Agricultural Drought Indices Definition and Analysis

An agricultural drought is considered to have set in when the soil moisture availability to plants has dropped to such a level that it adversely affects the crop yield and hence agricultural profitability. In brief, the definition of agricultural drought is concerned with the soil moisture deficiency in relation to meteorological droughts and climatic factors and their impacts on agricultural production and economic profitability. A soil water time series provides the framework for evaluating agricultural drought parameters. Soil moisture measurements are generally not available as time series. Hence drought could be better studied by means of a regional analysis involving a set of variables associated with the crop water consumption process, but the interactions are very complex. Consequently, an effort must be made toward an objective definition of agricultural drought and its related indices. In the present paper an attempt is made to give a simple interpretation of some traditional agriculraral drought indices and to define the functional relationship between crop yield and soil moisture deficit. This relationship can be used to identify the critical soil moisture deficit (related to the critical crop yield level) which leads to an unsatisfactory agricultural profitability. So conditions of real agricultural drought or aridity are present.