Spatiotemporal variability of rain-on-snow events in the arid region of Northwest China

Rain-on-snow(ROS)events involve rainfall on snow surfaces,and the occurrence of ROS events can exacerbate water scarcity and ecosystem vulnerability in the arid region of Northwest China(ARNC).In this study,using daily snow depth data and daily meteorological data from 68 meteorological stations provided by the China Meteorological Administration National Meteorological Information Centre,we investigated the spatiotemporal variability of ROS events in the ARNC from 1978 to 2015 and examined the factors affecting these events and possible changes of future ROS events in the ARNC.The results showed that ROS events in the ARNC mainly occurred from October to May of the following year and were largely distributed in the Qilian Mountains,Tianshan Mountains,Ili River Valley,Tacheng Prefecture,and Altay Prefecture,with the Ili River Valley,Tacheng City,and Altay Mountains exhibiting the most occurrences.Based on the intensity of ROS events,the areas with the highest risk of flooding resulting from ROS events in the ARNC were the Tianshan Mountains,Ili River Valley,Tacheng City,and Altay Mountains.The number and intensity of ROS events in the ARNC largely increased from 1978 to 2015,mainly influenced by air temperature and the number of rainfall days.However,due to the snowpack abundance in areas experiencing frequent ROS events in the ARNC,snowpack changes exerted slight impact on ROS events,which is a temporary phenomenon.Furthermore,elevation imposed lesser impact on ROS events in the ARNC than other factors.In the ARNC,the start time of rainfall and the end time of snowpack gradually advanced from the spring of the current year to the winter of the previous year,while the end time of rainfall and the start time of snowpack gradually delayed from autumn to winter.This may lead to more ROS events in winter in the future.These results could provide a sound basis for managing water resources and mitigating related disasters caused by ROS events in the ARNC.

Research Advances in Allelopathy of Plants in Arid Desert Regions of Northwest China

To investigate allelopathy of plants in desert ecosystems, related research achievements obtained in recent years, reported allelopathic plants, allelochemicals and releasing ways of alleochemicalds were summarized, and then the key problems of research into allelopathic plants in desert ecosystems were indicated. It was considered that the research of allelopathy of plants in desert regions has just started in China, and plants with atlelopathic potential were found in the Compositae, Leguminosae, Rosaceae, Scrophulariaceae and Gramineae; plants in desert regions re- lease allelochemicals mainly via natural volatilization, which is closely related to their growing environment; allelochemicals such as alkaloids, fla- vonoids, terpenoids have been identified. This study can provide theoretical basis and practical value for reasonable adoption of protection meas- ures of desert plants and comprehensive control of desertification.

Hydrological and water cycle processes of inland river basins in the arid region of Northwest China

The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China(ARNC). Water shortages also affect the stability of the region's oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources(including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that:(1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains;(2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains;(3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and(4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.

Influence of climate change and human activity on water resources in arid region of Northwest China: An overview

This study reviews the latest progress in research on climate change and water resources in the arid region of Northwest China, analyzes the cause of water resource changes within the region from the perspective of climate change and human activities, and summarizes future likely changes in water resources and associated adaptation strategies. The research shows that the climate in the region has experienced warming and wetting with the most significant warming in winter and the highest increase in summer precipitation since 1961. Areas with the most significant warming trends include the Qaidam Basin, the Yili River Valley, and Tacheng. Spatially, the increasing trend in precipitation becomes increasingly significant from the southeast to the northwest, and northern Xinjiang experienced the highest increase. Studies have shown a decrease in headwater of Shiyang River because runoff is mainly based on precipitation which shows a decrease trend. But an increase in western rivers was observed such as Tarim River and Shule River as well as Heihe River due to rapid glacier shrinkage and snowmelt as well as precipitation increase in mountain area. Meanwhile unreasonable human activities resulted in decrease of runoff in the middle and lower reaches of Haihe River, Shiyang River and Kaidu River. Finally, recommendations for future studies are suggested that include characteristics of changes in extreme weather events and their impacts on water resources, projections of future climate and water resource changes, climate change attribution, the selection of adaptation strategies relating to climate change and social economic activities, and use of scientific methods to quantitatively determine water resource allocation.

