Vegetation supply water index based on MODIS data Analysis of the in Yunnan in spring of 2012

摘要

Today, drought has become a world problem, which is affecting agriculture more and more seriously. China is a large agricultural country, so drought is nor ignored for China. Drought hazards in agriculture growing, so timely and accurate monitoring of the development of drought is necessary to reduce the harm of drought. Over the years, many scholars established a variety of drought monitoring models, aiming at better monitoring of drought. Southwest China has been the drought-prone areas and Yunnan Province is the most serious area. [Method]: In this paper, in February 2012-May period of remote sensing data obtained with moderate-resolution imaging spectrometer (MODIS) conducts dynamic monitoring of drought in Yunnan. Normalized Difference Vegetation Index (NDVI) is calculated with the first bang and the second bang of MODIS data and Negative NDVI values that are representative of the water and snow should be removed. By split window algorithm method, land surface temperature (LST) in Yunnan is retrieved with 31-band and 32-band of MODIS data, but some places in where there is much cloud are removed. Then the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) calculated Vegetation Supply Water Index (VSWI) that dynamically monitors the drought in Yunnan. this model's results are validated based on 10 cm-shallow soil moisture data measured by the meteorological stations at the 0.05 confidence level and passed the correlation test which indicates that the results calculated by the model is sensitive to changes in drought. In the soil moisture data, some data collection sites have been irrigated, so these data should be removed. So this drought index can be used to monitor drought developments and we can get real-time, accurate drought. These monitoring results as a basis, We can make timely and correct drought policy to reduce losses caused by the drought; [Conclusions] :from spring drought monitoring results can be seen that Northwest- Yunnan has been in a semi- arid and arid state. In February and May, it is more serious drought, drought affecting a wide range. There are two reasons about development of drought: First, the terrain reasons, northwest, eastern and Central Yunnan are the highland area, low rainfall, dry climate, so the severe drought in these areas; Second, the climatic reason, the spring belongs to the dry season, Rainfall is relatively small and its distribution is not balance. Relative to previous years, three months and it rarely rains in March and May, so it is severe drought. In recent years, natural hazards occur frequently on the world in witch drought is most. Drought is characterized by a wide spread range, long duration and great harm. China is a large agricultural country so it be harmed when drought occurred witch hinders the development of society. So it is necessity of Real-time, dynamic and accurate monitoring of drought. Only in this way, can we minimize the damage.