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Niu S.,Nanjing University of Information Science and Technology | Jia X.,Nanjing University of Information Science and Technology | Sang J.,Ningxia Institute of Meteorological Science | Liu X.,Nanjing University of Information Science and Technology | And 2 more authors.
Journal of Applied Meteorology and Climatology | Year: 2010

Joint size and fall velocity distributions of raindrops were measured with a Particle Size and Velocity (PARSIVEL) precipitation particle disdrometer in a field experiment conducted during July and August 2007 at a semiarid continental site located in Guyuan, Ningxia Province, China (36°N, 106°16́E). Data from both stratiform and convective clouds are analyzed. Comparison of the observed raindrop size distributions shows that the increase of convective rain rates arises from the increases of both drop concentration and drop diameter while the increase of the rain rate in the stratiform clouds is mainly due to the increase of median and large drop concentration. Another striking contrast between the stratiform and convective rains is that the size distributions from the stratiform (convective) rains tend to narrow (broaden) with increasing rain rates. Statistical analysis of the distribution pattern shows that the observed size distributions from both rain types can be well described by the gamma distribution. Examination of the raindrop fall velocity reveals that the difference in air density leads to a systematic change in the drop fall velocity while organized air motions (updrafts and downdrafts), turbulence, drop breakup, and coalescence likely cause the large spread of drop fall velocity, along with additional systematic deviation from terminal velocity at certain raindrop diameters. Small (large) drops tend to have superterminal (subterminal) velocities statistically, with the positive deviation from the terminal velocity of small drops being much larger than the negative deviation of large drops. © 2010 American Meteorological Society.


Hao L.,Nanjing University of Information Science and Technology | Zhang X.,Ningxia Institute of Meteorological Science | Liu S.,Nanjing University of Information Science and Technology
Natural Hazards | Year: 2012

China faces drought disaster risk under the changing climate. Risk analysis is a suitable approach in order to design ex-ante measure able to anticipate effects of drought on agricultural production. In this article, with the support of historic drought disaster data from 583 agro-meteorological observations (1991-2009), a risk analysis method based on information diffusion theory was applied to create a new drought risk analysis model, and the risk of China's agriculture drought disaster was evaluated on higher spatial resolution of county unit. The results show that in more than three hundred counties of China, risk probability was biyearly or annually when Drought Affected Index (DAI) was over 5%. When DAI was up to 40%, more than one hundred counties were prone to drought disaster annually or once every 5 years. This showed that the impact of drought disaster on China's agriculture, whether in frequency or intensity, was large. With the different level of DAI, China's agricultural drought risk pattern showed variable pattern characteristics. When DAI was low, the distribution of county agricultural drought risk in China presented the East-West pattern of differentiation, and high risk mainly lied in the eastern, low risk mainly in the western. On the other hand, when DAI was high, the distribution of county risk appeared a pattern of high in center, and the north areas higher than the south, increased gradually from southwest to northeast. Drought risk presents a clear zonal differentiation that may be result from stepped topography, different precipitation and hazard-affected bodies. Spread of high value area of drought risk in northern may be related to the southeast monsoon and ecological degradation in northern Ecotone. © 2011 Springer Science+Business Media B.V.


Hao L.,Nanjing University of Information Science and Technology | Hao L.,Key Laboratory of Agro meteorological Science of Jiangsu Province | Zhang X.,Ningxia Institute of Meteorological Science | Shu Z.,Ningxia Institute of Meteorological Science
Advanced Materials Research | Year: 2011

Accurate assessment to disaster risk is one of the keys to reducing disaster losses. However, due to the fact that the disaster situation data series in county unit are always relatively short, available data are often not sufficient for disaster risk analysis. In this paper, a risk analysis method based on information diffusion theory was applied to create a new disaster risk analysis model (CURAM), and the risk of disaster can be evaluated on higher spatial resolution of county unit. Visual Basic and Map Objects were used to establish CURAM applying object oriented technique and component technique. CURAM provided risk evaluate function to natural disaster in county unit, and thematic map making and output, etc. The risk assessment results calculated by CURAM indicated that information diffusion technology was highly capable of extracting useful information and therefore improved system recognition accuracy. © (2011) Trans Tech Publications.


Lu H.,Nanjing University of Information Science and Technology | Xiaoyu Z.,Ningxia Institute of Meteorological Science | Jingmin G.,Nanjing University of Information Science and Technology
Environmental Engineering and Management Journal | Year: 2011

Human activities can considerably change water resources of river basins. This is particularly true in Laohahe River Basin (LRB) located in upper Xiliaohe River in northern China, where intensive irrigation has resulted in almost full cessation of the water inflow, as well as the drastic drop in underground water level. The impact induced by climate change effects and human activities on stream flow changes in LRB was weighed up and distinguished by using Soil and Water Assessment Tool. Simulation of temporal water budgets shows a significant impact of human activities on stream flow reduction. The observed differences in stream flow are largely attributed to human activities. The biggest negative contribution induced by humans is during the period of 1990-2000, the least is during the period of 1968-1979. The negative contribution due to human accounts for 72.99% of the total for 1980-1989, the biggest among three periods. The lower streams of the watershed, with much human induced, experience a relative greater stream flow reduction than the upper.


