耦合湿地模块的流域水文模型模拟效率评价

耦合湿地模块的流域水文模型是开展流域湿地变化的水文效应及其水文功能评估的有效工具,其模拟效率直接关系到模拟精度和应用价值。选取中国湿地主要分布区之一的嫩江流域,利用PHYSITEL/HYDROTEL模型平台,构建孤立湿地和河滨湿地模块并与流域水文模型耦合,并从拟合优度指数和模拟效率角度评价了耦合湿地模块的流域水文模型模拟效率。结果表明,耦合湿地模块的流域水文模型,拟合和验证期间模型的拟合度指数均有所提高,嫩江富拉尔基和大赉水文站控制流域的Nash-Sutcliffe系数和克林效率系数平均提高了3.08%和4.64%,均方根误差和相对偏差平均降低了12.72%和55.93%,且整个研究时段模拟结果的流量指数总体更接近于观测的径流数据。可见,耦合湿地模块的流域水文模型可提高水文过程模拟精度,更好地定量评估湿地水文功能,为流域水资源精准调控与湿地修复保护提供重要支撑。     

Crustal structure beneath the Mount Cameroon region derived from recent gravity measurements

In this study, the recent update of the gravity database with new measurements has raised the opportunity of improving the knowledge of the crustal structure beneath the large volcanic system called Mount Cameroon, and its implication in the regional tectonics. The multi-scale wavelet analysis method was applied to highlight the geologic features of the area, and their depths were estimated using the logarithmic power spectrum method. The results reveal a complex crustal structure beneath Mount Cameroon with high variation in the lateral distribution of crustal densities. The upper and lower crusts are intruded by dense materials originating from the mantle with less lateral extension. The trends of Tiko and Ekona faults along the intrusion suggest tectonic activities as deep as 25 km. The difference in mantle composition or temperature between the East and the West of the studied area is clearly seen in detailed wavelet images and agrees with a mantle origin for the Cameroon Volcanic Line.     

Sediment Yield During Late Glacial and Holocene periods in the Lac Chambon Watershed,Massif Central,France

A sediment budget for the Late Glacial and Holocene periods was calculated for the Lac Chambon watershed which is located in a formerly glaciated temperate crystalline mountain area. It appears that over 15 500 years: (1) 69 per cent of eroded particles have been displaced by gravity processes and then stored within the watershed, compared to 31 per cent that have been displaced by running water and evacuated outward; (2) the mean mechanical erosion due to gravity processes on the slopes amounted to 16·1 ±6 m and only developed on a quarter of the watershed surface, whereas the mean mechanical erosion due to running water amounted 1·24 ± 0·37 m and involved the whole watershed surface. The mean sediment yields due to gravity processes on slopes were 2300 ± 1360, 1770 ± 960 and 380 ± 100 m³ km⁻³ a⁻¹, respectively, for basalts, and basic and acidic trachyandesites. Values of sediment yield due to running water were 49±15, 120±36 and 79±24 m³ km⁻² a⁻¹, respectively, during the Bôlling–Allerôd, the Younger Dryas and the Pre-Boreal–Boreal periods. They were 56±17 and 166±50 m³ km⁻² a⁻¹ during the Sub-Atlantic period before and after 1360 a BP , respectively. These values reflect variations in the natural environment and the impact of human-induced deforestation. © 1997 by John Wiley & Sons, Ltd.     

Paleoclimate Changes during the Early Oligocene in the Hoh Xil Region, Northern Tibetan Plateau

Sedimentological, cyclic-stratigraphic, paleomagnetic, and clay-mineralogical studies on the early Oligocene Yaxicuo Group in the Hoh Xil Basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan Plateau, provide abundant information of paleoclimate changes. A 350-m thick section in the middle-lower Yaxicuo Group was analyzed to reveal the climatic history that occurred in the Hoh Xil region during the early Oligocene interval 31.30-30.35 Ma, dated with the paleomagnetic chronostratigraphy. The results indicate that arid and cold climate dominated the Hoh Xil region during the early Oligocene in general, being related to the global cooling and drying events that occurred in the earliest Oligocene. Within this period, relatively warm and wet climate accompanied by strong tectonic activity occurred in the 31.05-30.75 Ma interval; while arid and cold climate and relatively inactive tectonics occurred in the 31.30-31.05 and 30.75-30.35 Ma intervals. Furthermore, spectral analyses of hig     

