A regional atmosphere-ocean coupled model, RegCM3-POM, was developed by coupling the regional climate model （RegCM3） with the Princeton Ocean Model （POM）. The performance of RegCM3-POM in simulating a persistent s...A regional atmosphere-ocean coupled model, RegCM3-POM, was developed by coupling the regional climate model （RegCM3） with the Princeton Ocean Model （POM）. The performance of RegCM3-POM in simulating a persistent snow storm over southern China and the impact of the Madden Julian oscillation （MJO） on this persistent snow storm were investigated. Compared with the stand-alone RegCM3, the coupled model performed better at reproducing the spatial-temporal evolution and intensity of the precipitation episodes. The power spectral analysis indicated that the coupled model successfully captured the dominant period between 30 and 60 days in the precipitation field, leading to a notable improvement in simulating the magnitude of intraseasonal precipitation variation, and further in enhancing the intensity of the simulated precipitation. These improvements were mainly due to the well-simulated low-frequency oscillation center and its eastward propagation characteristics in each MJO phase by RegCM3-POM, which improved the simulations of MJO-related low-frequency vertical motions, water vapor transport, and the deep inversion layer that can directly influence the precipitation event and that further improved the simulated MJOprecipitation relationship. Analysis of the phase relationship between convection and SST indicated that RegCM3-POM exhibits a near-quadrature relation between the simulated convection and SST anomalies, which was consistent with the observations. However, such a near-quadrature relation was not as significant when the stand-alone RegCM3 was used. This difference indicated that the inherent coupled feedback process between the ocean and atmosphere in RegCM3-POM played an important part in reproducing the features of the MJO that accompanied the snow storm.展开更多
This paper describes a modified version of SSIB through implementing a new snow model (SAST) in Simplified Simple Biosphere Model SSIB for climate study and presents the evaluation results by testing the scheme based ...This paper describes a modified version of SSIB through implementing a new snow model (SAST) in Simplified Simple Biosphere Model SSIB for climate study and presents the evaluation results by testing the scheme based on the field data from Russia and France. The relevant equations in the scheme are given, which describe complicated interactive processes among air-vegetation-snow-soil continuum through mass and heat exchange. An efficient numerical scheme is developed to solve the nonlinear equations successfully. By using the field data from Russia and France, the function of the new scheme is evaluated. The numerical results from the scheme show good agreement with field data. It indicates that the scheme developed here is workable and can be extended for climate study. Key words Snow cover model (SAST) - SSIB - Implementing - Evaluation This work was supported by the foundation from China: 1)NSF Grant 49835010, 2) National key program G1998040900—Part 1, 3) NSF 40075019, 4) NSF 49823002.展开更多
A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating ra...A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating rain-on-snow events that commonly occur in the Pacific Northwest of the United States. The resultant model was applied to the Lookout Creek Watershed in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon, and its ability to simulate streamflow was evaluated. The simulation was conducted at 24-hour and one-hour time scales for the period of 1996 to 2005. The results indicated that runoffand peak discharge could be underestimated if snowpack accumulation and snowmelt under rain-on-snow conditions were not taken into account. The average deterministic coefficient of the hourly model in streamflow simulation in the calibration stage was 0.837, which was significantly improved over the value of 0.762 when the Xin＇anjiang model was used alone. Good simulation performance of the XINSNOBAL model in the WS 10 catchment, using the calibrated parameter of the Lookout Creek Watershed for proxy-basin testing, demonstrates that transplanting model parameters between similar watersheds can orovide a useful tool for discharge forecastin~, in un^au^ed basins.展开更多
In order to develop a seasonal snow model of land surface process as accurately as possible for climatic study. it is necessary to fully understand the effects of important snow internal processes and interaction with...In order to develop a seasonal snow model of land surface process as accurately as possible for climatic study. it is necessary to fully understand the effects of important snow internal processes and interaction with air and to get an insight into influence of several relevant parameterization schemes with parameters' uncertainty to some degree. Using the snow model (SAST) developed by first author and other one and some useful field observation data, this paper has conducted a series of sensitivity studies on the parameterization schemes. They are relative to compaction process, snow thermal conduction, methodology of layering snow pack and to key parameters such as snow albedo, water holding capacity. Then, based on the results from the sensitivity studies, some useful conclusions for snow cover model improvement are obtained from the analysis of the results.展开更多
The snowmelt runoff model （SRM） has been widely used in simulation and forecast of streamflow in snow-dominated mountainous basins around the world. This paper presents an overall review of worldwide applications of...The snowmelt runoff model （SRM） has been widely used in simulation and forecast of streamflow in snow-dominated mountainous basins around the world. This paper presents an overall review of worldwide applications of SRM in mountainous watersheds, particularly jn data-sparse watersheds of northwestern China. Issues related to proper selection of input climate variables and parameters, and determination of the snow cover area （SCA）using remote sensing data in snowmelt runoff modeling are discussed through extensive review of literature. Preliminary applications of SRM in northwestern China have shown that the model accuracies are relatively acceptable although most of the watersheds lack measured hydro-meteorological data. Future research could explore the feasibility of modeling snowmelt runoff in data-sparse mountainous watersheds in northwestern China by utilizing snow and glacier cover remote sensing data, geographic information system （GIS） tools, field measurements, and innovative ways of model parameterization.展开更多
Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this pape...Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this paper, we measured and simulated the incoming longwave radiation to snow beneath forest at different canopy openness in the west Tianshan Mountains, China(43°16'N, 84°24'E) during spring 2013. A sensitivity study was conducted to explore the way that terrain influenced the incoming longwave radiation to snow beneath forest canopies. In the simulation model, measurement datasets, including air temperature, incoming shortwave radiation above canopy, and longwave radiation enhanced by adjacent terrain, were applied to calculate the incoming longwave radiation to snow beneath forest canopy. The simulation results were consistent with the measurements on hourly scale and daily scale. The effect of longwave radiation enhanced by terrain was important than that of shortwave radiation above forest canopy with different openness except the 20% canopy openness. The longwave radiation enhanced due to adjacent terrain increases with the slope increase and temperature rise. When air temperature(or slope) is relatively low, thelongwave radiation enhanced by adjacent terrain is not sensitive to slope(or air temperature), but the sensitivity increases with the decrease of snow cover area on sunny slope. The effect of longwave radiation is especially sensitive when the snow cover on sunny slope melts completely. The effect of incoming shortwave radiation reflected by adjacent terrain on incoming longwave radiation to snow beneath forest canopies is more slight than that of the enhanced longwave radiation.展开更多
Light absorbing particles（LAP, e.g., black carbon, brown carbon, and dust） influence water and energy budgets of the atmosphere and snowpack in multiple ways. In addition to their effects associated with atmospheric...Light absorbing particles（LAP, e.g., black carbon, brown carbon, and dust） influence water and energy budgets of the atmosphere and snowpack in multiple ways. In addition to their effects associated with atmospheric heating by absorption of solar radiation and interactions with clouds, LAP in snow on land and ice can reduce the surface reflectance（a.k.a., surface darkening）, which is likely to accelerate the snow aging process and further reduces snow albedo and increases the speed of snowpack melt. LAP in snow and ice（LAPSI） has been identified as one of major forcings affecting climate change, e.g.in the fourth and fifth assessment reports of IPCC. However, the uncertainty level in quantifying this effect remains very high. In this review paper, we document various technical methods of measuring LAPSI and review the progress made in measuring the LAPSI in Arctic, Tibetan Plateau and other mid-latitude regions. We also report the progress in modeling the mass concentrations, albedo reduction, radiative forcing, and climatic and hydrological impact of LAPSI at global and regional scales. Finally we identify some research needs for reducing the uncertainties in the impact of LAPSI on global and regional climate and the hydrological cycle.展开更多
Simulation and modeling the stream flow provide major data while it is a challenge in mountainous basins with regard to the important role of snowmelt runoff as well as the data scarcity in these places. The main purp...Simulation and modeling the stream flow provide major data while it is a challenge in mountainous basins with regard to the important role of snowmelt runoff as well as the data scarcity in these places. The main purpose of this paper is to examine the capability of an integrated application of remote sensing data and Snowmelt Runoff Model (SRM) to simulate scheme of daily stream flow in the snow-dominated catchment, located in the North-East region of Iran. The main parameters of the model are Snow Cover Area (SCA), temperature and participation. Regarding to the lack of measured data, the input variable and parameters of the model are extracted or estimated based on accessible maps, satellite data and available meteorological and hydrological stations. The changes of snow-cover, as spatial-temporal data, which are the most effective variable in performance of SRM, are obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) eight-day composite snow cover images. The evaluation of the model application efficiency was tested by the coefficient of determination and the volume difference, which are 0.85% and -4.6% respectively. The result depicts the relative capability of SRM though it is evident that the more accurate the estimation of model parameters, the more efficient simulation results can be obtained.展开更多
Snow water equivalent (SWE) is important for investigations of annual to decadal-scale changes in Arctic environment and energy-water cycles. Passive microwave satellite-based retrieval algorithm estimates of SWE now ...Snow water equivalent (SWE) is important for investigations of annual to decadal-scale changes in Arctic environment and energy-water cycles. Passive microwave satellite-based retrieval algorithm estimates of SWE now span more than three decades. SWE retrievals by the Advanced Microwave Scanning Radiometer for the Earth Observation System (AMSR-E) onboard the NASA-Aqua satellite ended at October 2011. A critical parameter in the AMSR-E retrieval algorithm is snow density assumed from surveys in Canada and Russia from 1940s-1990s. We compare ground SWE measurements in Alaska to those of AMSR-E, European Space Agency GlobSnow, and GIPL model. AMSR-E SWE underperforms (is less than on average) ground SWE measurements in Alaska through 2011. Snow density measurements along the Alaska permafrost transect in April 2009 and 2010 show a significant latitude-gradient in snow density increasing to the Arctic coast at Prudhoe Bay. Large differences are apparent in comparisons of our measured mean snow densities on a same snow cover class basis March-April 2009-2011 Alaska to those measured in Alaska winter 1989-1992 and Canadian March-April 1961-1990. Snow density like other properties of snow is an indicator of climate and a non-stationary variable of SWE.展开更多
Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale at- mospheric Weather Research and Forecasting...Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale at- mospheric Weather Research and Forecasting （WRF） model combining them with ground-based and satellite observations for modeling snow accumulation and snowmelt processes in the Votkinsk reservoir basin （184,319 km2）. The method is tested during three winter seasons （2012-2015）. The MODIS-based vegetation map and leaf area index data are used to calculate the snowmelt intensity and snow evaporation in the studied basin. The GIS-based snow accumulation and snowmelt modeling provides a reliable and highly detailed spatial distribution for snow water equivalent （SWE） and snow-covered areas （SCA）. The modelling results are validated by comparing actual and estimated SWE and SCA data. The actual SCA results are derived from MODIS satellite data. The algorithm for assessing the SCA by MODIS data （ATBD-MOD 10） has been adapted to a forest zone. In general, the proposed method provides satisfactory results for maximum SWE calculations. The calculation accuracy is slightly degraded during snowmelt periods. The SCA data is simulated with a higher reliability than the SWE data. The differences between the simulated and actual SWE may be explained by the overestimation of the WRF-simulated total precipitation and the unrepresentativeness of the SWE measurements （snow survey）.展开更多
Snow cover on the Tibetan Plateau(TP)is closely related to regional and continental biological and hydrological processes.The vast snow cover,special climatic conditions,and sparse vegetative cover over the TP facilit...Snow cover on the Tibetan Plateau(TP)is closely related to regional and continental biological and hydrological processes.The vast snow cover,special climatic conditions,and sparse vegetative cover over the TP facilitate the occurrence of blowing snow,leading to substantial heterogeneities in the snow cover and great promotion in the moisture supply from the land surface to the overlying atmospheric boundary layer.However,blowing-snow processes are significantly misrepresented or even neglected in current models,which causes considerable uncertainties of numerical model simulations and leads to erroneous estimates of snow-related processes in mountainous terrain.We present in this paper a brief review of our work in the past 5 years to serve as a basis for further development and improvement of the land-surface model.These studies can be divided into three parts:detection of the problems,development of the land-surface model,and application of the coupled model over the TP(the logical framework is presented in Figure 1).The origin and advances in the development of a land-surface model with consideration of blowing-snow effects are described herein;and the importance of blowing-snow processes in the land-surface model,especially over the TP,is highlighted.We expect that the blowingsnow studies over the TP will play a key role in documenting and understanding the land-surface processes(LSPs)and the cryospheric changes over the TP.展开更多
This study assessed the performances of the traditional temperature-index snowmelt runoff model(SRM) and an SRM model with a finer zonation based on aspect and slope(SRM + AS model) in a data-scarce mountain watershed...This study assessed the performances of the traditional temperature-index snowmelt runoff model(SRM) and an SRM model with a finer zonation based on aspect and slope(SRM + AS model) in a data-scarce mountain watershed in the Urumqi River Basin,in Northwest China.The proposed SRM + AS model was used to estimate the melt rate with the degree-day factor(DDF) through the division of watershed elevation zones based on aspect and slope.The simulation results of the SRM + AS model were compared with those of the traditional SRM model to identify the improvements of the SRM + AS model's performance with consideration of topographic features of the watershed.The results show that the performance of the SRM + AS model has improved slightly compared to that of the SRM model.The coefficients of determination increased from 0.73,0.69,and 0.79 with the SRM model to 0.76,0.76,and 0.81 with the SRM + AS model during the simulation and validation periods in 2005,2006,and 2007,respectively.The proposed SRM + AS model that considers aspect and slope can improve the accuracy of snowmelt runoff simulation compared to the traditional SRM model in mountain watersheds in arid regions by proper parameterization,careful input data selection,and data preparation.展开更多
人脸检测是人脸识别的首要步骤,在人脸识别领域有重要的应用价值。基于YCbCr彩色空间,提出一种RGB彩色图像的人脸检测方法。该方法利用YCbCr肤色模型进行肤色分割,得到类肤色区域作为侯选人脸区域;结合split up Sparse Network OfWinnow...人脸检测是人脸识别的首要步骤,在人脸识别领域有重要的应用价值。基于YCbCr彩色空间,提出一种RGB彩色图像的人脸检测方法。该方法利用YCbCr肤色模型进行肤色分割,得到类肤色区域作为侯选人脸区域;结合split up Sparse Network OfWinnows(SNOW)分类器准确定位人脸的位置应用matlab编程技术对多组图像进行实验,结果表明,该方法适用于复杂条件下的人脸检测,并且不受人脸表情的限制,对于多人脸检测同样适用。展开更多
In this study, the Glacier Lake Outburst Flood(GLOF) that occurred over Kedarnath in June 2013 was modeled using integrated observations from the field and Remote Sensing(RS). The lake breach parameters such as area, ...In this study, the Glacier Lake Outburst Flood(GLOF) that occurred over Kedarnath in June 2013 was modeled using integrated observations from the field and Remote Sensing(RS). The lake breach parameters such as area, depth, breach, and height have been estimated from the field observations and Remote Sensing(RS) data. A number of modelling approaches, including Snow Melt Runoff Model(SRM), Modified Single Flow model(MSF), Watershed Management System(WMS), Simplified Dam Breach Model(SMPDBK) and BREACH were used to model the GLOF. Estimations from SRM produced a runoff of about 22.7 m3 during 16–17, June 2013 over Chorabari Lake. Bathymetry data reported that the lake got filled to its maximum capacity(3822.7 m3) due to excess discharge. Hydrograph obtained from the BREACH model revealed a peak discharge of about 1699 m3/s during an intense water flow episode that lasted for 10–15 minutes on 17 th June 2013. Excess discharge from heavy rainfall and snowmelt into the lake increased its hydrostatic pressure and the lake breached cataclysmically.展开更多
