Drought Flashcards
a. “……………. is among the most devastating of natural hazards causing widespread human and animal deaths”
b. Since 1900 more than ……………… people have died as a consequence of drought and more than 2 billion have been affected by drought
c. drought denotes …………….. of water in a region
d. drought is a result of imbalance between soil moisture and …………………….. over a fairly long period
e ………………is indeed exacerbating drought in many parts of the world, increasing its frequency, severity and duration.
a. drought
b. 11 million
c. scaricity
d. evopo transpiration
e. drought
Aridity Vs. Drought
Aridity-Permanent feature
Culmination of many long- term processes
considers all climatic
features
Description of Climate
Drought
Temporary condition of scarcity of varying duration
Caused by deficient rainfall
Description of Water
availability
Definition of drought
An extended period of deficient rainfall compared to normal rainfall of the region.
American Meteorological Society defined drought as “a period of abnormally dry weather sufficiently prolonged for lack of water to cause a severe hydrological imbalance in the area affected”
Prolonged deficiencies of soil moisture adversely affect crop growth indicating
incidence of agricultural drought.
Classification of drought
duration-
Permanent drought :
characteristic of the desert climate
Seasonal drought :
This is found in climates with well defined rainy and dry seasons. Most of the arid and semiarid zones fall in this category
Contingent drought :
involves an abnormal failure of rainfall. It is usually brief, irregular and generally affects only a small area.
Criteria used
Meteorological drought
a condition where the annual precipitation is less than the normal over an area for prolonged period
Agricultural drought (Soil drought)
a period of dryness during the crop season, sufficiently prolonged to adversely affect the yield.
Is the result of soil moisture stress
Hydrological drought
is the prolonged meteorological drought
Drying up of the reservoirs and the tanks
time of occurrence
Early season drought:
It occurs due to delay in onset of monsoon or due to long dry spells after early
sowing
Mid season drought:
Occurs due to long gaps between two successive rains and stored moisture becoming insufficient during the long dry spell.
Late season drought:
Occurs due to early cessation of rainfall and crop water stress at maturity
stage.
using some specific terms
Relative drought:
The drought for one crop may not be a drought situation for another crop. This is due to mismatch between soil moisture condition and crop selection.
Physiological drought:
Refers to a condition where crops are unable to absorb water from soil even when water is available, due to the high osmotic pressure of soil solution, due to increased salt concentration, as in saline and alkaline soils.
It is not due to deficit of water supply.
Effect of drought on crop production
Crop-water relations
Photosynthesis
Anatomical changes
Metabolic reaction
Hormonal Relationships:
Nutrition
Growth and development
Yield
Crop Adaptations
mechanism for overcoming moisture stress
ability of crop to grow satisfactorily under water stress
Adaptation is structural or functional modification in plants to survive in a
particular environment.
adaptations to moisture stress
escaping drought
drought resistence- drought resistence-a. drought avoidance - conserving water
- improving water uptake
b. drought tolerance- mitigating stress
- high tolerance
Escaping Drought and avoiding stress
Escaping Drought
Evading the period of drought is the simplest means of adaptation of plants to dry
conditions.
Growing of the ephemerals right after the rainy season
Avoiding Stress
Stress avoidance is the ability to maintain a favourable water balance, and turgidity even when exposed to drought conditions, thereby avoiding stress and its consequences.
i) conserving water by restricting transpiration before or as soon as stress is experienced; or
ii) accelerating water uptake sufficiently so as to replenish the lost water.
Strategies for drought management
Adjusting the plant population
Conservation agriculture/tillage
Mid season corrections
a.Thinning b.Spraying water
Diversification of species
Mulching
Weed control
Water harvesting and life saving irrigation
Growing drought tolerant varieties
