应用气象学报

2017, 28(4)

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Abstract:

Introduction and Evaluation of a Rainstorm-caused Flood Forecasting System

Gan Yanjun, Xu Jing, Zhao Ping, Hong Yang, Chen Yun, Hao Ying, Bao Hongjun, Zeng Ziyue, Xu Hui, Di Jingyue

2017, 28(4): 385-398. DOI: 10.11898/1001-7313.20170401

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Abstract:
Flood disaster is one of the important factors that restrict the sustainable development of the economy and society of China. The development of a well-performing rainstorm-flood forecasting system is an important non-engineering flood prevention measure that would mitigate the loss of imminent flood disasters. A rainstorm-caused flood forecasting system, which is based on the distributed hydrological model CREST V2.1, is developed to provide refined streamflow, evapotranspiration, soil moisture, and other forecast products. By utilizing operational precipitation data from China Meteorological Administration (CMA) to serve as input for this system, nationwide flood forecasting is carried out by 0.125°×0.125° daily, and regional forecast is done by 30"×30" hourly. For the former, one typical watershed is selected for each of ten river basins as Songhua, Liao, Hai, Yellow, Huai, Yangtze, Southeast, Pearl, Southwest and Northwest River Basins, while for the latter just the Huai River Basin is taken as focus. The SCE-UA optimization algorithm is adopted to search the optimal parameter sets that maximize the Nash-Sutcliffe efficiency (E) between the observed and the simulated streamflow discharges for gauging stations of typical watersheds. E, correlation coefficient (C), and relative bias (B) are used to evaluate model performances before and after the calibration of model parameters. Validation tests are conducted by transferring calibrated parameter values to another flood event of the same watershed. Results show that the calibrated model can reproduce the observed flood processes and provide accurate hydrological forecasting service. Compared to the non-calibrated model, the calibrated one significantly improves E and B, and moderately improves C. It has good applicability in watersheds with different hydroclimatic, geological and geomorphological conditions, but has relatively weak forecasting ability for frequently fluctuating low-flow flood. For the model parameters, their values not only depend on the hydroclimatic, soil and vegetation conditions of the watersheds, but are also influenced by interactions among physical processes of the model. Besides, some empirical parameters need to be calibrated according to different levels of the flood events for the same watershed. Generally, this flood forecasting system show good forecasting accuracy and timeliness, which meets operational needs. However, further work is still needed to improve the prediction accuracy of the model. For example, the snowmelt module could be implemented into the CREST model to improve the prediction accuracy for flood disasters caused by snowmelt in the Northwest, Northeast, and Qinghai-Tibet Plateau regions. In addition, more observed streamflow discharge data should be collected to help calibrating model parameters for more watersheds. Furthermore, uncertainty quantification methods should be adopted to understand parameter behaviors, quantify and reduce parametric uncertainties.

Improving the Simulation of Typhoon Mujigae (2015) Based on Radar Data Assimilation

Feng Jianing, Duan Yihong, Xu Jing, Zhang Xinghai, Hu Hao

2017, 28(4): 399-413. DOI: 10.11898/1001-7313.20170402

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Abstract:
Typhoon intensity and precise structure are hardly to predict by all kinds of numerical model, and one key problem is the lack of precise initialization data. Through a WRF-based ensemble Kalman filtering (EnKF) data assimilation system, impacts of assimilating China's coastal Doppler radar velocity observations for track, intensity and structure of Typhoon Mujigae (2015) is examined.Furthermore, assimilating sensitivity of observations in relative regions are also explored. The experimental results show that mean track error and max track error is reduced by 15 km and 38 km, respectively. The track error of the EnKF analysis becomes smaller with more cycles of assimilating data, and so do the deterministic forecast driven by EnKF analysis field. Through data assimilation, offshore enhancement process in Mujigae is well simulated. Intensity error in both EnKF analysis and prediction are smaller than 25 hPa after assimilation. After 9 h cycling radar velocity data assimilation, the deterministic forecast shows the typhoon continue to strengthen before landfall, and the typhoon eye is contracted much after data assimilation. The diameter of typhoon eye is reduced by about 70 km, and the eye wall convection asymmetric structure is closer to observation.The sensitivity of radar observation assimilation is tested by different radial distance area. Numerical sensitivity experiments show that radar observations within 100 km of the typhoon's inner core play a dominate role to assimilation results. Typhoon track, intensity and structure are all closer to observation by assimilating radar data within 100 km from typhoon center (about 20% of total observation) showing equivalent effects as assimilating all data. Typhoon is somewhat modified by cycling assimilating observations within 100-200 km from typhoon center. There is no obvious enhancement in typhoon track, intensity and structure after assimilating data 200 km away from inner core. Therefore, radar observation located in typhoon kernel is the key to determine assimilation effects. Because of less data assimilated, the strategy of only assimilating inner core radar data can reduce computing time to 1/3 of all data with somewhat same assimilation result. Efficiency of radar assimilation can be much improved by this radar assimilating strategy, and it can give reference to official typhoon real-time data assimilation and prediction work.

