knowledge base model for evaluation of bio-physical tendency of dryland

The present study aims the evaluation of bio-physical characteristics towards soil-water-vegetation stress and a rule is envisaged to assess the degree of temporal changes. The digital rule for assessment is initialized through the index of land Instability (ILI) where the variance indicates the temporal instability of the pixel i.e., smallest land unit. It is assumed that the biophysical characteristic of land is in command of land-dynamics where there is no change in Land Use/Land Cover (LU&;LC). The intensity map on tendency of albedo (IALB) assesses the intensity of soil erosion and water stress whereas intensity map on tendency of NDVI (INDVI) appraises the stress on vegetation. The carry-out study covers a part of semiarid Western India. Primarily remote sensing technique, which carries the digital information of land temporally and spatially, is adopted in this paper. A part of the study area is represented using two sets of IRS 1A/1B LISS-I data of March with a decadal time domain (1989–1998) as a test area. It is assumed that the soil-water-vegetation stress is maximum during summer (March–April–May) in any tropical belt and decadal data will stretch the possibility of climate as well as man-made activity over the land.     

半干旱地区播前灌溉和地膜覆盖对春小麦产量形成的影响

两年大田试验研究了播前灌溉和地膜覆盖对春小麦产量形成及水分利用的影响。试验设4个处理, 对照(CK)、播种前灌水30mm(W), 覆膜60d(M)和播种前灌水30mm加覆膜60d(WM)。结果表明, 播前灌溉后土壤水分状况得到明显改善, 但由于土壤温度显著下降, 播前灌水会影响春小麦苗期的干物质积累。地膜覆盖在作物生育前期可以改善土壤水温条件, 促进干物质积累, 在后期则会导致土壤水分状况恶化, 导致收获指数的下降, 影响产量的形成和水分利用。在春小麦生产中将播前灌溉与地膜覆盖相结合: 一方面可以在作物出苗时及苗期改善土壤水温条件, 促进作物生长发育; 另一方面在产量形成的关键时期可以通过更好的水分条件去除覆膜的负效, 获得产量和水分利用效率的显著提高。     

Comparative hydrology: analysis of a semiarid and a humid tropical watershed

This paper analyses measured data from two small tropical watersheds: one in a semiarid (Aiuaba, Brazil, 12·0 km², 5 years of measurements) and another in a humid environment (Jaruco, Cuba, 43·5 km², 21 years of measurements). The watersheds are similar with respect to catchment area (tens of km²), potential evaporation (2·1–2·6 m year^?1), temperature (22–30 °C) and relief (mild hillslope steepness); but show considerable hydrological discrepancies: average precipitation in the humid watershed is two times higher; average river discharge (mm year^?1) is five times higher; and surface water availability (mm year^?1) is 14 times higher than in the semiarid watershed. Long‐term operation of hypothetical surface reservoirs in both basins is simulated. The analysis shows that 73% of the average river discharge are available (with 90% annual reliability) in the humid watershed, against only 28% in the semiarid. The main cause of this difference is the excess evaporation, which consumes 55% of the stored water in the semiarid reservoir, but only 12% in the humid one. The research concludes that: (1) although precipitation indicators are higher in the humid area, they are of the same order of magnitude as in the semiarid; and (2) fluvial‐regime and water‐availability variables are more than one order of magnitude higher in the humid basin, which shows a multiplication effect of these hydrological processes. Such major hydrological differences, despite the similarities between the two tropical watersheds, show the importance of further investigations in the field of comparative hydrology. Copyright © 2009 John Wiley & Sons, Ltd.     

