasingly acknowledged in development policies as well as in adaptation and migration discourse. In South Mediterranean countries, insufficient water supplies in oases are the biggest limitation on yields of sufficient quantity and quality and increase in arable land, in short, the development of agriculture. Insufficient income from agriculture, when it is the main source of revenue, can push people to migrate. However, migration does not have to be the measure of last resort. Proper adaption to this limitation, including proactive migration, can reduce forced movements from this region in the future. The main aim of this paper is to identify and analyse household strategies, including migration, to cope with and adapt to the impact of environmental changes and limitations on agricultural development in the South Mediterranean. This paper is based on field research carried out in the El Faouar oasis area in Tunisia using a mixed-method approach. The results show that the inhabitants of El Faouar must cope with unforeseen crop destruction limiting their daily expenses by selling livestock or, in years of drought, migrating to look for additional sources of income. The results also show that local households try to increase their resistance to climate change, environmental limitations, and permanent migration by developing their agricultural capacity, provided they have additional resources from such endeavours as work outside El Faouar or remittances. Moreover, migration has become part of a wider process of socio-economic transformation in which people leave in order to cope with or adapt to environmental changes.

Spatial-temporal evolution pattern and terrain gradient differentiation of ecosystem service value in Zhangye, Northwest China at the grid scale

Zhangye serves as a good case for studying ecological services because of its fragile ecological environment and its ecological importance. Using land use data from 1987, 2000 and 2016 as well as the modified ecosystem service value (ESV) equivalent, the ESV was estimated and its spatial and temporal changes and gradient differentiation characteristics were analyzed by dividing the studied region into a grid of 3 km×3 km in size. The results showed that from 1987 to 2016, the ESV in Zhangye increased by 564 million Yuan, with the mountainous areas in the south and the desert areas in the north being stable. The ESV of central oasis areas with concentrated human acti-vities significantly changed. Forests contributed to most of the ESVs. Water regulation value was the strongest among all the individual ESVs. The ESV showed strong spatial dependence. Based on the spatial pattern of the two aggregated poles, it shaped three "flower arrangement" clusters, including Ganzhou District, Yanzhi Mountain, and Jingtie Mountain. The ESV distribution showed a topographic differentiation as the value decreased from the Qilian Mountains to the plain oasis, and further to the desert areas. The linear correlation of the terrain and the ESV was negative. As the increasing elevation gradient, the ESV showed a "decreased-increased-decreased" trend, while and it had a "decreased-stable-decreased" in the increasing slope gradient. Overall, the ESV presented two turning zones on the terrain gradient, indicating that both the piedmont zone and the oasis desert transition zone acted as transition zones of the ESV. Areas with the strongest ESV were distributed in the low slope and low terrain relief zones, and the development of oases in flat terrain areas were strongly constrained by water resources.

Numerical Study of the Interaction between Oasis and Urban Areas within an Arid Mountains-Desert System in Xinjiang, China

The rapid oasis expansion and urbanization that occurred in Xinjiang province (China) in the last decades have greatly modified the land surface energy balance and influenced the local circulation under the arid mountains-plain background system. In this study, we first evaluated the ALARO regional climate model coupled to the land surface scheme SURFEX at 4 km resolution using 53 national climatological stations and 5 automatic weather stations. We found that the model correctly simulates daily and hourly variation of 2 m temperature and relative humidity. A 4-day clear sky period has been chosen to study both local atmospheric circulations and their mutual interaction. Observations and simulations both show that a low-level divergence over oasis appears between 19:00 and 21:00 Beijing Time when the background mountain-plain wind system is weak. The model simulates a synergistic interaction between the oasis-desert breeze and urban-rural breeze from 16:00 until 22:00 with a maximum effect at 20:00 when the downdraft over oasis (updraft over urban) areas increases by 0.8 (0.4) Pa/s. The results show that the oasis expansion decreases the nocturnal urban heat island in the city of Urumqi by 0.8 °C, while the impact of urban expansion on the oasis cold island is negligible.

