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181.
Evaluating the functionality and streamflow impacts of explicitly modelling forest–snow interactions and canopy gaps in a distributed hydrologic model
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Ning Sun Mark Wigmosta Tian Zhou Jessica Lundquist Susan Dickerson‐Lange Nicoleta Cristea 《水文研究》2018,32(13):2128-2140
Many plot‐scale studies have shown that snow‐cover dynamics in forest gaps are distinctly different from those in open and continuously forested areas, and forest gaps have the potential to alter the magnitude and timing of snowmelt. However, the watershed‐level impacts of canopy gap treatment on streamflows are largely unknown. Here, we present the first research that explicitly assesses the impact of canopy gaps on seasonal streamflows and particularly late‐season low flows at the watershed scale. To explicitly model forest–snow interactions in canopy gaps, we made major enhancements to a widely used distributed hydrologic model, distributed hydrology soil vegetation model, with a canopy gap component that represents physical processes of snowpack evolution in the forest gap separately from the surrounding forest on the subgrid scale (within a grid typically 10–150 m). The model predicted snow water equivalent using the enhanced distributed hydrology soil vegetation model showed good agreement (R2 > 0.9) with subhourly snow water equivalent measurements collected from open, forested, and canopy gap sites in Idaho, USA. Compared with the original model that does not account for interactions between gaps and surrounding forest, the enhanced model predicted notably later melt in small‐ to medium‐size canopy gaps (the ratio of gap radius (r) to canopy height (h) ≤ 1.2), and snow melt rates exhibited great sensitivity to changing gap size in medium‐size gaps (0.5 ≤ r/h ≤ 1.2). We demonstrated the watershed‐scale implications of canopy gaps on streamflow in the snow‐dominated Chiwawa watershed, WA, USA. With 24% of the watershed drainage area (about 446 km2) converted to gaps of 60 m diameter, the mean annual 7‐day low flow was increased by 19.4% (i.e., 0.37 m3/s), and the mean monthly 7‐day low flows were increased by 13.5% (i.e., 0.26 m3/s) to 40% (i.e., 1.76 m3/s) from late summer through fall. Lastly, in practical implementation of canopy gaps with the same total gap areas, a greater number of distributed small gaps can have greater potential for longer snow retention than a smaller number of large gaps. 相似文献
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183.
中国经济与人口重心的耦合态势及其对区域发展的影响 总被引:24,自引:2,他引:22
区域发展差距一直是中国区域协调发展所面临的重要问题,经济和人口的空间分布态势作为区域发展空间均衡过程的体现,与区域差距的形成有密切关联。通过计算1952年至2005年中国经济重心和人口重心的地理坐标以及重心间的空间重叠性与变动一致性,刻画了53年间我国经济和人口空间分布的耦合态势,证明了其与区域差距的大小高度相关。在构建经济、人口重心空间耦合过程的作用机制模型的基础上,用均衡点跃迁和势能差转化解释了区域发展的空间均衡过程,揭示了内生和外部因素在其中的作用机制,提出了区域发展差距的"多阶段倒U形"的演变规律,并据此分析了1952年以来中国区域发展空间均衡过程周期性变化的动因,并对促进区域协调发展的途径进行了讨论。 相似文献
184.
Effect of succession gaps on the understory water‐holding capacity in an over‐mature alpine forest at the upper reaches of the Yangtze River
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Bin Wang Fuzhong Wu Sa Xiao Wanqin Yang Meta Francis Justine Jiayi He Bo Tan 《水文研究》2016,30(5):692-703
The water‐holding capacity (WHC) of the understory in the headwater regions of major rivers plays an important role in both the capacity of the forest water reservoir and water quality and quantity in the butted rivers. Although forest gaps could regulate water‐holding patterns in the understory by redistributing coarse woody debris (CWD), fine woody debris (FWD), non‐woody debris (NWD) and understory vegetation, little information is available on the effects of forest gaps on understory WHC. Therefore, we investigated the WHCs of CWD, FWD, NWD, herbaceous vegetation, mosses, epiphytes (including fern and lichen growing on the surface of logs) and soils from the gap centre to the adjacent closed canopy in an alpine forest at the upper reaches of the Yangtze River. The total WHC of the alpine forest understory components was approximately 300 mm. Soil layer had the largest contribution to the total understory WHC (90%), and among the aboveground components, CWD and mosses contributed 5% and 4% to the aboveground WHC, respectively. With the exception of that of the herbaceous layer, the WHC of the forest floor increased from the gap centre to the closed canopy. Although mosses had the lowest biomass allocation on the alpine forest floor, the water‐holding ratio (k) of mosses reached 485%. In conclusion, biomass is the parameter that most strongly and positively correlated with the WHC of the alpine forest understory, and forest gap formation decreases the understory WHC of alpine forest resulting from a decrease in organic soils, CWDs and mosses. Copyright © 2015 John Wiley & Sons, Ltd. Highlights
- The effects of gaps on the understory WHC were examined in an alpine forest.
- Gaps decreased the understory WHC by decreasing the amounts of the larger WHC components.