Analysis on the Correlated Characteristics between Spring Precipitation in the Arid Region of Northwest China and Global Sea Surface Temperature

[Objective] The research aimed to study the correlated characteristics between spring precipitation in the arid region of Northwest China and global sea surface temperature. [Method] Based on GPCP global monthly precipitation data and NOAA ERSST sea surface temperature data during 1979-2008, the precipitation characteristics in the arid region of Northwest China in 30 years and its correlated distribution characteristics with the global sea surface temperature were analyzed by using the correlation and composite analysis methods. [Result] Spring rainfall presented the fluctuation increasing in the arid region of Northwest China during 1979-2008. The sea surface temperature of Indian Ocean in 15° S-22° N, 45°-105° E had the continuous influence on spring precipitation in the arid region of Northwest China. It could be as a stable factor for forecasting spring precipitation in the arid region zone of Northwest China. When the sea surface temperature was higher in Indian Ocean, Bay of Bengal and Arabian Sea, maybe spring precipitation in the arid region of Northwest China was more. If the sea surface temperature in the equatorial Eastern Pacific Ocean in prior summer, autumn and winter was higher, it was favorable for spring precipitation in the arid region of Northwest China in the next year. The sea surface temperature field in Arabian Sea, Central Indian Ocean and Western Pacific Ocean was the key factor which affected spring precipitation in the arid region of Northwest China. [Conclusion] The research provided the theory basis for the prediction and forecast of precipitation in the arid region.

Responses of phreatophyte transpiration to falling water table in hyper-arid and arid regions,Northwest China

Quantitative assessment of the impact of groundwater depletion on phreatophytes in(hyper-)arid regions is key to sustainable groundwater management.However,a parsimonious model for predicting the response of phreatophytes to a decrease of the water table is lacking.A variable saturated flow model,HYDRUS-1D,was used to numerically assess the influences of depth to the water table(DWT)and mean annual precipitation(MAP)on transpiration of groundwater-dependent vegetation in(hyper-)arid regions of northwest China.An exponential relationship is found for the normalized transpiration(a ratio of transpiration at a certain DWT to transpiration at 1 m depth,T_(a)^(*))with increasing DWT,while a positive linear relationship is identified between T_(a)^(*)and annual precipitation.Sensitivity analysis shows that the model is insensitive to parameters,such as saturated soil hydraulic conductivity and water stress parameters,indicated by an insignificant variation(less than 20%in most cases)under±50%changes of these parameters.Based on these two relationships,a universal model has been developed to predict the response of phreatophyte transpiration to groundwater drawdown for(hyper-)arid regions using MAP only.The estimated T_(a)^(*)from the model is reasonable by comparing with published measured values.

Potential risks and challenges of climate change in the arid region of northwestern China

In the arid region of northwestern China(ARNC),water resources are the most critical factor restricting socioeconomic development and influencing the stability of the area’s ecological systems.The region’s complex water system and unique hydrological cycle show distinctive characteristics.Moreover,the intensified hydrological cycle and extreme climatic and hydrological events resulting from global warming have led to increased uncertainty around water resources as well as heightened conflict between water supply and water demand.All of these factors are exerting growing pressures on the socioeconomic development and vulnerable ecological environment in the region.This research evaluates the impacts of climate change on water resources,hydrological processes,agricultural system,and desert ecosystems in the ARNC,and addresses some associated risks and challenges specific to this area.The temperature is rising at a rate of 0.31
C per decade during 1961–2017 and hydrological processes are being significantly influenced by changes in glaciers,snow cover,and precipitation form,especially in the rivers recharged primarily by melt water.Ecosystems are also largely influenced by climate change,with the Normalized Difference Vegetation Index(NDVI)of natural vegetation exhibited an increasing trend prior to 1998,and then reversed in Xinjiang while the Hexi Corridor of Gansu showed the opposite trends.Furthermore,the desert-oasis transition zone showed a reduction in area due to the warming trend and the recent rapid expansion of irrigated area.Both the warming and intensified drought are threatening agriculture security.The present study could shed light on sustainable development in this region under climate change and provides scientific basis to the construction of the“Silk Road Economic Belt”.

