Water management for irrigation,crop yield and social attitudes: a socio-agricultural agent-based model to explore a collective action problem

ABSTRACT

When rainfall does not meet crop water requirements, supplemental irrigation is needed to maintain productivity. On-farm ponds can prevent excessive groundwater exploitation – to the benefit of the whole community – but they reduce the cultivated area and require investments by each farmer. Thus, choosing the source of water for irrigation (groundwater vs on-farm pond) is a problem of collective action. An agent-based model is developed to simulate a smallholder farming system; the farmers’ long-/short-view orientation determines the choice of the water source. We identify the most beneficial water source for economic gain and its stability, and how it can change across communities and under future climate scenarios. By using on-farm ponds, long-view-oriented farmers provide collective advantages but have individual advantages only under extreme climates; a tragedy of the commons is always possible. Changes in farmers’ attitudes (and hence sources of water) based on previous experiences can worsen the economic outcome.     

Comparison of three remotely sensed drought indices for assessing the impact of drought on winter wheat yield

ABSTRACT

Agricultural drought threatens food security. Numerous remote-sensing drought indices have been developed, but their different principles, assumptions and physical quantities make it necessary to compare their suitability for drought monitoring over large areas. Here, we analyzed the performance of three typical remote sensing-based drought indices for monitoring agricultural drought in two major agricultural production regions in Shaanxi and Henan provinces, northern China (predominantly rain-fed and irrigated agriculture, respectively): vegetation health index (VHI), temperature vegetation dryness index (TVDI) and drought severity index (DSI). We compared the agreement between these indices and the standardized precipitation index (SPI), soil moisture, winter wheat yield and National Meteorological Drought Monitoring (NMDM) maps. On average, DSI outperformed the other indices, with stronger correlations with SPI and soil moisture. DSI also corresponded better with soil moisture and NMDM maps. The jointing and grain-filling stages of winter wheat are more sensitive to water stress, indicating that winter wheat required more water during these stages. Moreover, the correlations between the drought indices and SPI, soil moisture, and winter wheat yield were generally stronger in Shaanxi province than in Henan province, suggesting that remote-sensing drought indices provide more accurate predictions of the impacts of drought in predominantly rain-fed agricultural areas.     

给水度测定方法研究

本文对影响给水度的因素进行了综合分析．对给水度研究方法予以评价．结合试验研究．提出了在生产实际中精确测定变值给水度的方法。     

Dynamic model for constriction scour caused by large woody debris

Large woody debris (LWD) can have a significant impact upon local channel morphology by creating scour pools and zones of reduced shear stress in which sediment is deposited. It is important to predict scour depths associated with LWD, as it is becoming increasingly common for debris to be added into river channels to improve sediment retention and create pools for aquatic habitat. Engineered log‐jams should therefore be designed using factor of safety engineering analysis, which includes estimates of associated scour and deposition rates. However, the rate and total depth of scour associated with LWD have not been modelled comprehensively, with authors resorting to the use of generic local and constriction scour models to predict scour depths. Also, constriction scour models presented, to date, do not calculate the rate of scour development. In this paper a model is presented for predicting the rate and total depth of scour associated with a channel constriction. The model is one‐dimensional and is based upon the sediment continuity equation, the calculation of specific head changes through the constricted reach and also allows for a variable free surface elevation above the bed at the constriction. This model could be applied to any channel constriction problem but here is used to determine scour rates and depths associated with deflector‐type LWD jams. Deflector jams are one category of jam type presented in a debris jam classification scheme, in which jam type is a function of the ratio of average riparian tree height to average channel width. Deflector jams, as the name implies, partially block the flow and therefore act as a channel constriction, which results in constriction scour. Copyright © 2002 John Wiley & Sons, Ltd.     

广东冬季寒害对香蕉产量的影响

广东丰富的气候资源有利于香蕉生产的发展，但冬季寒害仍可使香蕉生产遭受重大损失，即使冬季最温暖的粤西南亦难幸免。阐述了广东香蕉寒害发生的情况，对几次突出的冬季寒害及其危害进行分析。严重影响广东香蕉主产区的寒害虽然平均约5年左右一遇，但是20世纪90年代寒害出现较频繁，加上反季节种植的春夏蕉由于经济效益较高，种植面积迅速扩大，使得其抽蕾或花芽分化在冬季，造成香蕉遭受寒害的几率增大，对香蕉产量影响很大。为此，广东香蕉生产的发展要重视寒害、风害及市场变化带来的风险，必须因地因时制宜，合理布局，搞好防灾减灾。     

SEDIMENT BUDGET OF THE ILLINOIS RIVER

1 BACKGROUND The Illinois River is the most significant river in the state of Illinois. The river drains nearly half of the state and has a drainage area of 28,906 mi2 (74,867 km2). Except for about a 4,000 mi2 (10,360 km2) area in Indiana and Wisconsin, the watershed is located in Illinois (see Fig. 1). The watershed contains the drainage basins of several of the state's significant rivers such as the Sangamon, LaMoine, Spoon, Mackinaw, Vermilion, Fox, Kankakee, and Des Plaines Ri…     

硅灰石合成高比表面积多孔二氧化硅及其表征

硅灰石与盐酸反应合成高比表面积多孔SiO2 条件为pH值≤ 1.5 ,添加剂为聚乙二醇和NH4Cl,反应后体系中和到pH =4.0 ,经固液分离 ,烘干 ,6 5 0～ 75 0℃灼烧 2h得产物。产物比表面积 479± 45m2 g ,表观密度 0 .34± 0 .0 3g cm3 ,DBP吸着率 173± 16ml 10 0g ,平均中位径D50 为 6 .9± 0 .5um ,孔径分布集中在 1～ 2nm。上述结果得到透射电镜分析证实。     

Sustaining productive ecosystems in face of risk

Ecosystems lacking human induced energy input from outside are in danger to degrade if man requires any sustainable yield. The risk of failure strongly depends on the amount of exploitation. This is shown by a simple one dimensional analytical feed-back model. Natural fluctuations determine the degradation probability of productive ecosystems. The stability behaviour of the latter is demonstrated by an analytical model in the two dimensional phase space. Full quantitative evaluation of the risk needs simulation experiments. One is carried out in the thorn shrub savannah rangelands at a site in Namibia where a fully calibrated simulation model shows that the less a sustainable yield is required, the more the breakdown is delayed. In this case of highly fluctuating rainfall any sustainability sensu strictu does not exist. This revised version was published online in August 2006 with corrections to the Cover Date.     

青南青北寒冻雏形土地温状况比较及对牧草产量的影响

青海南北二地寒冻雏形土分布区，由于海拔高度及地理环境不同，气候变化差异显著。但分析二地地温变化特征发现，青南青北地温分布趋势基本相似，差异不甚明显。这主要与二地土壤质地和湿度、植被覆盖程度不同等有关。表明地温变化是在气候引起变化的基础上叠加了局地土壤-植被性状影响下的结果。当年冬春地温低时，对应牧草产量较高，而地温较高的年份则牧草产量低，究其原因可能与地温低，土壤冻结深厚坚实，地表蒸发减小，易贮存较多的土壤水分有关。