To improve the forecast and early warning ability for the low visibility along the expressway, the hourly observation data of 10 traffic meteorological stations along Shaanxi section of the Lian-Huo expressway and the hourly reanalysis data of the European Center for Medium-Range Weather Forecasts are employed to analyze the distribution characteristics of low visibility and to explore the relationship of low visibility with other meteorological factors. The results show that along Shaanxi section of the Lian-Huo expressway, January has the most low visibility, while February has the least. During a day, the low visibility mostly happens from 00:00 to 10:00, and the low visibility of 0-50 m mainly occurs from 05:00 to 06:00. The low visibility duration is short with the majority of within 2 hours and the longest of 17 hours. The low visibility weathers occur frequently from Xingping to Changxing and Chencang section, where attention should be paid in daily traffic meteorological service. Accordingly to the analysis of the relationship between low visibility and other meteorological factors, the low visibility generally occurs under the conditions of air temperature from 0 to 5 ℃, relative humidity above 90%, wind speed less than 1.0 m·s-1 and northeast to east winds. The low visibility weather in summer and winter is mostly associated with precipitation, which usually occurs during or after the precipitation and is accompanied by weather systems always. Compared with the low visibility caused by radiation cooling, the low visibility associated with precipitation exhibits longer duration and the wider range. The low visibility weathers occur at different relative humilities in different seasons, which in winter, summer and autumn are high, while in spring are relatively low.
Under the background of global warming, the severity, duration, and influencing scope of drought disasters in China are all increasing in recent years. Meteorological drought is a prerequisite for the occurrence of drought disasters. On the basis of clarifying the causes of meteorological droughts, it is of great scientific significance to improve the drought early warning ability, to propose drought disaster coping strategies and defense measures. This study comprehensively sorts out the research progress of the causes of meteorological drought in China. Firstly, in view of the regional differences in the drought formation causes in the various regions, the causes of drought are summarized respectively in Northwest China, North China, Northeast China, East China, South China, and Southwest China. Considering the time persistence of drought, based on the seasonal drought, two-season drought, and three-season drought, the main influencing factors on the formation of meteorological droughts with different durations in various regions are summarized respectively, from the aspects of cooling and warming flow transport, geopotential height field, and sea surface temperature field anomaly. Secondly, the scientific problems and future research directions on causes of meteorological drought are put forward. In previous studies, the analysis of drought causes mostly considered a single influencing factor, or considering the multiple influencing factors, but there is a lack of in-depth elaboration and research on the synergy between multiple factors. The contribution rate to drought formation and the quantitative relationship between these multiple influencing factors are urgent to study.
The sunflower growing region in northern China is mainly located in arid and semi-arid areas, and the yield is governed by wet and dry conditions. The non-homogeneous variation of water resources between different regions in the context of climate change has increased uncertainty of sunflower production. Based on daily meteorological data from 296 stations in the sunflower growing region in northern China, the wetness index and standardized precipitation evapotranspiration index (SPEI) calculated on the basis of precipitation and crop evapotranspiration are used to analyze the spatial and temporal characteristics of dry and wet conditions and the influence of major meteorological factors on crop evapotranspiration in the sunflower growing season from 1961 to 2020, and the causes of changes in dry and wet conditions are explored by using sensitivity and contribution rate method. The results show that the frequency of drought in sunflower growing season in northern China generally presented a spatial distribution decreasing from west to east, among which the frequency of drought was higher in northern Xinjiang, northern Ningxia and western Inner Mongolia. In the last 60 years, both precipitation and evapotranspiration in sunflower growing season decreased. The SPEI had an abrupt change in 1980, and compared with the period of 1961-1980, the frequency of slight, medium and severe drought during 1981-2020 generally decreased by 5.63%, 4.41%, 2.49%. Obvious differences between different regions in terms of dry and wet conditions were found, with the climate in Chifeng of Inner Mongolia, southern Liaoning and the North China plain showing a warm and dry trend, and the climate in western Inner Mongolia and Xinjiang becoming wet. The change in temperature and relative humidity increased crop evapotranspiration, but the change in sunshine hours and wind speed decreased crop evapotranspiration in the last 60 years in sunflower growing season. The contribution rate of wind speed and sunshine hours at 55.39% stations to crop evapotranspiration is greater than that of temperature, resulting in a significant decrease of crop evapotranspiration.
Drought is one of the natural disasters with the widest impact and the most serious economic losses in China, which directly threatens the country’s food security and socio-economic development. The understanding and research on drought will help to improve the national capacity of drought prevention and mitigation. Since 1949, China’s research on drought meteorology has achieved fruitful results. Based on the research results of the scientific research project group related to drought meteorology carried out by the Key Open Laboratory of Arid Climate Change and Disaster Reduction of China Meteorological Administration since the 21st century, through the achievement retrieval, this paper summarizes the new progress in drought monitoring technology, drought temporal and spatial distribution, drought disaster-causing characteristics, drought disaster risk and its response to climate warming, as well as drought disaster risk management and defense technology. At the same time, based on the frontier development trend of drought meteorology research, on the basis of strengthening the comprehensive drought observation test in drought prone areas under the background of climate change, this paper puts forward that China’s drought meteorology research in future should study quantitatively the formation mechanism of drought from different dimensions and scales, build a new comprehensive drought monitoring method of multi-source data fusion and multi-method combination, reveal the mechanism of drought disaster-causing and evaluate scientifically the drought disaster risk, putting forward the executable risk management strategies. This work is of positive significance to promoting drought meteorological research in China.
