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中国天山西部巩乃斯河流域森林积雪过程研究
陆恒
学位类型博士
导师魏文寿
2015
学位授予单位中国科学院大学
学位授予地点北京
学位专业自然地理学
关键词森林积雪 能量收支 辐射模型 敏感性分析 积雪过程
摘要本研究选择位于中国天山西部巩乃斯河流域的森林积雪为研究对象,对不同开阔度林冠下大气温湿度、风速和辐射等常规气象要素、雪层物理特征以及融雪速率等进行观测,分析森林积雪表面的能量收支特征、森林积雪的积累和消融过程,研究了影响不同下垫面积雪消融过程的主要因素,建立了森林积雪表面辐射收支模型,并提出了一种在森林和复杂地形下积雪积累和消融过程的监测方法。本文主要结论如下: (1) 在阳坡无林地和80%开阔度林冠下,雪面通过净短波辐射和显热获取能量,通过净长波辐射和潜热损失能量;在20%开阔度林冠下,雪面通过净短波辐射、显热和净长波辐射获取能量,通过潜热损失能量。林下雪面入射短波辐射远小于阳坡无林地,森林开阔度越大,林下雪面入射短波辐射、雪面反射率和净短波辐射越大。阴坡林冠下雪面入射长波辐射大于阳坡无林地,林冠开阔度越小,林下雪面入射长波辐射和净长波辐射越大。森林积雪表面显热小于阳坡无林地,森林开阔度越大其潜热损失越大。 (2) 利用树高、林冠半径、树冠高度、胸径和林间距离等参数,能较好的模拟林下雪面入射短波辐射;通过融雪开始后天数、新降雪后天数、新降雪后累计风速、新雪反射率能较好的模拟雪面反射率;应用林冠开阔度、气温和林冠上入射短波辐射、林冠上方周围地形增加的长波辐射则可以较好的模拟林下雪面入射长波辐射,林下雪面发射长波辐射可根据气温进行模拟。 (3) 树高和林冠半径对林下雪面入射直接辐射影响显著,林下雪面入射直接和散射分别随林冠开阔度的增加呈指数和线性增加,林冠下雪面入射长波辐射随着坡度和气温的增加而增加,周围地形和植被冠层反射率对林下雪面入射短波辐射影响较大,但对入射长波辐射的影响则非常小。 (4) 林冠开阔度越大,拦截效率越小,积雪深度和雪水当量越大,积雪开始和完全消融的时间越晚;雪面净短波和净长波辐射之间的的比例决定了不同开阔度林下积雪消融速率及其日变化特征;植被冠层拦截降雪的升华量则明显大于林下和阳坡无林地雪面,森林冠层拦截降雪升华量随林冠开阔度的增加而减小。 (5) 影响阳坡无林地雪面能量收支和融雪过程的的最主要因素为大气中水汽增加导致的潜热损失减小,其次为由于气温增加导致的雪面显热增加;周围地形坡度和阳坡积雪消融状况是影响阴坡林下雪面能量收支和积雪消融的最主要因素。 (6) 利用距地表不同高度雪层和气温日较差变化特征可以很好的模拟复杂地形和森林积雪的雪深、雪层密度和雪水当量。当阳坡无林地和阴坡森林下雪层的内能分别小于0.1 MJ m-2和0.04 MJ m-2时,发生融雪洪水的风险增大。
其他摘要The study was conducted at the Kunnes River basin, and the air temperature, relative humidity, wind speed, radiation on snow surface, physical property of snow and snowmelt rate at open site on sunny slope (OPS) and beneath different forest canopy openness (BFC) was observed. The energy budget at snow surface, snow accumulation and ablation processes, the main influence factor of the snow ablation under different underlying surface were analyzed. And also, the radiation model on forest snow surface was constructed. A method to monitor the snow accumulation and ablation processes under complicated terrain and beneath forest canopy was proposed. The main results were displayed as follows: (1) Due to the effect of forest canopy and terrain, the net shortwave radiation (K) and sensible heat flux (H) were energy source, and net longwave radiation (L) and latent heat flux (LVE) were energy sinks at OPS and beneath 80% forest canopy openness (80% BFC), but the K, H and L were energy sources, and LVE was energy sink beneath 20% forest canopy openness (20% BFC).The downward shortwave radiation on snow surface at BFC was markedly lower than that at OPS, and the downward shortwave radiation, snow surface albedo and K was increased with the forest canopy openness increase. However, the downward longwave radiation at BFC was lower than that at OPS, and the downward longwave radiation and L was increased with the forest canopy openness decrease. Due to the influence of wind speed, the H on snow surface at BFC was lower than that at OPS. Generally, the LVE were negative at all sites during snowmelt period. The loss of LVE at 80% BFC was higher than that at OPS, and LVE was increased with the forest canopy openness increase. Due to the clam wind at nighttime, the exchanges of H and LVE on snow surface at BFC were mainly occurred at daytime. The difference of energy supplied by precipitation under the different underlying surfaces was increased with the increase precipitation. (2) According to Beer-Lambert Law, the downward shortwave radiation can be calculated using tree height, crown radius, crown depth, diameter of breast height and distance between trees. During snow accumulation period, snow albedo can be calculated using a combination of the new snow albedo and the number of days after fresh snowfall. In snowmelt period, snow albedo can be calculated using a combination of the number of days after the snowmelt began, the number of days after fresh snowfall and the accumulated wind speed after such fresh snowfall. The downward longwave radiation at BFC can be calculated using forest canopy openness, air temperature, downward shortwave