Could Rice Yield Change Be Caused by Weather?

Data from 4 counties of Hainan Province of China from 1991-2012 was used to determine the weather impact on rice yields in both early and late rice seasons with multiple regression models. The results show there is normal weather environment for rice in the heading stage for early season rice in May and the milking stage for late season rice in November. For early season rice, more rain in April and June is better for rice to boot and milk, the average temperature has negative effect for the season rice yield;for late season rice, the average temperature have positive effect for the difference between rice yield and the mean of total years but in seedling and booting stage;the rice yield difference between double season is compared and analyzed through the difference of meteorological factors, the results show that the precipitation gap in tillering stage has positive effect to rice yield increasing, but against in booting stage. The relative results should be use to forecast rice yield, and further provide the rice production guiding.

A METROD PREDICTING RESPONSE OF SEDIMENT YIELD TO POSSIBIE CHANGE OF PRECIPITATION DUE TO GLOBAL GREENHOUSE WARMING:AN EXAMPIE FROM NORTH FRINGE OF THE LOESS PLATEAU, CHINA

Starting from the supposition of time-space substitution, the Langbein-Schumm's Law was applied to deal with response of fluvial erosion System to the changes in mean annual Precipitation induced by global green-house warming. As a result, a simple method was put forward to predict change in sediment yield, with Ningxia Hui Autonomous Region in the northern fringe of the Loess Plateau of China as an example. Results show that, even the change in mean annual precipitation is the same, the direction and magnitude of the resultant chang in sediment yteld would be quite different in fferent physico-geographical zones. When mean annual precipitation is increased, sediment yield in arid or semi-arid areas with a mean anntal Peripitation of less than 400 mm will be increased, while sediment yield in sub-humid or humid areas with a mean annual precipitation of more than 400 mm will be decreased.Additionally, the complex response of fluvial erosion system in time series due to the lag of change in vegetation behind the changn in precipitation has also been qualitatively discussed in this paper.

Assessing the Effect of Natural Controls and Land Use Change on Sediment Yield in a Major Andean River:The Magdalena Drainage Basin,Colombia

马格达莱纳河是哥伦比亚安第斯山区的一个世界级的河流网络，该河流年产沙量约为150Mt，是全世界10大主要产沙河流之一。在本研究中，我们探讨主要自然因子和人类活动对马格达莱纳河流域产沙模式的影响，重建该区森林砍伐和农业活动时空模式，探讨土地利用变化与产沙趋势的关系。我们的研究结果表明，整个马格达莱纳河流域的产沙量可以用自然变量（包括径流量和最大河水流量）来解释。这两个因子解释了产沙量58％的变化。含沙率和土地利用的时间分析表明，在过去10～20年里流域侵蚀呈现增加的趋势。许多人类活动的影响，包括森林覆被在20年里减小了近40％．农业和牧场增加了65％、土壤保持差、开矿活动，以及城市化的加速，都促进了该地区域尺度上产沙量的增加。

Impacts of precipitation variation and soil and water conservation measures on runoff and sediment yield in the Loess Plateau Gully Region, China

The Loess Plateau of China has experienced a lengthy drought and severe soil erosion.Changes in precipitation and land use largely determine the dynamics of runoff and sediment yield in this region. Trend and mutation analyses were performed on hydrological data(1981–2012) from the Yanwachuan watershed in the Loess Plateau Gully Region to study the evolution characteristics of runoff and sediment yield. A time-series contrasting method also was used to evaluate the effects of precipitation and soil and water conservation(SWC) on runoff and sediment yield. Annual sediment yield declined markedly from 1981 to 2012 although there was no significant change in annual precipitation and annual runoff. Change points of annual runoff and annual sediment yield occurred in 1996 and 1997,respectively. Compared with that in the baseline period(1981–1996), annual runoff and annual sediment yield in the change period(1997–2012)decreased by 17.0% and 76.0%, respectively, but annual precipitation increased by 6.3%. Runoff decreased in the flood season and normal season, but increased in the dry season, while sediment yield significantly declined in the whole study period. The SWC measures contributed significantly to the reduction of annual runoff(137.9%) and annual sediment yield(135%) and were more important than precipitation. Biological measures(forestland and grassland) accounted for 61.04% of total runoff reduction, while engineering measures(terraces and dams) accounted for 102.84% of total sediment yield reduction. Furthermore, SWC measures had positive ecological effects. This study provides a scientific basis for soil erosion control on the Loess Plateau.

Attribution of Maize Yield Increase in China to Climate Change and Technological Advancement Between 1980 and 2010

Crop yields are affected by climate change and technological advancement.Objectively and quantitatively evaluating the attribution of crop yield change to climate change and technological advancement will ensure sustainable development of agriculture under climate change.In this study,daily climate variables obtained from 553 meteorological stations in China for the period 1961-2010,detailed observations of maize from 653 agricultural meteorological stations for the period 1981-2010,and results using an Agro-Ecological Zones（AEZ） model,are used to explore the attribution of maize（Zea mays L.） yield change to climate change and technological advancement.In the AEZ model,the climatic potential productivity is examined through three step-by-step levels：photosynthetic potential productivity,photosynthetic thermal potential productivity,and climatic potential productivity.The relative impacts of different climate variables on climatic potential productivity of maize from 1961 to 2010 in China are then evaluated.Combined with the observations of maize,the contributions of climate change and technological advancement to maize yield from 1981 to 2010 in China are separated.The results show that,from 1961 to 2010,climate change had a significant adverse impact on the climatic potential productivity of maize in China.Decreased radiation and increased temperature were the main factors leading to the decrease of climatic potential productivity.However,changes in precipitation had only a small effect.The maize yields of the 14 main planting provinces in China increased obviously over the past 30 years,which was opposite to the decreasing trends of climatic potential productivity.This suggests that technological advancement has offset the negative effects of climate change on maize yield.Technological advancement contributed to maize yield increases by 99.6%-141.6%,while climate change contribution was from-41.4%to 0.4%.In particular,the actual maize yields in Shandong,Henan,Jilin,and Inner Mongolia increased by 98.4,90.4,98.7,and 121.5 kg hm^（-2） yr^（-1） over the past 30 years,respectively.Correspondingly,the maize yields affected by technological advancement increased by 113.7,97.9,111.5,and 124.8 kg hm^（-2） yr^（-1）,respectively.On the contrary,maize yields reduced markedly under climate change,with an average reduction of-9.0 kg hm^（-2） yr^（-1）.Our findings highlight that agronomic technological advancement has contributed dominantly to maize yield increases in China in the past three decades.