Revisit of event-based rainfall characteristics at Shapotou area in northern China

Distribution of rainfall event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosystem dynamics in these regions. Rainfall event timing and magnitude are important drivers of ecosystem processes and are instrumental in creating land-scape heterogeneity in arid and semi-arid regions. Rainfall event characteristics were analyzed using an automatic tip-ping-bucket rain-gauge record across the entire summer monsoon season from 2008 to 2015 at the arid desert area of Shapotou in the Tengger Desert, China. Changing the minimum inter-event time （MIT） from 30 min to 24 h alters the number of rainfall events from 64 to 25 for the event depth larger than 0.1 mm. The mean rainfall intensity declined from 0.95 mm/h to 0.53 mm/h, and the geometric mean event duration rose from 0.55 h to 4.4 h. The number of rainfall events, mean rainfall intensity, and geometric mean event duration differed under different criteria of individual rainfall depths, except that for an individual rainfall depth of 0.5, 1.0, and 5.0 mm. The aforementioned features differed only at the lowest range of the mean rainfall intensity and depth for MIT=3 and 6 h. These findings suggest that identification of event-based rainfall in this specific arid region can be better achieved by setting the MIT at six hours. The wide variation in rainfall event properties indicate the need for paying more attention to the proper selection and reporting of event criteria in studies that adopt event-based data analysis. This is especially true in quantifying effective rainfall for soil water replenishment in terms of rainfall depth and intensity with infrequent rainfall events.

2005-2020年亚洲中部干旱区生态站月潜在蒸散量数据集

潜在蒸散表征大气蒸发能力,是衡量区域蒸发能力的重要指标,也是评价气候干旱程度变化、水资源供需平衡、植被耗水量等的关键参数。在收集中亚生态系统监测网络12个生态站和中国生态系统研究网络(CERN)11个位于西北干旱区生态站的气象观测数据基础上,经过数据质量控制与插补,采用Penman-Monteith模型计算潜在蒸散量,生成了2005-2020年亚洲中部干旱区生态站月潜在蒸散量数据集。本数据集时间序列较长、覆盖多种生态系统类型,可作为亚洲中部干旱问题研究的基础数据、模型输入数据、模拟结果验证数据等,也可为该区域水资源的合理开发与利用、生态环境保护等方面研究提供数据支撑。

Climatic Warming and Humidification in the Arid Region of Northwest China: Multi-Scale Characteristics and Impacts on Ecological Vegetation

The climatic warming and humidification observed in the arid region of Northwest China(ARNC) and their impacts on the ecological environment have become an issue of concern. The associated multi-scale characteristics and environmental responses are currently poorly understood. Using data from satellite remote sensing, field observations, and the Coupled Model Intercomparison Project phase 6, this paper systematically analyzes the process and scale characteristics of the climatic warming and humidification in the ARNC and their impacts on ecological vegetation. The results show that not only have temperature and precipitation increased significantly in the ARNC over the past 60 years, but the increasing trend of precipitation is also obviously intensifying. The dryness index, which comprehensively considers the effects of precipitation and temperature, has clearly decreased, and the trend in humidification has increased. Spatially, the trend of temperature increase has occurred over the entire region, while 93.4% of the region has experienced an increase in precipitation, suggesting a spatially consistent climatic warming and humidification throughout the ARNC. Long-term trends and interannual changes in temperature and precipitation dominate the changes in climatic warming and humidification. Compared to interannual variations in temperature, the trend change of temperature contributes more to the overall temperature change. However, the contribution of interannual variations in precipitation is greater than that of the precipitation trend to the overall precipitation change. The current climatic warming and humidification generally promote the growth of ecological vegetation. Since the 1980 s,82.4% of the regional vegetation has thrived. The vegetation index has a significant positive correlation with precipitation and temperature. However, it responds more significantly to interannual precipitation variation, although the vegetation response varies significantly under different types of land use. The warming and humidification of the climate in the ARNC are probably related to intensifications of the westerly wind circulation and ascending air motions.They are expected to continue in the future, although the strength of the changes will probably be insufficient to significantly change the basic climate pattern in the ARNC. The results of this study provide helpful information for decision making related to China's "Belt and Road" development strategies.