Considering the different disaster-pregnant environment, population density and economic condition, the drought disaster chain models in southwest and south China were constructed respectively by using history data and record of references. Here, the disaster-pregnant environment includes climate background, underlying surface, landforms, soil and river network. And on this basis that the transmission characteristics of disaster on separate disaster chains were analyzed. The results show that the drought disaster chain structure is similar in southwest and south China, but their transfer process of disaster on the two chain is different. There are obvious regional characteristics of disaster transfer on their chain. The incipient drought can cause crop drought in southwest China, while moderate drought can cause crop drought in south China. In southwest China, the moderate drought can lead to some problems such as people and livestock drinking water difficult and livestock forage shortage, but these corresponding problems can be generated by the severe drought in south China. Being the difference in disaster-pregnant environment, the rock desertification phenomenon appears in southwest China under the severe drought condition, but the probability of rock desertification is small in south China except for north Guangxi. In the same region, as far as the various disaster-affected bodies are concerned, the threshold of drought degree transmitting is different. For example, shipping problems usually result from the moderate drought, and forest fire and pest disaster are often led by the severe drought, while soil degradations appear in the extreme drought.
Based on precipitation from 280 meterological stations in west China and NCEP reanalysis data of OLR，the relationship between autumn precipitation anomaly and OLR in western China was analyzed using EOF，correlation analysis method．The main results are as follows:(1)The high value area of autumn OLR corresponded to the low value area of autumn precipitation，and the autumn OLR and precipitation had the remarkable opposite tendency，which indicated the increase((reduction)of autumn OLR would cause the reduction(increase)of autumn precipitation;(2)There was a large remarkable inverse correlative region between autumn OLR and precipitation in west China，especially in northwest and southeast area of west China，and in September inverse correlative area was biggest;(3)By the EOF analysis，the autumn OLR was most sensitive in the southern Xinjiang basin and northeast of Qinghai plateau，in Septemper the abnormal increase(decrease)of the autumn OLR in Turpan of Xingjiang，the autumn precipitation in southwest Xinjiang，north region of Qinghai plateau，Gannan plateau and middle Gansu was more(few)，but in the Tibet and western Sichuan plateau was few(more);In October the autumn OLR’s abnormity in west Inner Mongolia Xinjiang would resulted in remarkable inverse change of autumn precipitation in Xinjiang，north Shaanxi，north Sichuan and west Guangxi;In November the autumn OLR’s abnormity in Taklimakan desert would resulted in remarkable oppositive change of autumn precipitation in Shaanxi．The influence of OLR abnormity in sensitive area on autumn precipitation was maily in December of last year，April to June and August;(4)The low value center of OLR over the Qinghai－Tibet Plateau moved to southeast from winter to summer．In September the plateau OLR low value ascension was propitious to increase of precipitation in Tibet Plateau but decrease in the northeast side of the plateau．In October，the low value ascension of OLR was in favor of precipitation increase(reduction)in the plateau(middle Hexi Corridor)．In November both autumn OLR and autumn precipitation had no obvious correlation．The influence of OLR abnormity on autumn precipitation was maily in January，March and June．
Based on the monthly mean data of North Pacific Sea Surface Temperature(SST)and the ten－day precipitation data from 131 observational stations in Northwest China during 1961－2000，the impact of SST anomaly on precipitation of Northwest China from July to the first ten days of September are analyzed by using Singular Value Decomposition(SVD)method．The results show that the precipitation of Northwest China from July to the first ten days of September was closely related to the north Pacific SST anomaly in cor- responding period，the former spring and winter，which can be used as a good reference for prediction of precipitation from July to the first ten days of September in Northwest China．
The different level rainy days and its homologous precipitation quantity are obtained by using the daily precipitation data from May to September ( 1960 － 2004) of 17 stations in the Qilian Mountain area，thus，we know the daily precipitation intensity of light rainfall and moderate rainfall( and more) at each station． Based on regional mean value of the different level rainy days and rainfall intensity in Qilian Mountain area，the tendency of the different level rainy days and rainfall intensity was analyzed using linear trend coefficient and 5 levels main value function． The results show that both precipitation and different level rainy days from May to September in Qilian Mountain area presented more in the west side and less in the east side in the same latitude area，and more in the east and less in the west part of Qilian Mountain． In recent 45 years，the light rainfall days was descending，but the moderate rainfall days was ascending． The precipitation intensity of light rainfall and moderate rainfall ( and more) presented ascending trend too from May to September in Qilian Mountain area． The morlet wave analysis show that the light rainfall days had a period of five years，but the period of the moderate rainfall ( and more) days was more complex．
Over the past 50 years, temperature in the Northwest China p resented a significant rising trend, while p recip itation change was different in different p lace. Warming and drying trend is evident in the whole Northwest China, but the local appearswarming and wetting phenomenon. With the global warming, glaciers retreat and snow line rises, permafrost melts, wetlands degradation, lakes shrink, river flows decrease, water resource becomes scarcer, and eco - environmental degradation. According to IPCC forecast results, the climate warming trend in this region in the future will be more p ronounced. The countermeasures to p rotect the ecological environment, imp rove the comp rehensive climate change monitoring system, launch specific research on the key regional climate changep rocesses, and other suggestionswere put forward.
