Application of a water balance model to estimating hay growth in the peace river region

Abstract

A model that uses daily climate data for calculating hay crop growth in the Peace River region of British Columbia was developed and evaluated using data obtained over four growing seasons. The performances of the ratio of growth to transpiration and the ratio of growth to transpiration (J) divided by vapour pressure deficit (VPD) in estimating crop growth were compared. Transpiration was calculated by subtracting evaporation losses from the soil and foliage from the calculated evapotranspiration. Evapotranspiration was calculated using solar radiation and air temperature, and a one‐layer root zone water balance model, which accounted for soil water supply limitation. Soil water storage measurements showed that the water balance model worked well. The model provided satisfactory estimates of growing season yield of above‐ground dry matter. The use of the ratio of growth toT/ vpd showed no improvement in growth estimation over the ratio of growth to transpiration.     

辽宁春玉米出苗期水分胁迫试验初探

以丹玉39为试验材料,采用盆栽实验方法,研究辽宁春玉米25%、35%、45%、55%、65%、75%、85%、95%共8种供水处理条件下的玉米出苗率及玉米根系和叶片对水分胁迫的响应,旨在探索辽宁春玉米播种和出苗期间水分胁迫对玉米出苗及生长发育的影响,分析不同水分胁迫对其影响的程度。结果表明：玉米出苗率在中度到重度干旱条件下(<45%),为不能播种指标;在轻度干旱条件下(55%),为非经济播种指标;在适宜土壤水分条件下(65%—75%),为适宜播种指标;在85%左右时也为适宜播种指标;在偏湿条件下(95%),为可播种指标。玉米出苗期间,水分胁迫对玉米植株和根系的生长发育有较大影响,对根系影响比对植株的影响更显著。     

The influence of atmospheric stratification on the growth of water waves

The atmospheric surface layer over sea has a density stratification which varies with moisture content and air/sea temperature difference. This influences the growth of water waves. To study the effect quantitatively, the Reynolds equations are solved numerically. For given wind speed and surface roughness, wave growth is found to be more rapid in unstably stratified conditions than in stable conditions. This is due to an increase in turbulence, primarily caused by an increase of mixing length.Under the assumption of a Charnock relation between surface roughness and friction velocity, it is found that for large inverse wave age (u _*/c>0.07), the effect of stratification on wave growth is weell described by Monin-Obukhov scaling of the friction velocity. For smaller values ofu _*/c, Monin-Obukhov scaling overpredicts.The effect on duration-limited wave growth is studied with the third-generation WAM surface wave model driven by 10 m winds. Effects of stratification on the significant wave height are found to be of the order of 10%. The results are comparable to those of a recent reanalysis of field measurements, although the measured stratification effect is somewhat stronger. Implementation of a stratification-dependent growth in wave models is recommended, as it can lead to small but significant improvements in wave forecasts when accurate air and sea temperatures are available.     

承德春玉米需水量变化及其与气象因子的关系

利用1961—2009年气象资料和发育期资料,采用FAO的Penman-Monteith公式计算春玉米生育期内逐日需水量,研究承德春玉米需水量、水分盈亏的年内、年际变化规律,分析气象因子对春玉米需水量的影响。结果表明：承德春玉米生育期平均需水总量、水分盈亏分别为522.5 mm和69.4 mm。在生育期内,春玉米逐日需水量的变化规律表现为先缓慢增加后减小;春玉米需水量与气象因子密切相关。     

Growth of homogeneously nucleated water droplets: a quantitative comparison of experiment and theory

