RAINFALL PATTERN
The climate of Rajasthan state varies from arid to sub-humid. To the
west of the Aravalli range, the climate is characterised by low rainfall
with erratic distribution, extremes of diurnal and annual temperatures,
low humidity and high wind velocity. The climate is semi-arid to sub-humid
in the east of the Aravalli range, characterised by more or less the
same extremes in temperatures but relatively lower wind velocity and
high humidity with better rainfall. The entire state is characterised
by hyperthermic conditions.
The annual rainfall in the state varies significantly. The general
trend of Isohytes is from north-west to south-east. There is a very
rapid and marked decrease in rainfall west of the Aravalli range making
western Rajasthan the most arid part. The average annual rainfall in
this part ranges from less than 10 cm in north-west part of Jaisalmer
(lowest in the state), to 20 to 30 cm in Ganganagar, Bikaner and Barmer
regions, 30 to 40 cm in Nagaur, Jodhpur, Churu and Jalor regions and
more than 40 cm in Sikar, Jhunjhunun and Pali regions and along the
western fringes of the Aravalli range. On the eastern side of the Aravalli
range, the rainfall ranges from 55 cm in Ajmer to 102 cm in Jhalawar.
In plains, Banswara (92.0 cm) and Jhalawar (95 cm) districts receive
the maximum annual rain. Mount Abu (Sirohi district) in the south-west,
however, receives the highest rainfall in the state (163.8 cm). The
yearly total rainfall is highly variable at different places all over
the state and it is most erratic in the western half with frequent spells
of drought, punctuated occasionally by heavy downpour in some years,
associated with the passing low pressure systems over the region.
The southwest monsoon which has its beginning in the last week of June
in the eastern parts, may last till mid-September. Pre-monsoon showers
begin towards the middle of June and post-monsoon rains occasionally
occur in October. In the winter season also, there is sometimes, a
little rainfall associated with the passing western distribution over
the region. At most places, the highest normal monthly rainfall is
during July and August. The number of rainy days during this period
varies widely in different places, ranging from 10 in Jaisalmer to 40
in Jhalawar and 48 in MountAbu. Rainfall during the rest of the period
ranges from 2.1 cm at Jaisalmer to 7.2 cm at Jaipur, distributed over
2.5 to 6 rainy days.
