Ejina Oasis Research Articles

Finding Oasis Cold Island Footprints Based on a Logistic Model—A Case Study in the Ejina Oasis

Finding Oasis Cold Island Footprints Based on a Logistic Model—A Case Study in the Ejina Oasis

Long-term continuous changes of vegetation cover in desert oasis of a hyper-arid endorheic basin with LandTrendr algorithm

Ecological water diversion projects (EWDP) is one of the most important initiatives for oases restoration in arid endorheic basins. Fine monitoring of the long-term and continuous changes in vegetation cover before and after the EWDP is important to evaluate the effects of EWDP on ecosystem restoration. In this study, a trajectory-based change detection approach was applied with the Landsat-based detection of trends in disturbance and recovery (LandTrendr) algorithm on Google Earth Engine to map vegetation cover change trajectories in Ejina Oasis in the lower Heihe River Basin of China during 1990–2020. In addition to monotonic changes (i.e., continuous greening and continuous browning), LandTrendr also can flexibly capture the breaks of greening or browning events, including the greening with negative break, browning with positive break, browning to greening, and greening to browning. These changes mainly happened in shrub land and the area with land use transition. Approximately 82 % of the oasis ecosystem has been restored by the implementation of EWDP since 2000. However, in the past decade, the EWDP also caused some negative effects on vegetation cover in some areas. Both the categories of browning with positive break and greening to browning became widespread after 2010, with the cumulative proportions accounting for 79.4 % and 70.1 % of each category. The mean magnitude and slope of change in NDVI in these two categories after 2010 were −0.03 and −0.008 yr−1, −0.12 and −0.035 yr−1, respectively. This research demonstrated that the proposed approach was effective and useful for continuously monitoring the timing and extent of vegetation recovery processes in the hyper-arid endorheic basin. The EWDP plays an important role in vegetation restoration, but we also need to continuously monitor negative impacts which are crucial for environmental assessment and policy making in the arid endorheic basin.

Spatial variation in grassland vegetation and herbage mass in the Ejina oasis along the Heihe River in the southern Gobi Desert, China

AbstractOur study area, Ejina, is located in the southern Gobi Desert, Inner Mongolia, China, where the annual precipitation is <50 mm and the annual potential evaporation is >3,600 mm. The Heihe River flows from the Qilian Range through the study area, and the desert landscape along the river includes oases formed by forests and grasslands. We established a survey area of approximately 1.5 ha in grassland facing a seasonal swamp, a branch of the Heihe River. We posed the following questions in this desert grassland: (1) how do soil water content (SWC) and salinity change with distance from the riverbank? (2) How do vegetation, aboveground biomass, and species richness change with distance from the riverbank? (3) How much can be supplied to grazing animals, and how many animals can be grazed? Our results indicated that (1) the SWC is high within 20 m of the riverbank and low beyond 20 m, the standing biomass is positively correlated with SWC, but there was no evidence of a correlation between salinity and distance to water; the electrical conductivity was high both inland and adjacent to the riparian swamp. (2) Vegetation could be classified to six classes, following a gradient from the riverbank (swamp margin) to the dry inland area beyond 20 m from the riverbank. Species richness and aboveground biomass were highly correlated. Classification result led us to recommend that generalist species tolerant of the distinct moisture gradient in the site be used in restoration efforts. (3) Per‐hectare aboveground biomass was 478.93 dry weight (dw) kg, 321.2 ha of equivalent grassland would be required to graze 100 goats annually.

Evaluation of the Evolution of the Ecological Security of Oases in Arid Regions and Its Driving Forces: A Case Study of Ejina Oasis in China