The formation of aerosols proceeds through nucleation, growth and aging stages. The understanding of nucleation and droplet growth is essential for handling the more complex atmospheric condensation processes. To achieve this goal, measurements of the nucleation rate of various systems are performed in an expansion chamber. In this manner nucleation and growth are decoupled by applying a short nucleation pulse of about 1 ms during which the nuclei are formed. The subsequent droplet growth is quantitatively monitored by Mie-scattering. To this end, the Mie-maxima and -minima are detected as a function of time and compared to theoretical Mie-scattering calculations for increasing radii. In this fashion, a wealth of growth curves for pure water depending on supersaturations, number densities of droplets, and temperatures were obtained. Following the approach of Fuchs and Sutugin [Fuchs, N.A., Sutugin, A.G., 1970. Highly Dispersed Aerosols. Ann Arbor Science Publishers, Ann Arbor; Fuchs, N.A., Sutugin, A.G., 1971. In: Hidy, G.M., Brock, J.R. (Eds.), International Reviews in Aerosol Physics and Chemistry: Topics in Current Aerosol Research (Part 2), Pergamon, New York, p. 1], we calculated theoretical growth curves taking into account the depletion of water vapor, the increase of droplet- and system-temperature, temperature-dependent functions of the diffusion coefficient, surface tension, liquid density and latent heat of condensation. The calculated growth curves and experimental data for 230, 240 and 250 K with number densities of droplets between 5×10² and 2×10⁶ droplets/cm³ yield quantitative agreement between theory and experiment. This is remarkable in so far as the theory contains no adjustable parameters and assumes the sticking probability of the vapor molecules to be unity. Using a sticking probability smaller than 0.8 in the calculation leads to growth functions already outside the experimental error.     

Risky responsibilities for rural drinking water institutions: The case of unregulated self-supply in Bangladesh

The drinking water sector is off track to reach Sustainable Development Goal (SDG) 6.1 with over a quarter of the world’s population lacking safe and reliable services. Policy approaches are shifting away from provision of access towards managing the multiple risks of water supply and quality. By considering how infrastructure, information, and institutional systems evolved in Bangladesh, this article identifies the unintentional consequences of reallocating management responsibility for rural water services away from government agencies towards individuals and households.Between 2012 and 2017, we estimate up to forty-five unregulated tubewells were installed privately for every publicly funded rural waterpoint. This growth rate more than doubled total national waterpoint infrastructure since 2006. The scale of growth is reflected in the declining ratio of households per tubewell from over fifty-seven in 1982 to less than two in 2017, potentially approaching market saturation. This scale of growth aligns to an observed decrease in the real price of private market shallow tubewells by seventy percent between 1982 and 2017. In 2018, we estimate households invested up to USD253 million in tubewells, nearly sixty-five percent of the total national water and sanitation sector’s household-level finance. In effect, household investments became critical to achieve the Millennium Development Goal (MDG) target of improved infrastructure access, but now pose challenges for meeting targets of safely managed services. The scale of continued private investment provides an opportunity for policymakers to explore blended public finance models to meet emerging consumer preferences, while at the same time introducing regulatory and monitoring systems.     

江西省土壤体积含水量对降水的响应特征

利用2017—2020年江西省36站壤土质地土壤水分观测站土壤体积含水量资料和降水资料,研究了江西省土壤体积含水量对降水过程的响应特征.结果表明:1)土壤体积含水量对不同类型降水过程的响应差异大,对于小于10 mm的降水过程几乎无响应,对10—25 mm的降水过程响应深度为0—10 cm,对25—50 mm的降水过程响应深度为0—20 cm,对大于50 mm的降水过程响应深度为0—60 cm.2)土壤体积含水量对降水的响应分为快速增长和平稳减弱两个阶段,在快速增长阶段土壤体积含水量先快速增长到最大值,然后缓慢下降,且增长阶段的持续时间小于减弱阶段的持续时间,增长过程和减弱过程不对称.3)响应过程的持续时间主要集中在1—9 h,其中3—6 h占比高达49％.     

Influence of leaf water potential on diurnal changes in CO2 and water vapour fluxes

Mass and energy fluxes between the atmosphere and vegetation are driven by meteorological variables, and controlled by plant water status, which may change more markedly diurnally than soil water. We tested the hypothesis that integration of dynamic changes in leaf water potential may improve the simulation of CO₂ and water fluxes over a wheat canopy. Simulation of leaf water potential was integrated into a comprehensive model (the ChinaAgrosys) of heat, water and CO₂ fluxes and crop growth. Photosynthesis from individual leaves was integrated to the canopy by taking into consideration the attenuation of radiation when penetrating the canopy. Transpiration was calculated with the Shuttleworth-Wallace model in which canopy resistance was taken as a link between energy balance and physiological regulation. A revised version of the Ball-Woodrow-Berry stomatal model was applied to produce a new canopy resistance model, which was validated against measured CO₂ and water vapour fluxes over winter wheat fields in Yucheng (36°57′ N, 116°36′ E, 28 m above sea level) in the North China Plain during 1997, 2001 and 2004. Leaf water potential played an important role in causing stomatal conductance to fall at midday, which caused diurnal changes in photosynthesis and transpiration. Changes in soil water potential were less important. Inclusion of the dynamics of leaf water potential can improve the precision of the simulation of CO₂ and water vapour fluxes, especially in the afternoon under water stress conditions.     

