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1.
Water stored as part of the land surface is lost to evapotranspiration and runoff on different time scales,and the partitioning between these time scales is important for modeling soil water in a climate model.Different time scales are imposed on evapotranspiration primarily because it is derived from different reservoirs with different storage capacities, from the very rapid evaporation of canopy stores to the slow removal by transpiration of rooting zone soil moisture. Runoff likewise ranges in time scale from rapid surface terms to the slower base-flow. The longest time scale losses of water determine the slow variation of soil moisture and hence the longer time scale effects of soil moisture on precipitation. This paper shows with a simple analysis how shifting the partitioning of evapotranspiration between the different reservoirs affects the variability of soil moisture and precipitation. In particular, it is concluded that a shift to shorter time scale reservoirs shifts the variance of precipitation from that which is potentially predictable to unpredictable. 相似文献
2.
具有Horton及Dunne机制的径流模型在VIC模型中的应用(英) 总被引：20，自引：0，他引：20
地表径流主要由蓄满(Dunne)和超渗产流(Horton)机制产生;土壤性质的空间变异性、前期土壤水、地形及降水的空间变异性导致不同的径流机制。在研究区域或模型网格内,蓄满产流及超渗产流可能同时出现,缺乏考虑任何一种机制以及土壤性质的次网格空间变率可能导致地表径流的过高或过低估计,从而影响土壤水的计算。利用Philip入渗公式用于时间压缩逼近(TCA)给出了一种径流参数化方法,该方法可以动态实现模型网格中的Horton及Dunne产流机理,它考虑了土壤空间变异性对Horton和Dunne径流的影响。该径流模型应用到基于水文原理的陆面过程模型VIC,在淮河流域及美国宾西法尼亚州的一个流域进行了测试,结果表明:新的参数化方法对地表径流和土壤水分含量的分配起着重要作用,对于改进径流和土壤水的模拟有重要意义。 相似文献
3.
Summary Water stored in the soil serves as a reservoir for the evapotranspiration (ET) process on land surfaces, therefore knowledge of the soil moisture content is important for partitioning the incoming solar radiation into latent and sensible heat components. There is no remote sensing technique which directly observes the amount of water in this reservoir, however microwave remote sensing at long wavelengths (>10 cm) can give estimates of the moisture stored in the surface 5-cm layer of the soil. This approach is based on the large dielectric contrast between water and dry soil, resulting in emissivity changes from 0.96 for a dry smooth soil to less than 0.6.In this paper, basic relationships between soil moisture and emissivity are described using both theory and observations from various platforms. The ability of the approach to be extended to large regions has been demonstrated in several aircraft mapping experiments, e.g., FIFE, Monsoon 90, Washita 92 and HAPEX Sahel. Some results from Monsoon 90 are presented here. Applications of these soil moisture maps in runoff prediction, rainfall estimation, determining the direct evaporation from the soil surface and serving as a boundary condition for soil profile models are presented.With 10 Figures 相似文献
4.
A non-hydrostatic modeling study of surface moisture effects on mesoscale convection induced by sea breeze circulation 总被引：1，自引：0，他引：1
Summary Convection and subsequent precipitation induced by the sea breeze circulations are often observed in the Florida peninsula during summer. In this study, the mechanisms of initiation and maintenance of the convective clouds and precipitation are investigated. A fully-compressible fine resolution non-hydrostatic mesoscale numerical model is used in this study. Surface energy and moisture budget were included in this model to simulate the diurnal cycle of ground surface temperature and wetness. The model also has a sophisticated boundary layer and explicit cloud physics. A sounding obtained from Orlando, Florida at 1110 UTC 17 July 1991 as part of the Convection and Precipitation Electrification (CaPE) experiment is used for initialization. The initial data for the model is kept in geostrophic and thermal wind balance. Several sensitivity tests were conducted to investigate the effects of different treatments of ground surface moisture and temperature on the model forecast of the convection and precipitation induced by the sea breeze circulations. The simulations agree reasonably well with the observations when both surface energy and moisture budget were included in the model to predict ground surface temperature and wetness. The surface moisture has a significant impact on the formation, strength, sustenance, and the location of convection and precipitation induced by the sea breezes.With 17 Figures 相似文献
5.