Ecological security is an important guarantee of human security and survival, closely related to sustainable development. However, the ecological security evaluation and driving force analysis of oases in arid areas is still insufficient. Ejina Oasis’s ecological security has experienced significant shifts following the centralized management of the Heihe River’s water allocation. Understanding the shifts in ecological security in the Ejina region is paramount for the oasis’s long-term sustainability. This paper employed the Pressure–State–Response (P–S–R) model to select socioeconomic and ecological indicators, establish a comprehensive ecological security evaluation index system, and then analyze the evolving ecological security in the region. Additionally, this paper explored the relationship between changes in the water area, oasis area, and ecological security by using the gray correlation degree to quantify the influence of Land Use Changes (LUCCs) on the overall ecological security. From 2000 to 2012, the ecological security index of Ejina Oasis remained relatively stable at around 0.4. However, a noticeable upward trend in the ecological security index emerged from 2012 to 2020, indicating a shift toward improved ecological security in the region. Critical determinants of this change included the habitat degradation degree, total population, habitat quality, carbon stock, fractional vegetation cover (FVC), the proportion of tertiary industry, and the volume of water discharged from Wolf Heart Mountain. The degree of habitat degradation, fractional vegetation cover (FVC), and the proportion of tertiary industry had the greatest impact on the change in ecological security. The pressure index was dominant in influencing ecological security before 2012 but gradually transitioned to the state index. This study offers a valuable framework for assessing the intricate relationship between LUCCs and ecological security in water-scarce, arid-region oases.

Evapotranspiration Characteristics of Different Oases and Effects of Human Activities on Evapotranspiration in Heihe River Basin

Evapotranspiration plays a decisive role in the whole oasis ecosystem and is an important factor to maintain the ecological stability of oases. To quantitatively analyze the evapotranspiration differences of oases at different scales and the expansion of urbanization, it is necessary to compare and discuss them at different time scales. In this study, the spatial and temporal characteristics of evapotranspiration of Zhangye Oasis, Jinta Oasis, and Ejina Oasis in the Heihe River basin were analyzed by using the remote sensing dataset of daily surface evapotranspiration of 100 m resolution from 2010 to 2016. The difference in evapotranspiration intensity in different oases was analyzed, and the influences of irrigation and urbanization expansion on evapotranspiration were discussed. The conclusion is as follows: Zhangye Oasis is the largest oasis in the area and, compared with other oases, due to the largest proportion of wetland and farmland in the underlying surface, the intensity of evapotranspiration is also the largest, reaching 650 mm/year on average. There is no obvious annual change; the range of evapotranspiration changes fluctuates between positive and negative 60 mm/year. Jinta Oasis began to decline after 2012; the evapotranspiration value dropped from 620 mm/tear to 560 mm/year, while Ejina Oasis showed a slight increase after 2014. In the irrigation stage, the evapotranspiration intensity increased significantly. Especially in the peak season of crop growth, the evapotranspiration after irrigation increased by 4 mm/day compared with that before irrigation. The evapotranspiration in urban and oasis areas is different in summer: compare that of 2010 with 2016—the evapotranspiration intensity of the expanding towns in the northeast direction decreased by about 50 mm/month, the northwest expanding towns decreased by about 110 mm/month. There was no obvious annual change in evapotranspiration in the urban area. With the expansion of urbanization, the evapotranspiration intensity in oases decreased. The results of this study provide some reference for the study of oasis irrigation activities and urbanization expansion.

The Photosynthesis of Populus euphratica Oliv. Is Not Limited by Drought Stress in the Hyper-Arid Zone of Northwest China

The Ejin Oasis is located in the lower reaches of the Heihe River Basin of northwestern China. It is one of the most arid regions in the world, and Populus euphratica Oliv. is the foundation species of the desert riparian forests there. The photosynthesis of P. euphratica is one of the first physiological processes that is most likely to be affected by the extremely arid climate conditions. The factors impacting photosynthesis can be divided into stomatal and non-stomatal limitations. In order to investigate whether the photosynthesis of P. euphratica was limited and, if so, whether this limitation was caused by drought stress in the P. euphratica Forest Reserve on the Ejin River, we analyzed stomatal, non-stomatal, and relative stomatal limitations (reflecting the relative importance of the stoma in controlling the processes of photosynthesis) of photosynthesis. The results show that, at the beginning of the midday depression of photosynthesis, the values of stomatal limitation of photosynthesis (Ls) peaked, with its predominance being supported by sub-stomatal CO2 concentrations (Ci) being at a minimum. Thereafter, Ls decreased and non-stomatal limitation (Ci/stomatal conductance (gs)) increased sharply, indicating that the non-stomatal limitation of photosynthesis was predominant. Both Ls and relative stomatal limitation of photosynthesis increased in the morning, and then decreased, whereas Ci/gs showed the opposite trend. We concluded that P. euphratica did not experience drought stress by analyzing leaf water potential, groundwater table, and the decoupling coefficient (a parameter characterizing the coupling degree between vegetation canopy and atmospheric water vapor flux); however, the Ls values of P. euphratica were much greater than those of other species. This was likely because P. euphratica has a relatively conservative water use strategy even when growing under favorable water conditions. Extremely high temperatures caused the closure of the stoma to reduce transpiration, resulting in more intense stomatal limitations of photosynthesis.

