全国首个“吨谷市”

民以食为天。当今,人们吃着香喷喷的米饭时,或者难以想象改革开放前温饱不保的穷日子。改革开放后,汕头掀起粮食创高产的热潮,并于1991年成为全国第一个“吨谷市”。汕头由于人多地少,高产便成了政府粮食生产的主攻方向,并因此取得非常好的成绩而闻名全国。亲历者说:水稻育种演绎“粮食革命”“水稻育种一直是汕头市农科所的传统优势项目,特别是自1986年立项开展杂交水稻选育种研究工作以来。

International Trade and the Urbanization of Developing Countries:Evidence from Asia

A grain surplus and the grain trade are closely related to the urbanization of developing countries. However, existing literature has not given adequate attention to this issue. Our paper develops a theoretical model to explain the mechanisms whereby changes in the grain surplus constrain the level of urbanization in a closed economy context and the grain trade affects the level of urbanization by acting on the grain surplus in an open economy context. A test of the theoretical model applied to some developing countries in Asia during the period 1993-2010 shows that international trade is generally negatively correlated with level of urbanization. However, cereal and non-cereal trade vary in terms of their relation to urbanization： whereas the former is positively correlated with level of urbanization, thelatter is negatively correlated with it. Since the net import of cereals relaxes the constraint imposed on the level of urbanization by the domestic grain surplus, it can have a marked positive effect on the course of urbanization. Our research findings show that provided grain production or grain security is guaranteed, developing countries may adopt a policy of importing an appropriate amount of grain to increase their level of urbanization.

Classification of yearly extreme precipitation events and associated flood risk in the Yangtze-Huaihe River Valley

Fifty cases of regional yearly extreme precipitation events （RYEPEs） were identified over the Yangtze-Huaihe River Valley （YHRV） during 1979-2016 applying the statistical percentile method. There were five types of RYEPEs, namely Yangtze Meiyu （YM-RYEPE）, Huaihe Meiyu （HM-RYEPE）, southwest-northeast-oriented Meiyu （SWNE-RYEPE） and typhoon I and II （TC-RYEPE） types of RYEPEs. Potential vorticity diagnosis showed that propagation trajectories of the RYEPEs along the Western Pacific Subtropical High and its steering flow were concentrated over the southern YHRV. As a result, the strongest and most frequently RYEPEs events, about 16-21 cases with average rainfall above 100 mm, occurred in the southern YHRV, particularly in the Nanjing metropolitan area. There have been 14 cases of flood-inducing RYEPEs since 1979, with the submerged area exceeding 120 km2 as simulated by the FloodArea hydraulic model, comprising six HM-RYEPEs, five YM- RYEPEs, two TC-RYEPEs, and one SWNE-RYEPE. The combination of evolving RYEPEs and rapid expansion of urban agglomeration is most likely to change the flood risk distribution over the Nanjing metropolitan area in the future. In the RCP6.0 （RCPS.5） scenario, the built-up area increases at a rate of about 10.41 km2 （10 yr）-t（24.67 km2 （10 yr）-1） from 2010 to 2100, and the area of high flood risk correspondingly increases from 3.86 km2（3.86 km2） to 9.00 kin2（13.51 km2）. Areas of high flood risk are mainly located at Chishan Lake in Jurong, Lukou International Airport in Nanjing, Dongshan in Jiangning District, Lishui District and other low-lying areas. The accurate simulation of flood scenarios can help reduce losses due to torrential flooding and improve early warnings, evacuation planning and risk analysis. More attention should be paid to the projected high flood risk because of the concentrated population, industrial zones and social wealth throughout the Nanjing metropolitan area.

Numerical Model for the Characterization of Retro-reflective Materials Behavior in an Urban Street Canyon

In this work, a preliminary numerical model of the behavior of retro-reflective materials used as envelope coatings on street canyon buildings facades has been tested. Retro-reflective materials have a surface finish that allows to reflect the solar radiation back in the same direction of the incident radiation. In the last years this kind of materials has been studied as buildings envelope coating for their potentials in the reduction of the UHI effect. As a matter of fact, the angular dependence of their optical-radiative response would help to mitigate the phenomenon of radiative entrapment due to the urban fabric environment. For this reason, an urban canyon was selected as the most common urban architecture to perform the analysis. A virtual retroreflective material has been simulated considering its response as almost diffusive but in the same direction of the incident radiation. The assessment of the energy advantages of the adoption of a virtual retro-reflective material as envelope coating is investigated by means of a numerical model developed in MATLAB and based on the Gebhart factors theory. The final purpose of the numerical model is the evaluation of the surfaces solar loads by a comparison between perfectly diffusive materials and RR materials used as fa？ades coating.