Empirical downscaling of daily minimum air temperature at very fine resolutions in complex terrain

Available air temperature models do not adequately account for the influence of terrain on nocturnal air temperatures. An empirical model for night time air temperatures was developed using a network of one hundred and forty inexpensive temperature sensors deployed across the Bitterroot National Forest, Montana. A principle component analysis (PCA) on minimum temperatures showed that 98% of the spatiotemporal variability could be accounted for using the first two modes which described the coupling and decoupling of surface temperature from free air temperatures, respectively. The spatial character of these modes were strongly correlated with terrain variables and were then modeled to topographic variables derived from a 30 m digital elevation model. PCA scores were modeled using independent predictors from in situ observations and regional reanalysis that incorporate temperature, solar radiation and relative humidity. By applying modeled PC scores back to predicted loading surfaces, nighttime minimum temperatures were predicted at fine spatial resolution (30 m) for novel locations across a broad (∼45,000 km²), topographically complex landscape. Our results suggest that this modeling approach can be used with retrospective and projected predictors to model fine scale temperature variation across time in regions of complex terrain.     

How much influence does landscape-scale physiography have on air temperature in a mountain environment?

Spatio-temporal patterns of temperature in mountain environments are complex due to both regional synoptic-scale and landscape-scale physiographic controls in these systems. Understanding the nature and magnitude of these physiographic effects has practical and theoretical implications for the development of temperature datasets used in ecosystem assessment and climate change impact studies in regions of complex terrain. This study attempts to quantify the absolute and relative influence of landscape-scale physiographic factors in mediating regional temperatures and assess how these influences vary in time. Our approach was to decompose the variance in in situ temperature measurements into components associated with regional free-air temperature estimates and local physiographic effects. Near-surface air temperature data, collected between 1995 and 2006 from 16 meteorological stations in the Lake Tahoe region of California, USA were regressed against free-air temperature (North American Regional Reanalysis dataset) for the same period. Residuals from this fit represent spatial deviations from the regional mean and were modeled as a function of physiographic position on the landscape using variables derived from terrain analysis techniques. Linear models relating temperature residuals to physiographic variables explained roughly 10–90% of the variance in temperature residuals and had root mean squared error of 1.2–2.0 °C, depending upon the type of measurement and time of year. Results demonstrate that: (1) regional temperature patterns were the principle driver of surface temperatures explaining roughly 70–80% of the variance in in situ measurements; (2) the remaining variance was largely explained by spatial variability in landscape-scale physiographic variables; (3) the influence of physiographic drivers varied seasonally and was influenced by regional conditions. Periods of well-mixed atmospheric conditions lend themselves to the use of simple elevation-based lapse rate models for temperature estimation whereas other physiographic effects become more prominent during periods of enhanced atmospheric stability; and lastly (4) small differences in temperature due to landscape position, when integrated over time, can have a prominent effect on water balance and thus hydrologic and ecologic processes.     

重庆市NDVI对水热条件变化的响应及其空间特征

降水和气温是影响一个地区植被覆盖度的最主要的气候因子。在利用SPOT VGT-NDVI旬数据、重庆市及周边20个气象站点1999-2010年日气温与降水数据以及研究区相关图件资料的基础上,运用时滞互相关分析法分析了旬平均NDVI(TN)与旬均温(TT)和旬降水(TP)的相关性以及时滞情况。结果表明,NDVI与气温和降水之间存在较强的相关性,且NDVI与气温较与降水之间的相关性更强,表明在研究区气温是NDVI变化的限制因子;NDVI与气温和降水之间的相关性和时滞情况存在明显的东南-西北差异,东南地区时滞较长,相关性低,西北地区时滞较短,相关性高;各植被类型NDVI与气温和降水的相关程度高低以及响应速度的快慢决定于各植被类型的生长发育规律及其对气温或降水要求的高低。     