Response of runoff to change of atmospheric 0℃ level height in summer in arid region of Northwest China

Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China(ARNC),the change trends,abrupt change points,and their significance of runoff and 0℃ level height(FLH) were analyzed in ARNC in the last 50 years by using Mann-Kendall(MK) nonparametric test,and the quantitative relationship between runoff and FLH in summer was also analyzed with the linear regression and elastic coefficient methods.The results are indicated as follows:(1) in recent 50 years,there is a similar changing trend between the summer runoff and FLH in ARNC and each region has its own unique feature.The summer runoff has been significantly ascending in the Tianshan Mountains and on the northern slope of the Qilian Mountains(NSQM) compared to that of the northern slope of the Kunlun Mountains(NSKM).Likewise,the FLH has been taking on a markedly rising trend on the northern slopes of the Tianshan and Qilian Mountains(NSTM and NSQM) in comparison with the southern slope of the Tianshan Mountains(SSTM).However,the FLH on NSKM has been decreasing with the speed of 2.33 m every year.(2) Abrupt change analysis indicates that the period of abrupt change happened for summer runoff and FLH is totally different among the four typical study regions,and even in same region.(3) There is a positive significant relation between the summer runoff and FLH in ARNC(NSQM P <0.05;other three regions P <0.01).Therefore,the ascending and descending of the summer FLH is a vital factor inducing the change of summer runoff in ARNC.(4) The elastic coefficient of summer runoff to the change of summer FLH on NSKM,NSTM,NSQM,and SSTM are 7.19,3.80,2.79,and 6.63,respectively,which indicates that there exists the regional difference in the sensibility of summer runoff to the change of summer FLH in ARNC.The distinct proportion of glacial meltwater runoff is an important cause resulting in the regional difference of sensibility.

A Study of the Atmospheric Boundary Layer Structure During a Clear Day in the Arid Region of Northwest China

The local climate and atmospheric circulation pattern exert a clear influence on the atmospheric boundary layer （ABL） formation and development in Northwest China. In this paper, we use field observational data to analyze the distribution and characteristics of the ABL in the extremely arid desert in Dunhuang, Northwest China. These data show that the daytime convective boundary layer and night time stable boundary layer in this area extend to higher altitudes than in other areas. In the night time, the stable boundary layer exceeds 900 m in altitude and can sometimes peak at 1750 m, above which the residual layer may reach up to about 4000 m. The daytime convective boundary layer develops rapidly after entering the residual layer, and exceeds 4000 m in thickness. The results show that the deep convective boundary layer in the daytime is a pre-requisite for maintaining the deep residual mixed layer in the night time. Meanwhile, the deep residual mixed layer in the night time provides favorable thermal conditions for the development of the convective boundary layer in the daytime. The prolonged periods of clear weather that often occurs in this area allow the cumulative effect of the atmospheric residual layer to develop fully, which creates thermal conditions beneficial for the growth of the daytime convective boundary layer. At the same time, the land surface process and atmospheric motion within the surface layer in this area also provide helpful support for forming the particular structure of the thermal ABL. High surface temperature is clearly the powerful external thermal forcing for the deep convective boundary layer. Strong sensible heat flux in the surface layer provides the required energy. Highly convective atmosphere and strong turbulence provide the necessary dynamic conditions, and the accumulative effect of the residual layer provides a favorable thermal environment.