Snowmelt is an important component of any snow-fed river system.The Jhelum River is one such transnational mountain river flowing through India and Pakistan.The basin is minimally glacierized and its discharge is larg...Snowmelt is an important component of any snow-fed river system.The Jhelum River is one such transnational mountain river flowing through India and Pakistan.The basin is minimally glacierized and its discharge is largely governed by seasonal snow cover and snowmelt.Therefore,accurate estimation of seasonal snow cover dynamics and snowmeltinduced runoff is important for sustainable water resource management in the region.The present study looks into spatio-temporal variations of snow cover for past decade and stream flow simulation in the Jhelum River basin.Snow cover extent(SCE) was estimated using MODIS(Moderate Resolution Imaging Spectrometer) sensor imageries.Normalized Difference Snow Index(NDSI) algorithm was used to generate multi-temporal time series snow cover maps.The results indicate large variation in snow cover distribution pattern and decreasing trend in different sub-basins of the Jhelum River.The relationship between SCE-temperature,SCE-discharge and discharge-precipitation was analyzed for different seasons and shows strong correlation.For streamflow simulation of the entire Jhelum basin Snow melt Runoff Model(SRM) used.A good correlation was observed between simulated stream flow and in-situ discharge.The monthly discharge contribution from different sub-basins to the total discharge of the Jhelum River was estimated using a modified version of runoff model based on temperature-index approach developed for small watersheds.Stream power - an indicator of the erosive capability of streams was also calculated for different sub-basins.展开更多
One deficiency of the NCAR Community Land Model （CLM3） is the disappearance of the simulated snow even in the middle of winter over a boreal grassland site due to unrealistically modeled high downward turbulent flux...One deficiency of the NCAR Community Land Model （CLM3） is the disappearance of the simulated snow even in the middle of winter over a boreal grassland site due to unrealistically modeled high downward turbulent fluxes. This is caused by the inappropriate treatment of the vertical snow burial fraction for short vegetation. A new snow burial fraction formulation for short vegetation is then proposed and validated using in situ observations. This modification in the CLM3 largely removes the unrealistic surface turbulent fluxes, leading to a more reasonable snowmelt process, and improves the snow water equivalent （SWE） simulation. Moreover, global offline simulations show that the proposed formulation decreases sensible and latent heat fluxes as well as the ground temperature during the snowmelt season over short vegetation dominant regions. Correspondingly, the SWE is enhanced, leading to the increase in snowmelt-induced runoff during the same period. Furthermore, sensitivity tests indicate that these improvements are insensitive to the exact functional form or parameter values in the proposed formulation.展开更多
The removal of snow from a road or railroad results in an uneven surface and thus the formation of snowdrifts. However, the effect of a surface bump on the scale of a snowdrift is not clear. Snowdrift wind tunnel test...The removal of snow from a road or railroad results in an uneven surface and thus the formation of snowdrifts. However, the effect of a surface bump on the scale of a snowdrift is not clear. Snowdrift wind tunnel tests have long been performed to predict the snow cover distribution due to a snowstorm. However, such tests require a large-scale experimental device, have high installation and maintenance costs, and are not easy to perform. The present study thus used a small water tunnel that is easier to implement. The snowdrift pattern for the real phenomenon of a cube model was reproduced using the small water tunnel and the performance of the tunnel thus verified. The snowdrift water tunnel was then used to predict the snowdrift distribution for uneven surfaces. The tunnel well reproduced the snow cover distribution when the sedimentation velocity ratio and Stokes number in the water tunnel test were the same as those for the real phenomenon, again verifying the performance of the water tunnel test.展开更多
Radiative fluxes are of primary importance in the energy and mass balance of the sea-ice cover. Various parameterizations of the radiative fluxes are studied in a thermodynamic sea-ice model. Model outputs of the surf...Radiative fluxes are of primary importance in the energy and mass balance of the sea-ice cover. Various parameterizations of the radiative fluxes are studied in a thermodynamic sea-ice model. Model outputs of the surface radiative and heat fluxes and mass balance are compared with observations. The contribution of short-wave radiation is limited to a long part of winter. Therefore, simple schemes are often sufficient. Errors in estimations of the short-wave radiation are due mainly to cloud effects and occasionally to multi-reflection between surface and ice crystals in the air. The long-wave radiation plays an important role in the ice surface heat and mass balance during most part of a winter. The effect of clouds on the accuracy of the simple radiative schemes is critical, which needs further attention. In general, the accuracy of an ice model depends on that of the radiative fluxes.展开更多
基金supported by grants from the National Basic Research Program of China (973 Program,Grant Nos.2012CB955901 and 2011CB952002)the National Science and Technology Support Program of China (Grant No.2009BAC51B03)the National Natural Science Foundation of China (Grant Nos. 41105044 and 41105045)
文摘A regional atmosphere-ocean coupled model, RegCM3-POM, was developed by coupling the regional climate model （RegCM3） with the Princeton Ocean Model （POM）. The performance of RegCM3-POM in simulating a persistent snow storm over southern China and the impact of the Madden Julian oscillation （MJO） on this persistent snow storm were investigated. Compared with the stand-alone RegCM3, the coupled model performed better at reproducing the spatial-temporal evolution and intensity of the precipitation episodes. The power spectral analysis indicated that the coupled model successfully captured the dominant period between 30 and 60 days in the precipitation field, leading to a notable improvement in simulating the magnitude of intraseasonal precipitation variation, and further in enhancing the intensity of the simulated precipitation. These improvements were mainly due to the well-simulated low-frequency oscillation center and its eastward propagation characteristics in each MJO phase by RegCM3-POM, which improved the simulations of MJO-related low-frequency vertical motions, water vapor transport, and the deep inversion layer that can directly influence the precipitation event and that further improved the simulated MJOprecipitation relationship. Analysis of the phase relationship between convection and SST indicated that RegCM3-POM exhibits a near-quadrature relation between the simulated convection and SST anomalies, which was consistent with the observations. However, such a near-quadrature relation was not as significant when the stand-alone RegCM3 was used. This difference indicated that the inherent coupled feedback process between the ocean and atmosphere in RegCM3-POM played an important part in reproducing the features of the MJO that accompanied the snow storm.