Tree-Ring Stable Carbon Isotope-Based Mean Maximum Temperature Reconstruction in Northwest China and Its Connection with Atmospheric Circulations

The inter-annual stable carbon isotope ratio (δ13C) of three tree-ring cores of P. euphratica (Populus euphratica Oliv.) was determined from Ejina Oasis in Northwest China. A robust and representative δ13C chronology is generated from the three δ13C series using an arithmetic mean method. After eliminating the influence of the δ13C from elevated atmospheric carbon dioxide (CO2) concentration, we obtained a carbon isotopic discrimination (Δ13C) chronology. According to the significant correlation between the tree-ring Δ13C and instrumental data, we reconstructed the mean maximum temperature anomalies from previous December to current September (TDS) for the period 1901–2011. The reconstruction explained 43.6% of the variance over the calibration period. Three high-temperature periods (1929–1965, 1972–1974, and 1992–2006) and three low-temperature periods (1906–1926, 1966–1968, and 1975–1991) were found in the reconstructed series. Comparisons between the reconstructed TDS and the observed mean temperature from previous December to current September in Anxi meteorological station and the temperature index in north-central China demonstrated the reconstructed TDS has the advantage of reliability and stability. The significant spatial correlation declared that the reconstruction has a broad spatial representation and can represent the temperature variation characteristics in a wide geographical area. In addition, we found that the area of Ejina Oasis is smaller (larger) when the mean maximum temperature is higher (lower), which may be due to a conjunction effect of natural and anthropogenic activities. Significant periodicities and correlations suggested that the TDS variations in Ejina Oasis were regulated by solar radiation and atmospheric circulations at the interannual and interdecadal time scales.

Water allocation and climate-impacted riparian forest dynamics in the Ejina Oasis, Northwest China

Riparian forests in natural desert oases are extremely vulnerable to water shortages; of late these shortages have been associated with climate change and with increased human-led water allocation. This study covers a hundred-year history (1876–2017) of riparian forest growth at the Ejina Oasis, which is located in the lower reaches of the Heihe River basin of northwestern China. We collected tree cores from Populus euphratica, which is the major tree species found in the Ejina riparian forests. These samples allowed us to chart variations in riparian forest growth and to examine correlations between tree growth and local precipitation, temperature, drought indices, groundwater depth, and runoff volume from the middle reaches of the river. We found that groundwater depth (groundwater being mainly recharged by runoff) is the major factor limiting tree-stem radial growth. We compared runoff reconstruction series from upper reaches and P. euphratica radial growth in the lower reaches. We found a period of greatly decreased growth (1942–1951); which seems to have been due to human water diversion. We note that mountain runoff increased after 2000, but that riparian forest growth didn’t increase in tandem; the water that would otherwise have supported the forests had been diverted. Our study provides a warning for future water resource planning and suggests the desirability of policies that will balance the needs of natural ecosystems (riparian forests) with the requirements of artificial ecosystems (croplands).

Water Resource Management Implications for a Desert Oasis From Tree‐Ring δ18O Variations in Populus Euphratica in Northwest China