1960-2014年祁连山南坡及其附近地区气温时空变化特征

基于祁连山南坡及其附近19个气象站点的1960-2014年气温数据,利用线性趋势法、相关分析法、多项式趋势法、5年滑动平均、R/S分析方法、ArcGIS方法对其气温的时间变化与空间分布作了详细分析。结果表明:多年平均气温变化趋势为波动上升趋势,增长率为0.35℃/10 a,最低气温与最高气温的增长率分别为0.478,0.275℃/10 a,季节气温同样为上升趋势,其中冬季气温增幅最大,说明最低气温与冬季气温对气温上升贡献最大;从年代际变化来看,2000-2014年气温的升高趋势比1990-1999年有所下降,并不能说明全球变暖停滞,可能受到自然外强迫造成的;气温的Hurst指数为0.5 < H < 1,表明今后气温的变化趋势与过去变化趋势具有相同的特征;大部分气象站点多年平均气温与季节气温的变化均为增长趋势,通过显著性检验站点的比率较高,而年代际气温的空间变化差异较大。     

Explaining Rice Milling Quality Variation Using Historical Weather Data Analysis

Rice quality, specifically head rice yield (HRY), can vary inexplicably from one lot to another, and from year to year. In an effort to correlate air temperatures during various growth stages to HRY, growth staging data expressed in degree day units was used to predict the occurrence of sequential growth stages within a set of 17‐year historical data, which included HRY and 50% heading dates for two long‐grain rice cultivars, (Oryza sativa L) Newbonnet and Lemont, and area weather data. HRY was most strongly affected by the average daily low temperature (or nighttime temperature) during the R8 developmental stage. Lower HRY were associated with high nighttime air temperatures during this stage for both Newbonnet and Lemont. When used as a single variable in a regression model, the nighttime temperature during the R8 developmental stage explained over 25% of the variation in HRY.     

1960-2013年云南地面温度时空变化特征

利用云南省1960-2013年逐日0 cm地面温度观测资料,运用Mann-Kendall趋势和突变检验法、小波分析法等分析了云南地面温度的空间分布、变化趋势及突变特征、周期变化及可能的影响因素。结果表明:年平均地温、年平均最低地温整体上呈现"南高北低"的分布特点,年平均最高地温呈现出"西北、东北低,中部、南部高;深切河谷高,高原面较低,高耸山地更低"的分布特点;同时,也表现出明显的区域性差异;年平均地温、年平均最高（低）地温高值中心主要分布在元江河谷（元江站）,金沙江河谷（元谋站）,滇南澜沧江及其支流河谷（景洪站、勐腊站）;平均地温、平均最高（低）地温季节分布特点与年际分布大致相似。平均地温、平均最高（低）地温年际、季节及不同气候带均呈增温趋势;年平均地温、年平均最高（低）地温均以冬季增温幅度最大;年平均地温、年平均最低地温以高原气候带增温幅度最大,年平均最高地温以北热带增温幅度最大。年平均地温、年平均最高（低）地温及不同气候带地温均发生显著突变;其中,年平均地温、年平均最高（低）地温显著突变点分别为2000年、2004年、1997年;年平均地温、年平均最高（低）和不同气候带地温均以长周期变化为主周期;其中,年平均地温、年平均最高（低）地温主周期分别为28 a,26 a,26 a。年平均地温、年平均最高（低）地温与纬度和海拔呈极其显著的负相关;1960-2013年亚洲区极涡面积（强度）,西太平洋副高西伸脊点指数显著减弱,西太平洋副高面积（强度、脊线）、印缅槽、西藏高原、印度副高面积指数呈显著增加可能是引起云南地温变化的原因之一。     

Wavelet analysis of wintertime and spring thaw CO2 and N2O fluxes from agricultural fields