基金the foundation from China: 1) NSF Grant 49835010, 2) National keyprogram G1998040900-Part 1,3) NSF 40075019, 4) NSF 49823002.
文摘This paper describes a modified version of SSIB through implementing a new snow model (SAST) in Simplified Simple Biosphere Model SSIB for climate study and presents the evaluation results by testing the scheme based on the field data from Russia and France. The relevant equations in the scheme are given, which describe complicated interactive processes among air-vegetation-snow-soil continuum through mass and heat exchange. An efficient numerical scheme is developed to solve the nonlinear equations successfully. By using the field data from Russia and France, the function of the new scheme is evaluated. The numerical results from the scheme show good agreement with field data. It indicates that the scheme developed here is workable and can be extended for climate study. Key words Snow cover model (SAST) - SSIB - Implementing - Evaluation This work was supported by the foundation from China: 1)NSF Grant 49835010, 2) National key program G1998040900—Part 1, 3) NSF 40075019, 4) NSF 49823002.
基金supported by the National Natural Science Foundation of China (Grants No. 40901015 and41001011)the Major Program of the National Natural Science Foundation of China (Grants No. 51190090 and 51190091)+3 种基金the Fundamental Research Funds for the Central Universities (Grants No. B1020062 andB1020072)the Ph. D. Programs Foundation of the Ministry of Education of China (Grant No.20090094120008)the Special Fund of State Key Laboratories of China (Grants No. 2009586412 and 2009585412)the Programme of Introducing Talents of Disciplines to Universities of the Ministry of Education and State Administration of the Foreign Experts Affairs of China (the 111 Project, Grant No.B08048)
文摘A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating rain-on-snow events that commonly occur in the Pacific Northwest of the United States. The resultant model was applied to the Lookout Creek Watershed in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon, and its ability to simulate streamflow was evaluated. The simulation was conducted at 24-hour and one-hour time scales for the period of 1996 to 2005. The results indicated that runoffand peak discharge could be underestimated if snowpack accumulation and snowmelt under rain-on-snow conditions were not taken into account. The average deterministic coefficient of the hourly model in streamflow simulation in the calibration stage was 0.837, which was significantly improved over the value of 0.762 when the Xin＇anjiang model was used alone. Good simulation performance of the XINSNOBAL model in the WS 10 catchment, using the calibrated parameter of the Lookout Creek Watershed for proxy-basin testing, demonstrates that transplanting model parameters between similar watersheds can orovide a useful tool for discharge forecastin~, in un^au^ed basins.
基金This work is financially supported by 1) National Key Programme for Developing Basic Sciences.G1998040900-Part 1, 2) NSF (key
文摘In order to develop a seasonal snow model of land surface process as accurately as possible for climatic study. it is necessary to fully understand the effects of important snow internal processes and interaction with air and to get an insight into influence of several relevant parameterization schemes with parameters' uncertainty to some degree. Using the snow model (SAST) developed by first author and other one and some useful field observation data, this paper has conducted a series of sensitivity studies on the parameterization schemes. They are relative to compaction process, snow thermal conduction, methodology of layering snow pack and to key parameters such as snow albedo, water holding capacity. Then, based on the results from the sensitivity studies, some useful conclusions for snow cover model improvement are obtained from the analysis of the results.