The hydrological linkage of mountains and plains in the arid region of northwest China

Mountain regions supply a large amount of fresh water for the people in arid and semiarid regions, however, there is great uncertainty of the water quantification from mountains to lower areas. In order to assess the hydrological significance of mountains and the hydrological linkage of mountains and plains, the measured and simulated hydrological data of the arid region in northwest China were used in the present research which followed a catchment-based approach. Firstly, the Heihe River Basin, a well-documented area, was selected as a specific watershed to reveal the hydrological relationship between highlands (mountains) and lowlands (plains); and then, the significance and disproportion of mountain runoff of 8 river basins as cases in the arid region of northwest China were analyzed and compared following the above analysis. The results of the study showed that the proportion of mountain runoff in total basinal runoff (PMR) of most rivers is above 50%. The PMR are between 50%-95% in the rivers originated in the northern slope of the Tianshan Mountains where the aqueous vapor is relatively sufficient. And that, almost all the flow of the rivers originating from the Qilian Mountains, the southern slope of the Tianshan Mountains, and the northern slope of the Kunlun Mountains come from mountain regions. Also the PMR gradually increases from west to east in northwest China. The hydrological significance and disproportion of mountains water in the arid region of northwest China were given a systematic and thorough assessment, and the results could give potential guides for the scientific utilization of water resources in these regional areas for relieving the more and more serious shortage of water resources due to climate warming and population expansion.

西北干旱区荒漠植物叶片和细根碳、氮、磷化学计量特征

植物的叶片和细根是植物地上部分和地下部分最重要的营养器官,其碳(C)、氮(N)、磷(P)化学计量特征反映了植物的养分限制状况及叶片与细根间的协同作用,开展叶片与细根化学计量关系的研究,对认识植物养分利用策略及元素间平衡关系有重要意义。对西北干旱区21种荒漠植物叶片与细根C、N、P含量进行了测定,分析了C、N、P含量及其计量比在不同生活型及不同器官间的关系。结果表明:1)西北干旱区荒漠植物叶片与细根C含量相对稳定,叶N、P含量高于细根,说明在干旱生境中,植物对养分的分配侧重于地上部分,以完成其正常的生命活动;叶片与细根的N∶P无显著差异,有明显的保守性,表明植物地上与地下部分养分吸收策略与分配规律具有一致性;2)不同生活型植物叶片和细根的C、N、P含量及C∶N、C∶P存在显著差异,灌木与禾草具有较高的C∶N和C∶P,杂类草具有较高的N、P含量,说明灌木与禾草倾向于保守型养分适应策略,杂类草倾向于快速生长的资源竞争策略;3)21种荒漠植物叶片与细根N、P含量间均存在显著的正相关关系,表明西北干旱区荒漠植物体内N、P元素间存在相互作用;4)植物叶片与细根间C、N、P含量及C∶N、C∶P存在等速生长关系,表明植物光合产物和养分在地上与地下部分间的分配具有平行的比例关系,但这种关系受生活型影响。上述结果表明西北干旱区不同生活型植物在恶劣生境中存在不同的养分适应策略,且地上与地下部分的养分利用策略及分配规律存在协同作用,这为进一步认识西北干旱区荒漠植物的养分利用策略提供了试验基础。

