Computations on the influence of changing climate on the soil moisture and productivity in scots pine stands in southern and northern Finland

A model computation on the evaporative demand in relation to precipitation indicated that, under a changing climate with elevating temperatures, evapotranspiration could exceed the concurrent precipitation during the growing period in southern Finland (61° N), but not in northern Finland (66° N). This could reduce the supply of soil water to enable tree growth on sites with soil of low water holding capacity. This in turn could reduce the productivity of Scots pine more in southern Finland than in northern Finland. In northern Finland, the reduction in growth due to a limited supply of water was partly compensated by the enhanced growth due to a rise in temperature outside dry periods.     

Monoterpene concentrations in and above a forest of scots pine

Diurnal and vertical ambient air measurements of the monoterpenes have been made in and above a Scots pine (Pinus sylvestris) forest of central Sweden, within the boreal northern coniferous biome. Sampling was done with Tenax TA, and analysis by GC and ion trap detection. Daytime mixing ratios were on the order of tenths of a ppbv from the forest floor to the top of the forest, and a factor of 2 or 3 lower above the forest. Mixing ratios at night were at the ppbv level, highest near the forest floor and the crown, and decreased with height above the forest. The highest total concentration observed was 8 ppbv inside the forest at 3 am (GMT). The average terpene composition was 3-carene 32%, -pinene 29%, limonene 18%, -pinene 10%, -phellandrene 7%, camphene 5%, and sabinene at less than 2%. The 3-carene/-pinene ratio varied with wind direction and speed, relative humidity, and wet/dry vegetation, but not with ozone or NO₂ concentration, solar radiation, or temperature. Variations in the observed terpene composition at the sampling site are mainly caused by the influence of other vegetation in the vicinity of the site. It would seem that wet Scots pine emits more 3-carene relative to -pinene than does dry pine.     

Climate change impact on snow and soil temperature in boreal Scots pine stands

Scenarios indicate that the air temperature will increase in high latitude regions in coming decades, causing the snow covered period to shorten, the growing season to lengthen and soil temperatures to change during the winter, spring and early summer. To evaluate how a warmer climate is likely to alter the snow cover and soil temperature in Scots pine stands of varying ages in northern Sweden, climate scenarios from the Swedish regional climate modelling programme SWECLIM were used to drive a Soil-Vegetation-Atmosphere Transfer (SVAT)-model (COUP). Using the two CO₂ emission scenarios A and B in the Hadley centres global climate model, HadleyA and HadleyB, SWECLIM predicts that the annual mean air temperature and precipitation will increase at most 4.8°C and 315 mm, respectively, within a century in the study region. The results of this analysis indicate that a warmer climate will shorten the period of persistent snow pack by 73–93 days, increase the average soil temperature by 0.9–1.5°C at 10 cm depth, advance soil warming by 15–19 days in spring and cause more soil freeze–thaw cycles by 31–38%. The results also predict that the large current variations in snow cover due to variations in tree interception and topography will be enhanced in the coming century, resulting in increased spatial variability in soil temperatures.     

The effects of boreal forest expansion on the summer Arctic frontal zone

Over the last 100?years, Arctic warming has resulted in a longer growing season in boreal and tundra ecosystems. This has contributed to a slow northward expansion of the boreal forest and a decrease in the surface albedo. Corresponding changes to the surface and atmospheric energy budgets have contributed to a broad region of warming over areas of boreal forest expansion. In addition, mesoscale and synoptic scale patterns have changed as a result of the excess energy at and near the surface. Previous studies have identified a relationship between the positioning of the boreal forest-tundra ecotone and the Arctic frontal zone in summer. This study examines the climate response to hypothetical boreal forest expansion and its influence on the summer Arctic frontal zone. Using the Weather Research and Forecasting model over the Northern Hemisphere, an experiment was performed to evaluate the atmospheric response to expansion of evergreen and deciduous boreal needleleaf forests into open shrubland along the northern boundary of the existing forest. Results show that the lower surface albedo with forest expansion leads to a local increase in net radiation and an average hemispheric warming of 0.6°C at and near the surface during June with some locations warming by 1–2°C. This warming contributes to changes in the meridional temperature gradient that enhances the Arctic frontal zone and strengthens the summertime jet. This experiment suggests that continued Northern Hemisphere high-latitude warming and boreal forest expansion might contribute to additional climate changes during the summer.     