基金supported by the National Natural Science Foundation of China(Grant No51069017)the Special Fund for Public Welfare Industry of Ministry of Water Resources of China(Grant No201001065)+1 种基金the Open-End Fund of Key Laboratory of Oasis Ecology,Xinjiang University(Grant No XJDX0206-2010-03)the Open-End Fund of the China Institute of Water Resources and Hydropower Research(Grant NoIWHR-SKL-201104)
文摘The snowmelt runoff model （SRM） has been widely used in simulation and forecast of streamflow in snow-dominated mountainous basins around the world. This paper presents an overall review of worldwide applications of SRM in mountainous watersheds, particularly jn data-sparse watersheds of northwestern China. Issues related to proper selection of input climate variables and parameters, and determination of the snow cover area （SCA）using remote sensing data in snowmelt runoff modeling are discussed through extensive review of literature. Preliminary applications of SRM in northwestern China have shown that the model accuracies are relatively acceptable although most of the watersheds lack measured hydro-meteorological data. Future research could explore the feasibility of modeling snowmelt runoff in data-sparse mountainous watersheds in northwestern China by utilizing snow and glacier cover remote sensing data, geographic information system （GIS） tools, field measurements, and innovative ways of model parameterization.
基金funded by National Key Technology Research and Development Program of the Ministry of Science and Technology of China(Grant No.2012BAC23B01)National Natural Science Foundation of China(Grant Nos.41271098,41171066)China Special Fund for Meteorological Research in the Public Interest(GYHY201206026)
文摘Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this paper, we measured and simulated the incoming longwave radiation to snow beneath forest at different canopy openness in the west Tianshan Mountains, China(43°16'N, 84°24'E) during spring 2013. A sensitivity study was conducted to explore the way that terrain influenced the incoming longwave radiation to snow beneath forest canopies. In the simulation model, measurement datasets, including air temperature, incoming shortwave radiation above canopy, and longwave radiation enhanced by adjacent terrain, were applied to calculate the incoming longwave radiation to snow beneath forest canopy. The simulation results were consistent with the measurements on hourly scale and daily scale. The effect of longwave radiation enhanced by terrain was important than that of shortwave radiation above forest canopy with different openness except the 20% canopy openness. The longwave radiation enhanced due to adjacent terrain increases with the slope increase and temperature rise. When air temperature(or slope) is relatively low, thelongwave radiation enhanced by adjacent terrain is not sensitive to slope(or air temperature), but the sensitivity increases with the decrease of snow cover area on sunny slope. The effect of longwave radiation is especially sensitive when the snow cover on sunny slope melts completely. The effect of incoming shortwave radiation reflected by adjacent terrain on incoming longwave radiation to snow beneath forest canopies is more slight than that of the enhanced longwave radiation.
基金supported by the U.S.Department of Energy, Office of Science, Biological and Environmental Research, as part of the Earth System Modeling ProgramThe NASA Modeling, Analysis, and Prediction (MAP) Program by the Science Mission Directorate at NASA Headquarters supported the work contributed by Teppei J.YASUNARI and William K.M.LAU+2 种基金The NASA GEOS-5 simulation was implemented in the system for NASA Center for Climate Simulation (NCCS).M.G.Flanner was partially supported by NSF 1253154support from the China Scholarship FundThe Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC06-76RLO1830
文摘Light absorbing particles（LAP, e.g., black carbon, brown carbon, and dust） influence water and energy budgets of the atmosphere and snowpack in multiple ways. In addition to their effects associated with atmospheric heating by absorption of solar radiation and interactions with clouds, LAP in snow on land and ice can reduce the surface reflectance（a.k.a., surface darkening）, which is likely to accelerate the snow aging process and further reduces snow albedo and increases the speed of snowpack melt. LAP in snow and ice（LAPSI） has been identified as one of major forcings affecting climate change, e.g.in the fourth and fifth assessment reports of IPCC. However, the uncertainty level in quantifying this effect remains very high. In this review paper, we document various technical methods of measuring LAPSI and review the progress made in measuring the LAPSI in Arctic, Tibetan Plateau and other mid-latitude regions. We also report the progress in modeling the mass concentrations, albedo reduction, radiative forcing, and climatic and hydrological impact of LAPSI at global and regional scales. Finally we identify some research needs for reducing the uncertainties in the impact of LAPSI on global and regional climate and the hydrological cycle.
文摘Simulation and modeling the stream flow provide major data while it is a challenge in mountainous basins with regard to the important role of snowmelt runoff as well as the data scarcity in these places. The main purpose of this paper is to examine the capability of an integrated application of remote sensing data and Snowmelt Runoff Model (SRM) to simulate scheme of daily stream flow in the snow-dominated catchment, located in the North-East region of Iran. The main parameters of the model are Snow Cover Area (SCA), temperature and participation. Regarding to the lack of measured data, the input variable and parameters of the model are extracted or estimated based on accessible maps, satellite data and available meteorological and hydrological stations. The changes of snow-cover, as spatial-temporal data, which are the most effective variable in performance of SRM, are obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) eight-day composite snow cover images. The evaluation of the model application efficiency was tested by the coefficient of determination and the volume difference, which are 0.85% and -4.6% respectively. The result depicts the relative capability of SRM though it is evident that the more accurate the estimation of model parameters, the more efficient simulation results can be obtained.
