Desert-oasis Region Research Articles

Dry Matter Accumulation, Water Productivity and Quality of Potato in Response to Regulated Deficit Irrigation in a Desert Oasis Region.

As one of the most important food crops, the potato is widely planted in the oasis agricultural region of Northwest China. To ascertain the impact of regulated deficit irrigation (RDI) on various facets including dry matter accumulation, tuber yield, quality and water use efficiency (WUE) of potato plants, a two-growth season field experiment under mulched drip irrigation was conducted in the desert oasis region of Northwest China. Water deficits, applied at the seedling, tuber formation, tuber expansion and starch accumulation stages, encompassed two distinctive levels: mild (55-65% of field capacity, FC) and moderate (45-55% FC) deficit, with full irrigation (65-75% FC) throughout the growing season as the control (CK). The results showed that water deficit significantly reduced (p < 0.05) above-ground dry matter, water consumption and tuber yield compared to CK, and the reduction increased with the increasing water deficit. A mild water deficit at the tuber formation stage, without significantly reducing (p > 0.05) yield, could significantly increase WUE and irrigation water use efficiency (IWUE), with two-year average increases of 25.55% and 32.33%, respectively, compared to CK. Water deficit at the tuber formation stage increased starch content, whereas water deficit at tuber expansion stage significantly reduced starch, protein and reducing sugar content. Additionally, a comprehensive evaluation showed that a mild water deficit at the tuber formation stage is the optimal RDI strategy for potato production, providing a good balance between yield, quality and WUE. The results of this study can provide theoretical support for efficient and sustainable potato production in the desert oasis regions of Northwest China.

Irrigation and Fertilization Scheduling for Peanut Cultivation under Mulched Drip Irrigation in a Desert-Oasis Area.

The aim of this study was to investigate the impact of water and nitrogen regulation on the characteristics of water and fertilizer demands and the yield, quality, and efficiencies of the water and nitrogen utilization of peanuts cultivated under mulched drip irrigation in a desert-oasis region. The experiment, conducted in Urumqi, Xinjiang, centered on elucidating the response mechanisms governing peanut growth, yield, quality, water consumption patterns, and fertilizer characteristics during the reproductive period under the influence of water and nitrogen regulation. In the field experiments, three irrigation levels were implemented, denoted as W1 (irrigation water quota of 22.5 mm), W2 (irrigation water quota of 30 mm), and W3 (irrigation water quota of 37.5 mm). Additionally, two nitrogen application levels, labeled N1 (nitrogen application rate of 77.5 kg·ha-1) and N2 (a nitrogen application rate of 110 kg·ha-1), were applied, resulting in seven treatments. A control treatment (CK), which involved no nitrogen application, was also included in the experimental design. The results indicate a direct correlation between the increment in the irrigation quota and increases in farmland water-related parameters, including water consumption, daily water consumption intensity, and water consumption percentage. The nitrogen harvest index (NHI) demonstrated a higher value in the absence of nitrogen application compared to the treatment with elevated nitrogen levels. The application of nitrogen resulted in an elevation in both nitrogen accumulation and nitrogen absorption efficiency within pods and plants. When subjected to identical nitrogen application conditions, irrigation proved to be advantageous in enhancing water-use efficiency (WUE), nitrogen partial factor productivity (NPFP), and the yield of peanut pods. The contribution rate of water to pod yield and WUE exceeded that of nitrogen, while the contribution rate of nitrogen to nitrogen-use efficiency (NUE) was higher. The total water consumption for achieving a high yield and enhanced water- and nitrogen-use efficiencies in peanuts cultivated under drip irrigation with film mulching was approximately 402.57 mm. Taking into account yield, quality, and water- and nitrogen-used efficiencies, the use of an irrigation quota of 37.5 mm, an irrigation cycle of 10-15 days, and a nitrogen application rate of 110 kg·ha-1 can be regarded as an appropriate water and nitrogen management approach for peanut cultivation under mulched drip irrigation in Xinjiang.

Retrieving soil moisture using cosmic-ray neutron technology based on COSMIC model in the desert-oasis region.