Land use/cover and landscape pattern changes in Manas River Basin based on remote sensing

Large-scale water and soil development in inland river basins in arid areas has made changes in landscape composition and structure, threatening the ecological balance. In order to study the trend of land use/cover and landscape pattern change and its relationship with water resources utilization in Manas River Basin, the land-use data of five periods in 1976, 1990, 2000, 2010 and 2015 were analyzed. The results showed that: (1) During 1976-2015, farmland and construction land continuously increased, forest land and grassland continuously decreased, the water area initially reduced and then increased, the area of saline-alkali land initially increased and then reduced, the overall trend of unused land and the sandy area was decreasing and the area of different time periods is floating. The areas of land-use types either increased or decreased. This indicates that the landscape pattern of the basin changes dramatically, and human activities are the main reasons for this phenomenon; (2) The oasis area increased from 3480.2 km2 in 1976 to 7982.0 km2 in 2015, with an obvious increasing trend. The oasis area clearly increased during 1976-1990, the growth rate was 40.6%, the growth rate of the oasis area was 129.4%. In the last 40 years, the degree of desertification fluctuated and decreased. The increase of the oasis area directly leads to the increase of water resources utilization and aggravates the degree of water resources shortage; (3) The pattern of land-use types showed a non-equilibrium trend. In the region with increasing landscape heterogeneity, the overall landscape pattern was increasingly controlled by the majority of patches. The intensive land management model and drip irrigation under mulch have improved the utilization efficiency of water resources and saved water resources from engineering renovation and irrigation management. Keywords: arid area, Manas River Basin, land use/cover change, landscape pattern, remote sensing, driving force DOI: 10.25165/j.ijabe.20201305.4783 Citation: Li X L, He X L, Yang G, Liu H G, Long A H, Chen F L, et al. Land use/cover and landscape pattern changes in Manas River Basin based on remote sensing. Int J Agric & Biol Eng, 2020; 13(5): 141–152.

干旱内陆河流域生态安全格局的构建及优化——以石羊河流域为例

生态安全格局识别及构建是保障干旱区生态安全、实现可持续发展的基本空间途径。石羊河流域是典型的干旱内陆河流域，其生态环境极为脆弱、敏感。基于石羊河流域生态本底特征，选取并定量评估水资源、生物多样性、水土保持和沙漠化4种生态系统服务，识别生态源地；以建筑物指数和植被净初级生产力为阻力因子，应用加权叠加法构建基本阻力面，并运用最小累积阻力模型及水文分析法识别生态廊道和生态功能节点，进行生态安全格局构建及优化。结果表明：（1）2005-2015年，石羊河流域生态源地增加，生态环境质量趋于好转，特别是下游民勤绿洲区及上游祁连山区源地面积增加明显。2005、2010、2015年生态源地面积占流域总面积的比重分别为16.7%、14.7%、19.8%；（2）2005-2015年，生态廊道明显增加，流域整体生态安全格局网络趋向复杂完善。2005年和2010年提取的生态节点都为36个，2015年的生态节点为35个，生态廊道从2005年的23条增加到2015年47条，部分潜在廊道发展演化为廊道；（3）基于2005-2015年生态安全格局分析，构建了以二带区、三绿洲、五廊道、多中心为核心的绿洲廊道功能区的优化格局模式，以期为石羊河流域生态环境治理与恢复以及区域可持续发展规划提供借鉴与决策依据。;The identification and construction of ecological security pattern is the basic spatial approach to guarantee the ecological security of arid areas and realize sustainable development. Shiyang River Basin is a typical Arid Inland River Basin with extremely fragile and sensitive ecological environment. Based on the ecological background characteristics of Shiyang River Basin, this paper selected and evaluated four ecosystem services, including water resources, biodiversity, soil and water conservation and desertification, to identify ecological source areas. Using a new index-based built-up index(IBI)and net primary productivity(NPP)as resistance factors, the basic resistance surface was constructed by the weighted superposition method. The ecological corridor and ecological function node were identified by the minimum cumulative resistance(MCR) model and hydrological analysis, and the ecological security pattern was constructed. The results showed that(1)from 2005 to 2015, Shiyang River Basin's ecological source area increased, and the ecological quality improved, especially in Minqin oasis area in the lower reaches and Qilian mountain area in the upper reaches. In 2005, 2010 and 2015, the proportions of ecological source area in the total area of the basin were 16.7%, 14.7%, and 19.8%.(2)The spatial and temporal pattern of ecological corridor and ecological node showed that from 2005 to 2015, the total number of ecological nodes in Shiyang River Basin did not change significantly, while the number of ecological corridors increased significantly, and the overall ecological security pattern network in the basin tended to be complex and perfect. In both 2005 and 2010, 36 ecological nodes were extracted. In 2015, 35 ecological corridors were extracted. The number of ecological corridors increased from 23 in 2005 to 47 in 2015.(3) Based on the ecological security pattern analysis from 2005 to 2015, the optimal layout mode of functional area of oasis corridor with two zones, three oases, five corridors, and multiple centers as the core was proposed. This study provides reference and decision-making basis for ecological environment management and restoration, regional layout and planning of Shiyang River Basin.

