Study Of Hydrological Cycle And Water Balance Of Typical Forests In Beijing Mountainous Area

In this paper, I have measured the dynamic process of water balance of typical forests (Robinia pseudoacacia, Pinus tabulaeformis, Platycladus orientalis and Quercus variabilis) in Beijing mountainous areas from2007to2011, and then analysed quantitatively the data. Conclusions are:1、Water input process:1) The rainfall concentrates from May to October in Beijing mountainous areas, Accounting for more than88.29%.2) Penetration of rainfall is accounting for more than80%in growing seasons, and summer is the largest. The order of penetration is Robinia pseudoacacia> Platycladus orientalis> Pinus tabulaeformis> Quercus variabilis.3)Stem flow has a little change in the different years. The order for4seasons is summer>autumn>spring>winter. The order for stands is Platycladus orientalis> Robinia pseudoacacia> Quercus variabilis> Pinus tabulaeformis.4) Canopy interception is accounting for more than80%in growing seasons. The order is Quercus variabilis> Pinus tabulaeformis> Platycladus orientalis>Robinia pseudoacacia.5) The order of efficient interception of litter is Pinus tabulaeformis> Platycladus orientalis> Quercus variabilis> Robinia pseudoacacia. Pinus tabulaeformis (12.15t/hm2)is lagest, and Robinia pseudoacacia (5.40t/hm2) is smallest.2、Water output process:1) Tree transpiration is not significant in different years, it is accounting for more than50%in growing seasons, and summer is the largest. Its order is Quercus variabilis>Platycladus orientalis> Pinus tabulaeformis>Robinia pseudoacacia.2)Soil evaporation has a little change in the different years, it is accounting for more than50%in growing seasons, and spring is the largest. The peak is appeared in May. Its order is Robinia pseudoacacia>Pinus tabulaeformis>Quercus variabilis> Platycladus orientalis.3) Runoff has large changein the different years.Runoff is mainly produced in July and August. It is accounting for more than80%in growing seasons, and summer is the largest. Its order is Robinia pseudoacacia>> Pinus tabulaeformis Quercus variabilis> Platycladus orientalis.4)Soil water storage capacity has large changein different years, throughout the year was the water storage state.From May to Octoberis a critical period of the soil water storage. Its order is Platycladus orientalis>Robinia pseudoacacia>Pinus tabulaeformis>Quercus variabilis. 3、Analysis of water balance:1) The annual rainfall can meet the water requirement of stands in most years. Monthly rain can meet the water requirement of stands in June to September, and water balance is in a deficit state in others.Ratios of each component are, Robinia pseudoacacia:tree transpiration(48.83%)> soil evaporation(23.83%)> Canopy interception(11.52%)> soil water storage capacity(4.66%)> runoff(1.74%)> litter interception(0.51%). Pinus tabaefomis:treetranspiration(52.33%)> soil evaporation(22.93%)> Canopy interception(19.62%)> soil water storage capacity(4.80%)> litter interception(3.47%)> runoff(1.50%)。Platycladus orientalis:treetranspiration(54.94%)> soil evaporation(21.16%)> Canopy interception(17.41%)> soil water storage capacity(5.82%)> litter interception(2.89%)> runoff(0.34%). Quercus variabilis:treetranspiration(56.28%)> soil evaporation(22.43%)> Canopy interception(21.49%)> soil water storage capacity(3.31%)> litter interception(2.44%)>runoff(0.30%).4、Stand structure on the water balanceBased on the monthly data from2007-2011, the paper used spss18.0to analyse the impact between four kinds of stand structure parameters (leaf area index, canopy density, biomass and rainfall) and components of the water balance. The results are:the Fitting relationships of runoff, tree transpiration, Canopy interception and Woodland evapotranspiration are good,R2>0.5almost; Fitting relationships of soil evaporation and soil water storage capacity are not good,R2between0.2-0.4. Fitting relationships oftranspiration coefficient, evaporation coefficient, Retention rate, evapotranspiration coefficient, and impoundment change rate are not good; fitting relationship of runoff coefficient is good, R2about0.5.