Cosmic-ray neutron technology could estimate average soil moisture on scale of hectometers by monitoring the neutron intensity near the ground, which has been successfully applied in forest, grassland, farmland, and other ecosystems. To verify the reliability of Cosmic-ray Soil Moisture Interaction Code (COSMIC) model for retrieving mesoscale soil moisture in arid regions, we carried out soil moisture observation experiment by using the cosmic-ray neutron rover in the desert-oasis region of the middle reaches of Heihe River. The results showed that the fast neutron intensity in the desert-oasis region were 350-715 counts·(30 s)-1, and the calibrated high energy neutron intensity (Ncosmic) were (38.5±2.2) counts·(30 s)-1, which was affected by land surface characteristics. Both COSMIC model (root mean square error=0.019 g·g-1) and N0 equation (root mean square error=0.018 g·g-1) could well assess the mesoscale soil moisture, with the accuracy of soil moisture being higher considering soil lattice water. The average penetration depth was 19 cm in the oasis region and 36 cm in the desert region during the experiment. COSMIC model could be used to retrieve soil moisture by cosmic ray neutron in the desert-oasis regions, which had great potential to realize data assimilation of surface meteorological-hydrological-ecological variables by combining with land surface models.

Study on the Change in Vegetation Coverage in Desert Oasis and Its Driving Factors from 1990 to 2020 Based on Google Earth Engine

Fractional Vegetation Cover (FVC) is an important indicator to evaluate the quality of the regional ecological environment. Alar City is a typical desert oasis region. Investigating the spatial and temporal changes in its vegetation cover at different stages is a guide to the ecological balance and sustainable green development of the Tarim River basin. Based on the Google Earth Engine (GEE) cloud platform, this study analyzed the spatial and temporal characteristics and trends of vegetation cover changes in Alar City from 1990 to 2020 using the Hurst index and coefficient of variation. The results show that the spatial distribution of vegetation in the study area in the last 30 years shows a wave-like characteristic with an overall apparent upward trend. The vegetation cover in the study area is predominantly increasing and the spatial distribution shows a phased and regional character. Compared with 1990, there is a significant increase in the area of cultivated land in 2020. Among them, the areas of vegetation growth mainly occur in the basin around the Tarim River. Human activities have weakened the influence of natural factors on FVC. The results of the study suggest that the GEE platform can be an effective tool for permanently monitoring vegetation.

Environmental impacts of photovoltaic power plants in northwest China

In the past decade, approximately 17 % of the world's photovoltaic capacity has been installed in China, especially in the northwestern desert areas. The impacts of the construction and operation of large-scale photovoltaic power plants (PPPs) on local ecological environments have become urgent scientific issues in regional environmental protection decision-making. To quantitatively evaluate the local environmental impacts of the construction and operation of PPPs in the desert oasis region, thermal infrared and multispectral sensors mounted on unmanned aerial vehicles (UAVs) as well as X-ray fluorescence spectrometers and soil sensors were used in this study to monitor a large PPP in Northwest China. We found that the construction and operation of PPPs can promote biological soil crust development and vegetation growth and can thus improve the soil texture and nutrition. However, the Ca, S and Cl concentrations were found to be 3, 5 and 1.7 times higher inside the PPP area than outside the PPP area, respectively. In addition, the soil salinization is also more severe inside the PPP area. In future studies, it is essential to further elucidate the impacts of PPP operations and agricultural on desert ecosystems.

Deficit mulched drip irrigation improves yield, quality, and water use efficiency of watermelon in a desert oasis region

