Modelling lake stage and water balance of Lake Tana,Ethiopia

The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three‐dimensional finite‐difference ground‐water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

A soil‐water‐balance approach to quantify groundwater recharge from irrigated cropland in the North China Plain

Rapidly depleting unconfined aquifers are the primary source of water for irrigation on the North China Plain. Yet, despite its critical importance, groundwater recharge to the Plain remains an enigma. We introduce a one‐dimensional soil‐water‐balance model to estimate precipitation‐ and irrigation‐generated areal recharge from commonly available crop and soil characteristics and climate data. To limit input data needs and to simplify calculations, the model assumes that water flows vertically downward under a unit gradient; infiltration and evapotranspiration are separate, sequential processes; evapotranspiration is allocated to evaporation and transpiration as a function of leaf‐area index and is limited by soil‐moisture content; and evaporation and transpiration are distributed through the soil profile as exponential functions of soil and root depth, respectively. For calibration, model‐calculated water contents of 11 soil‐depth intervals from 0 to 200 cm were compared with measured water contents of loam soil at four sites in Luancheng County, Hebei Province, over 3 years (1998–2001). Each 50‐m² site was identically cropped with winter wheat and summer maize, but received a different irrigation treatment. Average root mean‐squared error between measured and model‐calculated water content of the top 180 cm was 4·2 cm, or 9·3% of average total water content. In addition, model‐calculated evapotranspiration compared well with that measured by a large‐scale lysimeter. To test the model, 12 additional sites were simulated successfully. Model results demonstrate that drainage from the soil profile is not a constant fraction of precipitation and irrigation inputs, but rather the fraction increases as the inputs increase. Because this drainage recharges the underlying aquifer, improving irrigation efficiency by reducing seepage will not reverse water‐table declines. Copyright © 2003 John Wiley & Sons, Ltd.     

Palaeoecological constraints on late Glacial and Holocene ice retreat in the Southern Andes (53°S)

Late Glacial to Holocene ice retreat was investigated along a 120 km long fjord system, reaching from Gran Campo Nevado (GCN) to Seno Skyring in the southernmost Andes (53°S). The aim was to improve the knowledge on regional and global control on glacier recession with special emphasis on latitudinal shifting of the westerlies. The timing of ice retreat was derived from peat and sediment cores, using mineralogical and chemical characteristics, and pollen as proxies. Stratigraphy was based on ¹⁴C-AMS ages and tephrochronology. The ice retreat of the Seno Skyring Glacier lobe is marked by an ice rafted debris layer which was formed around 18,300 to 17,500 cal. yr B.P. Subsequently, fast glacier retreat occurred until around 15,000 to 14,000 cal. yr B.P. during which around 84% of Skyring Glacier were lost. This fast recession was probably also triggered by an increase of the Equilibrium Line Altitude (ELA) from 200 to 300 m. Subsequently, the ice surface was lowered below the ELA in an area that previously made up more than 50% of the accumulation area. Much slower retreat and glacier fluctuations of limited extent in the fjord channel system northeast of GCN occurred between around 14,000 to 11,000 cal. yr B.P. during both the Antarctic Cold Reversal and the Younger Dryas. This slow down of retreat indicates a decline in the general warming trend and/or increased precipitation, due to a southward migration of the westerlies. After around 11,000 cal. yr B.P. pollen distribution shows evolved Magellanic Rainforest and similar climate as at present, which lasted throughout most of the Holocene. Only Late Neoglacial moraine systems were formed in the period 1220–1460 AD, and subsequently in the 1620s AD, and between 1870 and 1910 AD. The results indicate that the Gran Campo Nevado ice cap has reacted more sensitive and partly distinct to climate change, compared to the Patagonian Ice Field.     

Effect of bedrock permeability on subsurface stormflow and the water balance of a trenched hillslope at the Panola Mountain Research Watershed,Georgia, USA

The effect of bedrock permeability on subsurface stormflow initiation and the hillslope water balance is poorly understood. Previous hillslope hydrological studies at the Panola Mountain Research Watershed (PMRW), Georgia, USA, have assumed that the bedrock underlying the trenched hillslope is effectively impermeable. This paper presents a series of sprinkling experiments where we test the bedrock impermeability hypothesis at the PMRW. Specifically, we quantify the bedrock permeability effects on hillslope subsurface stormflow generation and the hillslope water balance at the PMRW. Five sprinkling experiments were performed by applying 882–1676 mm of rainfall over a ～5·5 m × 12 m area on the lower hillslope during ～8 days. In addition to water input and output captured at the trench, we measured transpiration in 14 trees on the slope to close the water balance. Of the 193 mm day^?1 applied during the later part of the sprinkling experiments when soil moisture changes were small, <14 mm day^?1 was collected at the trench and <4 mm day^?1 was transpired by the trees, with residual bedrock leakage of >175 mm day^?1 (91%). Bedrock moisture was measured at three locations downslope of the water collection system in the trench. Bedrock moisture responded quickly to precipitation in early spring. Peak tracer breakthrough in response to natural precipitation in the bedrock downslope from the trench was delayed only 2 days relative to peak tracer arrival in subsurface stormflow at the trench. Leakage to bedrock influences subsurface stormflow at the storm time‐scale and also the water balance of the hillslope. This has important implications for the age and geochemistry of the water and thus how one models this hillslope and watershed. Copyright © 2006 John Wiley & Sons, Ltd.     

