Larrea tridentata叶片解剖结构与保水特性的研究

为了解L.tridentata叶片在解剖学方面适应干旱的特征以及叶片的保水特性,采用石蜡切片法观察L.tridentata叶片的解剖结构,同时测定叶片保水曲线。结果显示：L.tridentata叶片厚233.6μm,表皮细胞大,具有较厚的表皮细胞外壁与角质层,上表皮外壁与角质层总厚度为23.7μm;栅栏组织发达,在叶片中占55%,细胞细长,排列紧密。从叶片保水曲线上看,L.tridentata叶片从失水到基本恒重的时间为120 h左右,显示其叶片抗脱水能力强。     

云南气象灾害的时空分布规律

云南主要的气象灾害有旱灾、洪灾、冷灾、雹灾、风灾和雷灾等6类,它们造成的经济损失超过地震灾害和地质灾害,是云南最大的自然灾害.6种主要气象灾害有明显的时空分布特征.旱灾区主要集中在滇东北、滇东、滇北和滇中地区;洪灾区主要集中在滇东北、滇东南、滇南和滇西南地区;冷灾区主要分布在滇东北、滇西北、滇东和滇中地区;雹灾区主要分布在滇东北、滇东、滇南、滇西北以及滇中局部地区;风灾区主要集中在滇东北、滇南地区;雷灾区主要集中在滇南、滇东南及滇北局部地区.旱灾以春季和初夏最为严重,洪灾主要出现在夏季和秋季,冷灾主要出现在冬春季和夏季,雹灾主要出现在春季和夏季,风灾主要出现在春季和夏季,雷灾主要出现在夏季和春季.     

吉林西部农业旱灾变化趋势及其成因分析

利用吉林西部近50年的农业成灾面积统计资料和气象资料，提示了西部的农业旱灾整体呈波动上升的变化趋势。特别是进入20世纪80年代以后，在全球温暖化的大环境背景下．旱灾已成为当地农业可待续发展的最主要的障碍因素，并引起一系列的生态环境问题。影响农业的旱灾既有自然因素又有人为因素。针对吉林西部的旱灾，提出了一系列减灾对策。     

我国旱涝空间型的马尔科夫概型分析

旱涝灾害在我国是影响最大、也最为频繁的气候灾害。本文利用马尔科夫概型分析的原理和方法，在验证了我国旱涝空间型序列具有马尔科夫性质的基础上，计算出各状态的转移概率，进而分析了旱涝空间型序列的静态和动态结构，并揭示出旱涝空间型各状态演化的优势倾向。     

国内外不同尺度的旱灾风险评价研究进展

作为旱灾风险管理实践的科学基础,旱灾风险评价愈来愈受到社会各界的广泛关注。在阅读大量文献的基础上,从4个不同的区域尺度对国内外旱灾风险评价研究进展作了综述。结果表明:(1)目前所有区域尺度研究中,农业旱灾风险评价研究较多;(2)地区尺度的旱灾风险评价是研究其他尺度的切入点,可为实现空间尺度上推(全球和国家尺度)和下推(县乡农户尺度)旱灾风险评价结果的转换提供依据;(3)随空间尺度从全球和大洲→国家→地区→地方尺度,旱灾风险评价的文献量逐渐增多,内容逐渐深入;(4)旱灾风险对饥荒和粮食安全的影响、农业系统和农作物承灾体的旱灾风险评价是目前研究的热点。在此基础上,指出旱灾发生频率较低但生态环境敏感区的旱灾风险评价需加强;从干旱灾害链的角度以及综合旱灾风险与脆弱性、恢复性、适应性的关系来研究旱灾风险是今后的重点。     

