The hydrological influence of black locust plantations in the loess area of northwest China

Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified.     

Variation of infiltration rate through karstic surfaces due to land use changes: A case study in Murgia (SE-Italy)

Groundwaters of the Murgia carbonate aquifer represent the main groundwater resource of the Apulia region (SE Italy). In the highlands (Alta Murgia) karst crops out in different forms and textures which have been preserved up to the 1970s: little evolved agriculture and sheep rearing produced only a marginal modification of the epikarst while a high degree of division into parcels by drystone walls helped in preserving soils from erosion. In the last years the original scenery of the Alta Murgia changed due to widespread transformations of surface karstic textures for agricultural purposes, with undeniable negative consequences on the hydrogeological balance, concerning both the infiltration and the runoff terms. Stone shattering led to flattening and deep alteration of a large part of the original karstic landscape and to demolition of drystone walls.In a study area of about 139 km² located in the Alta Murgia, the comparison of aerial photos related to the period 1950–2001 indicated that stone shattering had occurred for about 42% of the area.The hydrological behaviour of the first soil layer of experimental parcels representing both shattered stone and natural karstic surface textures was analysed by using the numerical model Hydrus-2D with the aim of estimating the variation on infiltration rate due to stone shattering. Intensive field and laboratory measurements concerned soil texture, soil water content, pressure head, saturated hydraulic conductivity, pan evaporation and meteorological parameters.     

Estimating groundwater evapotranspiration rates using diurnal water-table fluctuations in a semi-arid riparian zone

In semi-arid climates, phreatophytes draw on shallow aquifers, and groundwater evapotranspiration (ET_G) is a principal component of groundwater budgets. Diurnal water table fluctuations, which often are a product of ET_G, were monitored in the riparian zone of Red Canyon Creek, Wyoming, USA. These fluctuations were higher in a riparian wetland (2–36 mm) than a grass-covered meadow (1–6 mm). The onset and cessation of water-table fluctuations correspond to daily temperatures relative to freezing. Spatial differences were due to vegetation type and specific yield, while temporal changes were due to vegetation dormancy. Ratios of ET_G to potential evapotranspiration (PET), K _c,GW, were similar to ratios of actual evapotranspiration (ET) to PET, K _c, in semi-arid rangelands. Before vegetation senescence, K _c,GW increased between precipitation events, suggesting phreatophytes pull more water from the saturated zone as soil moisture decreases. In contrast, K _c decreases with soil moisture following precipitation events as ET becomes increasingly water-limited. Error in ET_G is primarily from estimates of specific yield (S _y), which is difficult to quantify in heterogeneous sediments. ET_G values may be more reliable because the range of acceptable S _y is smaller than K _c and S _y does not change with vegetation type or soil moisture.     

长江三角洲地区水和热通量的时空变化特征及影响因子

文中利用改进的K B模式和牛顿扩散方法及 196 1年以来的长江三角洲 (2 8～ 33°N ,118～ 12 3°E)地区的 4 8个测站的常规气象资料 ,估计了该地区近 4 0a来的蒸散量和感热通量。结合该地区的气温、太阳辐射等气候资料和 196 0年以来该区域土地资源利用变化等有关信息对该地区的潜热通量和感热通量的时 空间变化特征及其可能成因进行了综合分析。结果认为该地区自 2 0世纪 70年代开始平均蒸散量有逐渐减小的趋势 ,与 1980年相比 ,1998年区域年平均蒸散量减小了 2 4mm。区域平均感热通量与蒸散量相比在此期间变化并不明显。通过对该地区的云量、太阳辐射及土地利用变化资料分析认为 ,造成该地区平均蒸散量减少趋势的的原因之一是用于蒸发的能量即太阳辐射的减少 ,而造成太阳辐射减少的可能原因为云量及大气透明度的变化所至 ;原因之二是该地区地表覆盖条件的改变。近 2 0a来 ,该地区的水田、旱地及水域面积占总面积的比率分别减少 1.35 3% ,4 .4 4 2 %和2 .5 97% ,而城镇建设、工矿及其它建设用地面积则增加 3.345 %。耕地及水面的减小和城镇及建设用地面积的增加从整体上使区域平均蒸发量减少。     

