After reading this article you will learn about the Climate of Arid Zone in India:- 1. Climatic Condition of Arid Zone 2. Climatic Elements of Arid Zone 3. Climatic Parameters 4. Eco-Climatic Features.
Climatic Condition of Arid Zone:
The term ‘Climate’ has been defined by World Meteorological Organisation (1966) as “fluctuating aggregate of atmospheric conditions characterised by the states and developments of the weather of given area.”
An arid climate is defined as one in which for the greater part of the year, precipitation is less than the potential evapotranspiration and meets less than one third of the annual water need (PE). Arid Zones are characterised by low and erratic rainfall distribution, high evaporation and extreme variation of diurnal and annual temperatures.
The two most important factors that lead to aridity are the low frequency of occurrence of adiabatic rise of large bodies of air and the remoteness of a region from an oceanic moisture source in the prevailing wind direction.
The natural vegetation in these regions consists of mainly xerophytes of short lived annuals having a high degree of drought resistance because of the environmental constraint viz., limited moisture availability.
According to Meigs (1953) classification, hot arid-zone climates occur mainly within the latitudinal limits of 10° and 40° in each hemisphere.
The arid zone climate is largely determined by the time course of tin- amount of and flow of water through them. In hot arid zones the decisive factor is cither distance from the sea or topographic barriers which prevent the moisture carried by the winds from the sea from reaching the areas in question.
Climatic Elements of Arid Zone:
The climate of arid zone is subject to great extremes. High temperature and low humidity during day may be followed by comparatively cold nights. Long periods of drought are broken by torrential rainfall and flooding. Although arid zone rainfall tends to be seasonal, it is most erratic and the total annual precipitation varies considerably form year to year.
The climatic elements are temperature, humidity, precipitation, wind, solar radiation from sun and sky, and the soil-moisture conditions are also extremely important, although they are more difficult to measure continuously.
Climatic Parameters of Arid Zone:
The arid zone is one place where you can stand outside during a rain and not get wet. In the dry hot arid zone the rain evaporates before it hits the ground. You may even be able to see rain falling in the sky and still not get wet.
Arid zone rainstorms are probably the most localized in the world. Rain may fall beside the road you are driving on, yet not a drop may strike your windshield, or you may be travelling a sunlit road and suddenly run into an area where rain is pouring.
The rainfall is the most important factor limiting crop production and sustenance of life at a stress less level. A significant feature of the distribution of rainfall over the Indian arid zone is that a major part of the rainfall is received during the southwest monsoon period June-September.
The contribution of this seasonal rainfall to annual rainfall is quite high (91-96 per cent) over whole of the Gujarat and the south and central parts of western Rajasthan regions.
North of this region the percentage contribution by SW monsoon reduces to 78 per cent in Punjab and 80 to 85 per cent in Haryana and northwest Rajasthan because of a small contribution (6 to 12 per cent) by winter rainfall to these regions under the influence of western disturbances.
In contrast, the percentage contribution of June to September rainfall to annual rainfall decreases in the Maharashtra (81 to 63 per cent) region.
It is lowest in Mysore and Andhra Pradesh (48-67 per cent) as these regions receive considerable rainfall (21-32 per cent) during the NE monsoon season also. Thus the duration of the monsoon season set in the first fortnight of June and withdraws in the second fortnight of November as compared to the arid regions in NW India where the monsoon sets in during the first fortnight of July and withdraws in the first fortnight of September.
Another interesting feature of the rainfall is the high coefficient of variability in the annual rainfall which often exceeds 50 per cent in NW Indian arid zone and is higher than 70 per cent in the extreme regions of western Rajasthan where the annual rainfall is very low.
It is the prime characteristic of the Indian arid zone. There are extreme variations in the diurnal and annual temperatures. During the winter season the N.W. arid regions experience very cold temperatures which range from -9°C to – 14°C in the cold arid zone, to 30°C to 10°C in the hot arid regions of Punjab, Haryana and Rajasthan.
Frosts often occur in the northwest Indian arid zone with the passing of western disturbances. Gujarat and Maharashtra on the other hand experience minimum temperatures of the range of 11 °C to 15°C, while Karnataka and Andhra Pradesh record 16°C to 18°C.
In the northern arid zone the lowest temperatures are recorded in January while in the southern arid zone the lowest temperatures are recorded in December. The temperatures begin to raise from March onwards over
the whole arid zone. The arid region in NW India records the highest day temperature, and May and June are the hottest months when mean temperatures are above 40°C.
