Two sets of numerical experiments using the coupled National Center for Environmental Prediction General Circulation Model （NCEP/GCM T42L18） and the Simplified Simple Biosphere land surface scheme （SSiB） were carr...Two sets of numerical experiments using the coupled National Center for Environmental Prediction General Circulation Model （NCEP/GCM T42L18） and the Simplified Simple Biosphere land surface scheme （SSiB） were carried out to investigate the climate impacts of fractional vegetation cover （FVC） and leaf area index （LAI） on East Asia summer precipitation, especially in the Yellow River Basin （YRB）. One set employed prescribed FVC and LAI which have no interannual variations based on the climatology of vegetation distribution; the other with FVC and LAI derived from satellite observations of the International Satellite Land Surface Climate Project （ISLSCP） for 1987 and 1988. The simulations of the two experiments were compared to study the influence of FVC, LAI on summer precipitation interannual variation in the YRB. Compared with observations and the NCEP reanalysis data, the experiment that included both the effects of satellite-derived vegetation indexes and sea surface temperature （SST） produced better seasonal and interannual precipitation variations than the experiment with SST but no interannual variations in FVC and LAI, indicating that better representations of the vegetation index and its interannual variation may be important for climate prediction. The difference between 1987 and 1988 indicated that with the increase of FVC and LAI, especially around the YRB, surface albedo decreased, net surface radiation increased, and consequently local evaporation and precipitation intensified. Further more, surface sensible heat flux, surface temperature and its diurnal variation decreased around the YRB in response to more vegetation. The decrease of surface-emitting longwave radiation due to the cooler surface outweighed the decrease of surface solar radiation income with more cloud coverage, thus maintaining the positive anomaly of net surface radiation. Further study indicated that moisture flux variations associated with changes in the general circulation also contributed to the precipitation interannual variation.展开更多
Based on the analysis of hanging rivers' actuality in the lower Yellow River and researches related to the evaluation of dike breach risks,it is put forward that the influencing factors of dike beach risks in the ...Based on the analysis of hanging rivers' actuality in the lower Yellow River and researches related to the evaluation of dike breach risks,it is put forward that the influencing factors of dike beach risks in the lower Yellow River should involve four aspects,the flow and sediment movement,the regional crustal stability,the variation of river regime and the stability of river dikes.With this,the evaluation indexes system of dike breach risks is established,and with the support of geographic information systems technology,the model of multi-hierarchical fuzzy comprehensive judgment is applied to estimate the dike beach risks of the hanging rivers in the lower Yellow River under different flood conditions.The evaluation results of dike breach risks show the following distributing regularities of dike breach risks in the lower Yellow River:(1) Dike breach risks increase with the increase of the flood.(2) Dike breach risks decrease with the changes of river patterns along the channel.(3) There are great risks of dike breach in the wandering reaches,and it is relatively higher in the south bank than in the north in wandering reaches.(4) There is a higher dike breach risk in the north bank than in the south in winding reaches.Simultaneously,the evaluation results manifest that the evaluation indexes system established from the flow and sediment movement,the regional crustal stability,the variation of river regime and the stability of river dikes can represent the actual situation of the lower Yellow River more comprehensively.The application of multihierarchical fuzzy comprehensive judgment can preferably resolve the problem of hanging river dike breach,which has numerous influencing factors and complicated functionary mechanisms.The applications of geographic information systems technology with powerful spatial analysis functions make dike beach risks quantificationally displayed in different spatial positions,and reflect the differences of dike beach risks in different spatial positions of the channel in the lower Yellow River.展开更多
基金the Ministry of Science and Technology of China through public welfare funding under Grant No.2002DIB20070China Meteorological Administration Grant CCSF 2005-1the National Natural Science Foundation Grant NSF-ATM-0353606
文摘Two sets of numerical experiments using the coupled National Center for Environmental Prediction General Circulation Model （NCEP/GCM T42L18） and the Simplified Simple Biosphere land surface scheme （SSiB） were carried out to investigate the climate impacts of fractional vegetation cover （FVC） and leaf area index （LAI） on East Asia summer precipitation, especially in the Yellow River Basin （YRB）. One set employed prescribed FVC and LAI which have no interannual variations based on the climatology of vegetation distribution; the other with FVC and LAI derived from satellite observations of the International Satellite Land Surface Climate Project （ISLSCP） for 1987 and 1988. The simulations of the two experiments were compared to study the influence of FVC, LAI on summer precipitation interannual variation in the YRB. Compared with observations and the NCEP reanalysis data, the experiment that included both the effects of satellite-derived vegetation indexes and sea surface temperature （SST） produced better seasonal and interannual precipitation variations than the experiment with SST but no interannual variations in FVC and LAI, indicating that better representations of the vegetation index and its interannual variation may be important for climate prediction. The difference between 1987 and 1988 indicated that with the increase of FVC and LAI, especially around the YRB, surface albedo decreased, net surface radiation increased, and consequently local evaporation and precipitation intensified. Further more, surface sensible heat flux, surface temperature and its diurnal variation decreased around the YRB in response to more vegetation. The decrease of surface-emitting longwave radiation due to the cooler surface outweighed the decrease of surface solar radiation income with more cloud coverage, thus maintaining the positive anomaly of net surface radiation. Further study indicated that moisture flux variations associated with changes in the general circulation also contributed to the precipitation interannual variation.
基金The State Science Research Plan (Grant no.96-920-09-01)
文摘Based on the analysis of hanging rivers' actuality in the lower Yellow River and researches related to the evaluation of dike breach risks,it is put forward that the influencing factors of dike beach risks in the lower Yellow River should involve four aspects,the flow and sediment movement,the regional crustal stability,the variation of river regime and the stability of river dikes.With this,the evaluation indexes system of dike breach risks is established,and with the support of geographic information systems technology,the model of multi-hierarchical fuzzy comprehensive judgment is applied to estimate the dike beach risks of the hanging rivers in the lower Yellow River under different flood conditions.The evaluation results of dike breach risks show the following distributing regularities of dike breach risks in the lower Yellow River:(1) Dike breach risks increase with the increase of the flood.(2) Dike breach risks decrease with the changes of river patterns along the channel.(3) There are great risks of dike breach in the wandering reaches,and it is relatively higher in the south bank than in the north in wandering reaches.(4) There is a higher dike breach risk in the north bank than in the south in winding reaches.Simultaneously,the evaluation results manifest that the evaluation indexes system established from the flow and sediment movement,the regional crustal stability,the variation of river regime and the stability of river dikes can represent the actual situation of the lower Yellow River more comprehensively.The application of multihierarchical fuzzy comprehensive judgment can preferably resolve the problem of hanging river dike breach,which has numerous influencing factors and complicated functionary mechanisms.The applications of geographic information systems technology with powerful spatial analysis functions make dike beach risks quantificationally displayed in different spatial positions,and reflect the differences of dike beach risks in different spatial positions of the channel in the lower Yellow River.