文摘Snow water equivalent (SWE) is important for investigations of annual to decadal-scale changes in Arctic environment and energy-water cycles. Passive microwave satellite-based retrieval algorithm estimates of SWE now span more than three decades. SWE retrievals by the Advanced Microwave Scanning Radiometer for the Earth Observation System (AMSR-E) onboard the NASA-Aqua satellite ended at October 2011. A critical parameter in the AMSR-E retrieval algorithm is snow density assumed from surveys in Canada and Russia from 1940s-1990s. We compare ground SWE measurements in Alaska to those of AMSR-E, European Space Agency GlobSnow, and GIPL model. AMSR-E SWE underperforms (is less than on average) ground SWE measurements in Alaska through 2011. Snow density measurements along the Alaska permafrost transect in April 2009 and 2010 show a significant latitude-gradient in snow density increasing to the Arctic coast at Prudhoe Bay. Large differences are apparent in comparisons of our measured mean snow densities on a same snow cover class basis March-April 2009-2011 Alaska to those measured in Alaska winter 1989-1992 and Canadian March-April 1961-1990. Snow density like other properties of snow is an indicator of climate and a non-stationary variable of SWE.
文摘Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale at- mospheric Weather Research and Forecasting （WRF） model combining them with ground-based and satellite observations for modeling snow accumulation and snowmelt processes in the Votkinsk reservoir basin （184,319 km2）. The method is tested during three winter seasons （2012-2015）. The MODIS-based vegetation map and leaf area index data are used to calculate the snowmelt intensity and snow evaporation in the studied basin. The GIS-based snow accumulation and snowmelt modeling provides a reliable and highly detailed spatial distribution for snow water equivalent （SWE） and snow-covered areas （SCA）. The modelling results are validated by comparing actual and estimated SWE and SCA data. The actual SCA results are derived from MODIS satellite data. The algorithm for assessing the SCA by MODIS data （ATBD-MOD 10） has been adapted to a forest zone. In general, the proposed method provides satisfactory results for maximum SWE calculations. The calculation accuracy is slightly degraded during snowmelt periods. The SCA data is simulated with a higher reliability than the SWE data. The differences between the simulated and actual SWE may be explained by the overestimation of the WRF-simulated total precipitation and the unrepresentativeness of the SWE measurements （snow survey）.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA2006010101)the National Natural Science Foundation of China (41905012, 91837208 and 41661144043)+2 种基金the National Key Research and Development Program of China (2018YFC1505701)the Opening Fund of Key Laboratory for Land Surface Process and Climate Change in Cold and Arid Regions, the Chinese Academy of Sciences (LPCC2018002)the China Postdoctoral Science Foundation (2018M641489)
文摘Snow cover on the Tibetan Plateau(TP)is closely related to regional and continental biological and hydrological processes.The vast snow cover,special climatic conditions,and sparse vegetative cover over the TP facilitate the occurrence of blowing snow,leading to substantial heterogeneities in the snow cover and great promotion in the moisture supply from the land surface to the overlying atmospheric boundary layer.However,blowing-snow processes are significantly misrepresented or even neglected in current models,which causes considerable uncertainties of numerical model simulations and leads to erroneous estimates of snow-related processes in mountainous terrain.We present in this paper a brief review of our work in the past 5 years to serve as a basis for further development and improvement of the land-surface model.These studies can be divided into three parts:detection of the problems,development of the land-surface model,and application of the coupled model over the TP(the logical framework is presented in Figure 1).The origin and advances in the development of a land-surface model with consideration of blowing-snow effects are described herein;and the importance of blowing-snow processes in the land-surface model,especially over the TP,is highlighted.We expect that the blowingsnow studies over the TP will play a key role in documenting and understanding the land-surface processes(LSPs)and the cryospheric changes over the TP.
基金supported by the National Natural Science Foundation of China(Grant No.51069017)the International Collaborative Research Program of Xinjiang Science and Technology Commission(Grant No.20126013)
文摘This study assessed the performances of the traditional temperature-index snowmelt runoff model(SRM) and an SRM model with a finer zonation based on aspect and slope(SRM + AS model) in a data-scarce mountain watershed in the Urumqi River Basin,in Northwest China.The proposed SRM + AS model was used to estimate the melt rate with the degree-day factor(DDF) through the division of watershed elevation zones based on aspect and slope.The simulation results of the SRM + AS model were compared with those of the traditional SRM model to identify the improvements of the SRM + AS model's performance with consideration of topographic features of the watershed.The results show that the performance of the SRM + AS model has improved slightly compared to that of the SRM model.The coefficients of determination increased from 0.73,0.69,and 0.79 with the SRM model to 0.76,0.76,and 0.81 with the SRM + AS model during the simulation and validation periods in 2005,2006,and 2007,respectively.The proposed SRM + AS model that considers aspect and slope can improve the accuracy of snowmelt runoff simulation compared to the traditional SRM model in mountain watersheds in arid regions by proper parameterization,careful input data selection,and data preparation.