Identification Method and Analysis on Lightning Flash Initiation Phase and Size

Zhang Zhixiao, Zheng Dong, Zhang Yijun, Lu Gaopeng

2017, 28(4): 414-426. DOI: 10.11898/1001-7313.20170403

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Abstract:
Based on the observation of lightning mapping array, the statistical distribution of characteristic parameters describing the lightning flash initiation and size in a supercell storm occurring in New Mexico, United States on 5 October 2004 is studied. A method automatically identifying the start and end of the negative leaders in initial stage (IS) of lightning is developed. And the flash convex hull, total channel length, horizontal and vertical extent are used to represent the scale characteristics. Distributions and characteristics of flash initiation and size in this storm are shown as follows.Median values of the duration, three-dimensional displacement, vertical displacement and the average displacement velocity for the upward (downward) negative leaders during IS are 13.5 ms (7.5 ms), 1.4 km (1.0 km), 0.9 km (0.5 km), and 9.2×10⁴ m·s^-1 (1.2×10⁵ m·s^-1), respectively. In addition, the average flash initiation velocity decreases with height from 6 km to 11 km. With time going on, the speed of upward negative leader in initial stage decreases before 24 ms (to ensure the samples is larger than 100), while that of the downward negative leader increases before 12 ms (to ensure the samples is larger than 50). Moreover, negative leaders are dominantly tilted in initial stage, considering that the median angles between the 3-D displacement direction and the vertical direction are 40° for upward leader and 54° for downward leader, respectively.The probability density distribution of flash size described by flash convex hull and total channel length can be well fitted by negative power function, also showing that the distribution and evolution of flash convex hull is consist with that of total channel length. The median of flash duration is 271.0 ms, and the mean of that is 329.1 ms. The flash duration time and size are not significantly correlated. The flash with long duration time is not necessarily large. Moreover, the median of flash horizontal extent is 6.1 km while the vertical extent is 4.3 km, and there are 83% of flashes whose horizontal extent is greater than vertical extent. Flashes with horizontal extent greater than vertical extent are mainly initiated at 8.5 km high, and those with vertical extent greater than horizontal extent are mainly initiated at 11 km high. Greater horizontal displacement of the leader during initial stage accompanies less vertical extent, which indicates that the leader displacement direction at initial stage has an important influence on flash vertical scale.

Seasonal Relationships Between Tropospheric Ozone and Its Precursors over East Asia