Abstract Second generation land surface schemes are the subject of much development activity among atmospheric modellers. This work is aimed at, among other things, improving the representation of the soil water balance in order to simulate, more properly, exchanges with the atmosphere and to permit the use of model output to generate streamflow for model validation. The Canadian development program is centred on CLASS, the Canadian Land Surface Scheme, developed at Environment Canada. This paper focuses on the improvement of hydrology in CLASS. This was accomplished by designing a two‐way interface to WATFLOOD, a distributed hydrologic model developed at the University of Waterloo. The two models share many features, which facilitated the coupling procedure. The interface retains the three‐layer vertical moisture budget representation in CLASS but adds three horizontal runoff possibilities. Runoff from the surface water follows Manning's equation for overland flow. Interflow is generated from the near‐surface soil layer using a parametrization of Richard's equation and base flow is produced by Darcian flow from the bottom of layer 3. An approximation of the internal topography of grid elements is used to supply horizontal gradients for the runoff components. Tests are in progress in four Canadian study areas. Initial results are presented for the summer of 1993 for the Saugeen River in southwestern Ontario. The new scheme produces realistic hydrographs, whereas the old scheme did not. Bare ground evaporation is reduced by about 17% as a consequence of reduced water availability in layer 1. Evapotranspiration is not affected because the rooting depth extends into layer 3, in which soil moisture does not change appreciably with the new scheme. These results suggest that the new scheme improves the representation of streamflow in WATFLOOD/CLASS and of the soil moisture budget in CLASS. Work is in progress to validate this result over basins, such as the BOREAS study watersheds, where both runoff and evapotranspiration measurements are available. 相似文献
6.
D.L. Verseghy 《大气与海洋》2013,51(3):435-456
Abstract The performance of two Canadian land surface schemes of widely differing complexity is compared and contrasted in a pair of year‐long simulations using the GCM developed at Atmospheric Environment Service, Canada. The old land surface model incorporates the force‐restore method for soil temperatures and the bucket approximation for soil moisture; the new model, CLASS (Canadian Land Surface Scheme) features three soil layers, an explicitly modelled snow layer, a thermally separate vegetation canopy, and physically‐based calculations of heat and moisture transfers between all of the land surface components and the atmosphere. It was reported in previous papers that compared with observations, the old scheme tends to generate a climate which is characterized by anomalously high precipitation rates and cold temperatures over land. In this paper, by reference to field measurements and to the energy fluxes and temperatures generated by the two models at local scales, the hypotheses earlier postulated as to the underlying reasons for this are validated. The main factor contributing to the climate anomalies observed with the old scheme is found to be its generation of excessive evaporation rates; this is caused by the fact that the evaporation rate is never directly energy‐limited, the fact that the scaling of the evaporation rale with decreasing soil moisture content underestimates the effect of vegetation stomatal resistance, and the fact that the evaporation rate over bare soil depends not on the surface soil moisture, but on the moisture content of whole modelled soil column. The cold surface temperatures are additionally attributed to systematic errors incurred by the forward‐stepping temperature scheme, and to the fact that soils subjected to subzero temperature forcing in the winter are modelling as freezing completely. Finally, the inability of the old scheme to simulate partially frozen soils means that it proves unable to handle either shallow frost penetration at temperature latitudes, or the development of an active layer in permafrost. 相似文献
7.