radiation above forest canopy and the longwave radiation enhanced by adjacent terrain. The upward longwave radiation can be calculated using air temperature. (3) The downward diffuse radiation and downward longwave radiation was not influenced by tree height, crown depth and diameter of breast height, the downward direct radiation was hardly influenced by the crown depth and diameter of breast height, but the downward direct radiation was significantly influenced by tree height and crown radius. With the decreased in tree height and crown diameter, the direct radiation were decreased and increased, respectively. With the forest canopy openness increased, the downward shortwave radiation and downward diffuse radiation were increased exponentially and linearly, respectively. The downward longwave radiation was increased with slope of adjacent terrain and air temperature. When air slope (air temperature) is relatively low, the longwave radiation enhanced by adjacent terrain is not sensitive to slope (air temperature), but the sensitivity increases with the decreasing snow cover area at OPS. And the effect is especially sensitive when the snow cover at OPS melted completely. The downward shortwave radiation was obviously influenced by the albedo of adjacent terrain and forest canopy, especially when the slope of adjacent was relatively large, but the influence of the albedo of adjacent terrain and forest canopy on downward shortwave radiation was not significant. (4) The variation of snow depth and snowmelt rate beneath different forest canopy openness and under different slope has a same trend. With the increase in forest canopy openness, the interception efficiency of forest canopy decrease, the snow depth and snow water equivalent beneath forest canopy increase. The larger forest canopy openness, the later the start/end time of snowmelt. The value and the diurnal variation of snowmelt rate beneath different forest canopy openness were determined by the percentage K vis-à-vis L. The amount of water exchange due to sublimation and condensation was very small. The sublimation from interception snow was obviously bigger than sublimation from snow beneath forest canopy and at OPS. With the increased in forest canopy openness, the amount of sublimation losses in solid precipitation during whole snow period decreased. (5) An increase in water vapor is the most important factor for the variation of the energy budget at snow surface and snow ablation process at OPS. The H increasing with air temperature rise is the second important factor. The influences of air temperature and humidty on energy budget at snow surface and snow ablation process at BFC were slight. The slope of the adjacent terrain and the percentage of snow cover area at OPS were the most important factors. Against the background of a warming and more humid climate in the study area, the snowmelt rate will inevitably increase, the risk of snowmelt flood will also increase, especially toward the end of the snowmelt period. However, such snowmelt rate increases will also be influenced by the temporal distribution of precipitation. (6) According to the characteristics of snow thermal conductivity, the snow depth, snow density, snow water equivalent and cold content of snow under different underlying surface can be better estimated according to snow temperature of different heights above the ground surface. When the whole snow layers temperature increased to 0℃, the snowmelt rate drastically increased. When the cold content of snow at OPS and BFC were less than 0.1 MJ m-2 and 0.04 MJ m-2, respectively, the risk of snowmelt flood will increase.
学科领域自然地理学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14614
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
推荐引用方式
GB/T 7714
陆恒. 中国天山西部巩乃斯河流域森林积雪过程研究[D]. 北京. 中国科学院大学,2015.
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