Spatial and temporal assessment of drought in the Northern highlands of Ethiopia

With the development of global changes, researchers from all over the world increasingly pay attention to drought detection, and severe droughts that may have resulted from climate change. In this paper, spatial and temporal variability of drought is evaluated based on precipitation data and remotely sensed images. The standard precipitation index (SPI) and vegetation condition index (VCI) are used to evaluate the spatial and temporal characteristics of meteorological and vegetative drought in Tigray, Northern Ethiopia. Based on the drought critical values of SPI and VCI defining drought, the spatial and temporal extent of droughts in the study area is established. We processed 396 decadal images in order to produce the multi-temporal VCI drought maps. The results of the SPI and VCI analysis reveal that the eastern and southern zones of the study region suffered a recurrent cycle of drought over the last decade. Results further show that there is a time lag between the period of the peak VCI and precipitation values obtained from the meteorological stations across the study area. A significant agreement was observed between VCI values with the current plus last two-months of precipitation. The study demonstrates the utility of the vegetation condition index in semi-arid and arid regions.     

基于自回归分布滞后模型的地面沉降预测

地面沉降与地下水水位变化不同步,且地面下沉受自身影响较大,建立滞后作用下地面沉降预测模型,以某地区地面沉降为例进行模拟试验,并探讨模型拟合效果与预测精度。结果表明,自回归分布滞后模型的拟合效果较好,预测精度较高,可以用到地面沉降量计算中。     

Determination of aquifer parameters based on measurements of tidal effects on a coastal aquifer near Beihai,China

Measurements of the tide and groundwater levels in coastal zones are of importance in determining the properties of coastal aquifers. The solution to a one‐dimensional unsteady groundwater flow model in a coastal confined aquifer with sinusoidal fluctuation of the tide shows that the tidal efficiency decreases exponentially with distance and the time lag increases linearly with distance from the coast. The aquifer property described by the ratio of storage coefficient to transmissivity is determined if the damping constant of the tidal efficiency or the slope of the time lag with distance are obtained on the basis of tidal measurements. Hourly observations of the tide and groundwater levels at 10 wells on the northern coast near Beihai, China show that with distance from the coast, tidal efficiency decreases roughly exponentially and the time lag increases roughly linearly. The estimated ratio of storage coefficient to transmissivity of the confined aquifer ranges from 1·169 × 10^?6 d m^?2 to 1·83 × 10^?7 d m^?2. For a given transmissivity of 750 m² d^?1, the storage coefficient of the aquifer is 8·7675 × 10^?4 with the tidal efficiency method and 1·3725 × 10^?4 with the time lag method. The damping constant of the tidal efficiency with distance can be defined as the tidal propagation coefficient. The value of the confined aquifer is determined as 0·0018892 m^?1. Copyright © 2007 John Wiley & Sons, Ltd.     

Emplacement temperature determinations of proximal pyroclastic deposits on Santorini,Greece, and their implications

Received: 14 May 1998 / Accepted: 8 July 1999     

风对极端干旱区胡杨蒸腾速率的影响

以2014年4-11月的胡杨蒸腾速率和风速的实测数据, 分析了风对极端干旱区胡杨蒸腾速率的影响. 结果表明: 不同风速对胡杨蒸腾速率的影响存在差异, 风速的瞬时变动并不一定都会促进蒸腾速率的升高. 0~2 m·s^-1风速作用对胡杨蒸腾速率的影响不大; 2~8 m·s^-1风速作用下, 胡杨蒸腾速率显著升高, 且随着风速的增大, 蒸腾速率上升幅度增加. 其中, 2~4 m·s^-1风速作用下, 其变化幅度较0~2 m·s^-1时增加了4.51%; 4~6 m·s^-1风速作用下, 其变化幅度较2~4 m·s^-1时增加了7.03%; 6~8 m·s^-1风速作用下, 其变化幅度较4~6 m·s^-1时增加了16.19%. 当风速大于8 m·s^-1时, 胡杨蒸腾速率不再上升而呈下降趋势, 且随着风速的增加, 蒸腾速率降低的幅度也越大, 其中, 8~10 m·s^-1风速作用下, 蒸腾速率下降了8.08%; 大于10 m·s^-1的风速作用下, 胡杨蒸腾速率的下降幅度高达32.91%. 胡杨蒸腾速率和风速的错位相关分析表明, 风速对胡杨蒸腾速率的影响多为实时性的, 在极少数的大风天气影响下, 蒸腾速率恢复的时间较慢, 形成了个别日期的滞后效应. 风速和胡杨蒸腾速率的指数拟合关系最显著, 且2~8 m·s^-1风速下, 蒸腾速率随着风速呈指数增加趋势; 8 m·s^-1以上风速作用下, 蒸腾速率随着风速的增加呈指数减少趋势. 在0~2 m·s^-1风速作用下, 蒸腾速率变化不大.     