AbstractPaleoclimatic data has often been applied to demonstrate the influence of anthropogenic activities on runoff to desert rivers, and such features as reservoirs are clearly known to influence available water in downstream riparian settings. The impact of human activities on the hydrology of a downstream desert oasis is, however, an open question. High‐resolution hydroclimate paleo‐reconstructions for desert oases are lacking, partly because paleoclimate proxies in extremely dry deserts are insensitive to extremely low precipitation. Here, we first attempt to reconstruct regional precipitation (r = −0.743, p < 0.001, n = 49) for the interval 1886–2009 from the stable oxygen isotope ratio (δ18O) of five Populus euphratica trees growing in the Ejina Oasis, on the lower reaches of the Heihe River in extremely arid Northwest China. The δ18O series for P. euphratica in the oasis (∼900 m a.s.l) abruptly increases relative to an δ18O series of Qinghai spruce (Picea crassifolia) growing in upper limit of forest (∼3,000 m a.s.l) in Longshou Mountain (middle reaches of the Heihe River) after about 2000, when the Ecological Water Diversion Project on the Heihe River was implemented. This finding implies that the Ejina Oasis suffered from serious drought during the last decade, or at least that the Oasis is stressed more than expected by current climate conditions. Other evidence also indicates that human activities contributed to a decrease in air moisture in the Ejina Oasis after 2000. To mitigate water stress on the oasis, we recommend some practical measures to ensure the rational development of the desert oasis.

Runoff controls the development of eco-hydrological and economic conditions in an arid oasis of the downstream inland river basin

Oasis degradation and terminal lake shrinkage are prevalent consequences of the disputed distribution of water resources in inland river basins, hindering regional sustainable development. The Ecological Water Diversion Project (EWDP) is regarded as an important measure to restore the desert-oasis ecosystem in inland river basins, and thus it is essential to comprehensively evaluate the response of eco-hydrological and socioeconomic systems to the EWDP. Based on multiple indicators, we used trend analysis, linear regression, partial least square regression, and structural equation model to disentangle the quantitative effects of the EWDP on the change of eco-hydrological and socioeconomic conditions in the Ejina Oasis (EO) in the lower reaches of the Heihe River in northwest China. Our results indicate that the ecological deterioration was prevalent before the execution of the EWDP, including the increase of groundwater depth, the disappearance of lakes, the decrease of NDVI. After the EWDP, runoff released to EO increased 69.15%, the mean groundwater depth decreased 0.48 m, 52.28% of the study area showed a significant increase in NDVI, areas of forest and grassland increased 20.17 and 25.65 km2, respectively. The EWDP improved the hydrological regime and prompted the recovery of the oasis. Besides, socioeconomic development was facilitated under the restoration of the eco-hydrological conditions, characterized by the expansion of farmland and the thrive of the tourism industry. The hydrological variables promoted the improvement of the ecological condition with a direct strength of 0.93 and facilitated the development of the socioeconomic conditions in EO with an indirect strength of 0.84. Runoff was the most important positive contributor both to the NDVI and GDP in EO. This comprehensive evaluation framework can offer valuable insight for water resources management and sustainable development in the inland river basin of arid areas.

Energy Exchange and Evapotranspiration over the Ejina Oasis Riparian Forest Ecosystem with Different Land-Cover Types

Investigating the energy and water vapor exchange in oasis riparian forest ecosystems is of significant importance to improve scientific understanding of land surface processes in extreme arid regions. The Heihe Watershed Allied Telemetry Experimental Research (HiWATER) provided many observations of water vapor and heat fluxes from riparian forest ecosystem by using a network of eddy-covariance (EC) systems installed over representative surfaces in the Ejina Oasis, which is located in the downstream areas of the Heihe River Basin, northwestern China. Based on EC flux measurements and meteorological data performed at five stations and covering representative surface types of Populus euphratica tree with associated Tamarix chinensis shrub, Tamarix chinensis shrubland, cantaloupe cropland, and barren-land, this study explored the spatio-temporal patterns of heat and water vapor fluxes over the Ejina Oasis riparian forest ecosystem with five different surface types over the course of a growing season in 2014. Energy balance closure of the flux data was evaluated; footprint analysis for each EC site was also performed. Results showed that energy balance closure for the flux data was reasonably good, with average energy balance ratio (EBR) of 1.03. The seasonal variations in net radiation (Rn), latent (LE), and sensible heat flux (H) over the five contrasting surfaces were similar, and a reverse seasonal change was observed in energy partitioning into LE and H. Remarkable differences in Rn, LE, and H between the five surfaces were explored preliminarily, associated closely with the soil properties and foliage phenology. Over the growing season (May–October) in 2014, the total ET ranged 622–731 mm for mixed forest of P. euphratica trees with associated T. chinensis shrubs with average daily ET of 3.6–4.2 mm; ET from T. chinensis shrubland was about 541 mm, with average daily ET of 3.6 mm. ET for barren-land was 195 mm. The total ET in irrigated cantaloupe cropland with plastic mulch was 431 mm for its four-month growing period with a total average of 3.8 mm d−1. Determination of ET over riparian forest ecosystem helps to improve reasonable use of limited water resource in the Ejina Oasis.

