Arid Region Of Northwestern China Research Articles

Deficit Irrigation-Based Improvement in Growth and Yield of Quinoa in the Northwestern Arid Region in China

Given the current global water scarcity issues, which particularly affect arid regions such as northwestern China, it is crucial to find crop planting patterns that result in efficient water resource utilization. Quinoa, as a drought-resistant and highly nutritious crop, has garnered significant attention from agricultural researchers in recent years. From 2019 to 2020, a series of experimental studies were conducted under non-mulching drip irrigation conditions to investigate the growth adaptability and the response to different irrigation levels of quinoa in an arid region in northwestern China. A comparative analysis of quinoa’s dry matter accumulation, yield, thousand-grain weight, harvest index, and water use efficiency under varying irrigation levels revealed that increasing irrigation significantly enhanced quinoa’s dry matter accumulation and yield. By optimizing the irrigation strategies, we found that the water-saving practice of initiating moderate irrigation in the sensitive water-demanding stages (flowering and fruiting) of quinoa increased the yield. The experiment results showed that, in 2020, the optimal irrigation amount was 3675 m3·ha−1 during a 14-day irrigation cycle, meeting quinoa’s growth requirements while improving water resource utilization efficiency. This study not only provides a scientific basis for the efficient cultivation of quinoa in the arid regions of northwestern China, but also offers new insights into and technical support for agricultural water resource management in the region, contributing to the sustainable development of agriculture in arid areas.

Optimal Allocation of Water Resources in Canal Systems Based on the Improved Grey Wolf Algorithm

Xinjiang is located in the arid region of northwestern China, and agriculture accounts for an absolute share of total water use. Resource-based, engineering, structural, and managed water shortages coexist. Therefore, it is of great significance to vigorously develop water conservation technology and improve the efficiency of water transmission and distribution in canal systems. This research aims at addressing the problems of difficult manual regulation and the overall optimization of the final canal system, low-water-resource utilization efficiency, and management efficiency. Taking the branch-double two-stage canal system of Dongfeng branch canal in Mangxiang, Jinghe irrigation district, as a case study, and the rotation irrigation group and irrigation duration as decision variables, canal distribution is modeled with the goal of minimizing seepage losses. The improved grey wolf algorithm combined with particle swarm optimization is used for the first time and compared with the traditional grey wolf algorithm, genetic particle swarm optimization fusion algorithm, and northern goshawk algorithm. The results show that (1) on the basis of meeting the water discharge capacity and water demand requirements of the canal system, the diversion time of the water distribution scheme obtained by using the improved grey wolf algorithm is shortened from 11 d to 8.91 d compared with the traditional empirical water distribution scheme. (2) The improved grey wolf algorithm converges to the optimal value within 10 generations compared to the remaining methods, and the total water leakage is reduced from 16.15 × 104 m3 to 11.75 × 104 m3. (3) The number of gate adjustments is reduced, and the canal gates are opened and closed at the same time within each rotational irrigation group. The grey wolf algorithm improved by its combination with particle swarm has stronger optimization ability and convergence, which can better meet the requirements of efficient water resource allocation in irrigation canal systems, as well as a high application value.

Mechanical transport revealed by optical textures of heavy minerals in aeolian sand: A case study in the Badain Jaran Desert, Northwestern China

Determining whether and to what extent the relative abundance of heavy minerals in original detrital assemblage has been modified by mechanical transport is beneficial for understanding regional historical climate changes and acquiring modern sediment provenance information. Utilizing the frequency of surface mechanical optical textures of heavy minerals may be an effective approach to address this question. However, the connection between the frequency surface mechanical optical textures of heavy minerals and the variations in the relative abundance of these minerals remains uncertain. In this study, 12 modern aeolian sand samples were collected from the Badain Jaran Desert in hyper arid region of northwestern China, characterized by weak weathering to analyze their relative contents of five major heavy minerals. Then, 3796 transparent heavy mineral grains were photographed under the parallel light of a polarizing microscope, and the frequency of 13 surface mechanical optical textures were calculated. The results reveal that the variations in the relative abundance of heavy minerals are substantially influenced by mechanical transport. The decrease in the relative abundance of heavy minerals with weak mechanical stability primarily attributed to mechanical collision. Conversely, the variations in the relative abundance of heavy minerals with strong mechanical stability are primarily influenced by mechanical abrasion. Therefore, mechanical transport impact on the relative abundance of heavy minerals in regions with weak chemical weathering. Establishing heavy mineral characteristic indices for provenance studies using the relative abundance of mechanically unstable minerals may not directly indicate transport distance but rather the strength of wind forces, which have significant potential in palaeo wind regime studies. This study expands the research field of sediment surface micromorphology and has potential applications in inferring past climate changes and determining modern sediment provenance.

