[Applicability of daytime downward longwave radiation parameterized models in Changbai Mountains, Northeast China].

A total of eight clear-sky and eight cloudy-sky parameterized models for estimating daytime downward longwave radiation were evaluated by using the meteorological data measured in the Changbai Mountains region, Northeast China. The results indicated that the Satterlund model performed better in estimating clear-sky downward longwave radiation, and the bias (BIAS) and root mean square error (RMSE) were -23.34 and 28.55 W· m(-2), respectively. Although the coefficients were not significantly changed, the performance of Satterlund model was significantly improved after the locally calibrated, and the BIAS and RMSE decreased to -6.33 and 18.08 W · m(-2), respectively. Jacobs model was found to be best for modeling cloudy-sky downward long-wave radiation and the BIAS and RMSE were 0.38 and 29.29 W · m(-2), respectively. Sensitivity analysis showed that the vapor pressure was the most sensitive variable to the atmospheric emissivity and the temperature was not sensitive to it. The predicted results of the optimal model (clear- and cloudy-sky) were consistent with the measured data, while the performance of these models was affected by a sudden change of cloudy cover.

[Diurnal and seasonal variations of energy balance over Horqin meadow].

Based on the measurements of eddy flux and micrometeorological factors, this paper analyzed the diurnal and seasonal variations of energy balance over Horqin meadow. The results showed that annual energy balance ratio (EBR) of the eddy covariance system was 0.77, and EBR was biggest in growing season, middle in bare soil period and smallest in snow-covered period. Diurnal variations of energy components all presented bell-shaped curves. The peak of net radiation appeared around 12:00 and peaks of other components slightly lagged. Seasonal variation of net radiation presented a single-peak curve, and the annual average was 5.71 MJ x m(-2) x d(-1). Seasonal variation of latent heat flux was similar to that of net radiation, and the annual average was 2.84 MJ x m(-2) x d(-1). Seasonal variation of sensible heat flux presented a double-peak curve, and the peaks appeared in April and September, respectively. Annual averaged sensible heat flux was 1.87 MJ x m(-2) x d(-1). Maximum soil heat flux (3.47 MJ x m(-2) x d(-1)) appeared in April, and the soil heat flux became negative after September. Annual budget ratios of energy components presented a decreasing order of latent heat flux, sensible heat flux and soil heat flux, which accounted for 49.8%, 35.8% and 3.1% of net radiation, respectively. Seasonal variation of Bowen ratio (beta) presented a 'U' shape, and the annual average was 1.61. beta was small (0.18) and relatively stable in growing season, while it was large (2.39) and fluctuated severely in non-growing season.

[Accuracy evaluation of the TRMM satellite-based precipitation data over the mid-high latitudes].

Satellite-based precipitation product plays a significant role in analyzing spatial pattern of precipitation. TRMM 3B42 (3B42), as one of important precipitation products, is a key forcing factor for ecological, climate and hydrological models with its sufficient spatial and temporal scales. At present, there is still limited knowledge of accuracy and error structure of new version 3B42 V7, especially the lack of evaluating its accuracy in regions of mid-high latitudes, which restricts its application in the field of ecology, climate and hydrology. Based on 3B42 V7 product and data obtained from 53 weather stations in the period of 1998-2012 over Inner Mongolia, the paper evaluated the accuracy of 3B42 and revealed the spatial distribution of accuracy evaluation indices and its influencing factors. The result of overall accuracy evaluation indicated that there was overestimation of the amount of precipitation by 3B42 at daily, monthly and annual timescales. Error of 3B42 increased with the increasing timescale, and mean error and mean absolute error of daily precipitation were just -0.06 and 0.88 mm, respectively. It showed good performance for detecting the occurrence of rain events with equitable threat score (ETS) of 0.23, but slightly overestimated the frequency of rainy events. Moreover, altitude and average annual precipitation had impacts on data accuracy. The absolute error of precipitation decreased and yet the ability of detecting rain events be- came weak with the increasing altitude, while the effect of average annual precipitation on data accuracy was opposite.

