Relationship between drought and solar irradiation variables

Drought prediction for in many regions of the world has critical importance for strategic planning agriculture and water management. The occurrence of droughts cannot be predicted with certainty and thus must be treated as random variables. It is the main purpose of this paper to develop a new concept of drought features assessments based on triple drought related hydrometeorological and meteorological variables, namely, rainfall, solar irradiation and sunshine duration. Equal standard rainfall lines are drawn as a map with two reference variables as solar irradiation and sunshine duration. These are referred to as the triple graphical method (TGM) approach. It furnishes rich features of drought behaviour variation based on the rainfall, solar irradiation and sunshine duration. This analysis and the solar irradiation estimation method are applied to seven climatologically different stations in the Republic of Turkey for the monthly data period 1982-1991. The linear relations between drought and the variables of the Angström equation are found between 55% and 94% without Trabzon. Drought and Angström equation parameters are estimated by the proposed methodology. Relations between monthly drought and Angström equation variables are presented by the triple solar-drought graphical method. TGM provides information about the drought occurrences for different combinations of solar irradiation and sunshine duration. TGM graphs help to identify not only precipitation surplus (wet spells) or deficits (dry spells droughts) but also their variations with two more meteorological variables as solar irradiation and sunshine duration.