An instability mechanism in the atmosphere over a water body

Summary ?The previously unexplored mechanism of the hydrodynamic instability of the atmospheric boundary layer over a water body is theoretically investigated. In air, stratified with respect to moisture, vertical motions produce variations in specific humidity (mixing ratio) near the interface surface. This, in turn, causes variation in evaporation from the water surface and horizontal thermal inhomogeneities result on the surface which, under certain conditions, can strengthen the initial vertical motions. In this paper the linear problem of the stability of the system under consideration is solved. Boundaries of the unstable region in the space of physical parameters are defined, and specific values of growth rates of disturbances are investigated. The results show the possibility of the development of disturbances with horizontal scales of several hundred metres for a period of about one hour even for the stable stratified atmospheric layer over a water surface and in the absence of destabilizing shears of velocity. The horizontal sizes of the most rapidly growing modes, as a rule, are an order of magnitude larger than the vertical ones. Received November 17, 1998; revised November 20, 2001     

Estimating economic effects of changes in climate and water availability

Social, economic, and environmental systems can be vulnerable to disruptions in water supplies that are likely to accompany future climate changes. Coupled with the challenges of tightening environmental regulations, population growth, economic development and fiscal constraints water supply systems are being pushed beyond the limits of their design and capacity for maintenance. In this paper we briefly review key economic concepts, various economic measures and metrics, and methods to estimate the economic effects on water resources from water supply changes that could accompany climate change. We survey some of the recent empirical literature that focuses on estimates developed for U.S. watersheds at both national and regional scales. Reported estimates of potential damage and loss associated with climate and water supply changes that we observe are significant, though often the metrics vary and make valid and consistent direct cross-comparisons difficult. Whether in terms of changes in GDP or in terms of estimated changes in economic welfare based on associated changes in economic costs and benefits, both national and regional estimates suggest that governments and organizations incorporate prudent steps to assess vulnerabilities to plausible future water supply and demand scenarios and develop responsive adaptation strategies.     

1971-2018年黑龙江省玉米需水量与有效降水量耦合度演变特征

基于1971—2018年黑龙江省69个气象台站逐日气象资料,利用联合国粮农组织(FAO)推荐方法计算玉米需水量,应用美国农业部土壤保持局推荐方法计算有效降水量,采用Mann-Kendall检验、GIS反距离加权插值等方法分析黑龙江省玉米需水量与有效降水量耦合度及其演变特征。结果表明：黑龙江省玉米拔节以前生育时段大部地区有效降水增加,拔节以后各生育阶段大部地区有效降水呈减少趋势,不同区域变化趋势略有不同。受风速变小和日照时间减少等气象因子影响,黑龙江省大部地区玉米需水量减少,东部减速最快,北部最慢。黑龙江省中部和东北部玉米需水量与有效降水量耦合度较高,西部较低;拔节以前耦合度较低,拔节以后较高。各区域耦合度均呈“两落两起”变化趋势,2011—2012年为耦合度由低到高明显突变点。     

拉萨夏季大气可降水量的演变特征及其与降水的关系

根据拉萨站近40 a(1969—2008年)探空观测资料以及同期的地面降水资料,分析了拉萨近40 a夏季大气可降水量和地面降水的演变特征及其关系.结果表明:该站夏季大气可降水量和降水存在显著的正相关关系,两者存在相同的年际和年代际变化,均具有准3 a年际振荡和准11 a左右的年代际振荡;近40 a来两者均呈现出上升趋势,其中降水的增加趋势明显,其增幅大于可降水量的增幅.进一步通过对拉萨夏季降水转化率分析得知,拉萨夏季平均降水转化率约为26.06%,但存在明显的年际差异,夏季降水转化率最大值约为最小值的3倍;夏季降水转化率正(负)异常年,拉萨地区低层的辐合和高层的辐散均明显增强(减弱),拉萨地区垂直速度将增加(减弱),从而有(不)利于降水形成.     

