Rensheng Chen

A Cryosphere-Hydrology Observation System in a Small Alpine Watershed in the Qilian Mountains of China and Its Meteorological Gradient

Abstract The unavailability of sufficient data at higher elevations causes many uncertainties in research on cold regions. This study considers a cryosphere-hydrology observation system established in 2008 at the Hulu small alpine watershed in the Qilian Mountains of Northwest China. The altitudinal gradient of weather factors is analyzed using data from the Hulu watershed and routine stations located in the Heihe upstream. The data presented here provide the following knowledge of mountain meteorology at elevations from 3367 m to 4166 m/4248 m in the Qilian Mountains: (1) the yearly precipitation—altitude relationship is linear in regions below 4248 m in the Heihe upstream, where the precipitation gradient increased marginally from 1960 to 2011; (2) the yearly air temperature lapse rate (TLR) is weaker at higher elevations (>3000 m), and the seasonal TLR became more divergent between winter and summer half-years from 1960 to 2011 (yearly mean 5.6 °C km-1); (3) in the Hulu watershed, the LRs of water vapor pressure and absolute humidity are higher in warm seasons with yearly means of 1.1 hpa km-1 and 0.84 g m-3 km-1, respectively, and the maximum relative humidity value is found at elevations between 3500 and 3700 m in the Heihe upstream; (4) the long-term existence of snow increases the albedo to yearly means of 0.22, 0.30, 0.35, and 0.27 in areas of grassland, meadow, marshy meadow, and alpine desert in the Hulu watershed, respectively. The relationship between monthly net radiation and soil surface temperature (Ts) is linear, and the mean Ts LR was about 7.5 °C km-1 from July 2009 to September 2011.

Distribution and Estimation of Aboveground Biomass of Alpine Shrubs along an Altitudinal Gradient in a Small Watershed of the Qilian Mountains, China

Shrublands serve as an important component of terrestrial ecosystems, and play an important role in structure and functions of alpine ecosystem. Accurate estimation of biomass is critical to examination of the productivity of alpine ecosystems, due to shrubification under climate change in past decades. In this study, 14 experimental plots and 42 quadrates of the shrubs Potentilla fruticosa and Caragana jubata were selected along altitudes gradients from 3220 to 3650 m a.s.l. (above sea level) on semi-sunny and semi-shady slope in Hulu watershed of Qilian Mountains, China. The foliage, woody component and total aboveground biomass per quadrate were examined using a selective destructive method, then the biomass were estimated via allometric equations based on measured parameters for two shrub species. The results showed that C. jubata accounted for 1 — 3 times more biomass (480.98 g/m2) than P. fruticosa (191.21 g/m2). The aboveground biomass of both the shrubs varied significantly with altitudinal gradient (P<0.05). Woody component accounted for the larger proportion than foliage component in the total aboveground biomass. The biomass on semi-sunny Received: 2 January 2014 Accepted: 19 May 2014 slopes (200.27 g/m2 and 509.07 g/m2) was greater than on semi-shady slopes (182.14 g/m2 and 452. 89 g/m2) at the same altitude band for P. fruticosa and C. jubata. In contrast, the foliage biomass on semi-shady slopes (30.50 g/m2) was greater than on semi-sunny slopes (27.51 g/m2) for two shrubs. Biomass deceased with increasing altitude for P. fruticosa, whereas C. jubata showed a hump-shaped pattern with altitude. Allometric equations were obtained from the easily descriptive parameters of height (H), basal diameter (D) and crown area (C) for biomass of C. jubata and P. fruticosa. Although the equations type and variables comprising of the best model varied among the species, all equations related to biomass were significant (P < 0.005), with determination coefficients (R2) ranging from 0.81 to 0.96. The allometric equations satisfied the requirements of the model, and can be used to estimate the regional scale biomass of P. fruticosa and C. jubata in alpine ecosystems of the Qilian Mountains.

Aboveground Biomass and Water Storage Allocation in Alpine Willow Shrubs in the Qilian Mountains in China

The aboveground biomass allocation and water relations in alpine shrubs can provide useful information on analyzing their ecological and hydrological functions in alpine regions. The objectives of this study were to compare the aboveground biomass allocation, water storage ratio and distribution between foliage/woody components, and to investigate factors affecting aboveground biomass allocation and water storage ratio in alpine willow shrubs in the Qilian Mountains, China. Three experimental sites were selected along distance gradients from the riverside in the Hulu watershed in the Qilian Mountains. The foliage, woody component biomass, and water allocation of Salix cupularis Rehd. and Salix oritrepha Schneid. shrubs were measured using the selective destructive method. The results indicated that the foliage component had higher relative water and biomass storage than the woody component in the upper part of the crown in individual shrubs. However, the woody component was the major biomass and water storage component in the whole shrub level for S. cupularis and S. oritrepha. Moreover, the foliage/woody component biomass ratio decreased from the top to the basal level of shrubs. The relative water storage allocation was significantly affected by species types, but was not affected by sites and interaction between species and sites. Meanwhile, relative water storage was affected by sites as well as by interaction between sites and species type.