In the context of global warming, drought is a crucial factor affecting agricultural production, especially for the oasis farming areas of northwestern China, where water resources are extremely scarce. To reveal the response of watermelon water consumption (WC), yield, quality, and water use efficiency (WUE) to water deficit (WD) and to determine the optimal mode of irrigation in the desert oasis areas of Hexi, we applied different WD treatments on a field oasis watermelon in 2020 and 2021. The experiments employed two gradients of light (l) and moderate (m) WD treatments during the seedling (S), vine (V), expansion (E), and maturity (M) stages except for flowering and fruiting (F) stage, with full irrigation during the entire growth period as the control (CK). The results showed that the WC of oasis watermelon at each growth stage was in the order: E > V > S > M > F, in which WC by E stage accounted for 33.15–40.33%. Compared with the CK, WD had an obvious effect on water saving, and WD during the V or E stages inhibited the growth of vine leaves to a certain extent. The Sl treatment (light WD during S stage) had the highest yield and WUE, with significant increases of 5.23–5.38% and 7.10–7.37% (p < 0.05), respectively, in the two years, while the Mm treatment (moderate WD during the M stage) resulted in the best overall nutritional quality of watermelon, with soluble solids, soluble sugars, vitamin C, and soluble protein contents increasing by 11.31%, 33.43%, 24.03%, and 10.31% (p < 0.05), respectively. However, an integrated evaluation that coupled grey relation analysis (GRA) with a technique for determining order preference by its similarity to an ideal solution (TOPSIS) model, considering growth, yield, quality, and efficiency indicators, concluded that the Ml treatment (light WD during the M stage) achieved the highest comprehensive score, followed by the Sl treatment. Therefore, it is recommended that the optimal deficit irrigation mode for oasis watermelon is the Ml treatment, which can balance water savings, yields, and quality improvements, while the Sl treatment can be considered as a backup mode. This study provides theoretical and technical support for achieving efficient water-saving cultivation and scale development of watermelon production in desert oasis areas.

A causal structure-based multiple-criteria decision framework for evaluating the water-related ecosystem service tradeoffs in a desert oasis region

Study regionQira oasis, a typical catchment alluvial fan composed by agriculture and natural shrubs at the south margin of Taklimakan Desert, China Study focusWater management modeling involves causal interaction effects of various water-related ecosystem services (ESs) under multiple-criteria water management alternatives, measuring expected benefits of water-related ESs. Many multi-criteria decision tools have been developed to mitigate some of major challenges of ESs tradeoffs. However, few formal ES trade-off frameworks have focused on the multiple-criteria alternatives assessment and indifference point identifications of water-related ES. This paper proposes a causal structure-based multiple-criteria decision framework to model water-related ESs, and to detect the points where the decision makers would be indifferent between two alternatives and to compare with the optimum recommendation value using Bayesian networks (BNs) with analytic hierarchy process (AHP). New hydrological insights for the regionThe study confirms that the proposed causal structure-based multiple-criteria decision framework is a promising approach to modeling possible climate, irrigation, and water policy scenarios and to examining influences of those scenarios on water-related ESs. The framework can be used to effectively recommend optimum water management alternatives and to identify the indifference points by combining BNs into AHP under stakeholder participation. The framework also provides a qualitative and quantitative assessment to reduce the conflicts and uncertainties of multiple-criteria weights in diagnosing water-related ES trade-offs, owing to different stakeholder preferences.

Assessing landscape fragmentation in a desert-oasis region of Northwest China: patterns, driving forces, and policy implications for future land consolidation.

Landscape fragmentation is considered a serious threat to eco-environmental integrity and socioeconomic development. Although many studies have focused on landscape fragmentation resulting from agricultural production and urbanization, landscape fragmentation from the aspects of patterns, driving forces, and the policy perspective of ecosystems has rarely been investigated. Oases, as a unique landscape, face severe fragmentation in arid and semiarid regions. This study applied a combination of approaches, including remote sensing image interpretations, landscape fragmentation metrics, and community surveys, to analyze patterns and their driving forces, as well as the policy implications for future land consolidation, in the Hotan oasis of Northwest China from the space and time perspectives. Results show that the frequent occurrence of summer flood events changes the patch number, density, size, and splitting degree of oasis-desert ecotone vegetation. The socioeconomic factors including total population and irrigation area are more important driving forces on oasis landscape fragmentation, compared with natural factors such as temperature and precipitation. Rural expansion, road and canal system developments caused by population growth, and the rising number of households increase oasis landscape fragmentation. Rapid economic development, such as agricultural expansion and urbanization, has imposed the intensification of landscape fragmentation. Fragmentation reaches peak when agricultural development makes up 40-50% of study area. Rural residential reconstruction and farmland transfer policies facilitate the intensive utilization of land toward oasis fragmentation solutions, but many factors, such as landholders' household characteristics and living conditions, are partly responsible for the challenges in land consolidation. This study also demonstrates that intense human activities pose a great threat for land consolidation and sustainable development of oasis landscape.