Evaluation of the atmospheric moisture and hydrological cycle in the NCEP/NCAR reanalyses 总被引：1，自引：0，他引：1
An evaluation is carried out of the moisture fields, the precipitation P and evaporation E, and the moisture transport and divergence in the atmosphere from the global atmospheric National Centers for Environmental Prediction (NCEP)–NCAR reanalyses produced with four-dimensional-data assimilation. The moisture fields are summarized by the precipitable water which is compared with analyzed fields from NVAP based primarily on Special Sensor Microwave Imager (SSM/I) over the oceans and rawinsonde measurements over land, plus TIROS Operational Vertical Sounder (TOVS). The moisture budgets are evaluated through computation of the freshwater flux at the surface E?P from the divergence of the total moisture transport, and this is compared with the reanalysis E?P that is based upon a 6-hour integration of the assimilating model and thus depends on the model parametrizations. The P field is evaluated using Xie– Arkin global precipitation estimates which, although containing considerable uncertainties, are believed to be reliable and good enough to show that there are substantial biases in the NCEP P. There are many fields of interest and which are improved over previous information available. On an annual mean basis the largest evaporation of over 6?mm/day is in the subtropical Indian Ocean. However, the NCEP moisture fields are shown to contain large and significant biases in the tropics. The tropical structures are less well defined and values are generally smaller where they should be high and higher where they should be low. In addition, the NCEP moisture fields contain less variability from year to year. The NCEP model P generally reveals a double intertropical convergence zone in the central Pacific and the location of the South Pacific Convergence Zone is not well captured. Rainfall amounts are lower than observed in the oceanic tropical convergence zones. The variability in the central tropical Pacific of P associated with El Niño-Southern Oscillation (ENSO) is underestimated in the NCEP reanalyses and, moreover, is not very well correlated with the Xie–Arkin product. A bias for too much rainfall in the model over the southeastern USA and southeast Asia is also present in northern summer. The comparison of E?P from the moisture budget with the model results reveal some strong systematic differences. In particular, remarkably, many island stations show up as bull’s-eyes in the difference field. These are identified as originating from small but systematic differences in vertical moisture profiles from those in the surrounding oceans, raising questions about the influence radius of rawinsonde moisture observations. Biases in E are inferred from the E?P differences in some places implying some spurious land moisture sources. While usually better, the residual method E?P estimates are inferior to those from the model parametrizations in some places. Both estimates are affected by biases in moisture, as analyzed, and the moisture divergence depends critically on the velocity divergence field. The model estimates also depend upon the parametrizations of subgrid scale processes, such as convection, that influence E and P. A discussion is given of sources of errors contributing to the moisture budgets. 相似文献
8.
长江流域水分收支以及再分析资料可用性分析 总被引：9，自引：0，他引：9
首先利用实测资料定量计算了长江流域水分收支的各分量,包括降水、径流、蒸发、水汽辐合等,分析其季节循环、年际变化以及线性趋势变化。结果表明,多年平均该流域是水汽汇区,主要来自平均流输送造成的水汽辐合,而与天气过程密切相关的瞬变波则主要造成流域的水汽辐散。蒸发所占比例接近于径流,对流域水分循环十分重要。大部分要素的季节变化和年际变化都很大,只有蒸发和大气含水量的年际变化较小。降水和平均流输送造成的水汽辐合一般在6月达到年内最大,12月达到年内最小,而径流和大气含水量则一般滞后1个月于7月达到年内最大,1月降为年内最小。1958—1983年,夏半年降水略微增加,冬半年略微减少,各月实测径流为弱的增长趋势,但均不显著,年平均蒸发亦无显著的趋势变化。然后将实测资料同ECMWF及NCEP/NCAR再分析资料作进一步对比分析,以检验两套再分析资料对长江流域水分循环的描述能力。在量值上,NCEP/NCAR再分析资料中的降水、蒸发、径流均比实测偏大很多,大气含水量及由平均流输送所造成的水汽辐合则偏小很多;ECMWF再分析资料中的降水量、径流量基本上与实测接近,蒸发量偏大,大气含水量及由平均流输送所造成的水汽辐合偏小,但比NCEP/NCAR再分析资料要接近实测。另外,该两套再分析资料均可以较好地描述长江流域水分收支的季节循环和年际变化,而且同样是ECMWF再分析资料与实测资料的一致性更好。但是两套再分析资料在1958—1983年均存在十分夸张的线性趋势变化,尤其是ECMWF再分析资料。 相似文献
9.
Satellite Monitoring of the Surface Water and
Energy Budget in the Central Tibetan Plateau 总被引：1，自引：0，他引：1
The water and energy cycle in the Tibetan Plateau is an important component of Monsoon Asia and the global energy and water cycle. Using data at a CEOP （Coordinated Enhanced Observing Period）-Tibet site, this study presents a first-order evaluation on the skill of weather forecasting from GCMs and satellites in producing precipitation and radiation estimates. The satellite data, together with the satellite leaf area index, are then integrated into a land data assimilation system （LDAS-UT） to estimate the soil moisture and surface energy budget on the Plateau. The system directly assimilates the satellite microwave brightness temperature, which is strongly affected by soil moisture but not by cloud layers, into a simple biosphere model. A major feature of this system is a dual-pass assimilation technique, which can auto-calibrate model parameters in one pass and estimate the soil moisture and energy budget in the other pass. The system outputs, including soil moisture, surface temperature, surface energy partition, and the Bowen ratio, are compared with observations, land surface models, the Global Land Data Assimilation System, and four general circulation models. The results show that this satellite data-based system has a high potential for a reliable estimation of the regional surface energy budget on the Plateau. 相似文献
10.