Steady, annual, and monthly recharge implied by deep unconfined aquifer flow

We consider the response of a deep unconfined horizontal aquifer to steady, annual, and monthly recharge. A groundwater divide and a zero head reservoir constrain the aquifer, so that sinusoidal monthly and aperiodic annual recharge fluctuations create transient specific discharge near the reservoir and an unsteady water table elevation inland. One existing and two new long-term data sets from the Plymouth-Carver Aquifer in southeastern Massachusetts calibrate and confirm hydraulic properties in a set of analytical models. [Geohydrology and simulated groundwater flow, 1992] data and a new power law for tritiugenic helium to tritium ratios calibrate the steady recharge that drives the classical parabolic model of steady hydraulics [Applied Hydrogeology, 2001]. Observed water table and gradient fluctuations calibrate the transient recharge models. In the latter regard, monitoring wells within 1 km of Buttermilk Bay exhibit appreciable specific discharge and reduced water table fluctuations. We apply [Trans Am Geophys Union 32(1951)238] periodic model to the monthly hydraulics and a recharge convolution integral [J Hydrol 126(1991)315] to annual flow. An infiltration fraction of 0.79 and a consumptive use coefficient of 1.08×10⁻⁸ m/s °C relate recharge to precipitation and daylight weighted temperature across all three time scales. Errors associated with this recharge relation decrease with increasing time scale.     

土地利用和气候变化对海河流域蒸散发时空变化的影响

蒸散发（ET）是水文能量循环和气候系统的关键环节,研究ET的时空变化特征及其响应土地利用和气候变化的驱动机制对于理清流域水资源和气候变化的关系具有重要的意义。本文基于MOD16/ET数据集定量分析了海河流域2000-2014年ET的时空变化特征,并结合时序气温降水数据和土地利用数据,采用相关分析方法定量探索了ET与气候因子的驱动力关系。结果表明：① 海河流域2000-2014年ET表现为较为显著的空间分布格局,呈现出北部和南部高、西北部和中东部低的分布特性。不同土地利用类型的多年ET呈林地>草地>耕地>其他类型的特征;② 2000-2014年海河流域年均ET波动范围为371.96~441.29 mm/a,多年ET的均值为398.69 mm/a,平均相对变化率为-0.41%,整体呈下降趋势;③ 多年月ET与气温和降水均呈单峰型周期性变化趋势,年内月ET呈单峰变化趋势;④ 春秋两季的ET与降水和气温的相关性明显高于其他季节,ET与气温和降水的平均相关系数是-0.17和0.37,表明降水对于ET的响应程度强于气温;⑤ 驱动分区结果表明海河流域ET受气候因子驱动的主要类型是降水驱动型和降水、气温共同驱动型;⑥ 海河流域耕地ET变化气候因子驱动模式主要是降水、气温共同驱动型;林地、草地的驱动模式主要气温驱动型和降水驱动型,其他土地利用类型的驱动模式主要是受其他因素驱动。该研究将对海河流域水资源开发管理和区域气候调节起到科学指导作用。     

京津唐地区城市扩张对地表蒸散发的影响

以京津唐地区为例,基于SEBS模型,利用MODIS遥感数据和气象数据,计算了2000、2005和2010年四季代表月份的平均日蒸散发量,并结合3期土地利用图,定量评估了由城市扩张引起的日蒸散发量的变化。结果表明,不同土地利用类型的日蒸散发量在不同季节表现出不同的分布规律,春、夏和秋季的日蒸散发量分布规律为水域>林地>草地>耕地>城市用地,冬季的日蒸散发量在三年的分布不一致:2000年为林地>草地>水域>城市用地>耕地,2005年为水域>林地>草地>耕地>城市用地,2010年为林地>水域>草地>城市用地>耕地。以研究区土地利用变化不明显的区域为背景区域,评估了除土地利用/覆被变化外的其他因素对京津唐地区夏季日蒸散发的影响。除去该影响后得出土地利用/覆被变化,对日蒸散发的影响,结果表明,各土地利用类型转化为城市用地会使日蒸散发降低,且水域转化成城市用地后,其日蒸散发量降低最多,2000-2005年降低了0.977mm,2000-2010年其降低值为0.983mm。     