[Spatiotemporal variation characteristics and related affecting factors of actual evapotranspiration in the Hun-Taizi River Basin, Northeast China].

Based on the meteorological and hydrological data from 1970 to 2006, the advection-aridity (AA) model with calibrated parameters was used to calculate evapotranspiration in the Hun-Taizi River Basin in Northeast China. The original parameter of the AA model was tuned according to the water balance method and then four subbasins were selected to validate. Spatiotemporal variation characteristics of evapotranspiration and related affecting factors were analyzed using the methods of linear trend analysis, moving average, kriging interpolation and sensitivity analysis. The results showed that the empirical parameter value of 0.75 of AA model was suitable for the Hun-Taizi River Basin with an error of 11.4%. In the Hun-Taizi River Basin, the average annual actual evapotranspiration was 347.4 mm, which had a slightly upward trend with a rate of 1.58 mm · (10 a(-1)), but did not change significantly. It also indicated that the annual actual evapotranspiration presented a single-peaked pattern and its peak value occurred in July; the evapotranspiration in summer was higher than in spring and autumn, and it was the smallest in winter. The annual average evapotranspiration showed a decreasing trend from the northwest to the southeast in the Hun-Taizi River Basin from 1970 to 2006 with minor differences. Net radiation was largely responsible for the change of actual evapotranspiration in the Hun-Taizi River Basin.

[Characteristics of evaporation over broadleaved Korean pine forest in Changbai Mountains, Northeast China during snow cover period in winter].

Based on the measurement data of water vapor flux by open-path eddy covariance system and of the micrometeorological factors in broad-leaved Korean pine forest in Changbai Mountains during the snow cover period from 2002 to 2005, this paper analyzed the dynamics of snow cover evaporation and the relationships between the evaporation and meteorological factors. The energy balanced ratio during the snow cover period was 79. 9% , and the latent heat flux accounted for 21. 4% of net radiation. The diurnal variation of the evaporation presented a single-peak curve, and the evaporation rate during snow-melting period was higher than that during stable snow cover period. The half-hour evaporation presented liner relationship with net radiation and quadratic relationship with air temperature. The daily evaporation presented quadratic relationship with net radiation and exponential relationship with air temperature. The daily evaporation presented a dynamic trend of decreasing-stable-increasing, with the maximum at increasing stage and the minimum at stable stage. The maximum value of the daily evaporation was 0.73 mm d-1, and the minimum value was 0. 004 mm d-1. During the snow cover periods of 2002-2003, 2003-2004 and 2004-2005, the annual evaporation was 27.6, 25.5, and 22.9 mm, accounting for 37.9% , 19.5% , and 30. 0% of the precipitation in the same periods, respectively. The mean value of the daily evaporation in the three periods was 0. 17, 0. 19, and 0. 17 mm d-1, respectively.

[Measurement and estimation methods and research progress of snow evaporation in forests].

Accurate measurement and estimation of snow evaporation (sublimation) in forests is one of the important issues to the understanding of snow surface energy and water balance, and it is also an essential part of regional hydrological and climate models. This paper summarized the measurement and estimation methods of snow evaporation in forests, and made a comprehensive applicability evaluation, including mass-balance methods (snow water equivalent method, comparative measurements of snowfall and through-snowfall, snow evaporation pan, lysimeter, weighing of cut tree, weighing interception on crown, and gamma-ray attenuation technique) and micrometeorological methods (Bowen-ratio energy-balance method, Penman combination equation, aerodynamics method, surface temperature technique and eddy covariance method). Also this paper reviewed the progress of snow evaporation in different forests and its influencal factors. At last, combining the deficiency of past research, an outlook for snow evaporation rearch in forests was presented, hoping to provide a reference for related research in the future.

[Runoff process in forested basin of Hun River-Taizi River, Northeast China: a simulation study].