H. Douville 《Climate Dynamics》1998,14(3):151-172
Global soil moisture data of high quality and resolution are not available by direct observation, but are useful as boundary
and initial conditions in comprehensive climate models. In the framework of the GSWP (Global Soil Wetness Project), the ISBA
land-surface scheme of Météo-France has been forced with meteorological observations and analyses in order to study the feasibility
of producing a global soil wetness climatology at a 1°×1° horizontal resolution. A control experiment has been performed from
January 1987 to December 1988, using the ISLSCP Initiative I boundary conditions. The annual mean, the standard deviation
and the normalised annual harmonic of the hydrologic fields have been computed from the 1987 monthly results. The global maps
which are presented summarise the surface hydrologic budget and its annual cycle. The soil wetness index and snow cover distributions
have been compared respectively to the results of the ECMWF reanalysis and to satellite and in situ observations. The simulated
runoff has been validated against a river flow climatology, suggesting a possible underestimation over some large river basins.
Besides the control run, other simulations have been performed in order to study the sensitivity of the hydrologic budget
to changes in the surface parameters, the precipitation forcing and the runoff scheme. Such modifications have a significant
impact on the partition of total precipitation into evaporation and runoff. The sensitivity of the results suggests that soil
moisture remains one of the most difficult climatological parameters to model and that any computed soil wetness climatology
must be considered with great caution.
Received: 3 January 1997 / Accepted: 19 August 1987 相似文献
11.
土壤质地对中国区域陆面过程模拟的影响 总被引：6，自引：2，他引：4
利用陆面过程模式(CLM3.5)和中国区域两种土壤质地数据(分别来自第二次中国土壤调查SNSS和联合国粮食农业组织FAO),研究了土壤质地变化对于模式模拟的陆表水热变量的影响。结果显示,土壤质地对土壤水文学变量的影响远大于对土壤热力学变量的影响,尤其是对于饱和土壤含水量和饱和水力传导率的影响。对于模式的输出,土壤质地影响比较明显的有土壤湿度、总径流和土壤渗透等水文学变量以及地表潜热、地表感热和土壤热通量等热力学变量,而影响相对较小的有地面吸收的太阳辐射和地表反照率。同时,发现基于SNSS模拟的土壤湿度与站点观测值更加接近。因此,本研究认为基于SNSS土壤质地数据可以有效地改进模式模拟结果,建议以后在陆面模式试验中尽可能使用以观测为基础的SNSS土壤质地数据。 相似文献
12.
A regional mesoscale multi-level primitive equation model is used to predict the landfall and structure of a tropical cyclone. Three areas of model sensitivity are addressed in this paper; (1) the horizontal resolution, which includes the representation of orography; (2) the impact of an improved representation of the distribution of land surface soil moisture on the landfall problem; and (3) the sensitivity of the storm to lateral boundary conditions. A diagnostic part of this study describes a statistical regression approach to determining a ground wetness parameterization from moisture budget computations to derive estimates of surface fluxes, which are used to determine the parameterization. The model sensitivity analysis compares several versions of ground wetness parameterization. The experiment where perfect (i.e., based on analysis of observations) boundary conditions are used is defined as a bench-mark. At the highest horizontal resolution (=50km) using the ground wetness obtained from the regression, the best results were found for the structure and motion of the tropical cyclone. When the boundary conditions from a global model are used at a resolution T106 (roughly 100 km resolution for the transformed grid), the results degrade somewhat. The rain bands are predicted, but do not contain the same detail. Several other sensitivity experiments illustrate the degree of degradation of rain bands, precipitation distribution, hurricane structure, and phase speed errors as the lateral boundaries, resolution, and ground wetness parameterization are altered. 相似文献
13.
1. Introduction The soil moisture plays an important role in in- fluencing the climate change by altering the surface albedo, soil heat capacity and the heat flux between air and land (Ma et al., 2001). Near-surface soil mois- ture controls the partitioni… 相似文献
14.