Applicability of multiple remotely sensed vegetation indices for extracting key phenological metrics of Tamarix chinensis shrubs based on CO2 flux observation and Sentinel-2 data

We analyzed the relationship between gross primary productivity (GPP) and environmental factors at Sidaoqiao Superstation of the Ejina Oasis in China's Gobi Desert, by combining eddy flux and meteorological data from 2018 to 2019 and Sentinel-2 remote sensing images from 2017 to 2020. We evaluated the applicability of 12 remote sensing vegetation indices to simulate the growth of Tamarix chinensis and extract key phenological metrics. A seven-parameter double-logistic function (DL-7) + global model function (GMF) was used to fit the growth curves of GPP and vegetation indices. Three key phenological metrics, i.e., the start of the growing season (SOS), the peak of the growing season (POS), and the end of the growing season (EOS), were extracted for each year. Growing season degree days (GDD) and soil water content were the main environmental factors affecting the phenological dynamics of T. chinensis. Compared with 2018, the lower temperatures in 2019 resulted in slower accumulation rate of accumulated temperature before the SOS. T. chinensis required longer heat accumulation to enter growing season, which might cause later SOS in 2019. The hydrothermal conditions between SOS and POS were similar for 2018 and 2019. Howe-ver, the POS in 2019 was 8 days later than that in 2018, because of the late SOS in 2019. Following the POS in 2019, high GDD and low soil water content caused the T. chinensis to suffer from water stress, resulting in a shortened late growing season. The linear regression between the standardized Sentinel-2 vegetation index and the average value of GPP between 10:00 and 14:00 indicated that the enhanced vegetation index of the broadband vegetation index and the chlorophyll red edge index, inverted red edge chlorophyll index, and red-edge normalized difference vegetation index (NDVI705) of the narrowband vegetation index were highly consistent with the GPP of T. chinensis. Remote sensing extraction of SOS and POS of T. chinensis suggested that the Sentinel-2 narrowband vegetation index was more accurate than the broadband vegetation index. The modified chlorophyll absorption in reflectance index provided the most accurate extraction of SOS, while the MERIS terrestrial chlorophyll index provided the most accurate extraction of EOS. Conversely, the Sentinel-2 broadband vegetation index was the most accurate for extracting POS, especially the 2-band enhanced vegetation index and the near-infrared reflectance of vegetation. Overall, NDVI705 was the best index to estimate phenological metrics.

Delineation of groundwater potential zones using modified weight standardization method and GIS in arid environments: case study of Ejina Oasis, Inner Mongolia, China

Groundwater refers to a vital resource for sustainable development of the earth. As fueled by the economic development, population growth, and the expansion of irrigation area, groundwater has been increasingly demanded. It is noteworthy that groundwater seriously limits the sustainable development in the arid desert areas of Africa and Asia. To tackle down this issue, modified weight standardization (MWS) and improved fuzzy analytic hierarchy process (IFAHP) theories and geographic information system (GIS) were adopted to find the groundwater potential zones (GWPZ) in the Ejina Oasis of northwestern China. A range of thematic layers (i.e., lithology, lineament density, soil moisture, normalized difference vegetation index, rainfall, biomass, drainage density, slope, elevation, and land use/land cover) were built with the existing maps and the remote sensing data. The mentioned thematic layers were standardized using MWS. Subsequently, the IFAHP was adopted to assign weight to the thematic layers. Lastly, all the layers were integrated in GIS to map the GWPZ. The MWS-IFAHP–based groundwater potential map revealed four categories: “excellent” (13.91%), “good” (21.97%), “moderate” (34.79%), and “poor” (29.33%). As indicated from the validation of the results, GIS-based MWS and IFAHP technologies can be used to effectively generate groundwater potential map under an accuracy of 80%. The results of this study are critical to plan and develop scarce groundwater resources in arid areas efficiently at a low cost, which can ensure sustainable water supply in the future.