Wind speed changes and influencing factors in inland river basin of monsoon marginal zone

Scientific understanding of regional wind speed variation characteristics and driving mechanisms is of great practical significance to the management and rational utilization of wind energy resources, ecological protection and governance, and sustainable development of agriculture. Taking the Shiyang River Basin in inland river basin of monsoon marginal zone as the study area, this paper analyzed wind speed changes and influencing factors at different time and space scales. The results showed that, first of all, the annual average wind speed showed a downward trend as a whole in Shiyang River Basin, and the change of spring wind speed and the decreasing frequency of daily max-wind speed above Grade 5 were the main contributors. The turning point of annual average wind speed was consistent with that in spring and autumn (1981) and earlier than that in winter and summer (1982). Secondly, as far as the wind speed change tendency rate is concerned, before the turning point, Yongchang area had the largest decline rate with obvious “2000 m effect”, while after the turning point, Wuwei Basin had the largest rise rate with obvious “basin effect”. Focusing on the downstream desert oasis region, the sand-driving wind speed showed a decreasing trend as a whole, and showed a “cliff-like” decline after 1988. The rising trend of sand-driving wind speed after 2014 will pose greater challenges to ecological governance. Finally, under the background of unbalanced global warming, the wind speed changes in different periods were driven by the circulation system changes. In 1970–1981, the decline of the wind speed was the result of the combined action of Arctic Oscillation and Asia Polar Vortex. However, after 1981, it was affected by North Atlantic Oscillation, Asian Meridional Circulation, Tibet Plateau Circulation, India-Burma Trough, Western Pacific Subtropical High and Northern Hemisphere Subtropical High.

基于压力-状态-响应模型的黑河中游张掖市生态安全评价

生态系统服务的状态与生态是否安全密切相关，生态系统服务的正常发挥是实现生态安全的前提。近年来，中国西北荒漠-绿洲扩张速度加快，改变了生态系统服务的供给与传输，进而影响了区域生态安全。以典型荒漠-绿洲区域黑河中游的张掖市为例，基于压力-状态-响应模型，耦合生态系统服务理论，构建了黑河中游生态安全评价指标体系，评估了2001-2015年黑河中游生态安全演变趋势。研究结果表明黑河中游生态系统面临的资源消耗和环境污染压力越来越大，压力指数有所降低；部分地区出现植被退化、破碎化增加等现象，状态指数略有降低；在实施节水灌溉、产业转移、湿地保护等举措后，响应指数显著增加。总体来看，2001-2015年黑河中游生态安全水平呈现波动增长趋势，生态安全综合指数由0.3748增至0.5888，生态安全等级由"较不安全"达到"临界安全"状态，其中高效节水灌溉面积、生态用水量、地下水开采率等水资源相关要素是影响绿洲生态安全水平的主要因子。基于以上研究，提出了坚持生态保护优先、调整种植和产业结构、发展高效节水灌溉技术、提高公众生态保护意识等提高生态安全水平的相关对策与建议，以期为促进区域生态经济可持续发展提供支撑。;The state of ecosystem services is closely related to whether the ecosystem is safe or not. The normal play of ecosystem services is the premise of realizing ecological security. Recently, the expansion speed of desert oasis in Northwest China has accelerated which has changed the supply and transmission of ecosystem services, and further affected the regional ecological security. Taking the middle reaches of the Heihe River in typical desert oasis region as an example, based on Pressure-State-Response model, coupled with the ecosystem service theory, the ecological security evaluation index system of the middle reaches of the Heihe River was constructed, and the evolution trend of ecological security in the middle reaches of the Heihe River from 2001 to 2015 was evaluated. The results showed that the ecosystem in the middle reaches of the Heihe River was facing increasing pressure of resource consumption and environmental pollution, and the pressure index decreased accordingly. As vegetation degradation and fragmentation increased in some areas, the state index decreased slightly. After the implementation of water-saving irrigation, industrial transfer, wetland protection and other positive measures, the response index increased significantly. Overall, from 2001 to 2015, the ecological security level in the middle reaches of the Heihe River showed a fluctuating growth trend, the ecological security index increased from 0.3748 to 0.5888, and the ecological security level reached the state of critical safe from less safe. Among them, water resources related factors such as area of efficient water-saving irrigation, ecological water consumption and groundwater development rate were the main factors affecting the ecological security level of oasis. Based on the above research, this paper puts forward relevant countermeasures and suggestions to improve the ecological security level, such as adhering to the priority of ecological protection, adjusting planting and industrial structure, developing efficient water-saving irrigation technology and improving public awareness of ecological protection, in order to provide support for promoting the sustainable development of regional ecological economy.