长三角地区城市土地与能源消费CO2排放的时空耦合分析

探究城市土地与碳排放的时空耦合关系,是协调城市土地与生态环境亟待解决的重要问题。基于重心模型、总体耦合态势模型和空间耦合协调模型,使用建成区面积、能源消费和DMSP/OLS夜间灯光等数据,分析了1995—2013年长三角地区城市土地与能源消费碳排放的时空耦合特征,并考虑空间因素的影响,构建空间滞后面板Tobit模型分析其驱动因素。结果表明：① 1995—2013年,建成区面积与碳排放量总体上均呈增加趋势。建成区面积由1251 km ²,增加至4394 km ²,碳排放量由30389.49万t,增加至90405.22万t。城市土地与碳排放间呈显著的正相关;② 城市土地与碳排放空间差异明显,上海、南京、杭州、苏州和无锡的城市建成区面积相对较大,碳排放相对较高;③ 长三角地区城市土地与碳排放耦合关系总体上呈减弱-增强-波动的态势。协调关系处于不断演化过程中,低协调阶段的城市数量明显减小,高协调阶段的城市数量明显增加,且呈集聚分布特点。南京、无锡、苏州、杭州和宁波处于高协调阶段;④ 空间滞后面板Tobit模型结果表明：城镇化对城市土地与碳排放耦合协调度具有驱动和制动的双重作用。同时,人口密度、经济水平、产业结构和空间因素对其也具有重要影响。     

Effect of earth tide on deep well water level

On the basis of the partial differential equations of the water level in a deep well that is affected by the bulk strain tide, the boundary conditions of permeating each other between aquifer and well are considered. The solutions of the equations have been obtained by the superposition principle, inpulse theorem and separation of the variations. Some suitable values are given to the parameters of well aquifer in the solutions. By means of the numerical calculation the relations among the well tide coefficients and phase lag phenomenon of response of the well level to earth tides is well interpreted. The parametric studies and the obtained graphs show that the more the radius of casing in a well, the porosity of an aquifer and the bulk compressibility for solid matrix of an aquifer, the less the transmissibility of an aquifer, then the less the tidal coefficient of well level, while the more the phase lag for well level to respond to the tide is. The response of the well level to the tide of longer period is better than the shorter period events. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 66–75, 1991.     

利用地中渗透仪观测资料进行降雨入渗补给规律分析

利用郑州地下水均衡场地中渗透仪实测资料，分析了降雨入渗补给的年际变化以及入渗补给过程中的滞后现象。通过计算降雨入渗系数，确定了降雨量与入渗量的定量关系，评价了不同降雨量、不同包气带岩性和厚度条件下的入渗补给量。研究表明，地下水埋深较小时，降雨入渗系数随着埋深的增加而增大，1m以下则逐渐减少，3m以下趋于稳定；当包气带岩性单一时，降雨入渗系数随岩性的不同而变化，即砂质土大、粘性土较小，而含有薄层粘土夹层的亚砂土最小。     

毛乌素沙地风沙滩区降水入渗响应研究

为研究毛乌素沙地地下水浅埋区降水入渗补给滞后响应时间,确定补给滞后的影响因素,为该地水文生态保护与地下水资源评价提供科学依据,以陕北毛乌素沙地风沙滩区为研究区,基于原位试验数据和相关分析法,分析土壤含水率和地下水位对降水入渗的响应机制,运用土壤水均衡分析探讨降水入渗响应与各影响因素的关系式。结果表明,小雨型降水土壤含水率响应深度为0~10cm,中雨型为10~90cm,大雨型与暴雨型均>90cm。最大响应深度z与降水量P显著线性相关。在地下水位一定的前提下,随着前期累计降水增大,当前降水入渗响应深度也增大,前期累计降水对当前降水入渗的影响时段在144 h以内。雨后土壤水分与地下水补给均存在滞后。入渗响应滞后时间与土壤深度呈正比,与降水强度和土壤初始导水率的差成反比。     

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