The development of the universal combined index of the drought and humidity of the soil

The drought as natural phenomenon is the con-sequence of the lack of rainfall and water supply of lands. The existing indexes of the drought charac-terize quantitative assessment of dryness degree of lands by use of the data on rainfall and evapotran-spiration. However, the majority of spectral object indexes do not possess the property of interactivity, i.e. in they don’t have special operated parameter at which the change of condition of the studied ob-ject could be determined by change of value of the index. In present study the questions of develop-ment of rather simple universal index of the drought of humidity of the soil possessing interactive prop-erty are considered. According to the results of pilot studies of dynamics of temporary change of NDVI and LST, the nature of correlation communication between NDVI and LST undergoes high-quality change upon the transition from damp condition of the soil to the condition of the drought. If water is the limiting factor determining the growth of plants which is typical for low latitudes and the middle of the season of growth of plants, the correlation be-tween LST and NDVI is negative. However, if the limiting factor of growth of plants is solar energy typical for high latitudes and the beginning of a season of growth of plants, the correlation between LST and NDVI is positive. The considered index is formulated as scalar convolution of NDVI and LST with rated weight coefficients α1 and α2. Offered way of increase of reliability of application of the TCIM index in zones of negative correlation be-tween LST and NDVI is the following. If the varia-tion α1 is followed by corresponding change of the extremum of considered index that the judgment about the presence of the limiting development of vegetation of moisture factor is taken out. If the var-iation α1 does not lead to the change of size of the extremum of considered index, the judgment about the lack of moisture is taken out, i.e. solar energy appears the limiting factor in this case.