Differentiation characteristics of soil water under different landscape types in a desert-oasis region in the middle reaches of Heihe river basin, China

The tillage of oasis farmlands and construction of artificial protection forests in native grasslands around the oases would significantly affect differentiation characteristics of soil water. In this study, the establishment of belt transect with 13 different landscape types in the middle reaches of Heihe River basin was determined to analyze differentiation characteristics of soil water. Our results showed that firstly vertical variability of soil water under different landscape types was significant. Secondly, horizontal variability of soil water under different landscape types showed a significant difference. Thirdly, differentiation characteristics of soil water under different landscape types were mainly caused by interaction of multiple factors such as vegetation type, soil properties and human management etc, and spatial variability of soil water can be enhanced by the tillage of oasis farmlands and construction of artificial protection forests. Our results suggest that it has very important value for enhancing the soil water effect of irrigated vegetation in this region to fully conform the water consumption of plants and the water holding capacity of soil, to especially strengthen the management of water-saving irrigation of farm crops and artificial plantations.

Preface

The 2020 4th International Conference on Water Conservancy, Hydropower and Building Engineering (WCHBE 2020) was planned to be held in Lanzhou, China during July 3-5, 2020. WCHBE 2020 was hosted by AEIC Academic Exchange Information Center. Due to the impact of COVID-19, many communities from all over the world were under strict health measures and strict travel restrictions, and participants of 2020 4th International Conference on Water Conservancy, Hydropower and Building Engineering (WCHBE 2020) also meet with the difficulty of travel restrictions. For communities, if our conference was not held in a virtual form, it would add huge work on traffic system, Exit-Entry system, medical system, etc., which is quite a serious issue, to actively respond to the call of the government, to strengthen the protection work, to effectively reduce people gathering and prevent COVID-19, considering the situation that most of the authors would like to publish their articles and make academic communications as scheduled, WCHBE 2020 was held on-line instead of postponing the conference. It was a challenge, not only to the organizers, but also to the participants who were delivering their speeches using videoconference tools, under different time zones.The conference is an international conference for the presentation of technological advances and research results in the fields of water conservancy, hydropower and building engineering. The conference will bring together about 97 leading researchers, engineers and scientists in the domain of interest from China, Italy, Malaysia, Mexico and Thailand. The conference model was divided into two parts, including keynote presentations and online discussion. In the first part, each keynote speakers were allocated 30 minutes to present their talks via Zoom. After the keynote talks, all participants joined in a WeChat communication group to discuss more about the talks and presentations. We are honored to have invited three distinguished experts as our keynote speakers. Prof. Hengjia Zhang, Gansu Agricultural University, China, was the first one to perform a thought-provoking speech on Optimization of Limited Irrigation Schedules for Spring Maize (Zea mays) in a Desert Oasis Region. He also was the Conference Chair who mainly devoted to the teaching and research work of the efficient use of agricultural water and soil resources. Secondly, Prof. Shaohua Marko Hsu from Feng Chia University held his speech on Using Porous Material for Riverbank and Riverbed Protection. Thirdly, Prof. Ahmad Safuan Bin A. Rashid from Universiti Teknologi Malaysia, Malaysia talked about Application of UAV-TLS Photogrammetry in Determination of Rock Slope Stability. Their insightful speeches had triggered heated discussion in the second session of the conference. The WeChat discussion lasted for about 30 minutes. Every participant praised this conference for disseminating useful and insightful knowledge.We are glad to share with you that we still received lots of submissions from the conference during this special period. Hence, we selected a bunch of high-quality papers and compiled them into the proceedings after rigorously reviewed them. These papers feature following two categories but are not limited to: Civil, Architectural Engineering, Water conservancy and hydropower, and other related fields. All the papers have been through rigorous review and process to meet the requirements of International publication standard.We would like to express our gratitude to everyone involved. Without this dedicated cooperation, it would be impossible to hold the conference at such a high level and prepare the WCHBE 2020 proceedings.Committee of WCHBE 2020The Committee member is available in this pdf.