干旱半干旱地区草原灌丛荒漠化及其 生物地球化学循环

干旱和半干旱地区草地生态系统木本植物入侵及其导致的草原灌丛化已经成为全球范 围普遍发生的现象, 是草地沙化和荒漠化的一个重要标志。干旱生态系统中, 此种类型的植被变 化将对区域和全球生物地球化学循环产生显著影响。过度放牧、区域气候干旱化和自然火过程是 导致灌丛入侵和发展的主要控制因子。草原灌丛化过程中, 草地生态系统分布较为均匀的土壤养 分及相关元素在水平和垂直方向发生分异, 关键生命元素C、N、P 、S 生物地球化学循环的变化 将对全球气候变化产生显著作用。全球气候变化与草原灌丛荒漠化之间存在潜在的反馈机制, 人 类扰动的影响将使这种反馈作用变得更加迅速和灵敏。     

华北干旱和半干旱地区的水环境现状和水资源应用问题

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半干旱区沙地高速公路防风固沙林营造技术及其效益研究

榆靖高速公路穿越毛乌素沙地腹地,风沙对公路的危害十分严重,主要表现为风沙对路面和路基边坡的风蚀和沙埋。提出了榆靖高速公路两侧防风固沙林综合防护体系,从公路路基向外依次为平整固沙绿化带,上、下风侧带宽都为20 m;草方格沙障与植物固沙带,上风侧带宽为260～330 m,下风侧带宽为100～150 m;前沿阻沙带,设置1～1.2 m高的高立式栅栏,走向与主风方向垂直;封沙育林育草保护带,上风侧带宽为300～500 m,下风侧带宽为200～300 m。4个防护带融为一体,起到了降低风速,固定流沙的作用,发挥出强大的防风固沙效益,极大地减少了风沙对公路的危害,保证公路畅通无阻,安全运营。     

中国西北干旱半干旱区近46 a秋季气候变暖分析

 利用中国西北干旱、半干旱区137个测站,近46 a年平均地面气温资料,采用线性趋势分析、EOF、REOF、Mann-Kendall、子波分析等方法,分析了西北区秋季气温对气候变暖的响应。结果表明：①中国西北干旱、半干旱区秋季气温增温明显,近46 a增温率0.36 ℃/10a. 从1971年开始气温呈增加趋势,1988年有一次显著突变,其后达到一个更显著的增暖时期。②秋季气温标准差在青海高原西部、新疆东部—北疆和内蒙古是一个高值区。③秋季区域平均气温单调增温而无明显转型期,全区性的前10个偏热年,80%出现在1990年以后,各分区的异常偏热年,90%也出现在1990年以后;气温异常变化存在5 a左右和22 a的周期,无论从年代际的变化来看,还是从20 a以上的气候变化层次来看,振幅向高温增大,气温趋势仍在居高不下的位置。④秋季气温存在演变的地域差异,新疆区和蒙陕甘宁青区东西变化相反。⑤根据REOF分析将该区秋季气温异常细分为蒙陕甘宁区、北疆区、南疆区和高原区。西部干旱、半干旱区秋季气温的转折大致在20世纪60年代末期至70年代初期,由下降转为上升;各区秋季气温在1987—1988年发生一次突变。     

Numerical simulation and data assimilation of the water-energy cycle over semiarid northeastern China

The default fractional vegetation cover and terrain height were replaced by the estimated fractional vegetation cover, which was calculated by the Normalized Difference Vegetation Index(NDVI) of Earth Observing System Moderate-Resolution Imaging Spectroradiometer(EOS-MODIS) and the Digital Elevation Model of the Shuttle Radar Topography Mission(SRTM) system. The near-surface meteorological elements over northeastern China were assimilated into the three-dimensional variational data assimilation system(3DVar) module in the Weather Research and Forecasting(WRF) model. The structure and daily variations of air temperature, humidity, wind and energy fields over northeastern China were simulated using the WRF model. Four groups of numerical experiments were performed, and the simulation results were analyzed of latent heat flux, sensible heat flux, and their relationships with changes in the surface energy flux due to soil moisture and precipitation over different surfaces. The simulations were compared with observations of the stations Tongyu, Naiman, Jinzhou, and Miyun from June to August, 2009. The results showed that the WRF model achieves high-quality simulations of the diurnal characteristics of the surface layer temperature, wind direction, net radiation, sensible heat flux, and latent heat flux over semiarid northeastern China in the summer. The simulated near-surface temperature, relative humidity, and wind speed were improved in the data assimilation case(Case 2) compared with control case(Case 1). The simulated sensible heat fluxes and surface heat fluxes were improved by the land surface parameterization case(Case 3) and the combined case(Case 4). The simulated temporal variations in soil moisture over the northeastern arid areas agree well with observations in Case 4, but the simulated precipitation should be improved in the WRF model. This study could improve the land surface parameters by utilizing remote sensing data and could further improve atmospheric elements with a data assimilation system. This work provides an effective attempt at combining multi-source data with different spatial and temporal scales into numerical simulations. The assimilation datasets generated by this work can be applied to research on climate change and environmental monitoring of arid lands, as well as research on the formation and stability of climate over semiarid areas.     

