Characteristics And Model Simulation Of Soil Water And Heat Transport In Typical Forest Land In Nanbei Mountains,Xining City

In order to study the response law of soil moisture to rainfall,the hydrological ch aracteristics of the woodland,and the soil hydrothermal model of the three typical for est stands（Pine tabulaeformis pure forest,Qinghai spruce pure forest,and Qingyang p ure forest）in the Nanbei Mountains of Xining City,this paper analyzes the typical for est soil moisture model in Xining City.The soil water content of each layer and the rai nfall outside the forest were measured before and after the rainfall,and the data was p rocessed and analyzed through statistical analysis,and the response law of soil water c ontent of each layer to rainfall under different canopy closure degrees and different rai nfall grades in three typical forest lands in Xining City was obtained.;For the canopy layer（canopy interception）,shrub and grass layer（stock volume,maximum water hol ding capacity）,litter layer（litter water holding capacity）,soil layer(maximum water h olding capacity,Through statistical analysis,the hydrological characteristics of each l ayer of forest canopy,shrub and grass layer,litter layer,and soil layer were obtained.Soil bulk density,tree transpiration,soil evaporation,canopy density,stand density,ne ar-ground temperature,rainfall,forest age,soil depth and other indicators were period ically measured,and three typical forest soil soils in Xining City were studied by mea ns of multiple regression.Hydrothermal model.The result obtained is as follows:（1）The response law of soil moisture changes to rainfall in the three forest stands in Xining City was similar,and the depth of rainfall on forest soil moisture was 0-10cm.Under the same canopy closure,the greater the rainfall grade,the deeper the impa ct of rainfall on soil moisture.The effect of rainfall on 0-10cm soil moisture is the mo st significant,while the effect on deep soil moisture has a time lag,which mainly depe nds on the amount of rainfall.The greater the rainfall,the greater the fluctuation of de ep soil moisture content.Under the three rainfall conditions of small-grade rainfall,m edium-grade rainfall and large-grade rainfall,the response degree of soil water conten t to rainfall in woodland with different canopy closure degrees was 0.3-0.5 canopy clo sure degree>0.5-0.7 canopy closure degree>0.7-0.9 canopy closure The greater the ca nopy closure,the more obvious the interception ability and the stronger the hysteresis;under the same canopy closure,when the rainfall is small,the soil water content in ea ch layer of the Qingyang standard area changes the most.There is no change in the 20-50cm range of Chinese fir;when the middle grade rainfall occurs,the 0-10cm change range of the Qingyang standard land is the largest,and the 10-40cm Qinghai spruce h as the largest change range;when the heavy grade rainfall occurs,the soil moisture co ntent of the pine tabulaeformis standard land has the largest change range of 0-20cm The largest,20-30cm Qinghai spruce has the largest change,and the 40-50cm soil wat er content of Qingyang has changes.（2）The key hydrological characteristics of the three types of stand,such as canop y interception,shrub-grass layer,litter layer and soil layer water-holding capacity,wer e revealed.Under the same forest age,the canopy interception rate was used as the cri terion for judging the interception capacity of the canopy.The interception capacity of the three stands was Qingyang（0.589）>Pinus tabulaeformis（0.529）>Qinghai spruc e（0.505）;the water holding capacity of shrubs and grasses There is a positive correlat ion with biomass,the larger the biomass,the greater its water holding capacity;when the canopy density and forest age are close,the maximum water holding capacity is us ed as the standard for judging the water holding capacity of shrubs and grasses,and th e order of size is Qingyang（6.24 t/hm²）>Pinus tabulaeformis（5.03 t/hm²）>Spruce i n Qinghai（4.91 t/hm²）;The variation law is that it first increases with the increase of t ime,the trend becomes slower,and finally tends to a fixed value;the order of the max imum water holding capacity of each standard soil 0-20cm is 3（1532t/hm²）>2（1515t/hm²）>6（1499t/hm²）>1（1488t/hm²）>9（1445t/hm²）>4（1430t/hm²）>8（1424t/hm²）>7（1410t/hm²）>5（1390t/hm²）The order of maximum water holding capacity of 20-40cm soi l is 1（1463t/hm²）>6（1455t/hm²）>3（1433t/hm²）>2（1416t/hm²）>7（1402t/hm²）>4（1398t/hm²）>9（1396t/hm²）>5（1381t/hm²）>8（1314t/hm²）.The maximum water holding capaci ty of each standard land increases with the increase of soil depth.（3）Based on 11 indicators of soil bulk density,soil evaporation,tree transpiratio n,canopy closure,stand density,near-ground temperature,rainfall,forest age,soil dep th,soil moisture,and soil temperature,three types of typical Xining City were constru cted.Soil water-heat model of stand,the model is as follows:Y（pine tree）=10.937+14.473X₁-1.325X₂+7.515X₃+0.0004X₄+0.417X₅+0.334X₆-0.061X₇-0.013X₈-3.795X₉.Y（Qinghai Spruce）=-157.597+4.557X₁+0.706X₂-7.174X₃-2.031X₅+0.288X₆-0.251X₈+24.973X₉+305.693X₁₀.Y（green poplar）=43.253-25.324X₁-0.064X₂-7.892X₃-1.685X₅+0.576X₆+0.7X₇-0.236X₈+5.528X₉.