Dry climates and their classification- objectives and
activities of CRIDA
2.1 Indices of Aridity
Aridity refers to a condition of deficiency of water due to either insufficient
precipitation or excess water loss over supply. The term “arid” is derived from a
Latin word, “arere” which means ‘dry’.
Assessment of the degree of aridity of a place is necessary to serve as a base
for the application of technology, for the interpretation of resource assessment and
for transfer of technology. It also useful to analyse the climatic resources and to
identify specific climatic constraints for planning agricultural development.
The degree of aridity can be assessed from climatic parameters and plant
criteria. More than 50 classifications of agro-climate was made by many scientists.
Some of the important classifications are discussed below.
2.2 Classification of dry climates
2.2.1 Thornthwaite and Mather (1955)
They have taken the Moisture Index (Im) as the criteria for classification of dry
climates
Im = [(P-PE)/PE] 100
where, P = Precipitation, PE = Potential Evapo-transpiration
Im Quantity Climate classification
100 and above Per humid
20 to 100 Humid
0 to 20 Moist sub humid
-33.3 to 0 Dry sub humid
-66.7 to -33.3 Semi arid
-100 to -66.7 Arid
2.2.2 Troll (1965)
Based on thermal and hygric variables and number of humid months, climate
is classified and said to be of agricultural use. Humid month is one having mean
rainfall exceeding the mean potential evapotranspiration.ICRISAT classified the
Semi-arid tropics (SAT areas) in India by adopting this classification. According to
this classification, a climate which has 5 to 10 arid months(a month where
precipitation is less than PET) or 2 to 7 humid months is called semi arid tract (SAT ),
where as humid climate will have 7 to 12 humid months and arid climate has less
than 2 humid months.
Humid months Climate classification
12.0 to 9.5 Tropical rainforest
9.5 to 7.0 Humid Savannah
7.0 to 4.5 Dry Savannah (Wet – dry SAT)
4.5 to 2.0 Thorn Savannah (Dry SAT)
2.0 to 1.0 Semi desert (Arid)
1.0 to 0.0 Desert (Arid)
2.2.3. Papadakis (1961)
Moisture Index (H) based on precipitation, soil moisture storage and PET was
developed.
H = [P + W] / E
where,
P = Monthly precipitation
E = Monthly PET
W = Water stored from previous rainfall
H value Climate
Less than 0.25 Arid
0.25 to 0.50 Dry
0.50 to 0.75 Intermediate
0.75 to 1.00 Intermediate humid
1.00 to 2.00 Humid
More than 2.00 Wet
2.2.4 Hargreaves (1971)
Moisture Availability Index (MAI) is used for the classification. It is the ratio of
dependable precipitation to potential evapotranspiration. It is a measure of adequacy
of precipitation in supplying crop water demand.
MAI =
Potential evapo transpiration
Depandableprecipitation(75%probable rainfall)
MAI Climate classification
0.0 to 0.33 during all months Very arid
More than 0.34 for 1-2 months Arid
More than 0.34 for 3-4 consecutive months Semi arid
2.2.5 Steiner et al., (1988)
After careful consideration of several definitions, Steiner et al. (1988)
consider aridity index concept of the United Nations Conference on Desertification
based on the balance between precipitation (P) and evapotranspiration (ETP) to be
appropriate for wide scale adoption. According to this definition the areas with
P/ETP ratio between 0.03 and 0.20 are arid and areas with the ratio between 0.2 and
0.5 are semi-arid.
2.2.6 FAO classification
This classification is based on ‘growing period concept’ of the FAO. Areas
having a growing period between 1 and 74 days are classified as arid and those with
a growing period between 75 and 119 days are semiarid. (Growing period is the
number of days during a year when precipitation exceeds half the potential
evapotranspiration, plus a period to use an assumed 100 mm of water from excess
precipitation (or less, if not available) stored in the soil profile).
2.2.7 ICAR classification of agro- climatic zones
ICAR while establishing the dryland centers in different agro -climatic zones
of the country in 1970, used the simple formula of Thornthwaite (1955) for
estimating the moisture index.
