Vergara - 1976 - Physiological and morphological adaptability of ri

(tRoP PLANNING mo RAINFImL 53
is also significant. The tracks followed by these low-pressure systems after
crossing the coast. and their intensity and frequency’. are of considerable importance
in determining the spatial rainfall pattern in any single season and its longterrn
variability. Success or failure of cropping patterns. both in irrigated and
rainfed agriculture. is thus closely linked with the rainfall pattern.
SPATIAL DISTRIBUTION OF RAINFALL AND CROPPING
PATTERNS
Where adequate rainfall data are available. it is useful as a first step to demarcate
the regions which are meteorologically homogeneous and to identify low rainfall
areas. to indicate broad cropping patterns. This procedure is illustrated for
the Telangana region ofAndhra Pradesh in India bounded by lat. l6-20° N and
long. 77-82°E.
The area was demarcated into four broad regions for crop planning. taking
into account (1) probabilities of dry spells for different districts of the region,
(2) normal tracks of storms for the different months during the rainy season.
and (3) the number of rainy days coupled with rainfall intensity’.
Drought characteristics
Studies on drought using the probabilities of dry spell runs showed that the
Telangana area as a tvhole is prone to drought conditions with a probability of
more than 60% dry days (rainfall less than4 mmlday") during the southwest
monsoon season (Banerji and Chabra, 1963). In the southern districts, i.e.
Mahbubnagar, lelyderabad, and Nalgonda. a dry spell running continuously" for
nearly a month can be expected to occur each season. In the central districts,
dry spells are rather random. It became clear that the nature of drought occurrence
is different in the north, central, and southern regions.
After the onset of monsoonal rains in June. preceded by a few premonsoon
thunderstorms. the area experiences frequent drought conditions in late July and
August. The rainfall again increases in September and October at the end of the
southwest monsoon season. (Jccasionallyi, storms crossing the east coast of India
south of 15° N during October and November bring intense showers. July has
the highest number of rainy day's in all the districts. The next highest number of
rainy days is observed in August. but the total amount of rainfall received is
lower than that in September. This is particularly characteristic of the southern
districts of the Telangana area.
Mean air temperatures in the region are of the order of 26—28°C and show
very little variation from district to district. Lowest minimum temperatures
recorded ranged from 3° C in the Adilabad area to 9°C in the Khannnameth
district.
Spatial distribution of rainfall
For delineating the area. the following maps were considered:
l. Rainfall patterns for each month of the rainy’ season from May to November.
based on averages of 5O years for 100 stations.