Based on the hydrological data from the Beikouqian and Nandianyu stations in the upstream of Hun River and Taizi River as well as the meteorological data from the Qingyuan, Xinbin, and Benxi County stations, Northeast China in 1998-2007, a distributed hydrological model (DHS-VM) was applied to simulate the hydrological process in Hun-Tai basin. The scientific applicability of the model was validated, and the reference values of the most sensitive model parameters were provided. The simulated monthly runoff Nash-Suttclife coefficient (E value) for the source region of Hun River in calibration period (1998-2002) and validation period (2003-2007) was 0.9675 and 0. 8957, respectively, which could better reappear the monthly runoff process in this source region. The simulated monthly and annual runoff E values for the upstream of Taizi River were greater than 0.6, indicating that this model had good applicability in Hun-Tai basin, and the calibrated parameter scheme had a good reliability. This paper established a solid framework for the hydrological study over ungauged basin, and constructed a reasonable parameter scheme.

[Canopy conductance characteristics of poplar in agroforestry system in west Liaoning Province of Northeast China].

By using Granier' s thermal dissipation probe, the sap flow of poplar in a poplar-maize agroforestry system in west Liaoning was continuously measured, and as well, the environmental factors such as air temperature, air humidity, net radiation, wind speed, soil temperature, and soil moisture content were synchronically measured. Based on the sap flow data, the canopy conductance of poplar was calculated with simplified Penman-Monteith equation. In the study area, the diurnal variation of poplar' s canopy conductance showed a "single peak" curve, whereas the seasonal variation showed a decreasing trend. There was a negative logarithm relationship between the canopy conductance and vapor pressure deficit, with the sensitivity of canopy conductance to vapor pressure deficit change decreased gradually from May to September. The canopy conductance had a positive relationship with solar radiation. In different months, the correlation degree of canopy conductance with environmental factors differed. The vapor pressure deficit in the whole growth period of poplar was the most significant environmental factor correlated with the canopy conductance.

[Spatiotemporal changes of potential evapotranspiration in Songnen Plain of Northeast China].

Based on the daily meteorological data from 72 weather stations from 1961-2003, a quantitative analysis was conducted on the spatiotemporal changes of the potential evapotranspiration in the Plain. The Penman-Monteith model was applied to calculate the potential evapotranspiration; the Mann-Kendall test, accumulative departure curve, and climatic change rate were adopted to analyze the change trend of the evapotranspiration; and the spatial analysis function of ArcGIS was used to detect the spatial distribution of the evapotranspiration. In 1961-2003, the mean annual potential evapotranspiration in the Plain was 330 - 860 mm, and presented an overall decreasing trend, with the high value appeared in southwest region, low value in surrounding areas of southwest region, and a ring-belt increasing southwestward. The climatic change rate of the annual potential evapotranspiration was -0.21 mm x a(-1). The annual potential evapotranspiration was the highest in 1982, the lowest in 1995, and increased thereafter. Seasonally, the climatic change rate of the potential evapotranspiration in spring, summer, autumn, and winter was -0.19, 0.01, -0.05, and 0.03 mm x a(-1), respectively, suggesting that the potential evapotranspiration had a weak increase in winter and summer and a slight decrease in spring and autumn.

[Variation characteristics of runoff coefficient of Taizi River basin in 1967-2006].

Based on the daily precipitation and runoff data of six main embranchments (Haicheng River, Nansha River, Beisha River, Lanhe River, Xihe River, and Taizi River south embranchment) of Taizi River basin in 1967-2006, this paper analyzed the variation trend of runoff coefficient of the embranchments as well as the relationship between this variation trend and precipitation. In 1967-2006, the Taizi River south embranchment located in alpine hilly area had the largest mean annual runoff coefficient, while the Haicheng River located in plain area had the relatively small one. The annual runoff coefficient of the embranchments except Nansha River showed a decreasing trend, being more apparent for Taizi River south embranchment and Lanhe River. All the embranchments except Xihe River had an obvious abrupt change in the annual runoff coefficient, and the beginning year of the abrupt change differed with embranchment. Annual precipitation had significant effects on the annual runoff coefficient.

