| Daily land surface temperatures (LST) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data were analyzed to determine how the data were correlated with climatic water balance variables and NDVI anomalies during a growing season 2000 in western and central Kansas. Based on surface energy balance climatology, LST should respond to drying conditions well before plant response. To test this hypothesis, four daily water budget factors, percent soil moisture (SM), actual/potential evapotranspiration ratio (AE/PE), moisture deficit (MD), and moisture deficit/potential evapotranspiration ratio (MD/PE), were calculated. These variables were expected to have significant correlations with LST deviation from air temperature.; To perform correlation analyses on a weekly basis, daily MODIS data were integrated into three different types of weekly composites, including aggregations based on maximum observed LST, the driest day since last rainfall, and a combination of maximum temperature and the driest day. Results showed that the maximum-temperature composite had the highest, and the driest-day composite had the lowest, correlation with the climatic water budget parameters. Time-integrated, or cumulative values of the LST deviation showed even stronger relationships with the water budget factors, increasing the correlation coefficients by 33.4% on average.; To rescale the temperature signals from 0 to 1, the Standardized Thermal Index (STI) is proposed in this study. The STI, based on cumulative surface temperatures standardized with observed mean air temperatures, had significant temporal relationships with the hydroclimatological factors. STI classes in all the composite periods also had a strong correlation with NDVI declines during the drought episode. Results showed that, based on LST, air temperature observations, and water budget analysis, NDVI declines below a normal could be predicted as early as 8 weeks in advance in this study area.; Finally, the STASTGO database was used within a GIS environment to determine the influences of hydrologic soil properties on soil moisture and thermal emission. Two important variables, water-holding capacity (WHC) and hydrologic soil group (HSG), were evaluated in water budget experiments to determine their impacts on changes in soil moisture content (SMC). Results showed that HSG affected SMC changes very little, but that WHC variations explained most local variations of SMC. As a strong indicator of relative soil moisture deficit (MD/PE), the Standardized Thermal Index (STI) patterns were also influenced by WHC. Generally, the earlier SMC drops below WHC 40%, the earlier the STI reached the threshold value of 0.2. |