Fluxes of N₂O and CO₂ are not limited to the growing season; winter and spring thaw can represent a significant emission period. The objective of this study was to apply wavelet analysis to winter and spring thaw CO₂ and N₂O fluxes and soil temperatures, to yield additional information about underlying processes, examining temporal patterns and relationships among them. Fluxes used in this analysis were measured over 4 years using micrometeorological methods, in a study comparing two agricultural management practices, best management (BM) and conventional (CONV) practices. Cross-wavelet transform (XWT) and wavelet coherence (WCO) were applied to daily mean time series of N₂O fluxes for BM and CONV replicates and treatments, CO₂ vs. N₂O fluxes, CO₂ flux vs. air and soil temperatures, and N₂O flux vs. air and soil temperatures. N₂O fluxes for replicate plots had small differences in temporal variation while N₂O fluxes from BM and CONV treatments showed a large difference in their time series. XWT and WCO analysis confirmed differences in N₂O fluxes between management practices due to differences in temporal trends in the time series. Field emissions of N₂O and CO₂ fluxes showed times of common high fluxes, such as thaw events. Nitrous oxide and CO₂ flux time series showed a strong coherence with surface (air) temperatures. The relationship between N₂O fluxes and temperature decreased with depth but the relationship between CO₂ flux and temperature was similar for surface and at depth. The strong coherence between emissions and surface conditions does not support the suggested mechanism of trapped gas release. A release of trapped gases from below the ice formation would have been indicated by a strong coherence from CO₂ and N₂O with temperatures at depth as the trapping ice barrier melted. This study demonstrates the effectiveness of wavelets as a tool to investigate temporal relationships in GHG emissions, which is a relatively new application for this type of analysis.     

广东省裸地和草地地表温度时空分布特征

利用广东省86个站点裸地和草地2006-2008年自动观测资料,分析了两种下垫面地表温度日、年变化特征及其空间分布规律。结果表明：（1）裸地和草地温度（0cm）的日变化趋势一致,其日最高温度出现时间较日最高气温分别提前1.18±0.95h和1.37±1.05h,日最低温度出现时间比日最低气温分别提前0.20±0.66h和0.45±0.80h。（2）裸地和草地作为透水性下垫面,其日平均温度、日最高温度、日最低温度和日较差具有相同的温度变化趋势,但草地有草皮覆盖,日较差低于裸地。（3）广东裸地和草地日平均温度、日最高温度和日最低温度均有明显的纬向分布特征,日平均温度和日最高温度在夏半年由南向北递增,冬半年相反;受城市热环境的影响,广州及其附近的站点裸地和草地的温度指标也相应高于周边地区。     

Soil respiration as affected by vegetation types in a semiarid region of China

There are variations in soil respiration across vegetation types; however, it is unclear which factors are mainly responsible for the variations. A field experiment was conducted in 2008 and 2009 in a semiarid region of China to investigate the daytime and monthly variation of soil respiration across vegetation types and to determine the factors controlling the variation. An automated portable soil carbon dioxide (CO₂) flux measurement system was used to measure the soil respiration in shrubland, grassland, fallow land, and cropland during the growing periods. The results showed that the relative daytime variation amplitude of soil respiration in the fallow land and cropland was as small as that of shrubland and grassland during July, but greater than that of shrubland and grassland during August and October. A hysteresis effect for the relationship between the daytime soil respiration and daytime soil temperature was observed for all four vegetation types. There was also a hysteresis effect for the relationship between the daytime soil respiration and daytime air temperature for the grassland. Over the study period, the monthly soil respiration rates of the fallow land and cropland were statistically comparable and significantly lower than those of the shrubland and grassland, with the exception of August, during which the monthly soil respiration of the cropland was as great as that of shrubland and grassland. The factors responsible for the monthly soil respiration variation across the vegetation types differed from month to month. In general, the soil temperature and soil water content were mainly responsible in August and September; however, the root biomass predominated in July and October. The results are valuable for accurately estimating regional carbon fluxes by considering the temporal variability of the soil respiration variation across vegetation types in the Loess Plateau of China.     