Soil salinization in the oasis areas of downstream inland rivers —Case Study: Minqin oasis

Soil salinization is the main resource and environmental problem in arid and semiarid regions, and it seriously restricts regional ecological security and sustainable agricultural development. Accurate monitoring of soil salinization and analysis of its main influencing factors are of great significance to the improvement and management of soil salinization. In this paper, the normalized difference vegetation index (NDVI) and salinity index (SI) were extracted from Landsat images of the Minqin oasis from 2000 to 2018, and these data were used to construct a soil salinization remote sensing monitoring index model (SDI). The index extracted by the model was used to monitor the soil salinization information, and the index values were graded to obtain different degrees of soil salinized land. The measured data were used to verify the accuracy of the SDI through trend analysis, stability analysis and other methods, and explore the characteristics and main influencing factors of soil salinization in the Minqin oasis. The results showed that the spatial distribution characteristics of the different degrees of soil salinity extracted by the SDI model were consistent with the measured results. The area of salinized soil in the Minqin oasis exceeded 80%, and the proportion of lightly salinized soil was the largest. The area ratio of salinized soil did not change much from 2000 to 2018, but the changes between different degrees of salinized soil were large.The unused land in the Minqin oasis exhibited a high degree of salinization, which was manifested spatially in the northwest of the Minqin oasis and the areas surrounding Qingtu Lake. In addition, the soil salinization of the Minqin oasis exhibited obvious seasonal differences, and the different degrees of salinization also changed with the change in seasons. The analysis of the main influencing factors of soil salinization in the Minqin oasis revealed that the large land occupation ratio of salinized land in the Minqin oasis was related to the local climatic factors. In recent years, changes in soil salinity in parts of the Minqin oasis and Qingtu Lake area were mainly the result of ecological water conveyance.

Spatial-temporal changes in NPP and its relationship with climate factors based on sensitivity analysis in the Shiyang River Basin

As a typical inland river basin in China, the Shiyang River Basin is characterized by its special mountain-basin structure. The ecological health in the basin is related to the sustainable development of the economy and society. At present, there are few studies on net primary productivity (NPP) in the Shiyang River Basin, and the existing analysis of the relationship between NPP and climatic factors is lacking. The upper mountainous area and the middle and lower oasis areas in the Shiyang River Basin were selected as the study area. The NPP of the study area was estimated using the Thornthwaite Memorial Model. The spatial and temporal characteristics of NPP were analyzed by Sen’s slope method. Based on the sensitivity analysis, the correlation of the main climate factors to NPP was estimated. According to the aforementioned work, the variation trend of the future NPP was predicted. The results showed that NPP in the study area increased from 1981 to 2015 with the increase in temperature and precipitation. The spatial heterogeneity of the change trend of NPP was not significant, but the spatial heterogeneity of the rangeability was strong. The NPP was highly sensitive to precipitation, relative humidity and net solar radiation. By integrating the changes in climatic elements, the temperature, precipitation and relative humidity contributed the main parts of the change in NPP. The NPP is predicted to increase by 4.9–8.1% by 2050 according to the amplitude of climate change over the past 35 yrs.

