陕西渭北旱塬苹果种植分区土壤水分特征研究

以渭北旱塬为研究对象，在区域尺度和定位观测的基础上，揭示了渭北不同苹果种植分区土壤水分特征。得出如下结论：(1)渭北旱塬不同苹果种植分区土壤水分特征主要受自然降水和苹果地蒸散量的影响。(2)3种类型区苹果地土壤水分都存在亏缺现象，台塬东部区苹果地土壤水分平均潜在亏缺量为390．9mm，最大亏缺量为674．6mm，最小亏缺量为186．3mm；高原沟壑区苹果地水分平均潜在亏缺量、最大亏缺量分别为264．4和441．2mm，有时也出现水分盈余的现象；台塬西部区总体上表现为亏缺．但苹果地出现水分盈余的现象较高原沟壑区普遍，最大盈余量达151．8mm；(3)渭北旱塬苹果地水分储存量也存在区域分异，2m土层水分储存量在全生育期是渭北台塬西部区大于渭北高原沟壑区大于渭北台塬东部区，土壤水分储存量的变化特性与降水量的时空变化、苹果树对土壤水分的利用量及降水年型有关；(4)3种类型区苹果地耗水量以台塬东部区最大，旱塬沟壑区次之，台塬西部区最小。干旱年苹果全生育期耗水量低于丰水年份。从耗水组分上看，苹果地耗水主要来源于生育期间的有效降水，但在干旱年份，耗水量还有相当一部分依赖深层土壤贮水，耗水深度超过3m，表明深层储水在干旱年份对苹果树生长所需水分的供给起着不可忽视的重要作用。     

Monitoring soil moisture dynamics using satellite imaging radar in northeastern Jordan

This paper describes how synthetic aperture radar (SAR) data from the European Environmental Remote Sensing (ERS) satellite series were used to derive estimates of near-surface soil moisture for seasonally vegetated and bare soil surfaces in the area of the Jordan Badia Research and Development Programme (BRDP). Data were acquired between March 1995 and April 1998, covering both wet and dry seasons. A surface scattering model was calibrated using field data: first to understand how soil moisture affects the SAR signal and, secondly, to predict the response of the SAR signal to changes in volumetric soil moisture. Good agreement between predicted and observed estimates was obtained. Model inversion allowed soil moisture predictions to be made that were deemed realistic in terms of soil moisture values.     

中国西北气候干湿变化研究进展

西北地区对全球气候变化十分敏感,研究分析该地区干湿变化特征,对区域发展至关重要.本文从气象(降水、温度、蒸发)、水文(地表水、土壤湿度、陆地水储量)和植被等角度综述了近50年西北地区干湿变化特征.结果 表明:西北整体气温升高,降水增加,呈暖湿化.但考虑陆面因素作用的分析表明该地区呈现东西部分化的格局.考虑蒸发因素的结果...     

珠江流域多尺度极端降水时空特征及影响因子研究

基于珠江流域74个气象站点1952~2013年逐日降水和气温数据,采用POT抽样、Mann-Kendall（MK）趋势检验、泊松回归等方法,从降水量级、降水频率及发生时间等方面系统分析了珠江流域年、雨季及旱季3个时间尺度上的极端降水特征,并从降水对温度变化响应及ENSO影响等角度,探讨了极端降水变化特征的机理。研究表明：① 珠江流域极端降水年内分布不均,多发于4~9月,其中6月份发生频率最高;② 珠江流域极端降水频率在雨季及年际间分布较为均匀。但在旱季,珠三角地区极端降水在不同年份差异性较大;③ 在雨季及年际尺度上,极端降水年序列趋势性并不显著;而相对干旱季节,极端降雨量级、发生频次均随年份增加呈显著上升趋势,且发生时间提前。珠江流域农业以水稻(Oryzasativa)种植为主,旱季极端降水增加易导致冬汛及其引起的作物倒伏与农田渍涝等灾害,同时对秋冬防洪提出新的挑战,需要引起人们的关注;④ 温度升高和ENSO事件对珠江流域极端降水过程有显著影响。从ENSO影响的角度讲,在厄尔尼诺年,珠江流域西部极端降水量级和频率增加,而流域东部沿海区域极端降水量级减少,时间延后。     