Liu Z.,China Agricultural University | Yang X.,China Agricultural University | Lin X.,Kansas State University | Hubbard K.G.,University of Nebraska - Lincoln | And 3 more authors.
Science of the Total Environment | Year: 2016

Closing the gap between current and potential yields is one means of increasing agricultural production to feed the globally increasing population. Therefore, investigation of the geographic patterns, trends and causes of crop yield gaps is essential to identifying where yields might be increased and quantifying the contributions of yield-limiting factors that may provide us potentials to enhance crop productivity. In this study, the changes in potential yields, attainable yields, potential farmers' yields, and actual farmers' yields during the past five decades in Northeast China (NEC) were investigated. Additionally the yield gaps caused by non-controllable, agronomic, and socioeconomic factors were determined. Over the period 1961 to 2010 the estimated regional area-weighted mean maize potential yield, attainable yield, and potential farmers' yield were approximately 12.3tha-1, 11.5tha-1, and 6.4tha-1 which showed a decreasing tendency. The actual farmers' yield over NEC was 4.5tha-1, and showed a tendency to increase (p<0.01) by 1.27tha-1 per decade. The regional mean total yield gap (YGt), weighted by the area in each county dedicated to maize crop, was 64% of potential yield. Moreover, 8, 40, and 16% reductions in potential yields were due to non-controllable factors (YGI), agronomic factors (YGII), and socioeconomic factors (YGIII), respectively. Therefore, the exploitable yield gap, considered here as the difference between the potential yield and what one can expect considering non-controllable factors (i.e. YGt-YGI), of maize in NEC was about 56%. The regional area-weighted averages of YGt, and YGIII were found to have significant decreases of 11.0, and 10.7% per decade. At the time horizon 2010, the exploitable yield gaps were estimated to equal 36% of potential yield. This led to the conclusion that the yield gap could be deeply reduced by improving local agronomic management and controlling socioeconomic factors. © 2015 Elsevier B.V.


Zhao J.,China Agricultural University | Yang X.,China Agricultural University | Liu Z.,China Agricultural University | Lv S.,China Agricultural University | And 2 more authors.
Climatic Change | Year: 2016

As climate changes, suitability zones for the cultivation of some crops may shift. In Northeast China (NEC), it is critically important for the agricultural community (e.g. farmers, advisors) to understand the potential shift in suitable cropping zones for spring maize in order to adapt to climate change. The potential climatic suitability can be defined as how actual temperature and solar radiation conditions match the requirements of crop growth under non-limited situations. Here, we used yield potential to reflect the potential climatic suitability, which is determined by the characteristics of crop, solar radiation, temperature, and photoperiod, given the assumption that water, nutrients, pests, and diseases are not limiting the crop growth. We assessed the annual yield potential of spring maize during 1961–2010 in NEC with APSIM-Maize. And then we analyzed the variations in potential climatic suitability zones and the possible effects of these variations on maize production potential. The results show that growing degree-days (GDD) during the growing season for spring maize universally increased in all the locations of this study during the period of 1981–2010 (period II) as compared to the period of 1961–1980 (period I). A total of 66 % of the locations show a decrease in accumulated sunshine duration (ASD) during the growing season during period II as compared to period I. Both coefficient of variation (CV) of GDD and CV of ASD showed an increase during period II as compared to period I. Under the background of climate change, the potential climatic suitability for spring maize was worsened during the most recent five decades: the yield potential declined and the yield stability decreased. In particular, most of the very suitable zone in Jilin and Liaoning during period I turned into suitable or moderately suitable zone during period II. Meanwhile, the total area of marginally suitable zone and no suitable zone increased by 16 % during period II as compared to period I. We detected a close correlation between the decrease in ASD and the decrease in potential climatic suitability, R = 0.56, p < 0.01. We also found a close correlation between the increase in GDD and the decrease in potential climatic suitability, R = −0.25, p < 0.05. Given the same crop varieties and farming management, the total production potential for spring maize in the entire NEC reduced by 4.3 % during period II as compared to period I. © 2016 Springer Science+Business Media Dordrecht


Liu Z.,China Agricultural University | Yang X.,China Agricultural University | Lin X.,Kansas State University | Hubbard K.G.,University of Nebraska - Lincoln | And 3 more authors.
Earth Interactions | Year: 2016

Northeast China (NEC) is one of the major agricultural production areas in China, producing about 30% of China’s total maize output. In the past five decades, maize yields in NEC increased rapidly. However, farmer yields still have potential to be increased. Therefore, it is important to quantify the impacts of agronomic factors, including soil physical properties, cultivar selections, and management practices on yield gaps of maize under the changing climate in NEC in order to provide reliable recommendations to narrow down the yield gaps. In this study, the Agricultural Production Systems Simulator (APSIM)-Maize model was used to separate the contributions of soil physical properties, cultivar selections, and management practices to maize yield gaps. The results indicate that approximately 5%, 12%, and 18% of potential yield loss of maize is attributable to soil physical properties, cultivar selection, and management practices. Simulation analyses showed that potential ascensions of yield of maize by improving soil physical properties PAYs, changing to cultivar with longer maturity PAYc, and improving management practices PAYm for the entire region were 0.6, 1.5, and 2.2 ton ha-1 or 9%, 23%, and 34% increases, respectively, in NEC. In addition, PAYc and PAYm varied considerably from location to location (0.4 to 2.2 and 0.9 to 4.5tonha-1 respectively), which may be associated with the spatial variation of growing season temperature and precipitation among climate zones in NEC. Therefore, changing to cultivars with longer growing season requirement and improving management practices are the top strategies for improving yield of maize in NEC, especially for the north and west areas. © 2016.