SPATIAL VARIATIONS OF WATER LOSS DURING DROUGH A CASE STUDY1

ABSTRACT: A regional water conservation system for drought management involves many uncertain factors. Water received from precipitation may stay on the ground surface, evaporate back into the atmosphere, or infiltrate into the ground. Reliable estimates of the amount of evapotranspiration and infiltration are not available for a large basin, especially during periods of drought. By applying a geographic information system, this study develops procedures to investigate spatial variations of unavailable water for given levels of drought severity. Levels of drought severity are defined by truncated values of monthly precipitation and daily streamflow to reflect levels of water availability. The greater the truncation level, the lower the precipitation or streamflow. Truncation levels of monthly precipitation are recorded in depth of water while those of daily streamflow are converted into monthly equivalent water depths. Truncation levels of precipitation and streamflow treated as regionalized variables are spatially interpolated by the unbiased minimum variance estimation. The interpolated results are vector values of precipitation and streamflow at a grid of points covering the studied basin. They are then converted into raster‐based values and expressed graphically. The image subtraction operation is used to subtract the image of streamflow from that of precipitation at their corresponding level of drought severity. It is done on a cell‐by‐cell basis resulting in new attribute values to form the spatial image representing a spatial distribution of potential water loss at a given level of drought severity.     

TOWARDS CHARACTERIZING AND PLANNTNG FOR DROUGHT IN VERMONT‐PART II: POLICY IMPLICATIONS1

ABSTRACT: Vermont is one of approximately half a dozen states for which no official drought mitigation plan exists. Given the recurring nature of this natural hazard, current contingency measures should be expanded upon into a coherent mitigation framework. The types of drought and impacts resulting from the 1998 to 1999 event were the focus of a previous article in this volume. The present article builds on the understanding of drought characteristics specific to the Vermont context and introduces the rationale behind a proposed drought planning framework. Pivotal organizations and institutions that should be involved in this process are also presented.     

A TREE‐RING RECONSTRUCTION OF STREAMFLOW FOR THE COLORADO FRONT RANGE1

ABSTRACT: Water resource planning is based primarily on 20th century instrumental records of climate and streamflow. These records are limited in length to approximately 100 years, in the best cases, and can reflect only a portion of the range of natural variability. The instrumental record neither can be used to gage the unusualness of 20th Century extreme low flow events, nor does it allow the detection of low‐frequency variability that may underlie short‐term variations in flow. In this study, tree rings are used to reconstruct mean annual streamflow for Middle Boulder Creek in the Colorado Front Range, a semi‐arid region of rapid growth and development. The reconstruction is based on a stepwise regression equation that accounts for 70 percent of the variance in the instrumental record, and extends from 1703–1987. The reconstruction suggests that the instrumental record of streamflow for Middle Boulder Creek is not representative of flow in past centuries and that several low flow events in the 19th century were more persistent than any in the 20th century. The 1840s to early 1850s period of low flow is a particularly notable event and may have coincided with a period of low flow in the Upper Colorado River Basin.     

AN EVALUATION OF THE 1997 EDWARDS AQUIFER IRRIGATION SUSPENSION1

ABSTRACT: In early 1997, the Texas Edwards Aquifer Authority implemented a pilot Irrigation Suspension Program with the objectives of increasing springflow and providing relief to municipalities during drought. Irrigators were paid an average of $234 per acre to suspend water use, a price higher than regional land rental rates. Auction theory and program implementation details suggest that the program implementation partially caused inflated bids. The Irrigation Suspension Program is also compared to two alternative programs: (1) subsidizing more efficient irrigation technology and (2) buying land. The irrigation suspension is found to be more cost‐effective relative to subsidizing improved irrigation efficiency because it can be put in place only when aquifer levels are low. Land purchase is a cheaper alternative if the bid levels remain at the levels observed.     

巢湖流域旱涝时空特性分析

利用巢湖流域14个站点39年(1961~2000年)的降水观测资料,采用Z指数作为旱涝指标,运用地理信息系统(GIS)等方法,对巢湖流域汛期旱涝的时空变化特征进行了分析探讨,其结果表明:巢湖流域旱涝灾害十分频繁,旱涝灾害发生的频率和降水量呈现正相关关系,具有阶段性和周期性等特性,空间分布上存在一定的结构性,巢湖流域北部为易旱易涝区,西部为易旱区,东南部、南部是易涝区,中北部是不易旱易涝区。