Liliang Ren

Hydrologic evaluation of Multisatellite Precipitation Analysis standard precipitation products in basins beyond its inclined latitude band: A case study in Laohahe basin, China

[1] Two standard Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) products, 3B42RT and 3B42V6, were quantitatively evaluated in the Laohahe basin, China, located within the TMPA product latitude band (50°NS) but beyond the inclined TRMM satellite latitude band (36°NS). In general, direct comparison of TMPA rainfall estimates to collocated rain gauges from 2000 to 2005 show that the spatial and temporal rainfall characteristics over the region are well captured by the 3B42V6 estimates. Except for a few months with underestimation, the 3B42RT estimates show unrealistic overestimation nearly year round, which needs to be resolved in future upgrades to the real-time estimation algorithm. Both model-parameter error analysis and hydrologic application suggest that the three-layer Variable Infiltration Capacity (VIC-3L) model cannot tolerate the nonphysical overestimation behavior of 3B42RT through the hydrologic integration processes, and as such the 3B42RT data have almost no hydrologic utility, even at the monthly scale. In contrast, the 3B42V6 data can produce much better hydrologic predictions with reduced error propagation from input to streamflow at both the daily and monthly scales. This study also found the error structures of both RT and V6 have a significant geo-topography-dependent distribution pattern, closely associated with latitude and elevation bands, suggesting current limitations with TRMM-era algorithms at high latitudes and high elevations in general. Looking into the future Global Precipitation Measurement (GPM) era, the Geostationary Infrared (GEO-IR) estimates still have a long-term role in filling the inevitable gaps in microwave coverage, as well as in enabling sub-hourly estimates at typical 4-km grid scales. Thus, this study affirms the call for a real-time systematic bias removal in future upgrades to the IR-based RT algorithm using a simple scaling factor. This correction is based on MW-based monthly rainfall climatologies applied to the combined monthly satellite-gauge research products.

Assessment of the red-crowned crane habitat in the Yellow River Delta Nature Reserve, East China

As wildlife habitat is in constant evolution, periodic monitoring is essential to assess its quality. In this study, the change to the red-crowned crane habitat in the Yellow River Delta Nature Reserve was detected from multi-temporal remote sensing data from 1992 to 2008 in a geographic information system. Habitat fragmentation was derived from both physical constraints and human disturbance. The changing habitat quality was assessed against five landscape indices. The results obtained from Landsat TM images indicate that potential habitat shrank 37.9xa0% during 1992–2001, but recovered 99.4xa0% by 2008. Suitable habitat shrank by 4,329xa0ha to a level below that of 1992 despite an increase of 4,747xa0ha in potential habitat due to an increase of 9,075xa0ha in fragmented areas. Both landscape indices and the red-crowned crane population reveal that suitable habitat was the most fragmented in 2001, but the least fragmented in 1992. Therefore, it is inadequate to just restore wetland through artificial diversion of channel flow to the Reserve to preserve the crane habitat. Commensurate efforts should also be directed at improving habitat quality by minimizing human activities and spatially juxtaposing water and reed marshes harmoniously inside the Reserve.

Hydrological response to land use and land cover changes in a sub-watershed of West Liaohe River Basin, China

In recent years, the streamflow of the Laohahe Basin in China showed a dramatic decrease during the rainy season as a result of climate change and/or human activities. The objective of this work was to document significant streamflow changes caused by land use and land cover (LULC) changes and to quantify the impacts of the observed changes in Laohahe Basin. In the study area, the observed streamflow has been influenced by LULC changes, dams, and irrigation from rivers, industry, livestock and human consumption. Most importantly, the growth of population and gross domestic product (GDP) accompanied by the growth in industrial and agricultural activities, which led to LULC changes with increased residential land and cropland and decreased grassland since 2000s. Statistical methods and Variable Infiltration Capacity (VIC) hydrological model were used to estimate the effects of climate change and LULC changes on streamflow and evaportranspiration (ET). First, the streamflow data of the study area were divided into three sub-periods according to the Pettitt test. The hydrological process was then simulated by VIC model from 1964 to 2009. Furthermore, we compared the simulated results based on land use scenarios in 1989, 1999 and 2007, respectively for exploring the effect of LULC changes on the spatio-temporal distribution of streamflow and ET in the Laohahe Basin. The results suggest that, accompanied with climate change, the LULC changes and human water consumption appeared to be the most likely factors contributing to the significant reduction in streamflow in the Laohahe Basin by 64% from1999 to 2009.