Zhao J.,China Agricultural University | Yang X.,China Agricultural University | Lv S.,China Agricultural University | Liu Z.,China Agricultural University | And 2 more authors.
Regional Environmental Change | Year: 2014

Changing crop variety with different maturity types is one of the most effective ways for agricultural production to adapt to climate change. However, variability of climate resources and disaster risks under varying climate conditions makes selection of the proper variety for a certain region more difficult. Based on climate data from 1951 to 2010 and crop data from 1981 to 2007, the impact of climate change on maturity-type shifts of maize variety, the variability of available climate resources including heat, precipitation, and sunshine duration, and agro-meteorological disaster risks in Northeast China (NEC) were analysed. Larger middle- and late-maturity-type cropping areas were found during the second period (1981-2010) than during the first period (1951-1980). The area planted with early-maturity maize tended to decrease in the north-western portion of NEC. In sensitive cropping areas where the maturity types of spring maize shifted, growing degree days increased by 2.8-11.5 %, and the northern portion showed higher increasing amplitude than the southern portion. In addition, both accumulated precipitation and sunshine duration during the maize-growing season showed a significant increasing trend in the northern portion, although a significant decreasing trend was found in the southern portion of NEC. In conclusion, the maturity-type shift in spring maize caused more exposure to chilling damage and water deficiency in the sensitive cropping areas of NEC. The importance of taking full account of disaster risks was demonstrated when changing maturity types of spring maize to achieve higher production. © 2013 Springer-Verlag Berlin Heidelberg.


Zhao J.,China Agricultural University | Yang X.,China Agricultural University | Dai S.,University of Nebraska - Lincoln | Lv S.,China Agricultural University | And 2 more authors.
European Journal of Agronomy | Year: 2015

Global warming has lengthened the theoretical growing season of spring maize in Northeast China (NEC), and the temperatures during the growing season have increased. In practise, crop producers adjust sowing dates and alternate crop cultivars to take advantage of the lengthening growing season and increasing temperatures. In this study, we used crop data and daily weather data for 1981-2007 at five locations in NEC to quantify the utilization of the lengthening growing season and increasing temperatures by adjusting sowing dates and cultivar selection for spring maize production. If these two positive factors are not fully utilized, then it is important to know the potential impacts of these climatic trends on spring maize grain yields. The results show that in NEC, both the actual and theoretical growing seasons are lengthening, i.e., the sowing dates have been advanced and the maturity dates have been delayed. The actual sowing dates are 1-8days later and the actual maturity dates are 6-22days earlier than the theoretical perspective. Advancing sowing dates and changing cultivars led to 0-5days and 6-26days extension of the growing season. For the potential thermal time (TT), adjusting the sowing dates decreased the unutilized TT before sowing, while the cultivar selection increased the utilized TT and decreased the unutilized TT after maturity. On average, the unutilized heating resource before sowing is less than that after the maturity date (0.3-1.9% vs. 2.1-7.8%). During 1981-2007, for per day extension of the growing season, the spring maize grain yield increased by 75.2kgha-1. The spring maize grain yields have increased by 7.1-57.2% when both early sowing and changing cultivars during 1981-2007. In particular, adjusting the sowing dates increased the grain yield by 1.1-7.3%, which was far less than the increase effect (6.5-43.7%) from switching to late maturing cultivars. Therefore, selecting late maturing cultivars is an important technique to improve maize grain yields in NEC under the global warming context. Nevertheless, if the currently unutilized TT were fully explored, the local spring maize grain yield would have increased by 12.0-38.4%. © 2015 Elsevier B.V.


Zhou L.,University of Electronic Science and Technology of China | Xu W.,University of Electronic Science and Technology of China | Wang Z.,University of Electronic Science and Technology of China | Zhang W.,University of Electronic Science and Technology of China | And 3 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2013

The classification and mapping method is vital for many fields of research and has important societal and economic meaning. In this study, we applied QuickBird image to discuss a Multi-scale segmentation method about orchard in Taolin region, Ningxia province in China. Meanwhile, eCognition, as the leading object-oriented software in the world, was used to achieve the goal of classification and mapping. Then, based on the image object's attributes, relationship of each other etc, we formulated a orchard classification system, set a suit of remote sensing interpretation standard, and put forward a Multi-scale segmentation idea to realize sophisticated classification and get satisfied classification result. © 2013 IEEE.

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