中国西北旱区砂田表层土壤养分效应对连作响应的整合分析

为明确砂田表层土壤养分对连作的响应规律,深入揭示砂田性能逐年退化机理,文章基于国内外已发表的16篇相关文献的586组有效数据,借助Meta-analysis方法进行整合定量研究,定量分析覆砂1—3年农田与其他连作年限砂田(4—6年、7—9年、10—12年、13—15年、16—20年)在表层土壤水分状况(SWC)、养分特性(有机质SOM、全氮TN、全磷TP、全钾TK、碱解氮AN、速效磷AP、速效钾AK、全盐TSS)和酸碱环境(pH)方面的差异效应,系统阐释砂田表层土壤养分特性逐年变异的发生路径及驱动因素,进而综合评估其肥力水平。结果表明:伴随种植年限的增加,砂田表层土壤水分储量和养分强度整体呈现下降态势(P<0.05),4—20年的土壤SWC、SOM、TN、TP、TK、AN、AP、AK含量分别较1—3年减少39.06%、14.21%、14.96%、10.06%、8.20%、15.87%、37.01%、18.60%(P<0.05)。表层土壤SOM、TN、TP、TK、AN、AP、AK主要于10—12年开始大幅流失(P<0.05),而4—6年土壤SOM、TP、TK、AK含量的相对变化则不显著(P>0.05)。砂田在耕作12年内具有显著压盐效果,12年以后的表层土壤TSS含量则开始呈现逐年增加的发展趋向(P<0.05),其土壤pH整体增加1.29%(P<0.05)。连作年限是砂田表层土壤TN、TP和AK变异的关键因子;SWC则为土壤SOM、AP和TSS演化的主导要素。总体而言,砂田在连作10年左右即可出现明显的养分亏缺状态。因此,亟需提出科学合理的农田管理措施,以有效提升退化砂田的土壤肥力水平。

西北干旱区气候变化对灌溉春玉米生产的影响

基于河西走廊中部1984-2022年灌溉春玉米定位观测试验,结合同期气象资料,采用线性回归、相关分析和M-K突变检验等方法,分析气候变化对西北干旱区灌溉春玉米生育期和产量的影响。结果表明:春玉米全生育期平均气温以0.76℃·10a^(-1)的速率呈极显著上升趋势(P<0.01)。≥10℃活动积温呈显著增加趋势,平均每10a增加135.80℃·d。全生育期降水量增加趋势不显著,但乳熟-成熟期以4.50mm·10a^(-1)的速率显著增加(P<0.05)。1984-2004年日照时数以126.88h·10a^(-1)的速率显著增多,近19a以109.38h·10a^(-1)的速率显著减少。1984-2004年春玉米生长期长度以9.86d·10a^(-1)的速率显著延长,近19a以7.39d·10a^(-1)的速率显著缩短。播种-出苗期和七叶-拔节期长度与气温呈显著负相关;播种-出苗期、三叶-七叶期和吐丝-乳熟期长度与降水量呈显著正相关;各生育期长度均与日照时数呈显著正相关。研究期内春玉米产量呈波动变化,气候产量与全生育期内降水量呈显著负相关。综上所述,西北干旱区气候变化对当前灌溉方式下的春玉米生产不利。

1981—2019年西北干旱区暖湿化分析

[目的]探究我国西北干旱区20世纪80年代以来的暖湿气候变化情况。[方法]利用国家气象数据中心发布的1981—2019年0.5°×0.5°气温和降水量月值格点资料,采用线性倾向率、Mann-Kendall检验、累积距平法,对近39年来该地区气温和降水时空演变特征进行研究。[结果]近39年来西北干旱区平均气温呈现显著上升趋势,气温倾向率为0.377℃/10 a(P<0.01),天山亚区增温趋势最大;各季节平均气温均呈显著增高趋势,春季增温趋势最大,冬季增温趋势最小,气温倾向率仅为0.121℃/10 a(P>0.05);年平均气温在1997年发生增温突变,进入21世纪增温趋势减缓。西北干旱区年降水量整体呈增加趋势,降水量倾向率为9.509 mm/10a(P<0.01),天山亚区增湿趋势最大,降水量倾向率为25.673 mm/10 a(P<0.01);四季均呈降水量增加趋势,夏季增加趋势最大,冬季降水量增加趋势相对较小;年降水量在2001年发生突变,降水量增加趋势明显。[结论]西北干旱区整体处于暖湿阶段,尤其天山亚区暖湿化最显著。