人工固沙植被区土壤水分动态及空间分布

土壤水分是干旱区固沙植被生长发育最主要的限制因子,了解其动态变化特征对沙区人工植被建设具有重要意义。本研究利用EnviroSMART土壤水分监测系统,于2009-2013年对宁夏沙坡头地区人工固沙植被区的土壤水分动态进行连续监测。结果表明:(1)降水对土壤水分状况及动态变化有较大的影响。土壤水分总体处于过度消耗状态,在非生长季,土壤水分没有明显的回升现象。(2)生长季初期(4-5月)为土壤水分弱消耗阶段;生长旺盛期(6-8月)为土壤水分快速消耗阶段,水分变化波动较剧烈,空间异质性最强;生长季末期(9-10月)的土壤水分处于相对稳定状态。(3)土壤水分随深度增加呈“S”形变化趋势,浅层的土壤含水量明显高于其他深度,200 cm深度土壤含水量较低且年际间变化不大(1.53%~2.10%)。湿润年份土壤水分剧烈变化的土层深度为0～100 cm,而干旱年份为0～20 cm。(4)相对于干旱年份,湿润年份的土壤含水量不但较高,而且水分变化波动较为剧烈。当土壤水分较低时,其变异性会随着土壤水分含量的增加而增加。(5)试验区灌木盖度在5年间呈下降趋势,一年生草本受降水量影响年际变化较大。受降水时空分布影响的土壤水分是沙坡头人工植被演替的重要驱动力。     

Mesoscale Associations Between Midwest Land Surface Properties and Convective Cloud Development in the Warm Season

The study of land surface-atmosphere interactions is vital to understanding climatic variations in the Earth's planetary boundary layer, particularly given continual land cover modifications by humans on local to regional scales. An agriculturally important region ideal for the study of land surface-atmosphere interactions is the Midwest United States "Corn Belt." To evaluate the mesoscale relationships between Corn Belt land surface properties and a key indicator of the surface-atmosphere feedback in humid climates—warm-season convective cloud development—conventional meteorological data, digital maps of land surface properties, and satellite data were examined in a GIS framework for the May-September periods of 1991 through 1999. The results indicate associations between the surface and atmospheric moisture content and the formation of convective clouds: cumulus clouds initiate first and persist longer over a dry (moist) surface with an initially dry (moist) atmosphere. These relationships are evident when forcing from the free atmosphere is either extremely weak (i.e., when fronts and other disturbances are absent and 500 mb winds are <7 ms^-1), weak (same as extremely weak, except 500 mb winds are 7-13 ms^-1), or strong (same as extremely weak, except 500 mb winds >18 ms^-1). However, the association between convective cloud development and other land surface properties (e.g., land use-land cover [LULC], soil order, elevation, and slope) is not consistent spatially. We find that a surface moisture-convective cloud relationship dominates Corn Belt land surface-atmosphere interactions across a range of barotropic synoptic conditions under different atmospheric moisture contents. The study results can help lead to improved prediction of convective cloud formation, and more realistic modeling of land surface-atmospheric interactions for weather and climate forecasting.     

土壤水分及土壤-大气界面对麦田水热传输的作用

文章根据1996年在中国栾城农业生态试验站观测的田间试验资料,分析了土壤水分和土壤-大气界面对麦田水热传输的抑制和加速作用。对于显热和潜热输送,土壤水分起决定作用,土壤水分越小,显热通量越大,潜热通量越小,反之亦然。只在土壤水分较小时界面厚度对显热和潜热输送作用较大。对于土壤热输送,界面厚度起决定作用,界面厚度越大土壤热通量越小。分析还发现60cm深处土壤水势与叶水势和大气水势的相关系数较其它深度处的土壤水势大。0～60cm土层是确定土壤水分运动对界面水热传输影响的一个良好的指示层。     

ENSO and solar activity signals from oxygen isotopes in diatom silica during late glacial-Holocene transition in Central Andes (18°S)