Liu Ningwei, Ma Jianzhong

2017, 28(4): 427-435. DOI: 10.11898/1001-7313.20170404

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Abstract:
Satellite data of ozone with its various precursors and global reanalysis products of vapor throughout 2010 and 2012 are used to evaluate spatial-temporal variations of tropospheric ozone and its various precursors over East Asia with their correlations over East China. Northern and southern regions of East China are treated separately in order to address Asian Summer Monsoon's different influences on these two regions. It shows that the tropospheric column densities of NO₂ and CO are high in winter, while low in summer. The tropospheric column density of ozone reaches its maximum and minimum in summer and winter, respectively. Correlations between ozone and NO₂ varies similarly with seasons change, appearing positive in summer and autumn, while negative in winter and spring over both regions. There are significantly positive correlations between ozone and NO₂ over both northern and southern regions during summer, which demonstrates due to the strong sunlight, NO₂ appears short life-time and declined densities, thus the NO_x-involved photochemical cycles produce ozone actively in summer. The negative correlations during winter result from the depression of ozone photochemical cycles due to long life-time and high densities of NO₂ over most regions, especially in the northern region with much more heating emissions, leading to ozone depletion by NO. Owing to the transport of polluted air masses to the downwind directions, positive correlations between ozone and CO reach the maximum in summer and autumn over the northern region and summer over the southern region. There are slightly negative correlations between ozone and CO over the northern region in winter and over the southern region in summer, because CO reaches maximum companioned with the enhancement of NO that has the titration effect to deplete ozone. In addition, stratospheric intrusion might also cause inverse correlations between ozone and CO. In most time over northern and southern regions, correlations between ozone and vapor appear highly positive, while they appear highly negative in summer over the southern region and in winter over the northern region. Although southwesterly vapor is usually companioned by pollutant transport and photochemical reaction increasing, air masses from the sea bring sufficient vapor and little ozone in summer over the southern region, and vapor in clean marine air masses may deplete ozone as well. The inverse tracing relationships between ozone and vapor possibly result from stable weather condition variations. In both regions, correlations become more significant under slightly pollution conditions, however, they are insignificant in the severely polluted and background regions, indicating that due to enhanced NO, ozone is depleted through titration effects over severely polluted regions, whereas ozone elevates with the weaker NO titration over the downwind slightly polluted regions.

Observational Study on Aerosol Scattering Phase Function at Raoyang of Hebei, China

Zhang Linyi, Yan Peng, Mao Jietai, Zhang Xiao, Tian Ping, Chang Hairu

2017, 28(4): 436-446. DOI: 10.11898/1001-7313.20170405

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Abstract:

Aerosol radiative properties are key factors in the process of aerosol radiative forcing calculation. The scattering phase function and asymmetry factor facilitate the illustration of the direction of radiative transfer and the estimation of parameters in remote sensing.In the early summer of 2014, aerosol radiative parameters are obtained at Raoyang Meteorology Administration (an agricultural district) with a latest three-wavelength polar nephelometers (Aurora 4000) developed by EcoTech, Australia. Compared with the previous model, the instrument is unique in that it can measure the volume scattering coefficient from Θ through to 170° degrees and Θ is 10°, 15°, …, 90°. Based on the volume scattering coefficient, the scattering phase function can be computed with the traditional formula between them. What's more, one improved approach is proposed to calculate the asymmetry factor with the combination of scattering phase function and backscattering ratio. The backscattering ratio used can be calculated from the backscattering coefficient and total scattering coefficient as defined. Aerosol radiative properties of PM_2.5 including calculated scattering phase function and the fitted asymmetry factor are presented during the observation between 16 June and 18 August in 2014. The result suggests that the improved HG aerosol particle phase function can fit the aerosol scattering phase function observed at Raoyang Meteorology Administration of Hebei well. Observed results of forward scattering phase function (15°-20°) and the backscattering ratio are all in good agreement with the numerical results. The average asymmetry factors at the wavelength of 635 nm, 525 nm and 450 nm are 0.53, 0.57 and 0.57, respectively, with no significant difference possibly due to the size distribution of aerosol. The value of it at 525 nm are accordant with analysis of previous experiments, which indicate the asymmetry factor of dry aerosol are in the range of 0.55 and 0.63 (550 nm). Two examples of different pollution status (dirty period and clean one) are chosen, depending on the scattering coefficient, and the radiative properties are different. During two dirty periods, values of asymmetry factor are between 0.55 and 0.63, which is larger than those in clean periods. For asymmetry factor, mean values at 635 nm, 525 nm and 450 nm wavelength are in the range of 0.51-0.53, 0.54, 0.54, respectively. Such results provide more details and supports for further study of radiative effects of aerosol.