水分胁迫对华北平原冬小麦地上部分及产量的影响

以“济麦-22”为供试品种,利用中国气象局固城生态环境与农业气象试验站大型根系观测系统,研究冬小麦在重度干旱胁迫（≤40.0%）、轻中度干旱胁迫（40.1%-55.0%）和适宜（55.1%-80.0%）3种水分胁迫条件下地上部分对水分胁迫的响应,以探索水分胁迫对华北平原冬小麦产量的影响,分析不同水分胁迫对冬小麦产量的影响程度。结果表明：华北平原冬小麦在轻中度干旱胁迫和重度干旱胁迫下,小麦全生育期的天数缩短,株高、叶面积及灌浆速率均呈不同程度的减少。3种水分胁迫的株高增长量为适宜>轻中度胁迫>重度胁迫,灌浆速率为适宜>轻中度胁迫>重度胁迫。土壤水分胁迫引起冬小麦物质分配更多地向支持生长的茎秆转移,在生长发育过程中受到水分胁迫,小麦产量将降低,重度胁迫条件下小麦产量为适宜水分条件的69%。     

Modelling the sensitivity of wheat growth and water balance to climate change in Southeast Australia

A simulation study was carried out to assess the potential sensitivity of wheat growth and water balance components to likely climate change scenarios at Wagga Wagga, NSW, Australia. Specific processes considered include crop development, growth rate, grain yield, water use efficiency, evapotranspiration, runoff and deep drainage. Individual impacts of changes in temperature, rainfall and CO₂ concentration ([CO₂]) and the combined impacts of these three variables were analysed for 2050 ([CO₂] = 570 ppm, T +2.3°C, P ?7%) and 2070 ([CO₂] = 720 ppm, T +3.8°C, P ?10%) conditions. Two different rainfall change scenarios (changes in rainfall intensity or rainfall frequency) were used to modify historical rainfall data. The Agricultural Production Systems Simulator (APSIM) was used to simulate the growth and water balance processes for a 117 year period of baseline, 2050 and 2070 climatic conditions. The results showed that wheat yield reduction caused by 1°C increase in temperature and 10% decrease in rainfall could be compensated by a 266 ppm increase in [CO₂] assuming no interactions between the individual effects. Temperature increase had little impact on long-term average water balance, while [CO₂] increase reduced evapotranspiration and increased deep drainage. Length of the growing season of wheat decreased 22 days in 2050 and 35 days in 2070 conditions as a consequence of 2.3°C and 3.8°C increase in temperature respectively. Yield in 2050 was approximately 1% higher than the simulated baseline yield of 4,462 kg ha^???1, but it was 6% lower in 2070. An early maturing cultivar (Hartog) was more sensitive in terms of yield response to temperature increase, while a mid-maturing cultivar (Janz) was more sensitive to rainfall reduction. Janz could benefit more from increase in CO₂ concentration. Rainfall reduction across all rainfall events would have a greater negative impact on wheat yield and WUE than if only smaller rainfall events reduced in magnitude, even given the same total decrease in annual rainfall. The greater the reduction in rainfall, the larger was the difference. The increase in temperature increased the difference of impact between the two rainfall change scenarios while increase in [CO₂] reduced the difference.     

大气水汽中双水缔合分子的浓度

用化学热力学方法计算了在标准气压下,不同温度的饱和水汽中双水缔合分子的浓度以及在一定水汽压条件下双水缔合分子的浓度随温度的变化。计算结果与8—13μ大气窗区水汽吸收系数随温度的变化进行了比较,证明双水缔合分子的吸收是8—13μ水汽连续吸收的主要因子。     

Impact of future climate change on wheat production in relation to plant-available water capacity in a semiaridenvironment