The app lication of K drought index for droughtmonitor operation in Gansu was introduced in this paper, and the mainly analysiswas as follows: the definition, grades, criterion, app lication of K drought index, and the comparison between monitor results of K drought index and actual drought situation. Results indicate that there is a good effect in droughtmonitorwith K index compared to actual drought situation in sp ring, May, June, July to August, and Sep tember in 2008 in Gansu p rovince.
According to the climate data (1953 - 2006) in the farming - pasturing interlocked area of InnerMongolia (Duolun) , the response of local grassland p roductivity to the climate change is analyzed. Climate models (Miami and ThornthwaiteMemorial) are introduced to evaluate the grassland potential p roductivity. It is showed that ThornthwaiteMemorialmodel could better describe the main features of the grassland potential p roductivity change with climate factors in Duolun County, and both temperature and p recip itation increase could enhance the potential p roductivity, but p recip itation is the key climatic factor limiting the potential p roductivity. The grassland actual p roductivity observed in Duolun County is then compared with the effective potential p roductivity. The results show that the p roductivity level of natural grassland is very low (412 kg/hm2 ·a) , which is only 26% of its effective potential p roductivity, and there is a large room for imp roving. Both of the potential and actual p roductivities of the artificial grassland are much higher than those of the natural grassland, which indicates that the development of artificial grassland could be highly efficient for imp roving the local grassland p roductivity. The actual stocking rate in 2000 - 2002 is also compared with the estimated theoretical one, and an average overloading rate up to 79. 3% exists in this period.
The mainly research development over Qilian Mountain region in recent ten years is reviewed in this paper. The most research work focused on climate change and water resource. There are a lot of results about the paleoclimate and the interannual variability of neoteric climate and water resource over the QilianMountain region. The exp loitation and utilization of airwater resource over QilianMountain has been focused in recent years, which should be a way to mitigate water shortage in arid and semi - arid region in northwest China.
Based on the radar dense data of convectional cloud on June 12，2004 in Yongdcng county, choosing two similar convectional clouds as seeding and non一seeding cloud，the remarkable changes of radar echo parameters of the seeding cloud compared with the non一seeding cloud were discussed in this paper, and the rain enhancement effect was evaluated primarily with ground observational rainfall data. "hhc results show that many aspects of the seeding cloud，such as precipitation，life characteristic and vertical characteristic parameters change of radar echo, had remarkable differences compared with the non一seeding cloud，and about }0 min after seeding() .6 mm precipitation produced，while the non一seeding cloud experienced a short period from development to dissipation and didri t produce any precipitation in the ground，which can conclude this rainfall cnhanccment experiment reached some prospective effect.
By using the data of monthly surface runoff of Shule，Heihe and Xiying rivers，and spring wheat yields in Zhangye，Jiuquan and Wuwei regions more than 40 years，the impacts of the surface runoff of inland rivers on the spring wheat yields in Hexi region were analyzed.The results show that the spring wheat yieldis increasing fluctuatly due to the development of irrigation，agricultural technology and improved variety，additionally，it’s also impacted by the source of irrigation.The difference of runoff in spring could lead to annual fluctuation of spring wheat yield，short-term fluctuation of annual runoff impacts on yield is small butlong-term fluctuation is larger，especially the long tendency of runoff in spring decides measuring the amount of water inreservoirs，so it shows that agricultural production is impacted by climate change.
Using the data of aircraft artificial precipitation enhancement operation from 1991 to 2002 in Cransuprovince，the situation of it was analyzed statistically in late spring and early summer. According to the characteristic of weather system of Cransu，making use of sounding data and basing `discriminant model'，we can educe three types of high一level circulation of precipitation. These types were straight but some fluctuant，southwest and northwest air current weather system，respectively. Among the types，the straight but somefluctuant air current weather system emerged morefrequently. The typesof weather system of aircraft artificialprecipitation enhancement operation were sorted by `discriminant model'，result showed that the main type of aircraft artificialprecipitation enhancement operation was straight but some fluctuant air current weather system also，and the next type was southwest air current weather system.