Moisture Index = 100 [(P-PE)/PE]
Thornthwaite and Mather (1955) gave only six classifications while the ICAR
(Krishnan and Mukhtar Singh (1968) had eight moisture indices with eight moisture
belts indicating eight zones in India. The scale adopted in defining climatic zones in
terms of moisture indices are
Zone Moisture Index Moisture belt
1 < -80 Extremely dry
2 -60 to -80 Semi dry
3 -40 to -60 Dry
4 -20 to -40 Slightly dry
5 0 to -20 Slightly moist
6 0 to +50 Moist
7 +50 to +100 Wet
8 > +100 Extremely wet
All India coordinated Research Project on dryland Agriculture of ICAR has
divided climate into three types based on moisture deficit index (MDI)
MDI = [(P-PET)/PET]
where, PET is estimated based on temperature as PET= 2T where T is average
temperature in °C .
Climate MDI
Sub humid 0 to 33.3
Semi arid – 33.3 to 66.6
Arid > – 66.6
2.3Arid and semi arid zones
a) Arid regions: The arid zones will have moisture index between –66.7 to –100.
Precipitation is less than potential evaporation for the grater part of the year. Arable
crop production is not possible without irrigation. Growing period is between 1 to 74
days.
b) Semi arid zones: They have moisture index values between –33.3 to –66.7. Crop
production is possibly by adopting moisture conservation practices. Growing period
is between 75 to 119 days.
A semi arid climate is essentially a mixed climate in which a fairly moist or
rainy season alternates with a completely dry season. Hence, the climate is described
as alternating wet and dry climate. Rainfall occurs during 2 to 7 months of the year.
When number of wet months is 2.0 to 4.5, it is described as dry SAT and when rainy
months ranges from 4.5 to 7.0 it is called as wet SAT. Rainfall quantity ranges from
400 to 750 mm per year, with a variability of 20 to 30%. But, the onset, closure and
duration of rainy season exhibits wide variability between years. Distribution of
rainfall within the season also exhibits wide fluctuations between years. Mean annual
temperature is more than 18 °C.
Arid and Semi arid regions of India
Total area under arid and semiarid regions in India extends over 135.8 million
hectares
Climate Area (m ha) Regions
Arid Tropics 31.7 Rajasthan, Gujarat, Punjab, Haryana, Parts of
Karnataka and Andhra
Arid Temperate 7.0 Jammu and Kashmir
Semiarid Tropics 95.7 Maharastra, Karnataka, Andhra, Rajasthan,
Tamilnadu, Gujarat, Punjab, Haryana, Uttar
Pradesh, Madhya Pradesh
Semiarid
Temperate
1.4 Jammu and Kashmir
Temperature in arid and semiarid temperate region is maximum at 32°C in
July and minimum at -14°C in January – February. Temperature in arid and semiarid
tropics is maximum at 40-42°C in May and minimum varies from 3-5°C in Punjab and
Haryana and 18-24°C in Tamilnadu.
Distribution of arid and Semi arid regions of India
Arid Semiarid
State
Area (Sq km)
Per cent to
total area in
India
Area
(Sq km)
Per cent to
total area in
India
A. Tropics
Rajasthan 196150 61 121020 13
Gujarat 62180 20 90520 9
Punjab 14510 5 31770 3
Haryana 12840 4 26880 3
Uttar Pradesh – – 64230 7
Madhya Pradesh – – 59470 6
Maharastra 1290 0.4 189580 19
Karnataka 8570 3 139360 15
Andhra Pradesh 21550 7 138670 15
Tamilnadu – – 95250 10
All India 317090 – 956750 –
B. Temperate
Jammu & Kashmir 70300 – 13780 –
The words “Arid” and “Semiarid” must be understood differentially from dry
farming. All the dry farming areas are located in arid and semi arid regions only. But
not all the arid and semiarid regions come under dry farming areas. When irrigation
facilities are available, irrigated farming is practiced extensively in arid and semiarid
regions also. Eg. Punjab, Haryana.