白三叶草间作对亚热带丘陵茶园地温及生产的影响

利用亚热带丘陵区茶园白三叶草间作大田对比试验,研究其对茶园地温时空动态变化的影响。结果表明:茶园地温具有明显的时空变化特征和位相滞后现象,白三叶草间作改变了土壤热量交换层(地表层)的性质,对不同观察时刻、不同深度的土壤温度具有低温时增温、升温时降温、降温时保温及降低日较差、增强同一土层温度稳定性等综合动态调控作用,其调控效果表现出了0cm>5cm>10cm>15cm>20cm、13:00>19:00>7:00、降温>保温>增温、降温幅度随气温的升高而增大、增温和保温随气温的下降而加强的相同趋势,同时还降低了有害高温的出现次数,提高了茶园生态系统的自我调节能力,改善了茶叶品质,增加了茶叶产量。     

三江平原耕地归一化植被指数对气候因子的时滞响应

三江平原位于我国中温带北段,近年来气候变暖和耕地利用变化较为显著.基于2000—2015年三江平原耕作期(5—9月)耕地利用数据、旬气候数据、旬归一化植被指数(NDVI)数据,利用变异系数、趋势系数以及时滞互相关的研究方法在分析气候因子时间变化特征和耕地NDVI空间变化差异的基础上,分析区域旬气候因子对耕地旬NDVI的...     

Spatial and temporal variability of physical properties of Aquands under different land uses in southern Chile

The aquands found in southern Chile are derived from volcanic ash and contain high levels of organic matter. Due to the presence of an impermeable stratum, they have shallow soil profiles, which induce waterlogging for several months each year. These fragile soils, locally known as ‘Ñadi’, cover an area of 475 000 hectares and have undergone intensive land use changes, which have affected the soil physical properties. These are still not well understood but are relevant for the design of efficient drainage systems. The aim of this research was to analyse the impact of the land use change in Ñadi soils on the spatial and temporal variability of their soil physical properties. For the land use change from secondary native forest (sNF) to naturalized grassland (NG), the effective soil depth was measured at defined points. Time‐ and space‐dependent changes of water‐table depth and penetration resistance were recorded. Volumetric water content and soil temperature were measured with sensors installed at three depths and the water retention curve and air permeability at these depths were also determined. The changes in land use over time have induced a reduction in soil depth. Soils under NG showed a smaller soil water storage capacity, air capacity and permeability compared with soils under sNF, as well as waterlogging during winter and greater mechanical strength and soil profile temperatures during summer. Therefore, the land use change affected the spatial and temporal variability of soil physical functions across the field.     

The Spatial and Temporal Distributions of Spheroidal Carbonaceous Fly-Ash Particles (SCP) in the Sediment Records of European Mountain Lakes

Sediment cores were taken from 31 mountain lakes in 11 countries across Europe. For each core a full spheroidal carbonaceous particle (SCP) profile was produced. SCP are derived from the high temperature combustion of fossil-fuels and provide an unambiguous record of the atmospheric deposition of anthropogenic pollutants. The data from the sediment cores were therefore able to show both temporal and spatial trends in pollutant deposition across the continent from Svalbard to southern Spain and from Ireland to the Tatra mountains. In general, the temporal trends throughout Europe were remarkably consistent and were seen to be in good agreement with known historical emissions, combustion figures and modelled historical pollutant patterns for source countries. Spatial patterns showed that highest concentrations and accumulation rates were in central Europe, with clear decreases northwards and southwards from the region. An east to west decrease was also apparent. SCP profiles can be converted to full post-Industrial inventories and normalised against a ²¹⁰Pb inventory to create a ‘pollution index’ covering the whole of the SCP record. Such indices take into account sediment variability and some catchment influences and are therefore better for inter-site comparisons. These results were seen to show a clear latitudinal pattern, with a maximum at around 50°N and declining to the north and south. This agrees with European sulphur emissions data and are generally consistent with EMEP modelled distribution patterns. In many cases the SCP temporal profiles could only be explained by using emission and combustion statistics from more than one country emphasising the transboundary nature of particulate transport throughout Europe, in general, supporting EMEP modelled ‘blame matrices’.     