西北干旱区荒漠戈壁两次极端沙尘事件的对比研究

为深入理解极端沙尘暴事件的演变过程和驱动因子,结合多源卫星遥感及再分析数据,挑选2007年3月31日(“3·31”事件)和2021年3月14日(“3·14”事件)爆发于西北干旱区荒漠戈壁的两次沙尘暴事件,对比分析了其时空演变、高低空环流配置、近地面气象要素的变化。结果表明:(1)两次极端事件分别爆发于塔克拉玛干沙漠及戈壁荒漠,均受高低层天气系统影响。其中,“3·31”事件受地面冷锋和高空脊控制,脊前西北冷空气与地面冷锋引起的垂直运动配合,将沙尘往下游输送;而“3·14”事件则受蒙古气旋和高空槽影响,气旋后的偏北风和气旋引发的垂直运动将沙尘卷起至高层大气,并通过槽后西北风将其往下游输送;(2)两次极端沙尘事件均有持续时间长的特点,区别在于“3·31”事件主要受高压脊、均压场和周边地形影响,大气层结稳定,沙尘不易沉降和输送,而“3·14”事件则因中国北部持续性高压导致的偏南风和偏东风阻止了沙尘向下游扩散;(3)两次极端沙尘事件爆发前,塔克拉玛干和戈壁荒漠均出现了高温、降水减少及土壤水分枯竭现象,即强风和干燥土壤。为极端沙尘事件的爆发创造了有利的动力条件和物质基础。

西北干旱荒漠地区退耕还林还草工程综合效益评价

为对西北干旱荒漠地区新一轮退耕还林还草工程的实施提供科学指导,以吐鲁番市为研究区域,建立包含表征该区域特点的15个指标的综合效益评价指标体系,基于云模型与变异系数法组合确定指标权重,运用比重法无量纲化指标数据,采用加成综合法进行退耕工程综合效益评价分析,并通过灰色系统预测模型GM(1,1)对2021—2025年生态效益、经济效益、社会效益和政策响应指数进行了预测。结果表明:(1)在2004—2019年,综合效益指数逐年提高,新一轮退耕提升幅度是前一轮的两倍。(2)森林覆盖率提高、水土流失治理面积扩大、农民人均纯收入增加和人均林业产值增加,是生态效益和经济效益提高的主要因素。(3)退耕工程的实施促使产业结构和就业结构呈良性发展趋势。退耕所涉农户再退耕意愿的提升巩固了退耕成果,使其具有长效性。(4) 2021—2025年的生态效益、经济效益、社会效益和政策响应指数预测值均呈上升趋势,且经济效益指数>政策响应指数>生态效益指数>社会效益指数。依据预测结果,西北干旱荒漠地区在新一轮退耕工程的实施中应以生态建设为重点,加强生态补偿和乡村振兴战略的有效衔接,促进农业转移人口市民化,实现生态、经济、社会和政策响应间的协调发展。

砂土混合覆盖下的土壤水分蒸发特性及其因子分析

为明确不同砂土混合物覆盖对土壤蒸发过程的影响,基于土壤蒸发分阶段理论及微型蒸渗仪田间试验,深入探析了6种砂土混合覆盖模式(1.0,0.8,0.6,0.4,0.2,0,分别为M1~M6)下的土壤蒸发动态变化及其作用机制。结果表明:土壤蒸发分阶段理论能够真实刻画砂土混合覆盖下的土壤水分蒸发状况,其累计蒸发量可用砂土混合比与蒸发时间进行定量表征。当砂土混合比≥0.8时,土壤蒸发过程仅存在2个明显阶段,抑蒸效果显著;当砂土混合比<0.5时,M3~M6处理的土壤蒸发稳定高峰期明显,且集中于前2.53~2.66天,水分主要散失历时则分别较M1增加6.49,6.49,6.49,7.09天;而当砂土混合比介于0.5~0.8时,覆盖层易诱发且能够更早地形成结构致密的覆盖干层,整体保墒效果反而凸显。受土壤蒸发阶段特性及覆盖模式的影响,蒸发第1阶段主要受下垫面净辐射通量供应的限制;而在蒸发第2,3阶段,砂层结构的作用凸显,土壤水力特性调控效应逐渐占优。总之,砂层结构恶化将加快土壤失水过程,增加农田水分的无效损失,当砂土混合比<0.5时,其抑蒸保墒功效将逐渐丧失,这对西北旱区砂田退化机理的揭示及压砂地可持续健康发展具有现实意义。