Zhaodong Feng

Assessment of soil moisture using Landsat ETM+ temperature/vegetation index in semiarid environment

The surface moisture is one of the most important parameters in modeling water-plant coupled land surface processes and land-air coupled climatic systems. The use of remotely sensed data is potentially of great interest in such a context. Several methods have been proposed to estimate soil moisture conditions, but the limitations of these methods are obvious. In this study, we developed a method to detect soil moisture condition using surface temperature (Ts) and vegetation index (NDVI) derived from Landsat ETM+ data. We then applied this method to the semiarid area and mapped out the spatial distribution of soil moisture. We further compared the soil moisture distribution with the spatial distribution of desertification and found that desertification in semiarid area exerts a great effect on soil moisture conditions

The impact of climate change on potential distribution of species in semi-arid region: A case study of Qinghai spruce (Picea crassifolia) in Qilian Mountain, Gansu province, China

To restore the human-disturbed natural ecosystem and to assess the impact of the projected future climatic change on the natural ecosystem at a plant community level or at a plant species level, the potential distribution of the community and the species under current climate conditions need to be understood. Therefore many methods have recently been developed to simulate the potential distribution of a particular community or species [1]. However, very little has been done to assess the potential distribution of Qinghai spruce (Picea crassifolia) in Qilian Mountains where the spruce forest is extremely important ecologically and hydrologically. This study used Maximum Entropy model to simulate the potential distribution of Qinghai spruce under current climatic conditions. The validity of the model was verified by comparing the simulated potential distribution with the observed distribution of the spruce. The result shows the model is feasible to simulate the potential distribution of Qinghai spruce. Then this model was used to assess the impact of the projected climatic changes on the distribution of the spruce. The distribution of the spruce under current climate condition was compared with that under the projected climatic change scenario. The areal extent of the potential distribution may increase by 1% under the projected climatic change scenario. In addition, this study revealed that Mean Maximum Temperature of Warmest Month and Mean Temperature of Wettest Quarter are the most important factors which controlling the potential distribution of Qinghai spruce among the 19 environmental and climatic factors used in this model.

Simulating wildfire spreading processes in a spatially heterogeneous landscapes using an improved cellular automaton model

A better understanding of wildfire spreading processes is expected both for long-term wildfire management planning and effective suppression strategies so that wildfires-caused losses in natural resources, endangered species, human lives and properties can be reduced. The cellular automaton (CA) method is useful and powerful for modeling natural and artificial systems in which the constituent parts are locally and tightly interacted. The temporal and spatial characteristics of wildfires make the CA method a preferred choice to model the temporal and spatial variability. In this study, hexagonal tessellation space was used to develop a CA model and then the Rothermers fire spreading model (1972) was integrated to the CA model to simulate wildfire-spreading processes spatially and temporally. The hexagon-based wildfire spreading CA model was verified with the experimental data and also tested using the data obtained in the southern part of Gansu province (China), and the comparison between the simulated results and observed data suggests that this CA-based model can be used to provide useful information for managing wildfires over heterogeneous landscapes

Modeling canopy interception of Picea crassifolia forest in Qilian mountains using QuickBird satellite data

Canopy interception of rainfall plays an important role in hydrologic cycling and water balance of ecosystems in arid and semi-arid regions. At present, most research focuses on the characteristics of interception at the stand or plot scale. Studies of canopy interception at the river basin or landscape scale based on RS and GIS are lacking because the factors influencing canopy interception such as precipitation, vegetation are difficult to model spatially. A semi-theoretical and semi-empirical model of canopy interception was improved based on investigation in the study area. Considering the important influence of canopy structure, LAI was introduced to the model. After parameters in the model were spatialized using remote sensing data and GIS, the spatial distribution of canopy interception was estimated in the study area (i.e. Pailugou catchment). The results show that the amount of canopy interception in Pailugou catchment is between 97.9 mm and 236.6 mm and the mean interception amount is 161.8 mm. The minimum interception appears at the lower altitude area and the maximum interception presents at the higher altitude area. The interception percentage of Picea crassifolia forest is between 27.92% and 58.00%, which increases with increasing altitude and the maximum appears at 3100m, then decreases along with the increase of altitude.

Estimation of land surface evapotranspiration in the western Chinese Loess Plateau using remote sensing

Estimation of land surface evapotranspiration (ET) using remote sensing is increasingly becoming an effective approach to approximating the moisture and heat exchanges between soil and atmosphere systems. The ET in the western Chinese Loess Plateau is comprehensively estimated by inputting NOAA/AVHRR data-derived parameters into surface energy balance system (SEBS) model. The observed data in the western Chinese Loess Plateau are used to verify the estimates of input variables. ET estimation in this research shows that ET in the western Chinese Loess Plateau is primarily determined by vegetation coverage. Topography also plays an important role in controlling the estimated ET spatial distribution. This study also demonstrate the remote sensing-aided surface energy balance model can be used to estimate ET in semiarid areas.