Regional evaluation of the spatio-temporal variation in soil organic carbon dynamics for rainfed cereal farming in northern Kazakhstan

Abstract

A regional evaluation of the soil organic carbon (SOC) dynamics for the chernozem zone in northern Kazakhstan is now vitally important for agricultural and environmental policy making. The objectives of the present study were: (1) to predict spatial and temporal variability in C input as crop residues using multi-temporal MODIS satellite images, (2) to clarify spatial and temporal variability in CO₂ emission as SOC output using geostatistics and model s, (3) to clarify spatial and temporal variability in the SOC budget using the results from (1) and (2). The mean growing-season C input as plant residues in cereal fields ranged from 0.9 to 1.4 Mg C ha^?1, with higher values in wet years. Carbon input as plant residues was higher in the northern part of the area than in the other parts. The average growing-season CO₂ emission ranged from 0.9 to 1.1 Mg C ha^?1, and was also higher in wet years than in dry years. In addition, more CO₂ was emitted in the northern part of this area. Accordingly the average growing-season C budget ranged from –0.2 to 0.3 Mg C ha^?1 and showed a negative correlation with air temperature during the crop-growing season. The 5-year C budget for different crop rotation systems ranged from –1.0 (3-year cropped cereal with 2-year bare fallow) to 0.4 (5-year continuous cereal cropped) Mg C ha^?1. These results indicate that fallow-based crop rotation systems are degradative with regard to the SOC budget in the studied area.     

南亚热带果园土壤二氧化碳释放变异性研究

Temporal variability in soil CO2 emission from an orchard was measured using a dynamic open-chamber system for measuring soil CO2 effiux in Heshan Guangdong Province, in the lower subtropical area of China. Intensive measurements were conducted for a period of 12 months. Soil CO2 emissions were also modeled by multiple regression analysis from daily air temperature, dry-bulb saturated vapor pressure, relative humidity, atmospheric pressure, soil moisture, and soil temperature. Data was analyzed based on soil moisture levels and air temperature with annual data being grouped into either hot-humid season or relatively cool season based on the precipitation patterns. This was essential in order to acquire simplified exponential models for parameter estimation. Minimum and maximum daily mean soil CO2 effiux rates were observed in November and July, with respective rates of 1.98 ± 0.66 and 11.04 ± 0.96 μmol m^-2 s^-1 being recorded. Annual average soil CO2 emission （FCO2） was 5.92 μmol m^-2 s^-1. Including all the weather variables into the model helped to explain 73.9% of temporal variability in soil CO2 emission during the measurement period. Soil CO2 effiux increased with increasing soil temperature and soil moisture. Preliminary results showed that Q10, which is defined as the difference in respiration rates over a 10 ℃ interval, was partly explained by fine root biomass. Soil temperature and soil moisture were the dominant factors controlling soil CO2 effiux and were regarded as the driving variables for CO2 production in the soil. Including these two variables in regression models could provide a useful tool for predicting the variation of CO2 emission in the commercial forest Soils of South China .     

Coupled land-atmosphere modeling of the effects of shrub encroachment on nighttime temperatures

Changes in vegetation cover affect the interactions between the land surface and the overlying atmosphere with important impacts on surface energy balance and microclimate conditions. A major ongoing change in vegetation cover has been observed in dryland regions around the world, where desert shrubs are encroaching into arid grasslands. However, the impact of shrub encroachment on local climate has not been investigated. We used a mesoscale model coupled with a Land Surface Model to simulate the effects of shrub encroachment on nighttime temperatures. These effects can have an important effect on the establishment of shrubs and need to be represented well by land surface parameterization schemes that are also used in long-term climate simulations. Idealized 2-dimensional simulations were conducted with vegetation types corresponding to shrubland and grassland typical of the Northern Chihuahuan Desert. Simulated surface energy and radiation fluxes and near-ground air temperature were analyzed and compared with observations. Results show a good comparison between the simulations and observations as long as vegetation parameters are adjusted in the model to be in better agreement with the observed parameters. The sensitivity of the nighttime air temperatures to green vegetation fraction, albedo, emissivity and roughness length is investigated. The results indicate that the green vegetation fraction is the key factor that causes the higher nighttime temperature in shrubland than in adjacent grassland, mainly by its effects on soil surface insulation, soil thermal diffusivity, and therefore on ground heat fluxes.     