We apply a diagnostic based on moisture conservation in the atmosphere, integrated over planetary-scale ocean basins and drainage areas to evaluate freshwater fluxes over the ocean surface to three generations of the Hadley Centre climate model (HadCM3, HadGEM1 and HadGEM2-AO). The coherent inclusion of runoff by the diagnostic enables model surface freshwater fluxes to be compared directly with observational estimates of precipitation, evaporation and river discharge. We also introduce a normalised metric, based on model-observation RMS differences, to assess the representation of the fluxes by the model. This methodology could be a powerful tool for evaluating model performance during future model development and model intercomparison exercises. Using this diagnostic, and defining the drainage areas from the global river routing model TRIP, we obtain large-scale surface oceanic fluxes from ERA40 and NCAR-NCEP reanalysis data, which we compare with analogous budgets computed from a set of individual observational estimates of evaporation, precipitation and river discharge. The sum of errors in the Hadley Centre climate model in all ocean basins suggests a steady improvement over the three generations of the model. However, an analysis of sources and sinks of water vapour shows common errors in the models, like an excess of evaporation in the tropical-subtropical Atlantic, and a surplus of water vapour export from tropical-subtropical areas to the mid-latitude regions, making the oceanic surface fluxes too fresh at mid latitudes. Errors in the models are consistent with an excessively strong hydrological cycle. 相似文献
15.
Zengxin Zhang Qiang Zhang Chongyu Xu Chunling Liu Tong Jiang 《Theoretical and Applied Climatology》2009,95(3-4):331-340
In this paper, we explored the trends of the atmospheric moisture budget, precipitation, and streamflow in summer during 1961 to 2005 and possible correlations between them by using the linear regression method in the Yangtze River basin, China. The results indicate that: (1) increasing tendencies can be detected in the atmospheric moisture budget, precipitation and streamflow in the Yangtze River basin; however, the significant increasing trends occur only in the atmospheric moisture budget and precipitation in the middle and lower Yangtze River basin; (2) both the ratio of summer moisture budget to annual moisture budget and the ratio of summer precipitation to annual precipitation exhibit a significant increasing trend in the Yangtze River basin. The ratio of summer streamflow to annual streamflow is in a significant increasing trend in Hankou station. Significant increasing summer precipitation can be taken as the major controlling factor responsible for the higher probability of flood hazard occurrences in the Yangtze River basin. The consecutively increasing summer precipitation is largely due to the consistently increasing moisture budget; (3) the zonal geopotential height anomaly between 1991 and 2005 and 1961 and 1990 is higher from the south to the north, which to a large degree, limits the northward propagation of the summer monsoon to north China. As a result, the summer moisture budget increases in the middle and lower Yangtze River basin, which leads to more summer precipitation. This paper sheds light on the changing properties of precipitation and streamflow and possible underlying causes, which will be greatly helpful for better understanding of the changes of precipitation and streamflow in the Yangtze River basin. 相似文献
16.
We evaluate water budget components—namely, soil moisture, runoff, evapotranspiration, and terrestrial water storage (TWS)—simulated by the Noah land surface model with multi-parameterization options (Noah-MP) in China, a large geographic domain challenging for hydrological modeling due to poor observational data and a lack of one single parameterization that can fit for complex hydrological processes. By comparing the model simulations with multi-source reference data, we show that Noah-MP can generally reproduce the overall spatiotemporal patterns of runoff and evapotranspiration over six major river basins, with the annual correlation coefficients generally greater than 0.8 and the Nash–Sutcliffe model efficiency coefficient exceeding 0.5. Among the six basins evaluated, the best model performance is seen over the Huaihe River basin. The temporal trend of the modeled TWS anomalies agrees well with GRACE (Gravity Recovery and Climate Experiment) observations, capturing major flood and drought events in different basins. Experiments with 12 selected physical parameterization options show that the runoff parameterization has a stronger impact on the simulated soil moisture–runoff–evapotranspiration relationships than the soil moisture factor for stomatal resistance schemes, a result consistent with previous studies. Overall, Noah-MP driven by GLDAS forcing simulates the hydrological variables well, except for the Songliao basin in northeastern China, likely because this is a transitional region with extensive freeze–thaw activity, while representations of human activities may also help improve the model performance. 相似文献
17.