Patterns of soil nitrogen mineralization under a land‐use change from desert to farmland

AbstractUnderstanding how soil nitrogen (N) mineralization (Nmin) responds to environmental changes is critical for improving ecosystem management, especially in a resource‐constrained region. Intensive land exploitation in arid land has profound influences on soil ecosystems and thus on soil Nmin. A local‐scale field investigation was conducted to reveal the temporal dynamics of Nminunder land‐use change from desert to farmland, and to verify the mechanisms controlling Nminchange during this process in a typical desert oasis region. The results showed that Nminranged from −0.14 to 2.69 mg N kg−1day−1, with an average value of 0.74 mg N kg−1day−1. Nminin old oasis farmland (OOF) was significantly higher than that in GCF (Gobi desert conversion farmland) and SCF (sandy desert conversion farmland), and the average change rates of Nminwere 0.036 and 0.032 mg N kg−1day−1year−1in GCF and SCF, respectively. Structural equation modelling (SEM) was used to test whether the measured variables affected Nmin, and the results showed that soil organic matter (SOM), bulk density (BD) and sand content were the main soil factors affecting Nmin. These soil factors, together with farmland type and cropping time, can explain 31% of the variation in Nmin. Our observations revealed that Nminchanged substantially under the land conversion process from desert to farmland, and our findings will help with assessments and predictions of future N cycles in desert oasis regions in response to land‐use change.HighlightsWe used Nminas an observed variable to evaluate the dynamics of the soil evolution process under a land‐use change from desert to farmland.Cropping year was identified by using map image data to reveal temporal trend of Nmin.Nminwas primarily affected by soil organic matter, bulk density and sandy content. Intensive land exploitation in arid land profoundly influences soil Nmin.

Spatio-temporal distribution of irrigation water productivity and its driving factors for cereal crops in Hexi Corridor, Northwest China

The analysis of irrigation water productivity (IWP) can provide insights into taking measures to improve water-efficient irrigation. This study examines the temporal IWP trend of cereal crops over the Hexi Corridor in Northwest China by employing descriptive analysis, trend analysis, and change-point analysis. Spatial patterns of different typical years (dry, average and wet year) are analyzed by the spatial interpolation method and spatial autocorrelation method. The regional average IWP significantly increased from 0.51kg/m3 to 1.29kg/m3 during the period of 1981–2012 and no change point was detected. Spatial distribution of IWP reveals that IWP was higher in the plain oasis region, while lower in the mountainous and desert oasis region. The IWP ranged from 0.72 to 1.60kg/m3 for the dry year 2004, 0.77–1.66kg/m3 for the average year 2008, and 0.81–1.93kg/m3 for the wet year 2011, respectively. No significant spatial autocorrelation was observed. By 2012, there were still 3.9% of the area with IWP less than 1.0kg/m3, which implied an opportunity to increase IWP through better water management practices. The grey relational analysis of the influences of major driving factors (area supported by unit of irrigation water use, fertilization, agricultural film, agricultural pesticide, and annual mean temperature) on IWP showed that area supported by unit of irrigation water use, fertilization, and agricultural film had dominant impacts during the whole period.

Energy exchange and evapotranspiration over irrigated seed maize agroecosystems in a desert-oasis region, northwest China

Investigating the dynamics of energy and water vapor exchange in oasis agroecosystems is important to improve scientific understanding of land surface processes in desert-oasis regions. In this study, water vapor and energy fluxes were obtained by using an eddy covariance technique for two similar irrigated seed maize fields at Yingke and Pingchuan, in northwest China. Seasonal variabilities of evapotranspiration (ET) and relevant environmental and biophysical factors were explored. Results showed that the energy balance closures were reasonable, with energy balance ratio of 0.99 and 0.79 for a half-hourly time scale at Yingke and Pingchuan, respectively. The seasonal changes in net radiation (Rn), latent heat flux (LE), and sensible heat flux (H) of Yingke and Pingchuan were similar. Net radiation was 11.27MJm−1day−1 during the growing season. Latent heat flux accounted for 67.5% of net radiation, sensible heat flux was 25.0%, and soil heat flux was 7.5%. A reverse seasonal change was found in partitioning energy flux into LE and H. The seasonal variation in energy flux partitioning was significantly related to the phenology of maize. During the growing season, ET was 467 and 545mm, and mean daily ET 2.84 and 3.35mmday−1 at Pingchuan and Yingke, respectively. “Non-growing” season ET was 15% of the annual ET in the bare field (during October–March) and 85% of the annual ET for maize (during April–September). Daily ET was mainly controlled by net radiation and air temperature, and was significantly affected by leaf area index (<3.0m2m−2) and canopy conductance (<10mms−1). Furthermore, irrigation promoted daily ET greatly during the growing season. Accurate estimation of seed maize ET and determination the controlling factors helps to develop exact irrigation scheduling and improve water resource use in desert-oasis agroecosystems.