The late glacial-Holocene transition from the Lago Chungará sedimentary record in northern Chilean Altiplano (18°S) is made up of laminated sediments composed of light-white and dark-green pluriannual couplets of diatomaceous ooze. Light-white sediment laminae accumulated during short-term extraordinary diatom blooms whereas dark-green sediment laminae represent the baseline limnological conditions during several years of deposition. Diatom oxygen isotope ratios (δ¹⁸O_diatom) from 40 consecutive dark-green laminae, ranging from 11,990 to 11,450 cal year BP, show that a series of decadal-to-centennial dry–wet oscillations occurred. Dry periods are marked by relatively high isotope values whereas wet episodes are indicated by lower values. This interpretation agrees with the reconstructions of terrigenous inputs and regional effective moisture availability carried out in the lake but there is a systematic temporal disagreement between them owing to the non-linear response of the lacustrine ecosystem to environmental forcings. Furthermore, the δ¹⁸O_diatom record tracks effective moisture changes at a centennial scale. Three major phases have been established (11,990–11,800, 11,800–11,550, and 11,550–11,450 cal year BP). Each phase is defined by an increasing isotope trend followed by a sudden depletion. In addition, several wet and dry events at a decadal scale are superimposed onto these major trends. Spectral analyses of the δ¹⁸O_diatom values suggest that cycles and events could have been triggered by both El Niño-Southern Oscillation (ENSO) and solar activity. Significant ENSO frequencies of 7–9 years and 15–17 years, and periodicities of the solar activity cycles such as 11 years (Schwabe), 23 years (Hale) and 35 years (Brückner) have been recognised in the oxygen isotope time series. Time–frequency analysis shows that although solar and ENSO forcing were present at the onset of the Holocene, they were more intense during the late glacial period. The early Holocene might have been mainly governed by La Niña-like conditions that correspond to wet conditions over the Andean Altiplano.     

Realistic soil C sink estimate in dry forests of western Argentina based on humic substance content

Due to high temporal variation of soil organic matter in arid regions, estimates of annual sequestered C might be overestimate. We assessed the soil stable organic matter (humic substances) in the transitional area between Dry Chaco and Monte eco-regions in western Argentina, as an approach to estimate realistic soil C sink. Soil samples were taken during wet and dry seasons in four sites along precipitation gradient. In each site three soil cover situations (under tree, under shrubs and on bare soils) were sampled (n = 5) and the quantity and type of residues (tree and shrub leaves, woody material, grasses and forbs) were recorded. Soil organic matter and humic substances (humic and fulvic acids) content were analyzed and non-humic substances were calculated by the differences between organic matter and humic substances. Soil humic substance proportion respect to SOM was low (20%) in all sites and it did not correspond with the precipitation gradient. Non-humic substances were lower in wet season indicating high C lability. The most important factors that affected soil humic substance content were the type and quantity of organic residues and soil cover type. Our results suggest that previous C sink estimations in Argentina dry forest probably are overestimated.     

ANOMALOUS WET AND DRY SPELLS IN THE CENTRAL UNITED STATES, 1931–75

The Palmer Index (PI) was employed to compare anomalous dry spells with anomalous wet spells for 76 climatic divisions in the central United States. Comparisons were made in terms of the frequency, severity and persistence of wet and dry climatic episodes for the period 1931–75. The results indicated more frequent dry anomalies in the southwest (New Mexico and west Texas) portion of the study area and more frequent wet anomalies in the northeast (Illinois and Iowa). Not surprisingly, these are the most arid and most humid portions respectively. The results of the analysis for persistence were less clear. Typically dry anomalies lasted longer than wet anomalies, especially as the minimum length was increased. This was especially apparent when comparing the very longest dry spell with the very longest wet spell during the 45-year study period. Thus there are more but shorter wet spells and less frequent, but typically longer lasting dry spells. This final relationship posits the question of feedback processes between surface soil moisture and the persistence of atmospheric precipitation anomalies. [Key Words: Palmer Index, drought, moisture anomalies, wet spells, dry spells.]     