Comparing FY-2F/CTA products to ground-based manual total cloud cover observations in Xinjiang under complex underlying surfaces and different weather conditions

Abstract. Clouds are an important parameter of artificial water augmentation, which is of substantial significance to judge the precipitation capacity. Xinjiang is an arid region in northwestern China, where weather stations are sparsely distributed, the types of underlying surface are complex, and the climate between the southern and northern region varies greatly. However, the retrieval of the total cloud cover (TCC) from satellite in arid areas is a challenging task. Based on the TCC data observed by ground observation stations (GOSs) from June 2015 to May 2016 considering the complex underlying surfaces and different weather conditions, the precision, consistency, and error between the cloud total amount from the FengYun-2F stationary satellite (FY-2F/CTA) and manually observed TCC are compared and evaluated in the Xinjiang region. The findings of this study are as follows: (1) the precision rate (PR) of FY-2F/CTA in the Xinjiang region is 75.6 %, which gradually decreases from north to south, demonstrating a high false rate (FR) and a low missing rate (MR). The consistency rate (CR) is 51.5 %, with little difference among three subregions of Xinjiang, all showing a high weak rate (WR) and low strong rate (SR), which means that the TCC values inverted from FY-2 satellite data are generally lower than those observed by GOSs, especially in southern Xinjiang. The bias is −20 %, and all the error indexes (EIs) including bias, MAE, and RMSE increase from central to the north and south of Xinjiang; that means the EIs are the lowest in Tianshan and the highest in southern Xinjiang. FY-2F/CTA exhibits higher PR and CR in the underlying surface of vegetation compared to non-vegetation; that is to say that FY-2F/CTA performs best in the underlying surfaces of forest and plowland, while their performance is relatively poorer in the underlying surface of snow and ice. (2) With rising temperature the PR and CR of FY-2F/CTA increase, while the EIs decrease. Under various temperature conditions, FY-2F/CTA has always exhibited high MR, low FR (on the contrary in January), high WR, and low SR. From low elevation to high elevation, the PR and CR of FY-2F/CTA decrease, but the PR increases significantly when the altitude is higher than 2000 m. (3) Dust reduces the CR of FY-2F/CTA and increases their WR and MR but has a relatively minor impact on the identification of cloud and non-cloud. (4) Under different cloud cover levels, the PR and EIs of FY-2F/CTA are directly proportional to the amount of TCC, while the CR is inversely proportional to it: that is, the CR is higher and the PR and EIs are lower under clear-sky and partly cloudy conditions, and the CR is lower and the PR and EIs are higher under cloudy and overcast conditions. This study assessed the FY-2F/CTA under various conditions in arid areas of Xinjiang, including complex underlying surface, various temperature and altitude, dust effects, and different cloud cover levels. Thus, the research finding could serve as a valuable reference for satellite-based retrieval and applications related to TCC in arid regions.

Experimental Study of Water Vapor Adsorption on Bare Soil and Gravel Surfaces in an Arid Region of Ningxia, China

Water vapor adsorption on soil, a crucial non-rainfall water resource in arid regions, warrants further experimental investigation, particularly on two typical land surfaces: bare soil and gravel. This study examined the formation characteristics and influencing factors of vapor adsorption in an arid region of Northwestern China. Observations and analyses were conducted on adsorption and evaporation measurements taken by two small weighing lysimeters (SLSs); soil temperature at a depth of 5 cm; surface temperature; relative humidity; and air temperature at a height of 30 cm above the ground from 2019 to 2020. The adsorbed water in this area was more abundant at night and less abundant during the day, with a stable nightly adsorption rate of 0.013 mm/h. Adsorption was more frequent in spring and winter (from January to June and November to December), accounting for about 90% of the total annual adsorption. In 2019 and 2020, the ratio values of adsorption to evaporation were 0.16 and 0.10 for bare soil, and 0.10 and 0.12 for gravel, respectively. Adsorption was more likely to occur when the soil moisture content was less than 13%; the highest adsorption frequency was close to 20% when the RH was between 75 and 95%; low soil temperatures were more conducive to the occurrence of adsorption. The effect of temperature differences (Ta−Ts) on adsorption was stronger than that of relative humidity. The adsorption frequency generally showed a bimodal change with increasing temperature difference, but the effect of temperature differences was less effective for gravel than bare soil. When the relative humidity was high and the temperature difference was weakly positive, the maximum adsorption intensity could reach 0.18 mm/h.