However, on individual days temperatures of the order of 47 to 51 °C are also recorded in these regions when heat waves occur. The maximum temperatures recorded in the southern arid zone also range around 39°C to 41°C. While May happens to be month of highest temperature over the hot arid zone. In the cold arid zone highest temperatures arc recorded in the month of July.
iii. Soil Temperature:
The radiation energy available at the earth’s surface not only heats the air but penetrates into soil, and gives rise to fluctuations in the soil temperature, which it is essential to measure and consider in studies of the complete energy water balance at the earth’s surface.
iv. Wind Regime:
Strong hot winds, which are generally associated with sandstorms, are connected either with large-scale disturbances in the general circulation, or are of a local character.
The wind regime is strongest over the Gujarat region followed by western Rajasthan where mean wind speeds of more than 20 kmph are recorded during April, May, June and July months.
This period also coincides with the occurrence of dust storms (Andhi) over the northwest Indian arid zone. Mean wind regime however is weak over the Punjab and Haryana region varying from 2 to 10 kmph.
In the southern arid zone stronger wind regime (more than 18 kmph) prevails in the Anantapur, Kurnool regions of Andhra Pradesh and over Raichur region in Karnataka during the period June to August. The wind regime in general remains low (4 to 10 kmph) during the period October to April over major part of the southern arid zone.
In the cold arid zone mean wind speeds are very low varying from 3 to 7 kmph, being lowest in winter months and highest in the April to June period.
v. Solar Radiation:
The overall basic climatic element is the radiation received from the sun and sky (insolation) and the balance between the insolation which is absorbed by the earth, and the reflected and outgoing radiation from the earth. This net radiation governs the energy available for the origination of winds, for the dynamics of rainfall, for evaporation and other processes.
The low values of sunshine over the cold arid zone can he attributed lo the passing of many western disturbances over this region causing heavy i Winding. However during the summer season the pattern improves in northwest India.
The cold arid zone records less than 8 hours per day while the hot arid zone records 9 to 10 hours per day the highest being over Rajasthan, Gujarat and Maharashtra regions. After monsoon season the hours of bright sunshine decrease sharply to 4 to 5 hours per day in the southern arid zone and 4 to 7 hours per day in the northern arid zone respectively.
By October when the southwest monsoon had withdrawn over major part of the country the highest number of hours of sunshine (10 hrs/day) are recorded over western Rajasthan with a decreasing gradient southwards and are around 7-8 hours per day in the southern arid zone.
On an annual basis, the northern arid zone records slightly higher number of sunshine hours per day (more than 8 hrs/day) as compared to the southern arid zone (7-8 hrs/day).
vi. Potential Evapotranspiration:
Moisture losses from the ground and from vegetation, often referred to .is evapotranspiration, may be used as an important characteristic of i Innate, and are of great significance in semi-arid and arid regions.
In the hot arid zone in the NW India the annual potential evapotranspiration (PE) values increase from 130 cm in Punjab to 160 cm in Haryana and to over 200 cm in the Rajasthan. During May and June the PE values are the maximum varying from 18-20 cm in Punjab to and 22-23 cm in Haryana and 21 to 31 cm over Rajasthan.
The potential evapotranspiration (PE) varies from 1-2 cm during December and January to 10-14 cm during May to August in the cold arid zone. The annual PE in this region varies between 75-80 cm.
vii. Water Balance:
To most plants the essential factor for life is the availability of water to allow for transpiration. The study of the availability of water for plant growth calls therefore for a thorough knowledge of the annual fluctuations in the water balance, i.e., between income of water on the one hand (precipitation, dew, moisture carried to the region as groundwater), and loss of water (infiltration into the ground, run-off and moisture transfer from the ground and vegetation) on the other.
Eco-Climatic Features of Arid Zone:
Eco-climate over the arid zone is said to have been oscillating, within a broadly moisture deficit spectrum, over centuries especially from the post- glaciation to the present time.
Aridity in the Indian arid zone is mainly due to the acute shortage of precipitation to meet the water need over a major part of the year, the whole hot arid zone has magathermal regimes of climates indicative of suitable conditions for a forest type of vegetation. The mean annual thermal efficiency varies from 170 cm in NW Indian arid zone to 140 to 160 cm m the south Indian arid zone.
In the megathermal sections of the arid zone die summer concentrations are mesothermal in nature implying restricted development of forest type of vegetation. These features are of immense ecological significance as they influence profoundly the success of new introductions or thriving of exotic species of vegetation in these arid zones.