南岭山地森林流域退水规律及影响因素

采用水文气象长期定位观测数据,结合基于事件尺度的退水速率与流量关系分析方法,对2019—2021年典型南岭山地森林流域的退水过程变化进行识别,探索退水特征与同期土壤水分、地下水埋深、潜在蒸散发和实际蒸散发的关联程度,深入了解山地森林流域退水规律及主要影响因素。结果表明：1）相同流量情况下,流域在枯水条件下比丰水条件退水速率更快;2）流域土壤入渗能力较强,降水能迅速补给土壤水和地下水,地下水对降水的响应较土壤水略有延迟;3）地下水埋深对流域退水有显著影响,土壤水分次之,与之相比潜在蒸散发和实际蒸散发的影响并不明显;4）地下水埋深是影响山地森林流域出口退水过程的最主要因素,由于地下水位低于河床位置,流域出口河段处于地下水补给区,因此地下水埋深越深,河道水向地下水渗失越快,从而导致流域出口退水速率加快。可见,地下水埋深是流域退水规律分析乃至枯水期径流模拟不可忽略的关键变量。     

黄土高原北部河北杨林的土壤水分特征

以河北杨林为研究对象，在对其土壤水分进行7a定位观测的基础上，对其特点进行全面分析。结果表明：河北杨林土壤水分动态的周年变化规律主要受降水及其分配特点和生长期初土壤水分含量的影响。0cm-300cm深度内，生长期土层内土壤水分的年平均值多数年在64g/kg左右；特旱年仅50g/kg；特涝年也只有76g/kg；土壤水分条件较差；多数年份土壤水分的基本平衡；特旱、特涝年份土壤水分大量亏缺、积累，其值均达150mm以上。0cm-300cm深度内土壤水分剖面的垂直分布自上而下分为活跃层、过渡层和稳定层，但各层的厚度变化受年降水量的影响较大；土壤含水量的平均值随深度增加而减少，从72g/kg-57g/kg。除特涝年份的生长季中后期外，生长期内的北杨有较大的贮水库容，有利于土壤水的年际调节。     

北京城区的降水与湿度分析

本文通过对1963—1987年北京城、郊区测点的降水和相对湿度资料的对比分析,发现北京城区夏、秋季存在“干岛”现象,而冬、春季却存在明显的“湿岛”现象。城区四季都存在雨岛,雨岛现象夏季最明显。     

Summer Moisture Variability in East Central Sweden Since the Mid-Eighteenth Century Recorded in Tree Rings

To make predictions of future climate it is necessary to understand the past climate—temperature as well as precipitation. While a wealth of temperature proxies exist from northern latitudes, there is still a lack of information about past precipitation variability. Here we present a 300‐year‐long tree‐ring width chronology from xeric‐site Scots pines (Pinus sylvestris L.) in Tyresta National Park, east central Sweden. Tree‐ring widths were compared to the long observed temperature and precipitation records from Stockholm during 1786–2000. Analyses of the climate/growth relationship showed that, in general, May–June precipitation had a dominating influence on pine growth. However, during dry periods, negative responses to June–July temperature were stronger, especially evident in the late nineteenth century. Periods of below‐average growth were associated with dry conditions in May–June, but occasionally periods of wet and cool summers also produced narrow rings. Periods of above‐average growth were linked to wet, but sporadically also cool and dry, early summers. The years between 1815 and 1833 appear to be particularly dry in the 300‐year context. Since growth anomalies are found in other Swedish drought‐sensitive tree‐ring chronologies during this period, it is likely that this dry period had a regional extent. This is the first tree‐ring chronology from southern Sweden that provides multi‐century information of past summer drought and moisture variability with high resolution and the study will add important information regarding past climate variability in southern Sweden.     

CELLULOSE DECOMPOSTION IN TROPICAL PEAT SWAMPS

Given that organic soil is a complex substrate and there are many environmental factors which directly or indirectly control its decomposition processes, the use of standard substrate simplify the system in that the effect of substrate quality could be eliminated and influence of certain environmental conditions such as edaphic factors, acidity and moisture could be focused on. In addition to the forest floor, decomposition potential down the peat profile can also be examined. Cotton strip assay was used to estimate decomposition potentials in tropical peat swamp occupied by different Shorea Albida peat swamp forest communities, The 'Alan Batu' , the ' Alan Bunga' , the 'Alan Padang' and the ' mixed Alan' forest communities.Greatest decay rates on the peat surface took place during the wet period. The moist condition of the wet months appeared to favour the growth and stimulate activities of decomposer population and soil invertebrates. Generally, 50% of cotton tensile loss is achieved after four weeks     