Impact of climate change on vegetation patterns in Altay Prefecture, China.

Altay Prefecture, a typical arid region in northwestern China, has experienced the climate transition from warming-drying to warming-wetting since 1980s and has attracted widespread attention. Nonetheless, it is still unclear how climate change has influenced the distribution of vegetation in this region. In this paper, a reaction-diffusion model of the climate-vegetation system is proposed to study the impact of climate change (precipitation, temperature and carbon dioxide concentration) on vegetation patterns in Altay Prefecture. Our results indicate that the tendency of vegetation growth in Altay Prefecture improved gradually from 1985 to 2010. Under the current climate conditions, the increase of precipitation results in the change of vegetation pattern structures, and eventually vegetation coverage tends to be uniform. Moreover, we found that there exists an optimal temperature where the spot vegetation pattern structure remains stable. Furthermore, the increase in carbon dioxide concentration induces vegetation pattern transition. Based on four climate change scenarios of the Coupled Model Intercomparison Project Phase 6 (CMIP6), we used the power law range (PLR) to predict the optimal scenario for the sustainable development of the vegetation ecosystem in Altay Prefecture.

Redescription of two species and a new distribution record for China of the genus MelanogryllusChopard, 1961 and a report of one new species of the genus Velarifictorus Randell, 1964 (Orthoptera: Gryllidae; Gryllinae).

Dark body color is very common among crickets, and this article discusses four species of black field crickets with distinct distributions. There are three species of the genus Melanogryllus Chopard, 1961 and one species of the genus Velarifictorus Randell, 1964. Of them, Melanogryllus chopardi Bey-Bienko, 1968 was discovered in Southwest Xizang, on the border between China and Nepal; Melanogryllus desertus (Pallas, 1771) was primarily found in arid regions of northwestern China; Melanogryllus bilineatus Yang & Yang, 1994 was often collected from the Southeast China coastal region; and the last species, Velarifictorus yuanilandrevus sp. nov., is a new species that was collected in Yunnan, a province in Southwest China. In addition, the new species could be distinguished from the others by its black body coloration and the absence of yellow stripes on the head. Here, we describe these species in detail, with photographs of the genitalia, and provide a distribution map for them and keys for Chinese Melanogryllus species.

A new model for simulating root water uptake by vegetation under the impact of a dynamic groundwater table in arid regions

AbstractEcological water conveyance is an effective measure to mitigate or reverse vegetation ecosystem degradation in arid regions, which can lead to frequent fluctuations in the groundwater table. The depth of soil water that vegetation takes up varies in response to groundwater table fluctuations in arid environments. To better characterize the root water uptake process under dynamic changes in the groundwater table in arid regions, this study proposed a new model for simulating root water uptake. The model reduces the dominant effect of root density on water uptake by introducing a correction factor and accounts for the effect of changes in the water content profile on root water uptake in arid areas. The new model was incorporated into the HYDRUS code and tested against the monitoring data of typical vegetation in the arid region of northwestern China. The results demonstrated that the soil water content simulated by the new model matched well with the observed data, which was consistent with the water uptake process under the fluctuations of the groundwater table at the study site. Compared with other models, this model can flexibly alter water uptake layers according to soil moisture conditions in arid conditions, thus providing a new method to depict the dynamic process of water uptake influenced by fluctuations in the groundwater table.