Exploring Mid-Late Pleistocene lithic procurement strategies at Shishan Marsh 1: Preliminary geochemical characterization of chert sources around the Greater Azraq Oasis Area, Jordan

Recent excavations at the site of Shishan Marsh 1 in the Azraq basin, Jordan have uncovered several artifact-bearing layers that date within the Middle (266 ± 40 kya) and Late (125 ± 12 kya) Pleistocene. A paleoecological assessment of sediments from this period indicates predominantly warm and dry conditions in the region, similar to those of the present. Hominins living under these hot and dry conditions contracted around a receding spring- and wadi-fed water source for subsistence. As such, they were limited to the distances they could venture to acquire raw material resources. Consequently, Shishan Marsh 1 presents an opportunity to investigate lithic procurement strategies practiced by Paleolithic hominins in an arid environment. This paper presents the preliminary results of an on-going provenance study of lithic sources in the region and a sample of chert artifacts using LA-ICP-MS. The preliminary results indicate that predominantly local procurement was practiced. However, some artifacts were geochemically more consistent with distant sources and still others did not correlate with any sampled source. This latter group indicates that more sources need to be included, as there is greater variability within the Azraq basin than what is documented in this study.

Multi-Scale Validation of MODIS LAI Products Based on Crop Growth Period

Leaf area index (LAI) is one of the most important canopy structure parameters utilized in process-based models of climate, hydrology, and biogeochemistry. In order to determine the reliability and applicability of satellite LAI products, it is critical to validate satellite LAI products. Due to surface heterogeneity and scale effects, it is difficult to validate the accuracy of LAI products. In order to improve the spatio-temporal accuracy of satellite LAI products, we propose a new multi-scale LAI product validation method based on a crop growth cycle. In this method, we used the PROSAIL model to derive Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) LAI data and Gaofen-1 (GF-1) for the study area. The Empirical Bayes Kriging (EBK) interpolation method was used to perform a spatial multi-scale transformation of Moderate Resolution Imaging Spectroradiometer (MODIS) LAI products, GF-1 LAI data, and ASTER LAI data. Finally, MODIS LAI satellite products were compared with field measured LAI data, GF-1 LAI data, and ASTER LAI data during the growing season of crop field. This study was conducted in the agricultural oasis area of the middle reaches of the Heihe River Basin in northwestern China and the Conghua District of Guangzhou in Guangdong Province. The results suggest that the validation accuracy of the multi-scale MODIS LAI products validated by ASTER LAI data were higher than those of the GF-1 LAI data and the reference field measured LAI data, showing a R2 of 0.758 and relative mean square error (RRMSE) of 28.73% for 15 m ASTER LAI and a R2 of 0.703 and RRMSE of 30.80% for 500 m ASTER LAI, which imply that the 15 m MODIS LAI product generated by the EBK method was more accurate than the 500 m and 8 m products. This study provides a new validation method for satellite remotely sensed products.

New Maastrichtian-early Eocene ostracod species from the Kharga Oasis area, Western Desert, Egypt

Eighteen new ostracod species are recorded from the Maastrichtian-lower Eocene stratigraphic succession exposed at the Kharga Oasis in the Western Desert of Egypt. The new findings include eleven newly erected species, besides seven species recorded for the first time but left in open nomenclature. They have been taxonomically described and compared with nearest known and probably related taxa. The species described are assigned to 10 genera belonging to 9 families. Whereas some of recorded species display relatively long stratigraphic ranges in the studied sections, others display shorter ranges confined to a specific age in the Maastrichtian-early Eocene interval.