GIS-based improvement of C. O. Clark method for simulating watershed-scale overland flow in the Chinese Loess plateau

Traditional static methods have disadvantages of being lack of considering the spatiality of the data and new developments in spatial techniques (e.g., GIS) can help us in dealing with the spatiality problems. In this research, a semi-lumped conflux model (i.e., C. O. Clark method) is modified to be a semi-distributed conflux model by GIS- assisted partitions of spatial variables influencing the net precipitation into a spatially homogeneous watershed. Specifically, the spatial attributes of the dynamic processes were depicted through GIS-assisted DEM delineation of watershed geomorphology and spatiality of the factors modulating the hydrographs are considered by the adjustment factor K. Our results show that the GIS-assisted and spatially-improved Clark model generated more realistic results than the lumped original model, implying that the spatiality of the hydrogeomorphic factors that modulate the net precipitation plays a significant role in surface runoff generation in the entire watershed and thus in conflux processes in the outlet even within a small watershed.

Estimating spatial distribution of radiation below the Qinghai Spruce forest canopy in Qilian Mountains using hemispherical images and Airborne LiDAR data

Solar radiation transmission plays is an important process in the energy exchange in forest ecosystem. There are a lot of transmission models developed for a single canopy, but relatively fewer models for studying spatial distribution of radiation below the forest canopy. In this paper, we used a simple model that was related to canopy cover to calculate the solar radiation below the forest canopy. At the same time, the hemispherical photography integrated with airborne LiDAR to provide a data for the model. Especially, LiDAR data was used to obtain the spatial distribution of the canopy cover. We obtained a spatial distribution of solar radiation below the Qinghai Spruce forest canopy in Qilian Mountains. Results showed that modeled average daily total radiation below the canopy was 21.614 MJ/m2/d, ranging from 4.618 to 54.053 MJ/m2/d in our experimental zone.

Estimating morphological parameters of Tamarix ramosissima by Digital hemispherical image in the lower reaches of heihe river, northwest China

Tamarix ramosissima is a dominant shrub and mainly contributes to total biomass in the lower reaches of Heihe River. In order to study the biomass and growth status of the shrub, we need to measure the morphological parameters. Usually, the morphological parameters are measured by field survey. However, the method is low in efficient and accurate. In this study, the hemispherical photography was used to obtain the morphological parameters of Tamarix ramosissima. The hemispherical images of Tamarix ramosissima were obtained from the top of canopy by digital camera with fisheye lens, then processed and overlaid with the calibration parameter layer to estimate the morphological parameters. The results show that the hemispherical photography had high accuracy in estimating the morphological parameters. The method is a convenient and feasible approach, and can provide a scientific data for the biomass models.

Regional climate responses to the land use and land cover change in Heihe River Basin, China

Land use and land cover play an essential role in the process of land-atmosphere interaction, and their changes influence regional climate in complicated ways. This function is also regarded as a more important driving force in an arid area, where vegetation changes will greatly alter energy and water distribution at watershed scale, and further influence ecological balance and agricultural production. To explore the regional climate response to the land use and land cover change in Heihe River Basin, three vegetation change scenarios in 1998 summer are designed in RegCM3 (a regional climate model), and the variation of temperature and precipitation are analyzed. Results show that: 1) the increase of vegetation area in mountainous area will bring about temperature decline and precipitation growth in summer. 2) With the expansion of farmland, precipitation will increase slightly in the mountainous and oasis area, and temperature and precipitation will decrease in desert and semi-desert. 3) The spread of desert area will cause temperature rise and precipitation decrease in whole area.

GIS & RS assisted precipitation-flow generation simulation in a typical watershed of Chinese Loess Plateau

In this research, GIS technology was used to deal with the data preparation of the land use and soil type in the whole watershed. The spatial difference of the time-step based on typical precipitation was calculated by the interpolated method of the Inverse Distance Weight (IDW) provided in the GIS software Arc/info 9.0. The vegetation interception capacity was calculated based on the LAI (leaf area index), which was gained through remote sensing ways. The classical Horton theory of infiltration was used to calculate the infiltrated rainfall in view of the excess overland flow generation mechanism in semi-arid regions. After the calculation of the above, the water quantity balance function was used to calculate the overland flow generation. All of the variables involved in the hydrological portions calculation were ensured according to the results of the experiments in outside fields. Because of the small scale of the watershed, a high resolution of the DEM was selected. The result shows that the simulation methods above can be used to simulate overland flow generation in a basin-scale in the semi-arid Chinese loess plateau. In this research, remote sensing method was used to calculate the LAI and solve the problem of vegetation interception better.