Measuring and modeling evapotranspiration of a Populus euphratica forest in northwestern China

Vegetation is sparsely distributed in the arid regions of northwestern China, and accurately measuring and partitioning of evapotranspiration is of importance for ecosystems in such areas. In this study, we measured and analyzed diurnal and phenological variations in evapotranspiration using the eddy–covariance method based on the Penman–Monteith, Priestley–Taylor, Shuttleworth–Wallace models, a newly proposed improved dual source model and a clumped model in a forest reserve in the Ejin oasis of Populus euphratica in 2015 and 2016 growing seasons. A sensitivity analysis was performed for the models with higher accuracies and we examined the biotic and abiotic controls on evapotranspiration. The results show that the total amounts of evapotranspiration during the two growing seasons in 2015 and 2016 were 622 and 612 mm, respectively. Phenological variations in evapotranspiration produced single-peak curves, while diurnal variations reflected the influence of high temperatures on some afternoons. The Priestley–Taylor and the improved dual source models gave the most accurate evapotranspiration values at the daily scale and appeared to be most suitable for the estimation of evapotranspiration for the species in arid regions. In addition, both models were the most sensitive to net radiation (Rn).

Monitoring and Assessment of the Oasis Ecological Resilience Improved by Rational Water Dispatching Using Multiple Remote Sensing Data: A Case Study of the Heihe River Basin, Silk Road

The suboptimal management and utilization of water resources from the “Asian water towers” contributed to serious ecological crises in river basins along the arid Silk Road, such as the Aral Sea and the Heihe River in the 20th century. To improve the ecological resilience of the Ejina Oasis in the Heihe River downstream basin, the Chinese government implemented the ‘Ecological water dispatching project’ in 2000. However, it is still unclear what the optimal rational water allocation is for the sustainable development of economic, social, and ecological environments (so called “triple bottom line”) in these inland river basins. This study presents a decision-tree-based methodology for ecological monitoring and restoration strategies for Silk Road’s oasis eco-system. Using Landsat TM/OLI data as well as meteorological, hydrological, and water utilization data, we show that ~69% of the originally degraded land has been restored since 2000. Previously dry tail-end lakes in the Heihe River downstream basin have been rejuvenated, and the precipitation has also significantly improved (ρ = 0.047). We propose that the downstream water allocation should be no more than ~11 × 108 m3 and that the optimal ratio between downstream and midstream allocation is 0.4–1.7. This study provides an excellent example for ecological monitoring and assessment in the optimization of strategies for the restoration of Silk Road’s oasis eco-system.

Nesting and foraging behavior of Xylocopa valga in the Ejina Oasis, China.

Xylocopa valga is extinct in Latvia and Lithuania and is critically endangered in Poland, and its distribution in the Ejina Oasis, China, is currently unknown. Studies on the biology of X. valga are scarce, and thus, conservation efforts for this species are currently limited. Here, we investigated the morphological characteristics, nest architecture, nest structure and food type of offspring in the nest cells of X. valga. This research was conducted in the Populus euphratica forest reserve in the Ejina Oasis, China, between July 2014 and June 2019. The primary investigation methods included visual inspection, photography, observation and measurements of nest anatomy, and examination of pollen stores by microscopy. We found that in the Ejina Oasis, China, X. valga builds its nests in the dead wood of P. euphratica. X. valga is univoltine. Its lifestyle varies from solitude to symbiosis. When many females nest near each other, several females may share a single nest entrance, based on which they build their own cells. The nests are branched. According to our results, there is a significant difference between the thickness of the inner cell partition and that of the outermost cell partition in the branched tunnel. In the P. euphratica forest area, the food for the progeny of X. valga is mainly composed of the pollen and nectar of Sophora alopecuroide and Populus euphratica. Therefore, X. valga and S. alopecuroides exhibit close ecological interactions in the P. euphratica forest ecosystem.

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.

