Ecohydrology in water-limited environment using quantitative remote sensing - the Heihe River basin (China) case

摘要: Water-limited environments exist on all continents of the globe and they cover more than 30% Earth’s land surface. The eco-environments these regions tend to be fragile are changing in a dramatic way through processes like desertification, shrinking oases, groundwater depletion, soil erosion. These either human induced or results climate. Implications changes for both regional hydrologic cycle vegetation have been documented. Since occur over wide range scales space time, remote sensing methods needed monitor surface characteristics, observe hydrological states, compare with predictions from models. It is widely accepted that offer ability acquire spatially continuous measurements large areas. Remote can also help visualize complex because spatial data captured regularly time. China one several countries arid semi-arid Heihe River basin, situated inland northwestern China, areas severely affected by ecoenvironmental degradation recovery. problem degraded environment due overexploitation ground water leading including decline death natural vegetation, lowering table. Exhaustive (over-)use resources main cause lower reaches called Ejina oasis. whole basin therefore selected as study area this thesis analyze long-term eco-environmental changes. What happens river likely growing influence cycles, even affecting life. Effective management problems critical zone water-limited conditions will provide scientific evidence protecting improving eco-environment Chinese regions, eventually resulting improvement. Studies quantifying relationship between step developing an ecohydrological approach order minimize environmental degradation. us better understand effects their subsequent feedback at scale. information quantify heterogeneity change Therefore, objective develop methodology quantitative assessment scale integrating approaches. Chapter 1 outlines significance using applying them ecohydrology specific research objectives thesis. 2 quantifies vertical horizontal distribution Qilian Mountains area, representing upper based MODIS NDVI images year 2000 - 2006. Our analysis reveals elevation aspect two important impact factors mountainous area. increases maximum value certain threshold, then decreases beyond threshold. optimal growth shady side mountains less evapotranspiration. best combination temperature precipitation assessed providing good growth. 3 presents efficient method estimate annual evapotranspiration (ET) SEBS algorithm (Surface Energy Balance System) Zhangye middle basin. proposed daily collected meteorological stations. result shows ET increased gradually during period 1990-2004 factor increase was change. accuracy validated balance watershed validation used effectively 4 establishes runoff oasis, located River. In part, time periods distinguished corresponding before after implementation new allocation scheme GIMMS sets oasis first 1989-2002 second 2000-2006, respectively. decreasing trend 1989 2002 increasing Good relation found stages lag observed hysteresis effect year. addition, yearly smallest amount which sustains demand estimated 4×108 m3 images. 5 explores depth combining observation data. demonstrates suitable region ranges 2.8 m, depending species composition. Hardly any occurs when below m rooting occurring limited cannot maintain adequate supplies canopies m. situation since 2000. mean conversion bare into vegetated about 38 km2 per – 2008. reflects potential recovery 6 comprises conclusions outlook possible improvements future research. contribution successful integration occurrence provides evaluate dynamics, impacts presented serves sound foundation predicting