Partitioning Evapotranspiration in a Cotton Field under Mulched Drip Irrigation Based on the Water-Carbon Fluxes Coupling in an Arid Region in Northwestern China

Measuring evapotranspiration (ET) components in cotton fields under mulched drip irrigation is needed to improve water use efficiency and promote the development of water-saving agriculture. In this study, an Eddy Covariance (EC) system was used to observe the water-carbon fluxes of cotton fields under mulched drip irrigation in an arid region during two years (2021–2022). The Underlying Water Use Efficiency (uWUE) method was used to partition the ET into transpiration (T) and evaporation (E) in order to reveal the changing characteristics of ET and its components in cotton fields under mulched drip irrigation and analyze the effects of environmental factors on each component. The results showed that the diurnal variation of ET was the same as gross primary productivity (GPP), and their course of change showed a bimodal curve at budding, blooming, and boll stages. The relationship of T at different growth stages was the same as ET, which is blooming and boll stage > budding stage > boll opening stage > seedling stage. ET and its components were mainly affected by temperature (Tair) and net radiation (Rn). This study can provide a theoretical and practical basis for the application of uWUE in cotton fields under mulched drip irrigation and a scientific basis for the rational allocation of water resources and the formulation of a scientific water-saving irrigation system for farmland in an arid region.

Accelerated Restoration of Vegetation in Wuwei in the Arid Region of Northwestern China since 2000 Driven by the Interaction between Climate and Human Beings

The Wuwei area in the arid region of northwestern China is impacted by the harsh natural environment and human activities, and the problem of ecological degradation is severe there. In order to ensure the sustainable development of the regional social economy, it is necessary to monitor the changes in vegetation in Wuwei and its corresponding nonlinear relationships with climate change and human activities. In this study, the inter-annual and spatial–temporal evolution characteristics of vegetation in Wuwei from 1982 to 2015 have been analyzed based on non-parametric statistical methods. The analysis revealed that the areas of vegetation restoration and degradation accounted for 77 and 23% of the total area of the research area, respectively. From 1982 to 1999, vegetation degradation became extremely serious (14.4%) and was primarily concentrated in Gulang County and the high-altitude areas in the southwest. Since the ecological restoration project was implemented in 2000, there have been prominent results in vegetation restoration. The geographically and temporally weighted regression model shows that each climate factor has contributed to the vegetation restoration in the Wuwei area during the last 34 years, with their contributions ranked as precipitation (71.2%), PET (43.9%), solar radiation (34.8%), temperature (33.1%), and wind speed (31%). An analysis of the land-use data with 30 m resolution performed in this study revealed that the conversion area among land cover from 1985 to 2015 accounts for 14.9% of the total area. In it, the conversion area from non-ecological land to ecological land accounts for 5.7% of the total area. The farmland, grassland, and woodland areas have increased by 20.1, 20.6, and 8.5%, respectively, indicating that human activities such as agricultural intensification and ecological restoration projects have played a crucial role in vegetation restoration.

The Distribution and Influencing Factors of Hypolithic Microbial Communities in the Hexi Corridor.

The Hexi Corridor is an arid region in northwestern China, where hypoliths are widely distributed, resulting from large amounts of translucent stone pavements. In this region, the water and heat distributions are uneven, with a descent gradient from east to west, which can affect the area's biological composition. The impact of environmental heterogeneity on the distribution of hypolithic microbial communities in this area is poorly understood, and this is an ideal location to investigate the factors that may influence the composition and structure of hypolithic microbial communities. An investigation of different sites with differences in precipitation between east and west revealed that the colonization rate decreased from 91.8% to 17.5% in the hypolithic community. Environmental heterogeneity influenced both the structure and function of the hypolithic community, especially total nitrogen (TN) and soil organic carbon (SOC). However, the effect on taxonomic composition was greater than that on ecological function. The dominant bacterial phyla in all sample sites were Cyanobacteria, Actinobacteria, Proteobacteria, and Deinococcus-Thermus, but the abundances varied significantly between the sampling sites. The eastern site had the highest relative abundance of Proteobacteria (18.43%) and Bacteroidetes (6.32%), while the western site had a higher relative abundance in the phyla Cyanobacteria (62%) and Firmicutes (1.45%); the middle site had a higher relative abundance of Chloroflexi (8.02%) and Gemmatimonadetes (1.87%). The dominant phylum in the fungal community is Ascomycota. Pearson correlation analysis showed that the soil's physicochemical properties were also associated with changes in community diversity at the sample sites. These results have important implications for better understanding the community assembly and ecological adaptations of hypolithic microorganisms.