Effects of variability in landscape types on the microclimate across a desert–oasis region on the southern margins of the Tarim Basin, China

ABSTRACTMicroclimates play important roles in controlling water budgets and water vapor transportation, as well as vegetation growth characteristics. In order to understand the differences in meteorological parameters under different vegetation cover (VC) and terrain conditions, wind velocity, air temperature, relative humidity (RH), photosynthetically active radiation (PAR), and solar radiation were simultaneously monitored on shifting, semi-fixed and fixed sandy lands, and an oasis. The air temperature and RH differences among the four landscape types were obvious in the period from May to October. It was found that the higher elevations of semi-fixed sandy land can influence PAR and solar radiation during sand-blowing weather. The differences of air temperature and RH among the four sites during the dust-storm and rainy days were not obvious, but their differences during sand-blowing weather were greater than during rainy weather and less than during floating-dust and sunny weather. The differences of PAR and solar radiation among the four landscape types were most obvious during the dust-storm event. During most of the weather types studied, significant positive correlations were found between wind velocity and temperature, PAR, and solar radiation, as well as between temperature and PAR, and solar radiation. Meanwhile, significant negative correlations were found between RH and wind velocity, temperature, PAR, and solar radiation. VC and topography were found to be the main factors influencing the changes in meteorological parameters between desert–oasis ecotone and oasis.

Improving Estimation of Evapotranspiration under Water-Limited Conditions Based on SEBS and MODIS Data in Arid Regions

This study proposes a method for improving the estimation of surface turbulent fluxes in surface energy balance system (SEBS) model under water stress conditions using MODIS data. The normalized difference water index (NDWI) as an indicator of water stress is integrated into SEBS. To investigate the feasibility of the new approach, the desert-oasis region in the middle reaches of the Heihe River Basin (HRB) is selected as the study area. The proposed model is calibrated with meteorological and flux data over 2008–2011 at the Yingke station and is verified with data from 16 stations of the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) project in 2012. The results show that soil moisture significantly affects evapotranspiration (ET) under water stress conditions in the study area. Adding the NDWI in SEBS can significantly improve the estimations of surface turbulent fluxes in water-limited regions, especially for spare vegetation cover area. The daily ET maps generated by the new model also show improvements in drylands with low ET values. This study demonstrates that integrating the NDWI into SEBS as an indicator of water stress is an effective way to improve the assessment of the regional ET in semi-arid and arid regions.

Characteristics of soil evaporation, plant transpiration and water budget of Nitraria dune in the arid Northwest China