The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset II: Land use,hydrology and sediment production monitoring in Houay Pano,northern Lao PDR

Mountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land-use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long-term impact of the conversion of traditional slash-and-burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro-meteorological and soil loss parameters at both microplot (1 m²) and small catchment (0.6 km²) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land-use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment-scale models focused on hydrology and water quality issues. The dataset may be further used to, for example, assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g., contaminants other than faecal bacteria), and assess the relative impacts of both climate and land-use change on the catchment.     

Global effect of irrigation and its impact on the onset of the Indian summer monsoon

In a context of increased demand for food and of climate change, the water consumptions associated with the agricultural practice of irrigation focuses attention. In order to analyze the global influence of irrigation on the water cycle, the land surface model ORCHIDEE is coupled to the GCM LMDZ to simulate the impact of irrigation on climate. A 30-year simulation which takes into account irrigation is compared with a simulation which does not. Differences are usually not significant on average over all land surfaces but hydrological variables are significantly affected by irrigation over some of the main irrigated river basins. Significant impacts over the Mississippi river basin are shown to be contrasted between eastern and western regions. An increase in summer precipitation is simulated over the arid western region in association with enhanced evapotranspiration whereas a decrease in precipitation occurs over the wet eastern part of the basin. Over the Indian peninsula where irrigation is high during winter and spring, a delay of 6?days is found for the mean monsoon onset date when irrigation is activated, leading to a significant decrease in precipitation during May to July. Moreover, the higher decrease occurs in June when the water requirements by crops are maximum, exacerbating water scarcity in this region. A significant cooling of the land surfaces occurs during the period of high irrigation leading to a decrease of the land-sea heat contrast in June, which delays the monsoon onset.     

A case study of land cover change (1950-2003) and runoff in a Mediterranean catchment

Mediterranean environments have been subject to major land cover change since the end of the second world war. Housing, agricultural activities, forests, green spaces and other land uses have shifted due to urbanisation and tourism. These changes influence runoff, and municipal authorities often cannot estimate the net impact of complex land cover transitions. During this period, elected representatives have become increasingly sensitive to the risks of flooding and have implemented a number of channel management strategies. The main objective of this case study was to analyse the impact of land cover change on total storm runoff between 1950 and 2003 in a Mediterranean catchment near St Tropez, France. A secondary objective was to compare these changes to the impacts of channel management on bankfull discharge. Aerial photographs were used to classify land cover in 3 urban categories, vineyards and bare soil, forests, and green spaces. Stream discharge was estimated using a distributed event based total runoff approach. After validating the model for a large winter event (114 mm) for 1982, runoff was calculated for the same event for 1950 and 2003. Land cover changes occurred mainly in the alluvial plain area. Total gauge catchment urban area increased from 30.1 ha to 393.8 between 1950 and 2003 at the expense mainly of agricultural land, but this was compensated in part by an increase in grassed area. Some of the loss in vineyards was replaced by clearing forested land on the first hills close to the plain. Bank stabilisation and channel maintenance since the 1980’s reduced surface roughness and increased channel area, thereby greatly increasing bankfull discharge. While the impact of urbanisation on runoff was small, channel management effects increased bankfull discharge substantially. Flood damage from extreme events was not studied here.     

Exploration of the Outer Solar System by Stellar Occultations

Stellar occultations are a powerful method for exploring the outer solar system, where faintness and small angular diameters prevent us from exploring in details objects like satellites, rings, or Kuiper Belt Objects. Unique kilometric spatial resolutions or better can be reached through that method. Occultations usually observe identified objects whose trajectory is known, though the occultation events might be difficult to predict. It is also possible to explore populations of small objects populations whose density in the sky plane is large enough to search for serendipitous occultations. Various instrumental methods exist for both predicted and serendipitous occultation, both needing fast photometric recordings of target stars.