Vegetation-Temperature Condition Index and Its Application for Drought Monitoring

Most previous applications of the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (NOAA-AVHRR) remotely sensed data for drought monitoring were based on vegetation condition index (VCI),temperature condition index (TCI),and/or anomaly vegetation index (AVI),which extracted from AVHRR derived normalized difference vegetation index (NDVI) and brightness temperature data.These indices were often applied to monitor drought occurrence at a large scale or a regional level by comparing the indices' inter-annual changes for a special period of the covering years.On basis of the above drought monitoring results,an index called vegetation-temperature condition index (VTCI) was developed for drought monitoring in this study.The index can be used to monitor drought occurrence at a regional level for a special period (e.g.10 days) of a year,and to capture spatial variations of drought occurrences within the region.The new drought monitoring index is not only related to NDVI changes in a region,but also gives emphasis on land surface temperature changes of pixels which have the same NDVI value.The value of VTCI is from 0 to 1.The lower value of VTCI,the heavier the drought occurrence is.The index is site-specific and time-specific. A pilot study was carried out for drought monitoring for the last tenDays of March 2000 in the Guanzhong Plain area of Shanxi Province,China.The results showed that VTCI had betterFK(W15?40ZQ performances in classifying the relative drought occurrence levels and in studying the distribution of drought occurrences.There are different levels of drought occurrences in the Plain.The boundary between the Plain and Qingling Mountain,which is located in the south of the studied area,was clearly showed in the VTCI image.There was a strip area just to the north of this boundary with relatively heavy drought occurrence where VTCI values were less than 0.4.The other centralized heavy drought occurrence areas were the area at banks of the Yellow River valley,the area around Chengcheng county which is located in the Weibei tablelands,and the area to the north of Yangling city.The scattered drought occurrence pixels can also be found in the study area.In General,the monitoring results were accorded with soil surface (0~10 cm) moisture distribution which was simulated by using soil real thermal inertia model developed by the authors.For future development of the drought index,robust methods have to be found to enable estimation of the VTCI parameters for a long time series of data,and the index should be tested in more dryness areas.