Study on the Influence of Drought on Vegetation Net Primary Producti-vity in Southwest China

The Net Primary Productivity (NPP) of vegetation is an important indicator of theresponse of the ecosystem functions to climate change. The change intuitively reflects thedegree that how climatic and environmental conditions are influenced by ecosystem changes.Researching the interannual variation of NPP Index is of great significance in environmentalquality assessment, terrestrial carbon sink estimation and ecological processes regulation.Drought, as one of the most serious meteorological disasters, not only influences theproductions and lives of human and brings up economic losses, but also impacts animals andplants significantly. During the process of drought, changes in plant photosynthesis directlylead to the changes in the productivity of the entire region. Drought could interference withthe process of photosynthesis in other forms as well, then indirectly affect vegetationproductivity. Therefore,analysis on the function and influence of drought on NPP is conducive to the studies ofcarbon cycle and predictions of future climate change, and is of great significance to maintainecosystem balance, maintain sustainable economic economic development and achieveharmonious development between resources，environment and social economy.According to1960-2009average temperature and precipitation data from124stations inthe southwest, this paper calculates the distribution of drought in southwest based on SPI(standardized precipitation Index). Due to precipitation distribution is generally skewed distribution instead of the normal distribution, in drought disaster monitoring assessment which combined with precipitation,the paper adopt skewed distribution of probability, that is, AAA distribution to describe changes in precipitation. Standardized precipitation index (SPI) calculates theprobability of distribution of precipitation within a certain time period, then normal standardized and eventually divide drought levels with distribution of standardized precipitation accumulated frequencies. Therefore, it is justify for this paper to adopt the standardized precipitati on index to research seasonal and annual distribution characteristics of drought. Combined with Matlab software, this paper programs to calculate standardized precipitation index in Southwest China with0.1°*0.1°resolution and a total of12444points, divides spatial drought distribution according to National Meteorological Drought Classification Standards and studies spatial and temporal characteristics of drought in Southwest China in50years.CEVSA (Carbon Exchange between Vegetation,Soil and Atmosphere) model belongs to biogeochemical models, which modeling of energy exchange between vegetation, soil, air and water eco-physiological processes of carbon-nitrogen coupling loop.CEVSA model is verified in estimating in global scale and the biological and ecological principles and calculation equations and parameters adopted in the model are taken from the large number of laboratory and field test observations.Nearly16000.5°latitude and longitude grid values which are obtained from the simulations of CEVSA model are compared with the measured value indicates that they not only have a very strong correlation, the absolute values are close as well.CEVSA model has already used in research on the response of carbon cycling in terrestrial ecosystems to climate inter annual variability in both global and regional levels. Therefor, this paper adopts CEVSA model to estimate net primary productivity of vegetation and studies the impacts of drought on vegetation net primary productivity in the Southwest China.The results of Analysis showed that:(1) non-uniform precipitation distribution in the Southwest leads to the larger spatial and temporal differences in drought. There are more seriousdrought in winter while more humid in summer because of the higher rainfall;(2)The spatial distribution of annual NPP and season NPP is unbalanced, declining from Southeast to Northwest and upward in the overall.Annual and seasonal NPP are:200to1000gC/m2/a,30-280gC/m/a,75-500gC/m2/a,30-250gC/m2/a, and70-100gC/m2/a;(3) winter drought in the Southwest has a greater impact on NPP. There is a clear positive correlation between them, that is,more drought, more scarce precipitation, and lower net primary productivity of vegetation.