18.
Conceptual Framework for Changes of Extremes of the Hydrological Cycle with Climate Change 总被引：11，自引：0，他引：11
Kevin E. Trenberth 《Climatic change》1999,42(1):327-339
A physically based conceptual framework is put forward that explains why an increase in heavy precipitation events should be a primary manifestation of the climate change that accompanies increases in greenhouse gases in the atmosphere. Increased concentrations of greenhouse gases in the atmosphere increase downwelling infrared radiation, and this global heating at the surface not only acts to increase temperatures but also increases evaporation which enhances the atmospheric moisture content. Consequently all weather systems, ranging from individual clouds and thunderstorms to extratropical cyclones, which feed on the available moisture through storm-scale moisture convergence, are likely to produce correspondingly enhanced precipitation rates. Increases in heavy rainfall at the expense of more moderate rainfall are the consequence along with increased runoff and risk of flooding. However, because of constraints in the surface energy budget, there are also implications for the frequency and/or efficiency of precipitation. It follows that increased attention should be given to trends in atmospheric moisture content, and datasets on hourly precipitation rates and frequency need to be developed and analyzed as well as total accumulation. 相似文献
19.
The role of horizontal resolution in simulating drivers of the global hydrological cycle 总被引：1，自引：1，他引：0
Marie-Estelle Demory Pier Luigi Vidale Malcolm J. Roberts Paul Berrisford Jane Strachan Reinhard Schiemann Matthew S. Mizielinski 《Climate Dynamics》2014,42(7-8):2201-2225
The role of atmospheric general circulation model (AGCM) horizontal resolution in representing the global energy budget and hydrological cycle is assessed, with the aim of improving the understanding of model uncertainties in simulating the hydrological cycle. We use two AGCMs from the UK Met Office Hadley Centre: HadGEM1-A at resolutions ranging from 270 to 60 km, and HadGEM3-A ranging from 135 to 25 km. The models exhibit a stable hydrological cycle, although too intense compared to reanalyses and observations. This over-intensity is explained by excess surface shortwave radiation, a common error in general circulation models (GCMs). This result is insensitive to resolution. However, as resolution is increased, precipitation decreases over the ocean and increases over the land. This is associated with an increase in atmospheric moisture transport from ocean to land, which changes the partitioning of moisture fluxes that contribute to precipitation over land from less local to more non-local moisture sources. The results start to converge at 60-km resolution, which underlines the excessive reliance of the mean hydrological cycle on physical parametrization (local unresolved processes) versus model dynamics (large-scale resolved processes) in coarser HadGEM1 and HadGEM3 GCMs. This finding may be valid for other GCMs, showing the necessity to analyze other chains of GCMs that may become available in the future with such a range of horizontal resolutions. Our finding supports the hypothesis that heterogeneity in model parametrization is one of the underlying causes of model disagreement in the Coupled Model Intercomparison Project (CMIP) exercises. 相似文献
20.
利用常规观测资料和6 h一次的NCEP 1°×1°再分析场资料对新疆2015年2月12—14日北疆暴雪过程和2015年5月17—21日南疆暴雨过程的环流形势和主要影响系统进行分析,并基于HYSPLIT模式模拟的后向轨迹分析强降水的水汽来源和输送特征。结果表明：1）2次强降水过程均发生在高空低槽东移,低层有低涡,地面有锋面气旋,高空有辐散的天气背景下。2）冬季暴雪过程中,北疆水汽主要源自西亚和中亚地区。其中源自西亚地区的干气块下沉到近地面时从下垫面获得水汽,对强降雪的贡献最大;其次是起源于中亚西南部地区近地层的湿气块对强降雪的贡献。3）春季暴雨过程中,南疆的水汽主要来自中亚的哈萨克斯坦。其中来自哈萨克斯坦南部上空的干空气下沉到近地层时从下垫面获得水汽,对强降雨的贡献最大;其次是源自哈萨克斯坦东部和东南部对流层低层的湿气块对强降雨的贡献大。4）2次强降水过程中水汽主要来自陆地而不是海洋,气块在近地层移动或下沉到近地层时,下垫面水汽蒸发使气块变湿,是强降水的水汽主要贡献者;表明春季和冬季的水汽输送通道与夏季来自阿拉伯海等低纬的水汽通道不同。 相似文献