Simulation of a forest-grass ecological network in a typical desert oasis based on multiple scenes

Many areas on the earth are facing the threat of ecological degradation, and unreasonable economic development has further exacerbated environmental problems. Constructing ecological security patterns based on an ecological network is such an integrated approach to protecting regional ecological sustainability. This paper selected Denko County of Bayannaoer City, Inner Mongolia, which is located in the desert oasis area, as the study area. Ecological sources were identified through ecosystem importance assessment, and interaction force theory was used to model ecosystem processes in heterogeneous landscapes via comparing the minimum cumulative ecological resistance and the maximum ecological gravity between ecological sources, and thus to identify ecological corridors and to constructing forest-grass ecological network (FG eco-network) of the study area. This paper also set 11 development scenarios to study the impact of different development strategies on the FG ecological network. Moreover, the complex network theory was used to analyze the topology and statistical characteristics of the FG eco-network in 11 development scenarios. The results show that the ecological network in the study area has been gradually destroyed with the increase of the proportion of economic development in the development scenario; the connection between some ecological patches has changed and the connectivity and coreness, PageRank, etc. have gradually decreased. The study found that the network density increases slightly in the (0.9, 0.1) mode, while it gradually decreases in other scenarios with the increase of the proportion of economic development. Moreover, in the (0.9, 0.1) mode, although the destruction occurred at the edge of the desert, the FG eco-network within the sample circle expanded. This represents that economic development does not necessarily lead to the deterioration of the ecological environment in this area. Under the existing natural conditions, the study area still has room for economic development, but space is limited. Based on the interaction force theory, this study provides a new approach to identifying the ecological network. Also, the development scenarios set up in this study can provide a reference for sustainable development.

Assessment of changes in oasis scale and water management in the arid Manas River Basin, north western China.

Modern water-saving irrigation technology has expanded the scale of agricultural oases in arid and semi-arid regions of China. In this study, we used Landsat MSS and Landsat TM/ETM remote sensing data to assess changes in oasis scale and water availability with reference to differing water management practices in the Manas River Basin of north-western China from 1975 to 2015. We used the water-heat balance index H0 to determine oasis stability over time and constructed a suitable-scale calculation model for arid and semi-arid regions to assess the suitable development scale and cultivated land area in the study area. The implementation of water-saving technology in 2000 effectively improved the utilization efficiency of water resources and accelerated the formation of artificial oases; these expanded by 3873.3 km2 while natural oasis area was reduced by 3485.0 km2. The oasis stability index H0 was less than the critical stability index of 0.5 throughout the study period, implying that these areas were in a metastable state and unsuitable for further development. Therefore, in order to improve oasis stability, both scale and agricultural area should be further controlled. At present, actual oasis scale exceeds appropriate scale by 1.1 times and agricultural area exceeds suitable area by 2.5 times. To ensure the stability of the oasis, its area should be maintained at 3942.28-4481.06 km2 and the cultivated land should be maintained at 1576.91-1792.42 km2.

A New Optimization Method for the Layout of Pumping Wells in Oases: Application in the Qira Oasis, Northwest China

Oases are vital habitat areas for both humans and wild plants and animals in desert areas of arid Northwestern China. The efficient management of oasis water resources, especially groundwater resources, is very important for the environmental sustainability and economic development of the region. Pumping wells play a vital role in the oasis groundwater supply; therefore, optimizing the layout of these wells is essential for water resource management. In this study, we present a novel optimization methodology that implements a genetic algorithm and nonlinear programming model for the layout of pumping wells. The methodology was tested and evaluated in the real oasis case study of Qira Oasis located in southern Xinjiang Province, China. The optimization result shows that only 68 pumping wells are required for irrigation purposes of Qira Oasis, and this layout reduces the number of current pumping wells strongly by 59%. Thus, a large number of pumping wells can be closed to save resources. The optimizing method presented in this research is mathematically general and can be applied to other oasis areas without any obstacles. This method can provide decision-makers and managers with key information to ensure the optimal management and safety of valuable groundwater resources in oases.