三维变分同化中多变量平衡约束设计

在现代变分同化系统中,背景场误差协方差起着决定观测信息的空间分布特征、匹配不同变量间的关系和保证分析增量平衡的作用。基于NMC(National Meteorology Centre)方法,设计了一个新的多变量平衡约束算子:在物理变换中,构建相对湿度和其余控制变量间的平衡约束算子;同时分别采用经验正交函数方法和递归滤波器来模拟控制变量(ψ,χ_u,T_u,h_ru,p_su)^T的垂直误差协方差和水平误差协方差。利用2009年6月2日到8月9日间WRF模式的预报差值场,对新的背景场误差协方差进行模拟分析。单点观测试验表明,新的背景场误差协方差实现了观测信息在干湿变量之间的传递,而且相对湿度具有与温度相似的增量场分布。     

长江流域径流对全球升温1.5℃与2.0℃的响应

全球变暖影响着以流域径流要素为主导的水文水资源系统的变化。长江流域未来水资源量的时空分布对长江大保护与长江经济带的发展意义重大。为探究全球升温1.5℃和2.0℃对长江流域径流变化的影响,使用基于偏差校正的气候模式集合数据驱动两参数月水量平衡模型,比较两种升温情景下径流量的响应差异。结果表明：基于偏差校正的气候模式集合数据可以较好地代表长江流域历史时期（1976—2005年）的年平均降水和年平均蒸散发情势。两参数月水量平衡模型与参数区域化方法相结合能较好地模拟长江流域各子流域的月径流量。升温1.5℃时,无论是年径流量还是季节径流量均呈上升趋势,与历史时期相比,50%以上三级子流域的增幅超过5%;升温2.0℃时,增幅超过8%。这表明升温2.0℃情景下长江流域水资源量将进一步增加。相对于历史时期,升温1.5℃与2.0℃情景下长江流域北部降水量增幅较大;径流量增幅分布格局基本与降水量一致。汉江流域是全流域径流量增幅最显著的区域。     

Application of a Degree-Day Model for Determination of Mass Balance of Urumqi Glacier No. 1, Eastern Tianshan, China

In order to verify the feasibility and stability of a degree-day model on simulating the long time series of glacier mass balance, we apply a degree-day model to simulate the mass balance of Urumqi Glacier No. 1 for the period 1987/1988-2007/2008 based on temperature and precipitation data from a nearby climate station. The model is calibrated by simulating point measurements of mass bal-ance, mass balance profiles, and mean specific mass balance during 1987/1988-1996/1997. The opti-mized parameters are obt...     

黔北务一正一道铝土矿床不活动元素地球化学与质量平衡计算

贵州务川一正安一道真（务一正一道）铝土矿属于古风化壳沉积型铝土矿床,是黔中一渝南铝土矿成矿带的重要组成部分。铝土矿产于中下志留系韩家店组（S1-2hj）泥页岩或上石炭统黄龙组（C2h）灰岩的侵蚀面上,含矿层位为中二叠统梁山组（P21）。根据元素地球化学特征及相关分析表明,Ti、zr、Nb、cr、Th、Ga、Hf、Ta及V在铝土矿矿化过程中均为不活动元素。特别是Ti在铝土矿矿化过程中性质最稳定,故可对其用于质量平衡的计算。铝土矿化过程中一些元素的质量变化可以通过不活动元素在铝土矿（岩）和中下志留系韩家店组（s1-2。hj）泥页岩中的含量变化来估算。计算结果显示,大多数活动元素从铝土矿体系中移走,部分Si、Mg、K、Fe以及少量的弱活动性AJ向下渗透,并沉淀为伊利石（绢云母、绿泥石）、赤铁矿和石英或非晶体硅。通过系统研究和质量平衡计算,可初步确定SI1-2hj泥页岩为务一正一道铝土矿主要的成矿原岩。     

上海市耕地占补动态管理机制研究

探索建立耕地占补动态管理机制是解决上海土地资源瓶颈因素制约的有效途径,也是国家土地资源管理的创新需求。分析我国耕地占补平衡政策现存问题及未来发展趋势,结合上海市耕地占补的突出特点,构建以＂两级动态统筹占补平衡＂和＂多层次异地占补平衡＂为创新方向的耕地占补动态管理机制。该机制框架包括耕地占用指标市-区（县）两级的动态分配机制、耕地补充指标市-区（县）两级的动态筹集机制;该机制的细部设计则包括目标—责任动态考核机制、多途径激励参与机制、耕地指标市场交易机制、指标变化动态监督机制以及信息化技术保障等5个方面。     

Simulation and analysis of river runoff in typical cold regions

It is generally agreed that global warming is taking place, which has caused runoff generation processes and apparently total runoff amount changes in cold regions of Northwestern China. It is absolutely necessary to quantify and analyze earth surface hydrological processes by numerical models for formulating scientific sustainable development of water resources. Hydrological models became established tools for studying the hydrological cycle, but did not consider frozen soil or glacier hydrology. Thus, they should be improved to satisfy the simulation of hydrological processes in cold regions. In this paper, an energy balance glacier melt model was successfully coupled to the VIC model with frozen soil scheme, thus improving the models performance in a cold catchment area. We performed the improved VIC model to simulate the hydrological processes in the Aksu River Basin, and the simulated results are in good agreement with observed data. Based on modeling hydrological data, the runoff components and their response to climate change were analyzed. The results show: (1) Glacial meltwater recharge accounts for 29.2% of runoff for the Toxkan River, and 58.7% for the Kunma Like River. (2) The annual total runoff of two branches of the Aksu River show increasing trends, increased by about 43.1%, 25.95×10⁶ m³ per year for the Toxkan River and by 13.1%, 14.09×10⁶ m³ per year for the Kunma Like River during the latter 38 years. (3) The annual total runoff of the Toxkan River increased simply due to the increase of non-glacial runoff, while the increase of annual total runoff of the Kunma Like River was the result of increasing glacial (42%) and non-glacial runoff (58%).