Study on natural and human impacts on red-crowned crane habitat in the Yellow River Delta Natural Reserve

This study aims to assess the relative importance of natural and human influences on the change of the red-crowned crane habitat in the Yellow River Natural Reserve, East China using remote sensing and geographic information system (GIS). Two Landsat images were used to detect the change in potential crane habitat, from which suitable crane habitat was determined by excluding behaviorally and physically fragmented areas. It is found that suitable habitat decreased by 5,105 ha in spite of the increase of 4,747 ha in potential habitat during 1992-2008. Natural and anthropogenic forces exerted an almost equal influence on habitat change. Retrogressive succession accounts for 41.9% of the change arising from natural factors. By comparison, land use, the predominant anthropogenic factor, is responsible for 83.6% of the total human-induced change. Although the Yellow River flow has been diverted to the degraded wetlands since 2002, such an effort has not restored the habitat quality to its 1992 level due to physical fragmentation and intensified human disturbance. Thus, complementary restoration efforts should aim at implementing commensurate measures to rationalize the spatial allocation of reed marshes and water, and curbing anthropogenic influences inside the Reserve.

GWSC-VMR, a GIS supported conceptual distributed hydrological model for cold and arid regions

Our research focuses on the study of the particular hydrological process in cold and arid regions. Our aims are to develop a Geographical Information System (GIS) supported conceptual model that could be applied to simulate a drainage basins hydrological process in cold and arid regions and to verify it through a case study. We built a model named the Vertically-Mixed Runoff Model with Grid-based Water Storage Capacity (GWSC-VMR for short). GWSC-VMR includes two parts, i.e. the spatial distributed model of water storage capacity and the vertically-mixed runoff module. First, drainage basin land cover map and typical vegetation rooting depth were acquired by interpreting remote sensing images or accessing land cover database. Second, through the processing of DEM data, we decided water flow direction, catchment area, basin boundary, and the slope of grided basin. Third, we determined the spatial distribution of water storage capacity based on the vegetation rooting depth. Because vegetation root system is a complicated system which is affected by the depth of active soil layer, and the depth of active soil layer is related to the slope, we put forward a series of concepts—upper critical slope gradient, lower critical slope gradient and critical soil layer depth to describe the grid tension water storage capacity and the grid free water storage capacity. Lastly, we integrated the vertically-mixed runoff mechanism and the spatial distribution of drainage basin water storage capacity to develop the GWSC-VMR, which could be applied to simulate drainage basin hydrologic processes, such as snow melt, canopy interception, evapotranspiration, and flow concentration.

Effect of topography on simulated net primary productivity spatial scaling in a mountainous landscape

Gridding the land surface into coarse homogeneous pixels may cause important biases on ecosystem model estimations of carbon budget components at local, regional and global scales. One of the main causes resulted in these biases is overlooking of sub-pixel variability of topography, especially in a mountainous area. This study analyzes the significance of topography to correct net primary productivity (NPP) estimates, made at coarse spatial resolutions where the land surface is considered as homogeneous within each pixel. Its application to a remote sensing process-based model estimates made at a 1-km resolution over a mountainous forested watershed located in Baohe River Basin in China. Results of this study show that NPP spatial scaling in complex terrain depends on the amount of the distortion of the soil moisture field at the coarse resolution, and the spatial redistribution and movement of soil water in complex terrain tightly affect NPP distribution, suggest that it is indeed necessary to consider topography in NPP spatial scaling.