Estimation of possible climate change impacts on water availability, extreme flow events and soil moisture in the Goulburn and Ovens Basins, Victoria

A rainfall-runoff model (IHACRES) is applied on a daily timestep to a large area of the state of Victoria, Australia. Successful calibrations of this dynamic lumped parameter model were performed for 5 rivers contributing streamflow to the Ovens Basin, and for 9 rivers of the Goulburn Basin. This is the first application of the model on such a scale, involving two basins where the total drainage area of the catchments modelled is about 6,500 km². The models were tested by simulation over the entire common period of observation for the 14 catchments under consideration. The results show that the models closely simulate the observed streamflow.The effect of historical climate variability on streamflow was investigated. The models were used for estimation of the potential impact of climatic change on water availability for irrigation for different climate scenarios developed in the Division of Atmospheric Research, CSIRO. This allows conditional estimates to be made of water supply in these basins for the periods 2030 and 2070 under current vegetation conditions. Projecting the future hydrologic regime in this region is extremely important, in particular for supporting irrigation management of the Basin.The problem of estimating the impact of climate change on the probability of extreme events of the hydrological regime was analysed. Flood frequency was found to increase for the scenarios providing the maximum amount of water; to 50% at 2030 and 100% at 2070. The probability of flood events for the dry scenarios rapidly decreases for these dates. Drought frequency, as defined by a soil wetness index, increased 35% for the dry scenario at 2030 and 80% for this scenario at 2070.     

An assessment of potential change in wildfire activity in the Russian boreal forest zone induced by climate warming during the twenty-first century

The problem of forest fires is very important for Russia. In this paper we consider this problem in the connection with the projection of significant climate change. An approach to determine the magnitude of change in wildfire risk in Russia under the influence of climate warming is discussed. Observations for the European part of Russia and for Siberia have been used in this analysis. A statistical correlation between drought indices calculated by use of monthly sums of temperature and precipitation and the frequency of fire danger was obtained for the forest zone of Russia. The change in fire danger potential was evaluated using temperature and precipitation monthly means at the nodes of a regular spatial grid. Climate change scenarios were obtained from Global Climate Models (GCM) ensemble projections. The maximum increases (about 12–30%) of the number of days with fire danger conditions during the twenty-first century fire season were obtained for the southern forest zone boundary in both the European region of Russia and in Siberia. In the Baikal and Primoriye Regions, fire danger distributions in the twenty-first century are not projected to change significantly.     

基于土壤湿度和年际增量方法的中国夏季气温预测试验

本文利用中国160站月平均气温资料和欧洲中心ERA-Interim逐月再分析表层土壤湿度资料,通过相关分析选取欧亚大陆9个关键区的土壤湿度年际增量作为预测因子,采用变形的典型相关分析(BP-CCA)结合集合典型相关分析(ECC)的方法建立集合预测模型,对我国东部夏季气温年际增量进行预测,进而预测夏季气温。其中,1980—2004年的资料用于历史拟合试验,而2005—2014年的资料用于独立样本预测试验。首先利用BP-CCA方法对9个因子分别建立单因子预测模型,然后采用ECC方法对9个预测因子按照不同的组合方式建立集合预测模型,并且分析预测技巧。结果表明,不同预测因子的组合对我国夏季气温的预测能力不同:勒拿河下游地区、中国黄河以南地区、叶尼塞河下游地区、西西伯利亚平原地区以及印度半岛西北部地区的土壤湿度对华北夏季气温预测效果较好;中国黄河以南地区、叶尼塞河下游地区、印度半岛西北部地区、贝加尔湖东北地区以及贝加尔湖以西地区的土壤湿度对江淮夏季气温有较高预测技巧。所建立的两组集合预测模型均显示了较好的实际预测能力:华北气温预测模型预测气温距平的同号率为8/10,平均均方根误差为3.4%;江淮气温预测模型预测气温距平的同号率为7/10,平均均方根误差为2.7%。并且两组模型预测出的华北和江淮气温的预测评分(PS)均超过80分,而国际上通用的距平相关系数(ACC)均在0.3以上。这说明土壤湿度因子中包含对我国夏季气温有用的预测信号,可以考虑将土壤湿度应用于夏季气温预测业务中。     

基于集合卡尔曼滤波的土壤温湿度同化试验

以通用陆面模式CLM 3.0(Community Land Model 3.0)为模型算子,基于集合卡尔曼滤波(Ensemble Kalman Filter,En KF)发展了一个土壤温湿度同化系统,主要用于改进模式对土壤温湿度和地表水热通量的模拟精度,并考察集合样本数、同化频率及不同观测量的组合对同化效果的影响。该系统同化了FLUXNET两个站点(阿柔和Bondville)不同土壤深度、不同时间频率的土壤温度和湿度数据。通过对阿柔站不同集合样本数的设计,综合考虑计算成本和计算精度,最终将集合样本数设置为40。通过分析三种同化方案对同化频率的敏感性得出,同化土壤温度最为敏感,同时同化土壤温湿度次之,同化土壤湿度最不敏感。对于阿柔站点,同化系统对不同土壤深度温度和湿度的模拟精度均能提高90%,潜热通量的均方根误差由94.0 W·m~(-2)降为46.3 W·m~(-2),感热通量均方根误差由55.9 W·m~(-2)降为24.6 W·m~(-2)。Bondville站点浅层土壤温度的改进在30%左右,深层土壤温度改进达到60%,对土壤湿度的改进均在70%以上,潜热通量和感热通量的均方根误差分别从57.4 W·m~(-2)和54.4 W·m~(-2)降为51.0 W·m~(-2)和42.5 W·m~(-2)。试验结果表明,同化站点土壤温湿度数据对土壤水热状况及通量的模拟改进非常有效,同时也验证了同化土壤水分遥感产品的可行性和必要性。     