文摘人脸检测是人脸识别的首要步骤,在人脸识别领域有重要的应用价值。基于YCbCr彩色空间,提出一种RGB彩色图像的人脸检测方法。该方法利用YCbCr肤色模型进行肤色分割,得到类肤色区域作为侯选人脸区域;结合split up Sparse Network OfWinnows(SNOW)分类器准确定位人脸的位置应用matlab编程技术对多组图像进行实验,结果表明,该方法适用于复杂条件下的人脸检测,并且不受人脸表情的限制,对于多人脸检测同样适用。
基金conducted as part of the DST, Govt. of India, New Delhi sponsored research project titled "Risk Assessment for Kedarnath Glacial Lake Outburst Floods" under the national project "Mapping Your Neighborhood in Uttarakhand (MANU)"the financial assistance received under the project to accomplish this research
文摘In this study, the Glacier Lake Outburst Flood(GLOF) that occurred over Kedarnath in June 2013 was modeled using integrated observations from the field and Remote Sensing(RS). The lake breach parameters such as area, depth, breach, and height have been estimated from the field observations and Remote Sensing(RS) data. A number of modelling approaches, including Snow Melt Runoff Model(SRM), Modified Single Flow model(MSF), Watershed Management System(WMS), Simplified Dam Breach Model(SMPDBK) and BREACH were used to model the GLOF. Estimations from SRM produced a runoff of about 22.7 m3 during 16–17, June 2013 over Chorabari Lake. Bathymetry data reported that the lake got filled to its maximum capacity(3822.7 m3) due to excess discharge. Hydrograph obtained from the BREACH model revealed a peak discharge of about 1699 m3/s during an intense water flow episode that lasted for 10–15 minutes on 17 th June 2013. Excess discharge from heavy rainfall and snowmelt into the lake increased its hydrostatic pressure and the lake breached cataclysmically.
文摘Snowmelt is an important component of any snow-fed river system.The Jhelum River is one such transnational mountain river flowing through India and Pakistan.The basin is minimally glacierized and its discharge is largely governed by seasonal snow cover and snowmelt.Therefore,accurate estimation of seasonal snow cover dynamics and snowmeltinduced runoff is important for sustainable water resource management in the region.The present study looks into spatio-temporal variations of snow cover for past decade and stream flow simulation in the Jhelum River basin.Snow cover extent(SCE) was estimated using MODIS(Moderate Resolution Imaging Spectrometer) sensor imageries.Normalized Difference Snow Index(NDSI) algorithm was used to generate multi-temporal time series snow cover maps.The results indicate large variation in snow cover distribution pattern and decreasing trend in different sub-basins of the Jhelum River.The relationship between SCE-temperature,SCE-discharge and discharge-precipitation was analyzed for different seasons and shows strong correlation.For streamflow simulation of the entire Jhelum basin Snow melt Runoff Model(SRM) used.A good correlation was observed between simulated stream flow and in-situ discharge.The monthly discharge contribution from different sub-basins to the total discharge of the Jhelum River was estimated using a modified version of runoff model based on temperature-index approach developed for small watersheds.Stream power - an indicator of the erosive capability of streams was also calculated for different sub-basins.
基金supported by the Key Project of Chinese Academy of Sciences under grant KZCX2-YW-217the National Natural Science Foundation of China (40830103)+1 种基金supported by NSF (ATM0634762)NOAA (NA07NES4400002)
文摘One deficiency of the NCAR Community Land Model （CLM3） is the disappearance of the simulated snow even in the middle of winter over a boreal grassland site due to unrealistically modeled high downward turbulent fluxes. This is caused by the inappropriate treatment of the vertical snow burial fraction for short vegetation. A new snow burial fraction formulation for short vegetation is then proposed and validated using in situ observations. This modification in the CLM3 largely removes the unrealistic surface turbulent fluxes, leading to a more reasonable snowmelt process, and improves the snow water equivalent （SWE） simulation. Moreover, global offline simulations show that the proposed formulation decreases sensible and latent heat fluxes as well as the ground temperature during the snowmelt season over short vegetation dominant regions. Correspondingly, the SWE is enhanced, leading to the increase in snowmelt-induced runoff during the same period. Furthermore, sensitivity tests indicate that these improvements are insensitive to the exact functional form or parameter values in the proposed formulation.
文摘The removal of snow from a road or railroad results in an uneven surface and thus the formation of snowdrifts. However, the effect of a surface bump on the scale of a snowdrift is not clear. Snowdrift wind tunnel tests have long been performed to predict the snow cover distribution due to a snowstorm. However, such tests require a large-scale experimental device, have high installation and maintenance costs, and are not easy to perform. The present study thus used a small water tunnel that is easier to implement. The snowdrift pattern for the real phenomenon of a cube model was reproduced using the small water tunnel and the performance of the tunnel thus verified. The snowdrift water tunnel was then used to predict the snowdrift distribution for uneven surfaces. The tunnel well reproduced the snow cover distribution when the sedimentation velocity ratio and Stokes number in the water tunnel test were the same as those for the real phenomenon, again verifying the performance of the water tunnel test.
基金This study was a part of the Sino-Finnish long-term sea-ice research cooperationsupported by the National Natural Science Foundation of China under contract Nos 40233032 and 40376006.
文摘Radiative fluxes are of primary importance in the energy and mass balance of the sea-ice cover. Various parameterizations of the radiative fluxes are studied in a thermodynamic sea-ice model. Model outputs of the surface radiative and heat fluxes and mass balance are compared with observations. The contribution of short-wave radiation is limited to a long part of winter. Therefore, simple schemes are often sufficient. Errors in estimations of the short-wave radiation are due mainly to cloud effects and occasionally to multi-reflection between surface and ice crystals in the air. The long-wave radiation plays an important role in the ice surface heat and mass balance during most part of a winter. The effect of clouds on the accuracy of the simple radiative schemes is critical, which needs further attention. In general, the accuracy of an ice model depends on that of the radiative fluxes.