[Simulation of the effects of climate change on canopy transpiration over a broad-leaved Korean pine forest in Changbai Mountains].

To investigate the effects of climate change on canopy transpiration, a process-based carbon and water coupling multi-layer model was verified, and used to simulate the canopy transpiration over a broad-leaved Korean pine forest in Changbai Mountains. This multi-layer model could well estimate canopy transpiration. The simulated values fitted well with the measured data based on eddy covariance method. The simulation of the responses of canopy transpiration to climate change indicated that the latent heat flux (LE) increased with increasing air temperature, and decreased with the decline of soil water content or the increase of air CO2 concentration. Under the climate scenarios in this study, the LE was most sensitive to the associated variation of 10% reduction of soil water content in 0-20 cm layer and 190 micromol x mol(-1) increase of CO2 concentration, but not sensitive to the synchronous variation of 10% reduce of soil water content and 3.6 degrees C increase of air temperature.

[Baseflow separation methods in hydrological process research: a review].

Baseflow separation research is regarded as one of the most important and difficult issues in hydrology and ecohydrology, but lacked of unified standards in the concepts and methods. This paper introduced the theories of baseflow separation based on the definitions of baseflow components, and analyzed the development course of different baseflow separation methods. Among the methods developed, graph separation method is simple and applicable but arbitrary, balance method accords with hydrological mechanism but is difficult in application, whereas time series separation method and isotopic method can overcome the subjective and arbitrary defects caused by graph separation method, and thus can obtain the baseflow procedure quickly and efficiently. In recent years, hydrological modeling, digital filtering, and isotopic method are the main methods used for baseflow separation.

[Multiple time scale analysis of precipitation series in Changbai Mountain Region in 1959-2006].

Based on the 1959-2006 monthly and annual precipitation data from Songjiang, Donggang, Changbai, Helong, Linjiang, and Tianchi meteorological stations, and by using Morlet wavelet method, a multiple time scale analysis was made on the precipitation series from May to September (vegetation growth season), November to next April (snow season), and the annual in Changbai Mountain Region. The precipitation series was decomposed and low-frequency reconstructed at different levels by using the db5 wavelet of Daubechies wavelets, and the trend of the reconstructed series was identified and analyzed. In 1959-2006, there existed 3-6 years, 10-13 years, and 24-30 years cycles of precipitation series in vegetation growth season, 1-2 years, 5-7 years, and 17-20 years cycles in snow season, and 8-10 years, 16-20 years, and 25-30 years cycles in the annual, and the annual precipitation series showed an overall downward trend.

[Turbulent characteristics in forest canopy under atmospheric neutral condition].

Based on the micrometeorological data of broad-leaved Korean pine forest in Changbai Mountain in 2003, a second-order closure model was employed to calculate and analyze the turbulent characteristics within and above the canopy of the forest. The calculated mean wind profile was coincident with the measured one. The Reynolds stress within the forest was significantly attenuated. The turbulent strength, velocity flux, and skew were the largest at forest-atmosphere interface, as well the wind shear. With the increase of velocity skew, the turbulent intermittence became more significant, and the downward turbulent eddy within the canopy was limited. Most of the turbulent deeply within the forest canopy was produced by the non-local contributions above the canopy.

[Effects of atmospheric thermally stratified condition on sensible heat within forest canopy].

By using Eulerian second-order closure model, this paper studied the source-sink distribution and flux characteristics of sensible heat within forest canopy under atmospheric thermally stratified condition. In the daytime, a notable feature for the atmospheric stratification of forest canopy was the unstable stratification above the canopy and the stable stratification under the canopy. The changes of temperature profile indicated there was a 'hot spot' at about 2/3 of canopy height. The counter-gradient fluxes within the canopy were discovered by modeling the heat flux under weak stable atmospheric condition. Simulations of the diurnal variation of sensible heat flux were consistent with the measurements (R2 = 0.9035, P < 0.01). Adding buoyancy in the sensible heat balance equation could increase the simulation accuracy of inversion model, and improve the simulation capability for heat flux balance.