Timing and water temperature of drip irrigation regulate cotton growth and yield under film mulching in arid areas of Xinjiang.

Cotton (Gossypium hirsutum L.) is the fiber crop most widely cultivated globally and one of the most important commercial crops in China, irrigation is closely related to the growth of cotton. A water temperature for irrigation that is too low or too high inhibits cotton growth. Poor irrigation timing results in water and nutrient deficiencies that reduce cotton yield. Therefore, it is necessary to determine the appropriate irrigation timing and water temperature. We conducted an experiment in an arid region of northwestern China to assess the effects of irrigation timing and water temperature on soil temperature and the photosynthetic characteristics, biomass, total nitrogen (N), and seed cotton yield. Two irrigation times (daytime and nighttime) and four water temperatures (15, 20, 25, and 30 °C) were combined into eight treatments. Our results showed that water warming and nighttime irrigation improved the photosynthesis, biomass, N concentration (the proportion of total N weight in the plant biomass, g kg-1), N content (the mass of total N, g plant-1), and cotton yield. The optimal water temperature range for photosynthesis was 25.7-28.7 °C. Water warming also boosted the biomass allocation to the stem and increased the N allocation to the stem and leaf. Nighttime irrigation enhanced these phenomena. Water warming also increased the number of bolls per plant but reduced the single boll weight, increasing the seed cotton yield by 5.88%-11.46%. At the same water temperature, irrigation during the night increased the number of bolls per plant and the single boll weight, improving the seed cotton yield by 2.95%-4.31%. Among them, NI25 (nighttime irrigation with 25 °C water temperature) increased the yield by 14.13%-14.90% compared with CK (daytime irrigation with 15 °C water temperature), which offers the best combination for increasing the yield. Our study clarifies the optimal irrigation timing and water temperature for cotton production under drip irrigation with film mulching, providing valuable information for improving the cotton yield in arid areas with temperate continental climate. This article is protected by copyright. All rights reserved.

Plant DNA barcode library for native flowering plants in the arid region of northwestern China.

DNA barcoding is a well-established tool for rapid species identification and biodiversity monitoring. A reliable and traceable DNA barcode reference library with extensive coverage is necessary but unavailable for many geographical regions. The arid region in northwestern China, a vast area of about 2.5 million km2 , is ecologically fragile and often overlooked in biodiversity studies. In particular, DNA barcode data from the arid region in China are lacking. We develop and evaluate the efficacy of an extensive DNA barcode library for native flowering plants in the arid region of northwestern China. Plant specimens were collected, identified and vouchered for this purpose. The database utilized four DNA barcode markers, namely rbcL, matK, ITS and ITS2, for 1816 accessions (representing 890 species from 385 genera and 72 families), and consisted of 5196 barcode sequences. Individual barcodes varied in resolution rates: species- and genus-level rates for rbcL, matK, ITS and ITS2 were 79.9%-51.1%/76.1%, 79.9%-67.2%/88.9%, 85.0%-72.0%/88.2% and 81.0%-67.4%/84.9%, respectively. The three-barcode combination of rbcL + matK + ITS (RMI) revealed a higher species- and genus-level resolution (75.5%/92.1%, respectively). A total of 110 plastomes were newly generated as super-barcodes to increase species resolution for seven species-rich genera, namely Astragalus, Caragana, Lactuca, Lappula, Lepidium, Silene and Zygophyllum. Plastomes revealed higher species resolution compared to standard DNA barcodes and their combination. We suggest future databases include super-barcodes, especially for species-rich and complex genera. The plant DNA barcode library in the current study provides a valuable resource for future biological investigations in the arid regions of China.