Remote sensing and hydrological measurement based irrigation performance assessments in the upper Amu Darya Delta,Central Asia

In the Aral Sea Basin, where the Central Asian countries compete for limited water resources, reliable information on the actual water use for eight million ha of irrigated land are rare. In this study, spatially distributed land use data, seasonal actual evapotranspiration, and reference evapotranspiration derived from multitemporal MODIS data were combined with in situ water flow measurements for irrigation performance assessments in the upper Amu Darya Delta. The functioning of the major irrigation and drainage which supplies an agricultural area of 270,000 ha in the Uzbek province Khorezm was analysed using water balancing and adequacy indicators of irrigation water use.An average relative evapotranspiration of 95% indicated fulfilled water demands and partly over-irrigation, whereas values below 75% disclosed inadequate water supply in distant parts of the irrigation system. On the other hand, immense water withdrawals of approximately 24,000 m³ ha⁻¹ recorded at the system boundaries between April and September 2005 clearly exceeded the field water demands for cotton cultivation. Only 46% of the total irrigation amounts were consumed for crop production at field level. Throughout the vegetation period, approximately 58% of the total available water left the region as drainage water. Monthly observations of the depleted fraction and the drainage ratio highlighted drainage problems and rising groundwater levels at regional scale. In the most distant downstream subsystem, a high risk of groundwater and soil salinity during the main irrigation phase was found.A combination of high conveyance losses, hydraulic problems, direct linkages between irrigation and drainage, and low field application efficiencies were identified as major reasons for underperforming irrigation. The findings underlined the necessity of water saving and of reconsidering water distribution in Khorezm. The remote sensing approach was concluded as a reliable data basis for regular performance assessments for all irrigation systems in Central Asia.     

黄土高原陆面水分的凝结现象及收支特征试验研究

中国黄土高原是全球独特的地理区域,其陆面水分过程比较特殊。利用黄土高原陆面过程试验研究(LOPEX)的陇中黄土高原定西陆面过程综合观测站的资料,分析了陆面水分凝结现象及其出现频率与局地微气象条件的关系,研究了露水(霜)量及其出现频率的季节分布特征以及受降水和天气阴、晴的影响规律。同时,对比分析了降水、露水、雾水和土壤吸附水对陆面水分的贡献率,讨论了涡动相关法、蒸渗计和蒸发皿观测的陆面蒸发量的差别及其与陆面水分来源的年平衡关系,给出了半干旱区陆面水分平衡的日循环特征。发现露水对风速、大气湿度、近地层温度梯度的依赖很强,一般在风速为1.5 m/s、相对湿度大于80%和逆温强度为0.25℃的情况下露水(霜)量最大;刚降水后的晴天露水量比较大;实际蒸散量与蒸发力的差距十分明显,陆面水分平衡特征表现为一个"呼吸"过程。     

中国黄土高原塬区表层土壤水分盈缺状况的研究

陆地表层水分的盈缺直接关系到局地气候变化.本文利用黄土高原塬区初夏至盛夏期两次陆面过程野外试验(LOess Plateau land surface process field EXperiment 2005,LOPEX05和LOPEX06)的野外试验观测资料,分析了试验期间黄土高原白庙塬区不同下垫面的水分蒸散和表层土壤水分盈缺状况.结果表明:在土壤水分比较充足的条件下,植被蒸腾增加量在正午时的峰值为0.05 mm·h-1,而较大降水发生后的首个晴日.冬小麦地和裸地的蒸散分别可达4.60 mm·d-和3.70 mm·d-1.局地降水是影响陆面蒸散量变化的主要因素,而植被冠层的存在增加了陆面蒸散发量中的植物蒸腾量值.2006年4月下旬到7月中旬,裸地的水分缺失为16.3 mm·m2,冬小麦地的水分缺失为39.9mm·m2.其中缺失最严重的时间段为5月下旬到6月上旬,最大旬缺失量达16.5 mm·m2,7月上旬和中旬,由于降水季节来临,土壤水分有少量盈余.在2005年7月中旬至8月下旬,玉米地和裸地的水分盈余分别为17.9 mm·m2和25.3 mm·m2.不同时间尺度的统计均表明,降水不仅是影响陆面蒸散量的主要因素,而且也是表层土壤水分盈缺的决定性因子.