[Canopy interception in larch plantations: measurement and modeling in eastern Liaoning Mountainous Region].

Based on the 2005-2008 observation data of canopy interception in larch plantation in eastern Liaoning Province, and by using Gash model, the interception process was simulated. In the plantation, there was a significant positive correlation between throughfall and rainfall (R2 = 0.98), and the annual throughfall accounted for 77. 64% of the total rainfall. The canopy interception was positively correlated with rainfall and its intensity. The canopy interceptio simulated by Gash model was lower than the measured values, except for the results in 2007 because of the short intervals between rainfalls. The absolute error of simulated values had a negative exponential correlation with rainfall, and the range was 1.26%-68.96%, and the mean value was 29.09%. The estimated values were almost equal to the measured values, with the correlation coefficient being 0.91.

[Gas exchange measurement system based on chamber method and its applications in gas exchange research of plant ecosystems].

Gas exchange measurement system based on chamber method is commonly used for the researches of carbon and water cycles in plant ecosystems, especially for the researches in soil and plant organizational scales. According to the gas path frames of the measurement system, this paper summarized in detail the principles and computing methods of closed, semi-closed, open, and semi-open path gas exchange measurement chamber systems. The commercial gas exchange measurement chamber systems commonly in use were enumerated, and the development and applications of some handcrafted systems were also reviewed. Finally, some disadvantages of gas exchange measurement chamber systems were indicated, and their improvement measures were suggested.

[Relationships between horqin meadow NDVI and meteorological factors].

Based on the 2000-2006 MODIS 8-day composite NDVI and day-by-day meteorological data, the seasonal and inter-annual variations of Horqin meadow NDVI as well as the relationships between the NDVI and relevant meteorological factors were studied. The results showed that as for the seasonal variation, Horqin meadow NDVI was more related to water vapor pressure than to precipitation. Cumulated temperature and cumulated precipitation together affected the inter-annual turning-green period significantly, and the precipitation in growth season (June and July), compared with that in whole year, had more obvious effects on the annual maximal NDVI. The analysis of time lag effect indicated that water vapor pressure had a persistent (about 12 days) prominent effect on the NDVI. The time lag effect of mean air temperature was 11-15 days, and the cumulated dual effect of the temperature and precipitation was 36-52 days.

[Construction and application of a coupled slope surface-subsurface flow model for forested watershed].

A coupled slope surface-subsurface flow model which can be solved by finite difference method was constructed with saturated infiltration theory, Saint-Venant equation, and Richards equation, and a series of slope runoff generation experiments under conditions of different slope grades and rain intensities were conducted in laboratory. The results showed that the simulated and observed processes of surface-subsurface flow accorded well, with the relative errors of peak time, flow duration, peak flow, and gross flow being mostly less than 10%. This precise and practicable model could be used in further studying the mechanisms of subsurface flow and in providing theoretical basis for improving rainfall-runoff watershed models.

[Characteristics of macropores in two forest soils on northern slope of Changbai Mountains].

By using dye tracing and image analysis, the characteristics and distribution of macropores in brown coniferous forest soil and dark brown forest soil on northern slope of Changbai Mountains were studied, with the factors affecting the formation of the macropores discussed. The results showed that the vertical distribution pattern of soil macropores could be indirectly known by the variation of dyed area with soil depth. The dyed area of the two soils tended to decrease with increasing soil depth. In 24 hours, the macropore flow transferred 10-20 cm deeper in brown coniferous forest soil than in dark brown forest soil, and there were more macropore flow paths in brown coniferous forest soil. By unit area, brown coniferous forest soil had 6 paths, while dark brown forest soil only had 1 path. The existence of macropore flow could accelerate the infiltration speed by 2 or 3 times at least. Bio-factor was the key factor affecting the formation of macropores in the two kinds of forest soil. There were more macropores formed by soil animals, and the diameter was mostly between 2 and 4 mm.