Impacts of climate change on the wetlands in the arid region of Northwestern China over the past 2 decades

Climate change has caused inland wetlands shrinkage and exacerbated problems, such as sustainable development and ecological security, for years. These issues are mainly pronounced in the inland arid area. The ecological environment’s deterioration is especially severe in the drylands of the interior. However, dryland wetland changes and their response to climate are poorly understood. This study uses the K-means algorithm in Google Earth Engine (GEE) to classify two typical dryland wetlands (Ebinur and Bosten Lakes) for rapidly and accurately detecting dryland wetland changes. Moreover, it explores the long-term spatial–temporal variation in wetland distribution. In addition, it investigates the response of various lakes to climate change in northern and southern Xinjiang using wavelet analysis. The study’s results showed that K-means clustering in the GEE platform has a high classification accuracy (Kappa > 0.8) in wetland classification, making it a feasible approach. The terminal lake wetland types, represented by the Ebinur Lake, changed significantly between 2001 and 2021. In contrast, the inflow-outflow lake wetland types, represented by the Bosten Lake, perform more consistently. Significant spatial–temporal variation is observed at Ebinur Lake, with the lake gradually shrinking and transforming into a marsh, where the largest marsh proportion degrades into non-wetland during the year. Bosten Lake experienced frequent conversions between marsh and non-wetland throughout the year. Furthermore, the responses of various dryland lakes to climate change are consistent, and a low precedes precipitation and follows evapotranspiration. However, their sensitivity to climate response varies, with the terminal lake being most affected by climate change. Mastering the dynamic changes and climate response of dryland wetlands achieves the sustainable development goals of drylands, including carbon neutrality and peak carbon dioxide emissions.

Assessment of Fungal Diversity in Minqin County, a Typical Arid Region in Northwestern China.

Minqin County is located in the Shiyang River Basin. As a typical arid area, it is eroded by the Badain Jaran and Tengger Desert all year round, and knowledge of the fungal diversity in this area is limited. Therefore, fungal community structure and distribution in the soil of the artificial forest, desert transition zone, farmland, and desert were investigated using amplicon sequencing of the fungal ITS gene. Ten fungal phyla and 23 classes were identified, including 1131 fungi OTUs, Sordariomycetes, Dothideomycetes, Pezizomycetes, and Agaricomycetes were the most abundant classes. Although most OTUs are shared among habitats, fungal community composition among samples was highly variable, which may influence the design of restoration practices in this area.

Accuracy Performance of Three 10-m Global Land Cover Products Around 2020 in an Arid Region of Northwestern China

Accuracy Performance of Three 10-m Global Land Cover Products Around 2020 in an Arid Region of Northwestern China

Study of the Flood Frequency Based on Normal Transformation in Arid Inland Region: A Case Study of Manas River in North-Western China

Flood disaster is one of the natural disasters which cause the most serious economic losses, the most casualties, and the greatest social impact. Flood frequency analysis is very important for reducing flood disaster. In this paper, based on the flood data of Manas River and tools of Box–Cox and Johnson normal transformation, the nonparametric statistical method for flood frequency analysis is studied in order to analyze the adaptability between it and the rivers in arid region of north-western China. The calculation result of the fitness index is divided into two parts: high flood discharge and low flood discharge. One of the two evaluation indexes has an advantage in fitting, and the number of advantages of the three methods in each part has been counted. After analysis, for the flood peak discharge frequency of rivers in arid region of north-western China, the frequency curve of Johnson transformation fits best with empirical data. The high flood discharge advantage is 6, and the low flood discharge is 4. For the flood volume frequency of rivers in arid region of north-western China, Box–Cox transform fits well with empirical data at the high flood discharge frequency curve, and its advantage is 12; Johnson transformation has a better fit between the low flood discharge frequency curve and empirical data, and its advantage is 12. Therefore, it is the way of improving the precision of flood frequency analysis to use the method of P-III distribution and normal transformation comprehensively.

Evolution and Climate Drivers of NDVI of Natural Vegetation during the Growing Season in the Arid Region of Northwest China

Vegetation plays an important role in linking water, atmosphere, and soil. The dynamic change in vegetation is an important indicator for the regulation of the terrestrial carbon balance and climate change. This study applied trend analysis, detrended correlation analysis, and the Hierarchical Partitioning Algorithm (HPA) to GIMMS NDVI3g data, meteorological data, and natural vegetation types for the period 1983 to 2015 to analyze the temporal and spatial changes in NDVI during the growing season and its driving factors in the arid region of northwestern China. The results showed that: (1) the growing season length (GSL) was delayed, with a regional trend of 8 d/33 a, due to a significant advancement in the start of the growing season (SOS, −7 d/33 a) and an insignificant delay to the end of growing season (EOS, 2 d/33 a). (2) The regional change in NDVI was mainly driven by temperature and precipitation, contributing to variations in NDVI of forest of 36% and 15%, respectively, and in the NDVI of grassland, of 35% and 21%, respectively. In particular, changes to forested land and medium-coverage grassland (Mgra) were closely related to temperature and precipitation, respectively. (3) The spatial distribution of the mean NDVI of forest was closely related with precipitation, temperature, and solar radiation, with these meteorological variables explaining 20%, 15%, and 10% of the variation in NDVI, respectively. Precipitation and solar radiation explained 29% and 17% of the variation in the NDVI of grassland, respectively. The study reveals the spatial–temporal evolution and driving mechanism of the NDVI of natural vegetation in the arid region of Northwest China, which can provide theoretical and data support for regional vegetation restoration and conservation.