- The contribution of CWD and mosses to the aboveground WHC was large.
- The WHC of dead debris was higher than that of the vegetation.
185.
186.
常德市2002年5月13日大暴雨成因解析 总被引:3,自引:0,他引:3
用多普勒天气雷达产品、NCEP 1°×1°再分析资料、卫星云图产品、实时探测资料及MM5数值模拟,对2002年发生在湖南常德境内的"5.13"大暴雨进行解析,得出此次暴雨过程由高空低槽、中低层切变及西南急流、地面倒槽和弱冷空气共同影响产生,急流形成、发展与减弱对降水强度有直接的影响.暴雨中心与云图上的"U"形缺口区、多普勒基本速度场上的中低层急流轴线位置有较好的对应关系.多普勒基本速度场上急流强弱振荡出现的时间、低层暖平流之上(高层)出现冷平流的时间、低层气旋式涡旋流场的形成与维持以及低层垂直风切变强度变化对强降水发生的时间有明显的指示作用.数值模拟证实雷达探测到的中尺度涡旋、急流及辐合带是正确的.这些结论对暴雨临近预报业务具有明确的参考价值. 相似文献
187.
Sources of uncertainty in estimating stream solute export from headwater catchments at three sites
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Ruth D. Yanai Naoko Tokuchi John L. Campbell Mark B. Green Eiji Matsuzaki Stephanie N. Laseter Cindi L. Brown Amey S. Bailey Pilar Lyons Carrie R. Levine Donald C. Buso Gene E. Likens Jennifer D. Knoepp Keitaro Fukushima 《水文研究》2015,29(7):1793-1805
Uncertainty in the estimation of hydrologic export of solutes has never been fully evaluated at the scale of a small‐watershed ecosystem. We used data from the Gomadansan Experimental Forest, Japan, Hubbard Brook Experimental Forest, USA, and Coweeta Hydrologic Laboratory, USA, to evaluate many sources of uncertainty, including the precision and accuracy of measurements, selection of models, and spatial and temporal variation. Uncertainty in the analysis of stream chemistry samples was generally small but could be large in relative terms for solutes near detection limits, as is common for ammonium and phosphate in forested catchments. Instantaneous flow deviated from the theoretical curve relating height to discharge by up to 10% at Hubbard Brook, but the resulting corrections to the theoretical curve generally amounted to <0.5% of annual flows. Calibrations were limited to low flows; uncertainties at high flows were not evaluated because of the difficulties in performing calibrations during events. However, high flows likely contribute more uncertainty to annual flows because of the greater volume of water that is exported during these events. Uncertainty in catchment area was as much as 5%, based on a comparison of digital elevation maps with ground surveys. Three different interpolation methods are used at the three sites to combine periodic chemistry samples with streamflow to calculate fluxes. The three methods differed by <5% in annual export calculations for calcium, but up to 12% for nitrate exports, when applied to a stream at Hubbard Brook for 1997–2008; nitrate has higher weekly variation at this site. Natural variation was larger than most other sources of uncertainty. Specifically, coefficients of variation across streams or across years, within site, for runoff and weighted annual concentrations of calcium, magnesium, potassium, sodium, sulphate, chloride, and silicate ranged from 5 to 50% and were even higher for nitrate. Uncertainty analysis can be used to guide efforts to improve confidence in estimated stream fluxes and also to optimize design of monitoring programmes. © 2014 The Authors. Hydrological Processes published John Wiley & Sons, Ltd. 相似文献
188.
189.
《地理研究》2012,31(9)
从居民效用与开发商收益视角下,以Smith租差理论为基础,构建多智能体模型,并结合纳什均衡解决居民修缮决策博弈,模拟中产阶层化进程。研究表明:在效用最大时,增加居民收入将降低中产阶层化发生频率。而在利润最大时,开发商资本的投入与中产阶层化发生频率正相关。资本投入越大,中产阶层化发生频率越高。但资本并非万能,当它的投入超出限值时,中产阶层化进程渐趋稳定。提高开发商投资门槛,将强化房地产业的垄断,开发商为获取巨额垄断利润,一方面,他们可能故意提高局部地区的资本化地租,这导致了中产阶层化更快、更多地发生;另一方面,他们在任意区位开发都能获取高额利润,这间接造成中产阶层化程度下降。 相似文献
190.
从居民效用与开发商收益视角下,以Smith租差理论为基础,构建多智能体模型,并结合纳什均衡解决居民修缮决策博弈,模拟中产阶层化进程。研究表明:在效用最大时,增加居民收入将降低中产阶层化发生频率。而在利润最大时,开发商资本的投入与中产阶层化发生频率正相关。资本投入越大,中产阶层化发生频率越高。但资本并非万能,当它的投入超出限值时,中产阶层化进程渐趋稳定。提高开发商投资门槛,将强化房地产业的垄断,开发商为获取巨额垄断利润,一方面,他们可能故意提高局部地区的资本化地租,这导致了中产阶层化更快、更多地发生;另一方面,他们在任意区位开发都能获取高额利润,这间接造成中产阶层化程度下降。 相似文献