近50年来中国干湿气候界线的10年际波动

利用中国北方1951～1999年降水量和年蒸发量资料，计算了干燥度指数（D）。并据此将中国划分为干旱区（D（0.20）），半干旱区（0.20-0.50）和湿润区（D(0.50）），近50a中国干湿气候波动显著，区域差异大；50a波动幅度东北区为20～400km，华北区为40～400km，西北东部为30～350km，西南区为40～370km，以80年代为界，在20世纪80年代以前（包括80年代），西南区气候具有显著变湿趋势；西北东部稍变湿；华北区和东北区具有变干趋势，且华北区变干程度比东北区严重。进入90年代。西南区和西北东部气候有变干迹象。华北区西部气候的干旱程度有所增加，华北区东部有所减弱，东北区气候进一步变湿，半干旱区是湿润区与干旱区之间的过渡区，是中国季风的边缘地带，也是环境变化的敏感区，20世纪60～70年代中国（北方）干湿气候存在一次突变，由较湿润变为干旱。50年来干湿气候界线呈现出整体移动和东西、南北相异波动的特征，当干湿气候界线同时向西或向北移动时，中国北方气候就变得相对湿润；当同时向东或向南移动时，北方气候就变得相对干旱；当干湿气候界线东西、南北相异移动时，北方气候的干旱程度就介于二者之间。     

藏北高原地气之间的水分循环

利用GAME－Tibet期间所取得的高分辨率土壤温度、含水量以及降水量资料，对藏北高原地气之间的水分循环过程进行了分析。结果表明，唐古拉山以南平坦地表7－8月份地表蒸发的水汽量可达177.1mm，占同期降水量的73．2％；唐古拉山以北平坦地表7－8月份地表蒸发的水汽量可达73.3mm，占同期降水量的57．7％。地表土壤通过蒸发不但将大量的水分输送给其上的大气，而且将热量传给了其上的大气，从而抑制了土壤温度的升高。如果仅就唐古拉山南北地表蒸发而言，引起其较大差异的原因主要是降水量的不同。     

祖厉河流域降雨径流泥沙变化特征研究

祖厉河流域位于年降水量200～400 mm之间过渡带,是气候变化最敏感和最为复杂的区域之一。运用祖厉河流域1955-2013年径流量、输沙量与年降雨量的变化趋势、时段特征进行了分析。结果表明：祖厉河流域降雨量、径流量和输沙量存在年际变化大、逐年减小的变化趋势;年降雨量在1995年出现突变点,降雨量存在明显的丰水和枯水变化,丰水时段（1955-1989年）年降水量为376.2 mm,枯水时段（1990-2013年）年降水量为224.9 mm;径流量和泥沙量的突变点分别出现在1995年和2000年;依据UF_k值信度变化趋势,将径流量、输沙量变化分为非显著减少（1955-1971年）、显著减少（1972-1985年）、较显著减少（1986-2000年）和极显著减少（2001-2013年）四个时期。     

Growth, ionic and osmotic relations of an Allenrolfea occidentalis population in an inland salt playa of the Great Basin Desert

Variation in growth, physiology and ionic relations patterns of Allenrolfea occidentalis, a perennial halophyte of dry habitats, was studied under field conditions from May 1996 to November 1997. An A. occidentalis community has a characteristic soil pH of 7·3–8·3. During the two years, the population was exposed to great variations in soil salinity, from 29 to 146 dS m⁻¹, and soil moisture, ranging from drought (9·2%) to wet (19%). The salt concentrations were significantly higher in the surface soil layers than in the subsurface layers. Seasonal changes in dry weight are directly related to soil salinity stress. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na⁺and Cl⁻ions were accumulated in plant tissues in much greater amounts than K⁺, Ca²⁺, and Mg²⁺. Soil salinities were significantly reduced at the end of the growing season. Water potentials of the shoots decreased significantly with increasing salinity. The plant (F_v/F_mratio) was more affected by salinity and irradiation levels during the summer period.     

Spatial and temporal variation of soil moisture near the interface of high/low stands

1 IntroductionSurface inhomogeneities occur at scales ranging from a single leaf to a region[1], up to the whole earth. Spatial shift of biome boundaries is of special importance because large gradients exist in the ecotone[2]. It makes biome areas heterogeneous and bridges the gap between each of sub-areas. Hicks and Wesely (1981) compared the surface eddy fluxes of heat and momentum over adjacent fields of soybeans and maize[3]. Gash (1986) observed the growth of the equilibrium layer downw…