Effects of organic fertilizer proportion on the distribution of soil aggregates and their associated organic carbon in a field mulched with gravel

Gravel and sand mulching is an indigenous technology that has been used for increasing soil temperature and improving crop yield and water use efficiency for at least 300 years in northwestern China. However, long-term application of inorganic fertilizer with gravel and sand mulch could decrease the soil organic carbon content, and how to improve soil fertility under gravel and sand mulching remains largely unknown. Thus, we evaluated the effects of the application of inorganic (chemical) and organic (manure) fertilizers on the distribution of soil aggregates and their associated organic carbon in a field mulched with gravel and sand. A 5-year (2014–2018) field experiment was conducted in the arid region of northwestern China. Total organic carbon (TOC), permanganate oxidizable carbon (POC), TOC reserves in soil aggregates with different particle sizes, and watermelon (Citrullus lanatus) productivity in gravel-mulched fields were analysed for the following six fertilization modes: no N fertilizer input as a control (CK), N fertilizer without organic fertilizer (CF), and organic fertilizer replacing 25%, 50%, 75%, and 100% of mineral nitrogen (recorded as OF-25%, OF-50%, OF-75% and OF-100%, respectively). The results showed that, higher manure to nitrogen fertilizer ratios were positively correlated with the percentage of soil macroaggregates (> 0.25 mm), mean weight diameter (MWD), TOC and POC concentrations, and their ratios in different particle sizes. Compared with CF, the treatments with 50% to 100% organic fertilizer significantly increased TOC storage (5.91–7.84%) in the soil profile (0–20 cm). Moreover, the CF treatment did not increase SOC concentrations or TOC storage, compared with CK. The fruit yield (2014–2018) of watermelon significantly increased by an average of 31.38% to 45.70% in the treatments with 50% to 100% organic fertilizer, respectively, compared with CF. Our results suggest that the partial replacement of chemical fertilizer with organic manure (OF-50%, OF-75% and OF-100%) could increase the proportion of macroaggregates, POC and TOC concentrations, and TOC stock in aggregates with different particle size and improve the yield of watermelon in the gravel fields of arid northwestern China mulched with gravel and sand.

Impacts of Gauge Data Bias on the Performance Evaluation of Satellite-Based Precipitation Products in the Arid Region of Northwestern China

It has been reported that systematic bias exists in gauge measurements, which are usually used as the evaluation benchmark, so it is crucial to investigate the impacts of gauge data bias on the evaluation of satellite precipitation products. Six satellite precipitation products (IMERG, CMORPH, GSMaP, PERSIANN, PERSIANN−CCS, and PDIR−Now) and gauge data are collected from 2003 to 2015 in the arid region of Northwestern China. A daily correction for precipitation biases from wind-induced undercatch, wetting loss, and trace error is made for gauge measurements. The changes in metrics, including four continuous and four categorical metrics, are calculated to illustrate how the gauge data bias impacts the evaluation of six satellite precipitation products. The results show the following: The overall performances of six satellite precipitation products are undervalued by the gauge bias. Compared to other satellite products, the performance of IMERG is the best, whether before or after bias correction. However, the performances of all six satellite products are still not good enough even after bias correction and need to be improved. The impacts of gauge bias on the evaluation of the satellite precipitation products also differ by subregion, season, satellite precipitation product, precipitation intensity, and precipitation phase. In conclusion, the impacts of the gauge bias on the performance assessment of satellite products are obvious over the study region, implying that bias correction for gauge measurements is needed to obtain an accurate understanding of the performance of satellite precipitation products if choosing the gauge data as the evaluation benchmark.