Mercury cycling in the Allequash Creek watershed,northern Wisconsin

Although there have been recent significant gains in our understanding of mercury (Hg) cycling in aquatic environments, few studies have addressed Hg cycling on a watershed scale. In particular, attention to Hg species transfer between watershed components (upland soils, groundwater, wetlands, streams, and lakes) has been lacking. This study describes spatial and temporal distributions of total Hg and MeHg among watershed components of the Allequash Creek watershed (northern Wisconsin, USA). Substantial increases in total Hg and MeHg were observed as groundwater discharged through peat to form springs that flow into the stream, or rivulets that drain across the surface of the wetland. This increase was concomitant with increases in DOC. During fall, when the Allequash Creek wetland released a substantial amount of DOC to the stream, a 2–3 fold increase in total Hg concentrations was observed along the entire length of the stream. Methylmercury, however, did not show a similar response. Substantial variability was observed in total Hg (0.9 to 6.3) and MeHg (<0.02 to 0.33) concentrations during synoptic surveys of the entire creek. For the Allequash Creek watershed, the contributing groundwater basin is about 50% larger than the topographic drainage basin. Total Hg concentrations in groundwater, the area of the groundwater basin, and annual stream flow data give a watershed-yield rate of 1.2 mg/km²/d, which equates to a retention rate of 96%. The calculated MeHg yield rate for the wetland area is 0.6 to 1.5 mg/km²/d, a value that is 3–6 fold greater than the atmospheric deposition rate.     

The CO2 concentration in soils of montane cloud forests of southern Mexico

We studied the CO₂ concentration in the soil air of Folic Albic Podzols at heights of 2500 and 2400 m a.s.l. within the area of montane cloud forests of southern Mexico. Soil air samples were collected from the depths of 5, 10, 20, 30, 40, and 50 cm every three hours from 9 a.m. to 18 p.m. during one day. The mean CO₂ concentrations in the soil air at the heights of 2500 and 2400 m a.s.l. reached 2170 and 6930 ppm, respectively. The spatial and temporal variability of the CO₂ concentration in the soil air of the Podzols of the montane cloud forest were revealed. The spatial variability was controlled by the differences in the species composition of the surface vegetation and the depth of the soil organic horizon, whereas the temporal variability was related to the generally low level of aeration of the topsoil layer and, presumably, to the cyclic pattern of the root respiration.     

陕北、渭北冬季负积温变化特征及趋势预测

利用陕北、渭北各气象站1960-1990年日平均气温资料统计各站的负积温，用小网格分析法分析其空间变化规律；选择榆林、绥德、延安、洛川和铜川等5个代表站，对40年负积温进行3年滑动平均模拟，分析时间变化特点和变化趋势，发现它们都有4年和9年的基本周期；分析确定了冬季冷暖评判指标；根据负积温变化趋势和变化规律，选择直线回归和方差分析叠加，对未来几年冬季冷暖状况进行预测。     

长沙地区樟树林穿透水空间变异及稳定同位素特征

于2018年4月至2019年3月在长沙地区典型樟树林收集降水、穿透水和相应的冠层信息,分析穿透水量的空间变异及穿透水稳定同位素的特征,旨在揭示林冠层水文过程,为林地水文生态系统的科学管理提供参考。结果表明:樟树林下总穿透水量为340.1 mm,占林外总降水量的71.2%;受观测点距树干距离和冠层叶面积指数等因素的综合影响,穿透水量具有较大的空间变异,且在时间变化上相对稳定。分析表明,研究区穿透水量的空间变异系数随降水量增加而减小,体现了降水特征对穿透水空间变异的重要影响;相对穿透水量而言,穿透水稳定同位素组成受冠层结构和大气条件的影响较小,其空间变异较小,在时间变化上不稳定;大部分降水事件中穿透水稳定同位素较降水稳定同位素富集,但其平均值之间不具有显著性差异,说明穿透水在形成过程中经历了较弱的蒸发作用;穿透水与降水中稳定同位素和过量氘的偏离还暗示了冠层具有选择性穿透效应。