What are the agricultural drought indices?

Drought is a complex natural hazard that impacts ecosystems and society in many ways. According to the WMO and other litratures drought could be divided in four types, namely: (a) Meteorological drought resulted from a lack of precipitation, (b) Agricultural drought related to a shortage of available water for plant growth, and is assessed as insufficient soil moisture to replace evapotranspirative losses, in the other words, it refers to a period with declining soil moisture and consequent crop failure without any reference to surface water resources.(c) Hydrological drought is a broad term related to negative anomalies in surface and subsurface water. Examples are below-normal groundwater levels or water levels in lakes, declining wetland area, and decreased river discharge., and (d) The socio-economic drought which is associated to the failure of water resources systems to meet water demands.

Several drought indices have been created in recent decades. Commonly, a drought index is a unique variable for assessing the effect of a drought and defining different drought parameters, which include intensity, duration, severity and spatial extent. It should be noted that a drought variable should be able to quantify the drought for different time scales for which a long time series is essential.

A decline of soil moisture depends on several factors which affect meteorological and hydrological droughts along with differences between actual evapotranspiration and potential evapotranspiration. Several drought indices, based on a combination of precipitation, temperature and soil moisture, have been derived to study agricultural droughts.

If we can monitor agricultural drought indices in a perfect way, then we can get a proper decision in regards to the amount of yields, for the farmers and then we can prevent to further damages.

There are different indices that use in all over the world, for agricultural droughts. In DMAP (Drought Monitoring And Prediction) tool in Agrimetsoft, we are added three important of them, namely:

• ARI (Agricultural Rainfall Index), Nieuwolt, 1981
• SMDI (Soil Moisture Deficit Index), Narasimhan and Srinivasan, 2005
• ETDI (Evapotranspiration Deficit Index),Narasimhan and Srinivasan, 2005

Nieuwolt S, 1981. Agricultural droughts in Peninsular Malaysia. Malaysian Agricultural Research and Development Institute, Serdang, p: 16.

Narasimhan, B., and Srinivasan, R. 2005. Development and Evaluation of soil Moisture Deficit index and Evaporation Deficit Index for Agriculture of Drought Monitoring, Agricultural and Forest Meteorology, 133-69-88.