前期土壤湿度、海表面温度对中国夏季极端气温的预测能力评估

基于中国587站日最高、最低气温观测资料、月平均的ERA_interim土壤湿度（Soil Moisture,SM）再分析资料及扩展重建的海表面温度（Sea Surface Temperature,SST）资料（ERSST）,对极端气温指数进行了定义,利用变形的典型相关分析和集合典型相关分析方法（Ensemble Canonical Correlation,ECC）,分析了1979-2009年我国夏季极端气温与前期（春、前冬）SM、SST间的线性联系,建立了中国夏季极端气温预测模型,并对独立样本检验的效果进行了评估。结果表明：1）与中国夏季极端气温联系密切的前期SST异常的空间分布为类PDO（Pacific Decadal Oscillation）型,前期土壤湿度异常的区域为华南、青藏高原、东北和西北地区。2）交叉检验结果表明基于前冬预测因子的极端气温预测模型技巧高于春季,基于SM的极端气温预测模型技巧高于SST。3）独立样本检验表明基于前期SM、SST的ECC模型对中国东部夏季极端气温有一定的预测能力。因此,可以在夏季极端气温的预测业务中考虑前期SM、SST的影响。     

The impact of soil moisture availability upon the partition of net radiation into sensible and latent heat fluxes

The impact of soil moisture availability on the Bowen ratio and on the partition of net radiation flux into sensible, latent and soil heat fluxes was investigated by using one-dimensional primitive equations with a refined soil parameterization scheme. Simulation results presented that as soil moisture availability increases, the Bowen ratio and the partition of net radiation flux into sensible and soil heat fluxes decrease. The partition of net radiation flux in-to latent heat flux, however, increases. Quantitative relationships between Bowen ratio and the partitions with soil moisture availability were also given in this study.     

Relevance of ion-induced nucleation of sulfuric acid and water in the lower troposphere over the boreal forest at northern latitudes

The relevance of ion-induced nucleation of sulfuric acid and water (IINSW) in the troposphere over the boreal forest at northern latitudes is investigated by combining two existing and previously published models (MALTE — model to predict new aerosol formation in the lower troposphere; PARNUC — a parameterized steady-state model of neutral and ion-induced nucleation of sulfuric acid and water for atmospheric conditions). Simulations were performed for 4 days with observed new particle formation at ground level by using input data from the SMEAR II station in Hyytiälä, Finland. The selected days were chosen to cover a wide range of values of the parameters most relevant for IINSW. The results showed that ion-induced nucleation of sulfuric acid and water can contribute up to 15% to the total amount of newly formed particles in the size range of 3–10 nm inside the mixed layer at the Hyytiälä site. The importance of IINSW seemed to increase in the free troposphere above the boundary layer, however, lack of measurements in the vertical structure of the input parameters suggest that the model results are burdened with high uncertainties.     

Relevance of ion-induced nucleation of sulfuric acid and water in the lower troposphere over the boreal forest at northern latitudes

The relevance of ion-induced nucleation of sulfuric acid and water (IINSW) in the troposphere over the boreal forest at northern latitudes is investigated by combining two existing and previously published models (MALTE — model to predict new aerosol formation in the lower troposphere; PARNUC — a parameterized steady-state model of neutral and ion-induced nucleation of sulfuric acid and water for atmospheric conditions). Simulations were performed for 4 days with observed new particle formation at ground level by using input data from the SMEAR II station in Hyytiälä, Finland. The selected days were chosen to cover a wide range of values of the parameters most relevant for IINSW. The results showed that ion-induced nucleation of sulfuric acid and water can contribute up to 15% to the total amount of newly formed particles in the size range of 3–10 nm inside the mixed layer at the Hyytiälä site. The importance of IINSW seemed to increase in the free troposphere above the boundary layer, however, lack of measurements in the vertical structure of the input parameters suggest that the model results are burdened with high uncertainties.     

黄河源玛多县退化草地土壤温湿度变化特征

利用青藏高原中部玉树隆宝湿地2015年7月-2016年7月的观测资料,分析了土壤冻结、融化前后土壤温、湿度和地表能量收支特征,结果表明：冻土持续时期为12月至次年4月,深层土壤的冻结较浅层土壤滞后,融化过程快于冻结过程,5-40 cm土壤全部冻结历时51 d,全部融化历时19 d。土壤体积含水量年变化幅度达0.6 m³/m³。冻结过程5-40 cm土壤体积含水量下降,融化过程5-10 cm土壤体积含水量升高。土壤冻结之后,感热通量白天的值升高,潜热通量白天的值降低,净辐射和土壤热通量均降低,土壤热通量日变化幅度增大。土壤融化之后,潜热通量、净辐射和土壤热通量白天的值升高。地表反照率、鲍恩比、土壤热导率和土壤热扩散率冻结后增大融化后减小,土壤热容量冻结后减小融化后增大。