What is drought?
THE HANS INDIA |
Jul 15,2017 , 03:36 AM IST
Drought is the consequence of a natural reduction in the amount of precipitation over an extended period of time, usually a season or more in length, often associated with other climatic factors (viz. high temperatures, high winds and low relative humidity) that can aggravate the severity of the drought event. Different types of drought are: Meteorological Drought; Hydrological Drought; Agricultural Drought; and Socio-Economic Drought.
In India, according to India Meteorological Department, meteorological drought over an area is defined as a situation when the seasonal rainfall received over the area is less than75% of its long term average value. It is further classified as "moderate drought" if the rainfall deficit is between 26-50% and "severe drought" when the deficit exceeds 50% of the normal.
Hydrological Drought can be defined as a period during which the stream flows are inadequate to supply established use of water under a given water management system. Agricultural Drought occurs when available soil moisture is inadequate for healthy crop growth and cause extreme stress and wilting.
Abnormal water shortage affects all aspects of established economy of a region. This in turn adversely affects the social fabric of the society creating unemployment, migration, discontent and various other problems in the society. Thus, meteorological, hydrological and agricultural drought often lead to what is termed as Socio-economic drought.‘
In our country, a year is considered to be a Drought Year in case the area affected by moderate and severe drought, either individually or together, is 20-40% of the total area of the country and seasonal rainfall deficiency during south-west monsoon season for the country as a whole is at least 10% or more.
IMD has developed aridity indices to monitor agricultural drought scenario in the country based on rainfall, potential evapotranspiration and actual evapotranspiration using water budgeting method. Agricultural droughts have been classified into mild, moderate and severe based on aridity anomaly index values.
Mild (Aridity anomaly 1 – 25%), Moderate (Aridity anomaly 26 – 50%) and Severe ((Aridity anomalies more than 50%) Factors aggravating drought include: Lower Soil Moisture Retention; shortage of farm inputs; lack of resources including credit on reasonable terms; non-availability of alternate seeds; short supply of electric power and diesel oil for ground water pumpsets; and poor or non-existent medical help for the needy. (Source: http://imd.gov.in/section/nhac/wxfaq.pdf)