Comparisons of Doppler Spectral Density Data by Different Bands Pointing Vertically Radars

Sun Hao, Liu Liping, Zheng Jiafeng

2017, 28(4): 447-457. DOI: 10.11898/1001-7313.20170406

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Abstract:
The attenuation of the radar echo has always been a difficult problem in radar detections. Results corrected by the common methods have some differences with the real detecting value. Due to the richness of the micro physical and dynamic information by the power spectrum data of vertical detecting radars, the mechanism of attenuation could be investigated in the power spectrum layer. And then, a direction of the improvement of attenuation correction could be found by power spectrum data.Comparative research is carried out using the power spectrum data by Ka-band millimeter-wave radar, C-band frequency-modulated continuous-wave radar and Ku-band micro rain radar at Yangjiang of Guangdong during May-June in 2014 and Longmen of Guangdong during April-May in 2016. The power spectrum shapes by three radars are almost consistent, especially for the peak velocity and the first atmospheric signal, indicating data of three radars are reliable. In the detection of big particle size precipitation, the radar echo is affected by Mie scattering effects, especially shorter wavelength echoes. The reflect of Mie scattering effects on the power spectrum is a rapid decline of echo intensity during a speed point, which shrink the tail end of the spectrum, reduce signal spectrum width and affect the intensity value. The performance of power spectrum is the overall down of spectrum, and it leads to underestimation. In convective cloud precipitation detections, results calculated by the normal empirical formula may have difference with real value. Spectrum distribution could be taken into account in such condition, and the correction methods should be improved by the power spectrum density layer.Finally, the study of the attenuation correction, especially the study in the strong precipitation process, the power spectrum data could be used. But the question how the attenuation effect the power spectrum, the study just offers a direction. It still needs to explore in the quantitative research.

Main Influencing Factors of Summer Precipitation and Prediction Method of Annual Increment in Shaanxi

Xiao Keli, Zhao Guoling, Fang Jiangang, Sun Xian

2017, 28(4): 458-469. DOI: 10.11898/1001-7313.20170407

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Abstract:
Basic conditions that affect main factors of summer precipitation in Shaanxi are determined, which means that the correlation coefficient is high and the significance is verified, the physical meaning is clear, abnormalities of meteorological factors could be reflected and have lasting effect. NCEP/NCAR reanalysis data of the monthly mean 500 hPa height, sea surface temperature, ERA-40 climate index, and 74 meteorological characteristics of National Climate Center are used in the investigation. Six main climatic factors are met by the census, including the western Pacific subtropical high intensity, equatorial strata, zonal wind, lower-level equatorial airflow, atmospheric angular momentum, equatorial Pacific SST, and the equatorial 500 hPa height field. The analysis of the correlation between anomalies of inter-annual increment, the standard deviation in the six incremental factors and the summer precipitation in Shaanxi, showing that the inter-annual increment factor have obvious signal amplification effect. The standard deviation of six increment factors is 1.5 times larger than anomaly factors, and the correlation coefficient of the increment factor is about 0.1. Both predictive factors and predictive variables have long-term changes, and changes are often inconsistent, resulting in unstable factors. After incrementally transformed in meteorological elements, long-term changes of summer precipitation and main factors are effectively filtered out, and the stability of factor quality and prediction model is improved. Based on the increment and anomaly of six main factors, the summer precipitation forecasting model of Shaanxi is established. Results show that the incremental forecasting model have obvious advantages with good accuracy. The cross test of the same rate show that the increment is 70% and the anomaly is 66%. The distribution of SST in the eastern equatorial Pacific in the precious summer is closely related to summer precipitation in Shaanxi. When the annual increment of the sea area is positive, 700 hPa subtropical high is abnormally northerly or westerly in the next summer, the west periphery side of it is strong southerlies, leading to rainy circulation situation. On the contrary, 700 hPa subtropical high being abnormally easterly prone to drought circulation situation in Shaanxi.