Aerosol radiative properties in the semiarid Western United States

Characterization of aerosol optical properties, such as aerosol optical depth, Angstrom exponent, and volume size distribution at the semiarid site of Tombstone Arizona (31°23′N, 110°05′W, 1408 m) will be presented for one annual cycle. In this region, extensive observations of selected optical parameters such as aerosol optical depth (AOD) have been made in the past and reported on in the literature. Less is known about other optical characteristics that are important in climate modeling and remote sensing. New observational techniques and inversion methods allow for the expansion of the earlier information. Observations have been taken with a state of the art sun photometer for a 1-year period and their analysis will be presented here. Monthly mean AODs at 500 nm were found to be in the range of 0.03–0.12; the monthly mean Angstrom exponent ranged from 0.9 to 1.6, being higher in spring and summer and lower in late fall and winter. Volume size distributions exhibit clear dominance of smaller particles, with a gradual increase in size from winter to spring and into summer. Annual variation of the radii of the smaller and the larger particles ranged between 0.05–0.4 and 4–8 μm, respectively. Radiance measurements at 940 nm were used to estimate precipitable water. The retrieved values compared within limits of uncertainty with independently derived estimates from the National Center for Environmental Prediction (NCEP) regional weather forecast model. An interesting outcome from this study was the consistency found in aerosol optical depths as observed in this study and those derived about two decades ago.     

The San Dimas experimental forest: Hydrologic research in semiarid steepland terrain

The San Dimas Experimental Forest (SDEF) is located in southern California and is representative of the chaparral shrublands of the Southwest USA. Chaparral – including genera of Ceanothus, Adenostoma, Quercus, Salvia and Arctostaphylos – is a dense, drought-tolerant vegetation assemblage with a closed canopy 3–5 m in height. Chaparral is a fire-prone ecosystem and wildfires have burned the SDEF about every 40 years. The SDEF was established in 1933 to quantify the water cycle in a steep, semiarid landscape. Study catchments range in size from 15 to 1160 ha and measurements of stream runoff are made in a nested weir and flume arrangement to account for the very flashy flows. Apart from native chaparral vegetation, streamflow measurements in these study watersheds have also quantified the hydrologic response of vegetation type-conversion and fire. Innovations in hydrologic monitoring developed on the SDEF include a critical depth flume (the San Dimas flume) and tilted rain gages to better sample precipitation in mountainous terrain. Subsurface runoff and plant water relations have been measured in a large lysimeter complex. Water quality monitoring shows that stream water in the SDEF has very high levels of nitrate, derived from atmospheric deposition of chronic air pollution, that approach the Federal EPA standard of 10.0 mg L⁻¹ for nitrate-N. Spreadsheets of rainfall and streamflow (from 1938 to 2015) – the San Dimas Experimental Forest hydrologic database – may be found at the right-hand side of the web page at https://www.fs.fed.us/psw/ef/san_dimas/index.shtml . Hard copy charts, tables and other records associated with the foregoing data streams are available from the USDA Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, California, 92501 USA or at pete.wohlgemuth@usda.gov .