Minimal value of the hydrous deficit index estimate on the earth-atmosphere system in southern part of Chad

This paper proposes a method to estimate an index of the deficit of water in the system Earth-Atmosphere in the southern region of Chad under the condition of insufficient, even total absence of data traditionally used, i.e. the temperatures of the earth surface and air. This method is based only on the exploitation of the maximum and minimum temperatures of the air since these are the two parameters traditionally registered in almost all the meteorological stations of Chad. The maximum temperature of the air was assimilated to the temperature of the Earth surface. This enables us to compute the estimated minimal annual and monthly values of this index, the maximum values of the relative error generated by this assumption and at last we proceed to the modelling of the time variation of the annual composite of that index over the whole region. The analysis of these numerical characteristics shows that the obtained results are acceptable and lead us to the general conclusion that this method is to be improved for the operational work in the considered area and this improvement can be done as needed data will be progressively available.