Relationship Between Areal Rainfall and Circulation Characteristics in Xijiang River Basins

Zhong Lihua, Zeng Peng, Shi Caixia, Gu Wenbao, Li Yong

2017, 28(4): 470-480. DOI: 10.11898/1001-7313.20170408

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Abstract:
The reanalysis grid data of daily average 850 hPa and 500 hPa geopotential height field during 1971-2015 provided by NCEP/NCAR are used for computing six daily circulation indices of Xijiang River Basins using Lamb-Jenkinson atmospheric circulation classification method. The daily circulation is divided into straight wind type, rotary type and mixed type according to the relationship between the geostrophic wind speed, wind direction and the geostrophic vorticity. The circulation frequency of precipitation weather circulation in Xijiang River Basins is researched, showing that the probability of precipitation is the greatest when the circulation is southwest wind type at 850 hPa and west wind type at 500 hPa, which is the dominant circulation for precipitation in Xijiang River Basins.The contribution rate of different types of circulation to the total areal rainfall is calculated, and types with top 3 contribution rates are called the dominant circulation pattern. It's found that for the annual total rainfall and sub basin rainfall, the cyclone type at 850 hPa and westerly type at 500 hPa has the maximum contribution in each layer. The contribution of areal rainfall is larger in the east part and smaller in the west part of Xijiang River Basins. The main configuration of south wind type at 850 hPa and anticyclone type at 500 hPa causes rainy autumn over the western sub basin.By the influence situation of the first dominant circulation configuration of season total areal rainfall contribution for strong precipitation, it shows that the probability of strong precipitation are 21.1%, 18.7% and 2.0% while the configuration are cyclone at 850 hPa and west wind type at 500 hPa in summer or spring, south wind at 850 hPa and anticyclone type at 500 hPa in autumn, southwest wind at 850 hPa and west wind type at 500 hPa in winter, respectively.Analysis on the dominant circulation configuration for season rainfall indicate that, in spring and summer it's cyclone at 850 hPa and westerly at 500 hPa, in autumn it's southerly at 850 hPa and anti-cyclone at 500 hPa, and in winter it's southwest wind at 850 hPa and westerly at 500 hPa. The corresponding probability of heavy rainfall are 21.1%, 18.7%, 4% and 2%.In the past 45 years, areal rainfall contribution rates of cyclone at 850 hPa and the west wind at 500 hPa are increasing, which has a significant positive correlation (correlation coefficients are 0.63 and 0.69), indicating that it is the dominant circulation pattern with the trend of rainy in Xijiang River Basins.

Assessment of Solar Energy Resource and Its Exploitation Potential in South China

Liang Yulian, Shen Yanbo, Bai Long, Guo Peng, Chang Rui

2017, 28(4): 481-492. DOI: 10.11898/1001-7313.20170409

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Abstract:
Based on the exposure radiation data and sunshine hourly data of 156 standard meteorological observatories in south China during 1981-2010, temporal and spatial distribution of solar energy resource in south China is evaluated. Results show that the annual irradiation on optimal inclined plane is 1291 kW·h·m^-2, 3% higher than that on the horizontal plane. The distribution of solar energy in Guangxi and Guangdong increases as the latitude decreases, whereas it appears as high in the west and low in the east of Hainan. The stability of solar energy resource in most area of south China is at stable level except the eastern Guangxi and the northwest corner of Guangdong. Hainan's solar energy resource stability is the highest: Larger than 2/3 of its area is at very stable level and only a few parts of eastern Hainan is at stable level. Combined with terrain data and land cover data, the exploitation suitability and potential usability of solar energy resource in south China are divided and analyzed with the resolution of 90 m×90 m and 1 km×1 km. Under the resolution of 90 m×90 m, solar energy exploitation suitability zoning results show that the area of class Ⅰ, Ⅱ and Ⅲ account for more than 80% of the total area in south China (occupying 22.1%, 32.4%, 26.7%, respectively), and their proportions of solar energy are slightly higher than their proportions of area. Solar energy exploitation potential results show that bare land and shrub-grass area accounts for only 13.9% of the total area in Ⅰ, Ⅱ and Ⅲ classes. While cultivated land (34.8%) and forest land (29.2%) are the largest two land cover types in these three usable regions. In the actual exploitation and application project, besides to give priority to using bare land and shrub-grass area, cultivated land and forest land should not be abandoned directly. Under the principle of no changing land use properties of cultivated land and forest land and no sacrificing the vegetation coverage, solar energy resource should be rationally exploited in these areas. Suitability zoning results derived from data with 1 km×1 km resolution are not the same with that using data with 90 m×90 m resolution, then make statistical results of exploitation potential different. Results mainly affected by the difference of the resolution of terrain data and the acquisition time of land cover data. While making solar energy development plan, reasonable data should be chosen according to the size of actual project.