Conceptions encompassing climate change are irreversible rise of atmospheric carbon dioxide (CO₂) concentration, increased temperature, and changes in rainfall both in spatial- and temporal-scales worldwide. This will have a major impact on wheat production, particularly if crops are frequently exposed to a sequence, frequency, and intensity of specific weather events like high temperature during growth period. However, the process of wheat response to climate change is complex and compounded by interactions among atmospheric CO₂ concentration_, climate variables, soil, nutrition, and agronomic management. In this study, we use the Agricultural Production Systems sIMulator (APSIM)-wheat model, driven by statistically downscaled climate projections of 18 global circulation models (GCMs) under the 2007 Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 CO₂ emission scenario to examine impact on future wheat yields across key wheat growing regions considering different soil types in New South Wales (NSW) of Australia. The response of wheat yield, yield components, and phenology vary across sites and soil types, but yield is closely related to plant available water capacity (PAWC). Results show a decreasing yield trend during the period of 2021–2040 compared to the baseline period of 1961–1990. Across different wheat-growing regions in NSW, grain yield difference in the future period (2021–2040) over the baseline (1961–1990) varies from +3.4 to ?14.7 %, and in most sites, grain number is decreased, while grain size is increased in future climate. Reduction of wheat yield is mainly due to shorter growth duration, where average flowering and maturing time are advanced by an average of 11 and 12 days, respectively. In general, larger negative impacts of climate change are exhibited in those sites with higher PAWC. Current wheat cultivars with shorter growing season properties are viable in the future climate, but breading for early sowing wheat varieties with longer growing duration will be a desirable adaptation strategy for mitigating the impact of changing climate on wheat yield.     

The collection efficiency of a rime-covered target for water droplets

A laboratory investigation of the collection efficiency of a target riming by the collection of supercooled water droplets has shown that the target, which represents a soft-hailstone inside a thundercloud, collects more droplets than theory indicates. The additional growth is due to enhanced collection on the “feathers of rime” that grow on the target surface. The effect is greatest when the rime density is low, which occurs with low droplet impact speeds and at cold temperatures.By comparison of the results with collision efficiency theory for smooth targets, it is possible to determine an effective target size. For example, at an impact speed of 3 m s⁻¹, a rough 5 mm diameter collector has an effective smooth diameter of 3.2 mm and at 5 m s⁻¹ the effective smooth diameter is 4.8 mm.This work has relevance to the charging of soft-hail within thunderstorms where the charge transfer is highly sensitive to the surface conditions of the hail pellet.     

Upward flushing of sea water through first year ice

Abstract

Observations in both the ice and slush layers suggest that sea water intrudes into the snow layer following a snow storm. Ice temperature values recorded at 1 cm below the snow‐ice interface show that the upward flux of sea water is of short duration. This is followed by a period of intense brine drainage characterized by the migration of a salty brine layer, with salinities up to 42 psu. These results suggest that a snow storm induces a complete (upward) flushing of the brine channel network and major modifications of snow and ice characteristics.

Melt rates and downward brine fluxes were calculated using salinity measured in a 40 cm deep box placed on the ice‐water interface, which isolated a 50 × 50 cm area of sea ice from ocean mixing processes. In this semi‐isolated environment, observed salinity changes allowed us to determine melt water fluxes and brine drainage or flushing even though ice thickness measurements did not show any significant change. Melt rates up to 21 cm/month and equivalent growth rates up to 32 cm/month were measured.     

Possible impacts of climatic warming scenarios on water resources in the Saskatchewan River Sub-basin,Canada

Regional scale studies of the impacts of global warming scenarios provide a useful mechanism for identifying potential regional sensitivities, data gaps and research needs, and for raising awareness of the global warming issue at the regional level. Thus, a pilot study of water resources in the Saskatchewan River Sub-basin was undertaken in order to provide first-cut estimates of impacts in this region, and to identify future research needs. Thirty scenarios were constructed, using two hypothetical growth rates for irrigation, five scenarios based on outputs from General Circulation Models (GCMs), and ten hypothetical warming scenarios. During the course of this study, a number of methodological questions were raised, including the representativeness of data points, interpolation of observed and scenario data, and the quantification of uncertainty.Results indicated decreases in summer soil moisture and increases in irrigation demand, but no consensus on changes in runoff or annual net basin supply, primarily due to differences in the GCM-based scenario output at the Rocky Mountains, the major source region for runoff. There were a number of recommendations for follow-up research and monitoring.