The relationship between runoff and ground temperature in glacierized catchments in China

A single parameter index method, in which ground temperature and air temperature is the sole input variable, respectively, is used to evaluate and compare the glacial runoff in three typical glacier catchments, Dongkemadi glacier catchment in Tibetan plateau, Koxkar glacier catchment and the headwater catchment of Urumqi River catchment in Tianshan Mountains in West China. The method based on ground temperature is an attempt to evaluate glacier runoff in elevated terrains, as few studies have focused specifically on the association between glacier runoff and ground temperature. The results identify ground temperature versus a certain depth, which is a critical factor that affected glacier hydrological processes and showed that runoff data is much better correlated with ground temperature than air temperature. Especially, at the latter two catchments, the largest coefficients of exponential relationship R2 between glacier runoff and ground temperature are 0.9 and 0.83, respectively. The accuracy of the method makes it possible to estimate the glacier runoff with a certain depth ground temperature at a certain site, which may provide a new approach to evaluate the glacier runoff for areas where there is a lack of observation data.

Estimation of global radiation in China and comparison with satellite product

A modified solar radiation model, incorporating into several satellites remote sensing information such as NCEP/NCAR data, EOS-AURA satellite data, and Chinese FY-2C geo-stationary meteorological satellite data, is presented. The model is an attempt to modify Chen’s radiation model and examine its estimation accuracy at various places in six different climatic zones of China. The verification of model is also carried out by comparing between calculated radiation value using modified model and radiation product of FY-2C satellites. According to the NSE values, the adaptability of model is reasonably high in Mid-Temperate Zone (MTZ), Warm Temperate Zone (WTZ), Tibetan Plateau Zone (TPZ), and Cold Temperature Zone (CTZ) climate regimes and slightly low in Subtropical Zone (SZ) and Tropical Zone (TZ) climate regimes. The comparison between modeled radiation values and FY-2C radiation product values shows that the radiation product of FY-2C satellites is superior to the modified model in SZ and TZ climate regimes.

New methods for calculating bare soil land surface temperature over mountainous terrain

Land surface temperature (LST) causes the phase change of water, links to the partitioning of surface water and energy budget, and becomes an important parameter to hydrology, meteorology, ecohydrology, and other researches in the high mountain cold regions. Unlike air temperature, which has common altitudinal lapse rates in the mountainous regions, the influence of terrain leads to complicated estimation for soil LST. This study presents two methods that use air temperature and solar position, to estimate bare LST with high temporal resolution over horizontal sites and mountainous terrain with a random slope azimuth. The data from three horizontal meteorological stations and fourteen LST observation fields with different aspects and slopes were used to test the proposed LST methods. The calculated and measured LST were compared in a range of statistical analysis, and the analysis showed that the average RMSE (root mean square error), MAD (mean absolute deviation), and R2 (correlation coefficient) for three horizontal sites were 5.09°C, 3.66°C, 0.92, and 5.03°C, 3.52°C, 0.85 for the fourteen complex terrain sites. The proposed methods showed acceptable accuracy, provide a simple way to estimate LST, and will be helpful for simulating the water and energy cycles in alpine mountainous terrain.

Two-year comparative study of snow cover dynamics and its impact factors on glacier surface

Snow cover on glacial surfaces is a sensitive environmental indicator. However, it is difficult to differentiate snow cover from a bare ice surface, and snow cover also changes rapidly during the melt season. Monitoring these dynamics requires sufficient time and spatial resolution; thus, traditional satellite data lack the necessary spatial resolution and rarely used to monitoring snow cover on glacier surface, which induced monitoring of snow dynamics on glacier is more challenging. Time-lapse photography has the advantage of obtaining images with high time and spatial resolution. By using an automated time-lapse digital camera, this paper documents two successive years snow cover dynamics on the Shiyi glacier and compared the meteorological conditions which induced different melt conditions. Monitoring indicate that the 2012 melt season experienced a higher snow cover fraction than the 2013 melt season because of a greater accumulated snow depth, lower air temperature and fewer sunlight hours. Successive photographs also indicate that, on the Shiyi glacier, atmospheric dust accelerates the snow melt speed and attenuates the snow depth. For the bare ice surface, the effects of atmospheric dust were reduced because the dusts were composed of Fine particles and are more easily washed away by melt water or rain. Studies on the Shiyi glacier indicate that the snow cover fraction is a key parameter that indicates the status of glacial accumulation or ablation.