Nitraria, a widely growing shrub plant in the dry desert area of China, can fix moving sand along its canopy and form a large number of sand dunes. The Nitraria dune is one of the most effective ways to fix moving sand and protect oasis in Northwest China. However, after dune formation, Nitraria plants gradually die and then release the fixed sand which causes damage to the oasis again. A decrease in the ratio of transpiration (T) to evapotranspiration (ET) was assumed to be the main reason for Nitraria dune degradation because more water was used for soil evaporation, however, this assumption has remained untested because of the difficulty in measuring the Nitraria dune transpiration rate. To overcome this challenge, an intensive field experiment was carried out in 2008–2012 in the Minqin, a typical desert-oasis region in Northwest China. Four measurement sites (early growth stage, rapid growth stage, peak growth stage, and senescence stage) represent the different succession stages of a Nitraria dune. Meteorological parameters were measured by Bowen ratio system, vegetation features and soil physical properties were measured by conventional methods, soil evaporation and transpiration by thermal remote sensing and three-temperature model (3T model), soil moisture by gravimetric and neutron probe method, and evapotranspiration (ET) by Bowen ratio energy balance and water balance methods. Results showed that in a wet year (2008), annual ET was 121, 108, 114, and 126mm, for the four stages, respectively. The ratio of ET to precipitation (P) was 103, 92, 97, and 107%, respectively. In a dry year (2010), ET was 75, 89, 79, and 79mm, respectively, while the ET/P was 106, 126, 112, and 112%, respectively. ET accounted for 92–107% of the precipitation in the wet years and 106–126% in the dry years. ET was nearly equal to precipitation in the wet years and greater than precipitation in the dry years, indicating almost all water from precipitation evaporated in all sites. Our results also showed that vegetation coverage in the four stages was 0.15, 0.35, 0.74, and 0.23, respectively. Instantaneous value of T was 0.021, 0.014, 0.033, and 0.003mmh−1, respectively for the four stages. Instantaneous value of soil evaporation (E) was 0.054, 0.013, 0.004, and 0.009mmh−1, respectively. The corresponding ET was 0.075, 0.027, 0.037, and 0.012mmh−1 for the four stages, respectively. The ratio of T/ET was 0.28, 0.52, 0.89, and 0.25, respectively for the four stages. The ratio reached to its maximum value of 0.89 and then began to decrease, which clearly proved our hypothesis. It concluded that the Nitraria plant not only consumes all the rainfall in the growing season, but also some of the water stored in the soil, which gradually consumes all the soil water storage and finally causes the Nitraria plant death. It also concluded that increasing T, decreasing E and keeping a high T/ET ratio is crucial for desert plants to survive. These results show that the above hypothesis is true and it will be useful for vegetation rehabilitation in the desert area.

Effects of variability in land surface characteristics on the summer radiation budget across desert-oasis region in Northwestern China

The oasis area in the middle reaches of the Heihe River has changed since a water diversion scheme was implemented in 2000. The resultant variation land surface characteristics affects radiation budget during the oasisification process. The aim of this study was to investigate the variation in radiation budget within land surfaces during the oasisification process, through spatial instead of time-successional sequence method. Radiant data in the oasis fringe (maize field) and the desert-oasis ecotone was observed during the summer of 2009. The results showed that solar radiation (SR) in the oasis fringe was identical to that of the desert-oasis ecotone on selected clear, cloudy, and rainy days. Surface reflective radiation (SRR) and surface effective radiation (SER) both decreased from clear day to cloudy day and were lowest on the rainy day. The diurnal variation in radiation budget for cloudy and rainy days did not follow the same cycle as on clear day. The albedo values in the oasis fringe and the desert-oasis ecotone were 0.18 and 0.26, respectively. The diurnal variation in albedo tended toward a “U-shaped” curve on clear day. When the solar elevation angle was greater than 40°; the albedo was symmetrical in the a.m. and p.m. time frames. The radiation budget changed within land surfaces during the oasisification process. In summer, the albedo decreased, as did SER, with the transition from desert to oasis interior; whereas the surface-absorbed radiation (SAR) and net radiation (NR) both increased. More than half of the absorbed net energy in the desert was released in longwave form. The absorbed energy in the oasis was conserved to ensure stable light and heat resources utilization for agricultural production.

Optimization of Limited Irrigation Schedules for Spring Maize (&lt;i&gt;Zea mays&lt;/i&gt;) in a Desert Oasis Region

An experiment was carried out to optimize limited irrigation (LI) schedules for spring maize in a desert oasis region. The grain yield, water use efficiency (WUE), irrigation water use efficiency (IWUE), and integrated evaluation index for soil nutrients (IEISN) in 0~40 cm soil depth of maize field subject to LI were selected as the synthetical factors in evaluating and optimizing the LI schedules. The unifactor matrix and weighing coefficient matrixes of evaluating factors were formed for fuzzy judgement and the synthetical evaluation index (SEI) determination. Compared to the minimum in MI4, the SEI for spring maize was respectively improved by 46.5%, 20.9%, 38.9%, 27.8%, and 23.8% in MI1, MI2, MI3, MI5, and CK. Therefore, the MI1 irrigation regime was recommended as the optimized LI schedule for spring maize in the desert oasis region due to its maximum SEI caused by the least water application, maximum grain yield, WUE, and IWUE, and 95.2% of the maximum IEISN.