2.3 Progress of dryland Agricultural Research in India
Though dryland farming is as old as agriculture, the systematic research work
was started only from 1923 with the start of Research Centre at Manjri near Pune, in
Bombay province by V.A. Tamhane. Later Imperial Council of Agricultural Research
(presently Indian Council Agricultural Research) started research schemes at
Bombay, Madras, Hyderabad and Punjab provinces. Around 1933, systematic work
was started on different aspects of crop production under rainfed conditions. The
findings of the period were related to rainfall analysis. It was found that rainfall was
not only scarce but also erratic. The dry spells during the crop period ranged from 20
to 55 days. Therefore, the emphasis on research was given to conserve soil moisture
and to reduce evaporation. Based on the studies conducted between 1933 and 1943,
package was developed for better crop production under rainfed conditions. The
important practices are:
1. Formation of contour bunds.
2. Repeated harrowing in black soils to conserve moisture.
3. Addition of farm yard manure to maintain the soil fertility.
4. Wider spacing for crops grown on residual moisture.
The package of practices were named after the province from which they
were developed as Bombay dry farming practices, Madras dry farming practices,
Hyderabad dry farming practices and Punjab dry farming practices. The adoption of
these practices was low due to marginal increase in yield. Government programmes
mainly concentrated on contour bunding which provided employment during
drought periods. During 1954, the soil conservation training and demonstration
centres were established by Indian Council of Agriculture Research at eight locations.
These centres concentrated on soil conservation techniques and training of officers
on soil conservation, while crop production received low importance. During 1970,
ICAR started All India Coordinated Research Project on Dryland Agriculture at 23
locations spread all over India. Under the scheme, an integrated approach was
adopted to solve the problems of dryland agriculture, by including the disciplines of
agronomy, soil science, plant breeding and agricultural engineering. The important
practices developed under the scheme are contingent cropping, efficient crops and
cropping systems, water harvesting and supplemental irrigation, drought resistant
varieties, fertilizer recommendation and agricultural implements. Watershed
approach was fallowed to popularise these technology by including soil conservation
practices with improved dryland practices, alternate crops and other ancillary
enterprises. In 1983, 47 model watersheds were developed. Based on the success of
this approach in increasing the productivity of drylands, the national watershed
development programme for dryland agriculture was started through out the
country.
The chronology of events in dryland agricultural research in India is as
follows.
1920 Scarcity tract development given importance by the Royal Commission on
Agriculture
1923 Establishing Dryland Research Station at Manjri (Pune) by Tamhane
1933 Research Stations established at Bijapur and Solapur
1934 Research Stations established at Hagari and Raichur
1935 Research Station established at Rohtak (Punjab)
1942 Bombay Land Development act passed
1944 Monograph on dry farming in India by N.V. Kanitkar (Bombay, Hyderabad,
Madras Dry Farming Practices)
1953 Establishing Central Soil Conservation Board
1954 Establishing Central Soil Conservation Centres
1970 Research Centres established under AICRPDA in 23 locations
1972 Establishment of ICRISAT
1976 Establishment of Dryland Operational Research Projects
1983 Starting of 47 model watersheds under ICAR
1984 Initiation of World Bank assisted Watershed Development Programmes in
four states. Establishing Dryland Development Board in Karnataka
1985 Birth of Central Research Institute for Dryland Agriculture at Hyderabad
1986 Launching of NWDPRA programmes by Government of India in 15 states.
Recognizing the importance of rainfed agriculture, the ICAR gave a new
impetus by launching the All India Coordinated Research Project for Dryland
Agriculture (AICRPDA) in 1970, based at Hyderabad with 23 cooperating centres
spread across the country. Pooling of expertise and leveraging the strengths of
AICRPDA net work eventually resulted in the establishment of Central Research
Institute for Dryland Agriculture (CRIDA) at Hyderabad, on April 12, 1985 to provide
leadership in basic strategic research in dryland agriculture while continuing
research on location specific ORP‘ s at AICRPDA centres. At present the AICRPDA
centres are located at 25 places.
Mandate/objectives of CRIDA
a) To conduct basic and applied researches that will contribute to the
development strategies for sustainable faming systems in the rainfed areas.
b) To conduct basic and applied researches that will contribute to the
development strategies for sustainable faming systems in the rainfed areas.
c) To act as a repository of information on rainfed agriculture in the country
d) To provide leadership and co ordinate network with state agricultural
universities for generating location specific technologies for rainfed areas
e) To act as a centre for training in research methodologies in the fields basic to
management of rainfed farming systems
f) To collaborate with relevant national and international agencies in achieving
the above objectives , and
g) To provide consultancy