Effects of Cultivar Shifts on Winter Wheat Phenology Under Two Parameterization Methods

Wang Fang, Wu Dingrong, Wang Chunyi

2017, 28(4): 493-503. DOI: 10.11898/1001-7313.20170410

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Abstract:
Phenology and growth duration of crops have been significantly changed by the combined effects of climate change and cultivar shifts. For the need of accurately evaluating the response of crops phenology to future climate changes, effects of cultivar shift on phenology and its quantitative simulation has become a research hotspot. However, most recent studies are based on the single parameterization method, with less attention paid to effects of different parameterization methods, leading to a certain degree of assessment uncertainty.Winter wheat phenology data and daily meteorological data in 47 agrometeorological observation stations in North China Plain during 1986-2010 are collected. Based on these datasets, a most commonly used phenology model is used to quantize effects of cultivar shifts on phenology, and effects of two parameterization methods on simulated results are also analyzed. The first method uses fixed three cardinal temperatures (Method 1), while in the second method (Method 2) three cardinal temperatures are obtained by minimizing the root mean square error of simulated phenology.Results show that winter wheat critical phenology in North China Plain changes significantly under the frequently change of cultivar during study period. Both two methods perform well in parameterizing the simulation of durations from turning green to heading and from heading to maturity in the winter wheat simulation. The growth duration is prolonged by cultivar shift in the duration from turning green to heading and the duration from heading to maturity, though values given by Method 1 are higher. Both methods indicate effects of cultivar shifts on the duration from heading to maturity is higher than those on the duration from turning green to heading. In addition, the range of simulated trends and their regional distribution are also affected by the different parameterization method used. Among them, the difference of simulation results between two methods in the duration from turning green to heading is higher than the duration from heading to maturity. In the regional distribution, the difference of simulation results between two methods is bigger in the duration from heading to maturity. It verifies that simulation results are potentially affected by parameterization method. Therefore, the selection of parameterization methods and uncertainties introduced by different methods should be carefully considered.

Drought Risk Regionalization of Potatoes in Inner Mongolia

Wang Yongli, Hou Qiong, Miao Bailing, Yun Wenli, Jia Chengzhen

2017, 28(4): 504-512. DOI: 10.11898/1001-7313.20170411

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Abstract:
Drought is a primary determinant agro-meteorological disaster which constrains the potato yield in Inner Mongolia. The classification of drought risk is particularly significant for disaster risk assessment and mitigation. Utilizing meteorological data of 73 stations from 1979 to 2013, historical drought disaster records with potato yield data and social attribute data, the extent of the potato drought disaster in Inner Mongolia is investigated.Results from the use of GIS spatial analysis and the fuzzy clustering method are pertained from the aspects of drought-causing factor risk indices, the vulnerability of disaster-bearing bodies, the exposure of the disaster environment and the evaluation index system of disaster prevention and mitigation capacity in the region.Based on the regression model, thresholds for light drought, medium drought and heavy drought are derived from the regression model portrayed as linear between the percentage of negative anomalies of precipitation and the relative meteorological yield in the central western and eastern Inner Mongolia, combined with the agricultural drought grade and the precipitation anomaly percentage under the national criterion of meteorological and drought grade.It opens up opportunities to fully exploit the use of drought index as an indicator of the distribution of the drought risk, and thus it is of immense importance in monitoring the smooth decreasing tendency from west to east.High risk areas covering 19.1% are mainly distributed in northeastern Ordos, southern and northern Hohhot, most regions in Wulanchabu and Xilinhhot in the southern region. The middle risk zone is primarily distributed in some areas of Hohhot, the central and southern of Chifeng, the northwest of Tongliao, the northeast of Xing'an League, the northern of Hulunbeier, coveringing 20.1% of the total area. The lower risk areas cover 41% of the total area including the western and northern of Chifeng, the southeast of Tongliao, the southwest of Xing'an League, the southeastern of Hulunbeier, and so on.

Vol.28, NO.4, 2017