Agriculture intensification increases summer precipitation in Tianshan Mountains, China

The land-use and land-cover change has a significant impact on the climate at different spatio-temporal scales. In this study, we explored the long term oasis expansion effects on regional summer precipitation in the north slope of Tianshan Mountains, China using high-resolution regional climate model. The results indicate that the oasis expansion increases the summer precipitation in the middle Tianshan Mountains while it has only a small effect over the oasis regions itself. The results indicate further that the oasis expansion affects mainly the late afternoon summer convective precipitation. The advection of air with additional moisture from the oasis areas to the mountains due to the mountain/plain circulation system during the day triggers the orographic precipitation in the middle mountain regions. These new results indicate that the oasis expansion could attribute significantly to the recent finding from observational studies about the increasing trend of precipitation in the middle Tianshan Mountains.

Integrating Biophysical and Sociocultural Methods for Identifying the Relationships between Ecosystem Services and Land Use Change: Insights from an Oasis Area

Identifying the relationships between ecosystem services (ESs) and land use change is crucial for ES management and sustainable regional development. The Manas region in China has witnessed dramatic reclamation activities in its desert areas that resulted in ecological problems. The changes in eight ESs, including crop production (CP), livestock production (LP), soil conservation (SC), water yield (WY), sand fixation (SF), carbon sequestration (CS), habitat quality (HQ), and nature landscape recreation (NLR), were investigated by using biophysical and questionnaire methods. At the regional scale, provisioning services (i.e., CP and LP) showed some performance improvements, whereas most of the regulating services (i.e., WY, CS, and HQ) along with NLR showed a performance decline. Five ES bundles—Upper Mountain, Foothill, Oasis, Oasis–Desert Transition, and Desert bundle—were identified at the township scale via k-means clustering. From 2000 to 2015, the Oasis bundle sprawled as a result of oasisization, whereas the Oasis–Desert Transition and Foothill bundles decreased. We performed a questionnaire survey and a statistical analysis to identify the causes behind the performance improvement/decline of these ESs and found that the land use changes in the Manas region had a significant impact on these services. More than 50% of the survey respondents identified land use changes as the primary driver of the changes in some ESs (i.e., CP, CS, HQ, and NLR). In the correlation and partial correlation analyses, oasisization was significantly and positively correlated with CP but was negatively correlated with WY, CS, HQ, and NLR. We enhanced the reliability of our conclusions by integrating biophysical and sociocultural methods into our investigation of ES and land use change. In view of the huge losses in regulating and cultural services, the Manas region should limit its desert reclamation activities to control the expansion of its oasis and to improve the quality of its cropland. Our results can help formulate effective ES management and land use decisions in the Manas region or similar areas.

Environmental significance and zonal characteristics of stable isotope of atmospheric precipitation in arid Central Asia

