Study On Eco-hydrological Patterns Based On Determination Of Net Primary Production And Rainfall Use Efficiency Across The Tao River Basin

Under the background of climate change, the variation of terrestrial ecosystem affects the hydrological cycle and hydrological process in a variety of scales. Particularly, the research of the eco-hydrological patterns based on the coupling of regional vegetation dynamics and hydrological effects have great significance for scientific understanding of the natural formation, distribution and the reasonable planning and utilization of the limited resources. In this study, we select the Tao River Basin(TRB) as the study area. We collect the hydrometeorology data from the hydrological and meteorological stations in the TRB and around it, along with the collection of the MODIS NDVI data. On the basis of analyzing the hydrometeorology changes, the Carnegie-Ames-Stanford Approach(CASA) was adopted to calculate the Net Primary Production(NPP) and the Rainfall Use Efficiency(RUE) of vegetation in the TRB. By quantifying the changeable characteristics of the key variables in the eco-hydrology system, we make a comprehensive study on the patterns and variabilities of the eco-hydrology across the TRB. This work will play a positive role in the improvement of the eco-hydrology research and provide technology method and scientific support for the resources management and ecological protection in a river basin. Conclusions are summarized as the following.1) Results of hydrometeorology series analysis showed that the air temperature significantly increased during 1951-2010. The increasing of air temperature mainly occurred in cold seasons in the loess area, while in warm seasons in the Gannan Plateau. The precipitation variabilities were quite different in the two regions. There was an increasing trend in the Gannan Plateau and a decreasing trend in the loess area. Annual runoff was decreased in both regions of the TRB. The decreasing rate in the Gannan Plateau was larger than that in the loess area. The runoff reduced significantly in warmer time in the two regions but increased slightly in colder time in the loess area. During 2001-2010, the actual evapotranspiration(ET) reduced in June and July, while increased in the other months in the Gannan Plateau. However, in the loess area, ET showed a decrease in February to April and an increase in any other months. ET presented increase in the forest and grassland in areas of the eastern upstream, while in areas of the midstream and downstream ET increased significantly along the valleys and decreased in areas with longer distance to the valleys.2) The CASA’s application made good results in calculating NPP of the TRB. The annual NPP is 9.45 Tg C in the hole river basin,including 8.38 TgC and 1.07 TgC in the Gannan Plateau and the loess area, respectively. The differentiation characteristics of NPP are obvious in space. The forest has the largest NPP value among different land cover types, while the farmland has the second larger value. During 2001 to 2010, NPP increased along the valley, but reduced in the most of the rest in the Gannan Plateau. In the loess area, NPP increased generally. The temperature is more sensitive to the NPP in the Gannan Plateau, but the precipitation affects more significantly on the NPP in the loess area.3) There are obvious differences of RUE in different cover types of TRB, ranges in the order of the broadleaf forest > needle-leaf forest > farmland > bush > high coverage grassland > swamp > middle coverage grassland > low coverage grassland > built-up > bare rocks. The average RUE is larger in the Gannan Plateau than that in the loess area. From 2001 to 2010, RUE presented an increase trend, the main increase areas are in the farmland of the Gannan Plateau and the central of loess area. The significant decrease of precipitation is the main reason of the increase of RUE in the Gannan Plateau, while RUE increase in the loess area because of the increase of NPP. Altitudinal differentiation between high and low RUE was not apparent for different cover types.4) The relationship between NPP and RUE were well illustrated in the TRB. The temperature and precipitation both affect the production capacity of vegetation ecosystem and rainfall use efficiency, both water-heat conditions with low temperature and drought are not conducive to the growth of vegetation and the considerable use of water. The eco-hydrological patterns of TRB can be divided into five main kinds, including areas of the alpine meadow in the upper reaches, the alpine grassland-bush-forest in the middle-upper reaches, the higher-altitude meadow-forest-farmland area in the upper-middle reaches(the areas of Die Mountain),the lower-altitude meadow-forest-farmland in the middle-lower reaches(the areas in the north of Min Mountain and Taizi-Baishi Mountains) and the drought agriculture in the downstream.