Partitioning groundwater recharge sources in multiple aquifers system within a desert oasis environment: Implications for water resources management in endorheic basins

The global expansion of irrigation-based agricultural practices is causing an overexploitation of groundwater resources. A thorough understanding of groundwater recharge processes is necessary for restoring groundwater and improving water resources management, especially in desert oasis aquifers in endorheic basins. In this paper, the Ejina Oasis in the downstream of Heihe River Basin was selected as the representative case for such an endeavor. Based on stable isotopes and end member mixing analysis, we found that the shallow groundwater was modern water, with 13% originating from local precipitation and 87% from river water infiltration. The semi-confined groundwater is a mixture of shallow groundwater (30%), lateral groundwater flowing from the middle Heihe River Basin (MHR; 52%), and confined groundwater (18%). Confined groundwater was old water formed in paleo-climatic humid and cold conditions. Shallow groundwater levels were restored substantially after implementation of the Ecological Water Diversion Project (EWDP) began in 2000 in the Heihe River Basin, but the semi-confined groundwater levels still declined slowly. These different responses to EWDP are attributed to the differences in primary recharge sources of the two aquifers. Because river water infiltration was the main sources of shallow groundwater, increases in river discharge into the Ejina Oasis resulted in increased shallow groundwater levels over a short time scale. Continued over-pumping of groundwater for irrigation in the MHR reduced lateral groundwater flow into the lower Heihe River Basin, which was the primary source of semi-confined groundwater. For successful groundwater restoration and maintenance of groundwater for the future, EWDP implementation must integrate water management of river water and groundwater diversion across the whole basin. Our results can provide useful information on policy decision makers for sustainable use of water resources in the oases of other similar watersheds around the world.

A landscape management analysis framework and its preliminary application in Ejina Oasis, Northwest China

The implementation of integrated landscape management to support local and regional human well-being is crucial in arid regions, but its application to date is very limited. Although analytical frameworks have been established to maximize ecosystem services via trade-offs between different landscape configurations, consumption factors such as water resources are rarely and weakly considered in such frameworks. In this paper, an improved integrated landscape-management analysis framework, called the Consumption-integrated Landscape Management to Ecosystem Service (CLMES), is proposed. In this framework, consumption factors are integrated at the same level as ecosystem services. The improved analytical framework is then used to assess and optimize landscape design in the Ejina Oasis, an extremely arid region in western China. Three landscape conditions (past, current, and future) are evaluated, based on the CLMES. Our results indicate that the Heihe River water-allocation program effectively promoted ecosystem services in the Ejina Oasis from 2000 to 2011. However, the excessive expansion of cropland led to a slight decline in habitat quality. An optimized landscape configuration and policy suggestions are proposed, which may be beneficial to the improvement of total water-use efficiency, oasis stability, and resilience of the ecological-social system in the Ejina Oasis.

Aggregation of area-averaged evapotranspiration over the Ejina Oasis based on a flux matrix and footprint analysis

The determination of area-averaged evapotranspiration (ET) over a heterogeneous land surface at the satellite pixel scale/model grid scale (103–104 m) is crucial to the evaluation of the remote sensing ET products and development of the parameterization schemes of general hydro-meteorological models. The Heihe Watershed Allied Telemetry Experimental Research (HiWATER) flux matrix of multi-site eddy-covariance (EC) and large aperture scintillometers (LASs) provided an unprecedented opportunity to establish an aggregation scheme for determining area-averaged surface fluxes. Based on the HiWATER flux matrix datasets and high-resolution land-cover map, a new flux aggregation method was developed by using footprint analysis and multiple-linear regression. The area-averaged sensible heat fluxes aggregated from the multi-site EC flux measurements using the developed method were compared with the LAS measured fluxes. The results showed that the new method produced reasonable estimates of sensible heat flux with a mean absolute percentage error (MAPE) value of around 20–30%. The new aggregation method also significantly outperformed other methods being applied commonly, such as the rather simple area-weighted method. The daily ET of various land-cover types and the area-averaged ET over the key area of the Populus euphratica forest reserve in the Ejina Oasis were separately estimated using the established disaggregation and aggregation schemes of the new method. The area-averaged ET over this key area ranged between 1 and 5 mm d−1 for the 68 days growing period in 2014. Results of this study can be used for the evaluation of relevant remote sensing models and land surface process models.