To analyse the environmental significance and zonal characteristics of stable isotopes of precipitation in Arid Central Asia systematically, this study took the Pan-Hexi region as an example study area. A total of 1747 precipitation samples were collected from 25 sampling points from May 2013 to July 2014. The results showed that the elevation effects of δ18O and δ2H of precipitation in the Pan-Hexi region were − 0.07‰/100 m and − 0.17‰/100 m, respectively. However, the elevation effects of δ18O and δ2H were lower in the oasis area than the mountainous section of the study area. The temperature effect was significant in the oasis area when the temperature was <10 °C and >15 °C, but it was only significant in the mountain area when the temperature was <0 °C. The evaporation rate of falling raindrops (f) and the enrichment rate (E) were significantly higher in the oasis area (E: 34.87%; f: 20%) than in the mountain area (E: 20.56%; f: 11.71%), and the E and f values showed a significant decreasing trend from oasis area to mountain area. Sub-cloud evaporation had a significant effect on the stable isotopes in precipitation. It was found that if f increases by 1%, E increases by 0.58% in the oasis area and by 0.86% in the mountain area. The precipitation amount effect mainly occurs during summer (June to August) in the Pan-Hexi region, especially in the oasis area. This effect was caused mainly by sub-cloud evaporation rather than by monsoon circulation. Further analysis demonstrated that when precipitation is higher, sub-cloud evaporation of falling raindrops is lower and enrichment of δ18O is weaker. Therefore, rainfall events with higher precipitation amounts had more depleted δ18O and vice versa. Thus, it can be concluded that precipitation amount effect in the study area is dominated by sub-cloud evaporation, which provides new information pertaining to the isotopic evolution of precipitation in arid regions.

Spatio-temporal characteristics and driving forces of landscape structure changes in the middle reach of the Heihe River Basin from 1990 to 2015

The oasis, desert–oasis ecotone (DOE) and desert compose the typical landscape structures in arid regions. The detection of landscape structure changes and quantification of the driving forces are vital to sustainable ecosystem management. Previous studies did not integrate the three landscape types, especially considering the role of the DOE, to detect landscape changes. (1) Detect the spatio-temporal dynamics of the landscape structure in the middle reach of the Heihe River Basin from 1990 to 2015. (2) Identify the key driving factors for landscape structure changes and quantify their contributions. The decision tree classification algorithm was combined with visual interpretation to extract oasis, DOE and desert areas. Status and trend indicators, transition matrix and landscape metrics were used to characterize the landscape changes. Redundancy analysis and variation portioning analysis were integrated for quantification of driving forces. Landscape change was characterized by oasis expansion (+ 37.21%) via a one-way transition with an unbalanced status. The contraction of DOE (− 12.73%) and desert (− 8.50%) areas mainly occurred on the periphery of the oasis. The landscape structure changes were mainly driven by the population, river flow and gross domestic product with unique contributions of 35.99, 9.01 and 7.68%, respectively, and a cumulative contribution of 96.64%. The mutual transformations among landscapes showed distinct spatio-temporal variations. Human activities, especially demographic factors, drove the changes in landscape structure. The development of oasis areas should be controlled within a suitable scale, and the DOE should be protected to maintain the stability of ecosystems in arid regions.

Suitable oasis and cultivated land scales in arid regions based on ecological health

A suitable oasis scale and a cultivated land scale are important for water resources management in arid regions. This paper developed an approach to calculate a suitable oasis scale and a cultivated land scale by combining water-heat balance theory and wind-sand dynamics theory with ecological health assessment (i.e., WHBEHA model). The oasis effective vegetation coverage was determined using the wind-sand dynamics theory. The oasis ecological health was assessed by constructing the ecological health index system. This index system considered groundwater depth, ratio of farmland shelterbelt, vegetation coverage status, and occurrence frequency of strong winds as ecological health evaluation indicators and was illustrated using the middle reaches of Heihe River basin as the case study. The results of the proposed WHBEHA model revealed that the most suitable ecological and cultivated areas under different hydrologic years were 363–442 km2 and 1450–1767 km2 in the middle reaches of Heihe River basin. They summed up to the total suitable oasis areas were in the range of 1813–2209 km2. Status quo 2013 was a high flow year, according to WHBEHA, the scale of cultivated land in 2013 has exceeded the suitable scale, and should be reduced by 334 km2. Compared with the current oasis scale based on land-use and land-cover information and the oasis scales computed using oasis water-heat balance and oasis circle theory (WHBOCT), the proposed WHBEHA model is more suitable by considering the factors that affect the ecological health of arid regions. Furthermore, this study may provide a guideline for determining a sustainable socio-economic scale, especially cultivated scale in arid regions.