CORE Aravalli Rain-Shadow Structure
The Aravalli rain-shadow effect on western Rajasthan is the structural starting point of the state's climate. The range runs broadly south-west to north-east, almost parallel to the Arabian Sea branch of the southwest monsoon, so it does not force a strong windward rise across most of Rajasthan. Moisture weakens as it moves inland from Gujarat and the western districts remain dry, while the south and south-east receive more rain through local relief and monsoon convergence. Jaisalmer, Barmer and Bikaner form the hot arid side; Udaipur, Banswara, Dungarpur, Kota and Jhalawar show the wetter edge. This is not a simple west-is-desert, east-is-humid rule. The Aravalli axis, dune fields, distance from sea and monsoon pulse timing all shape the gradient. The 50 cm isohyet broadly follows the Aravalli belt as a practical rainfall divide: west of it, annual rainfall commonly falls below 50 cm; east and south-east of it, 50-100 cm or more supports better moisture conditions. The effect also explains why Rajasthan's desert is not only a temperature phenomenon. Low rainfall, high evaporation, sparse vegetation and dust storms reinforce each other. A climate answer should connect Aravalli orientation with monsoon behaviour, rainfall gradient and Thar aridity. The same structure influences settlement and water storage: western villages rely on tanks, beris and deep groundwater, while the south-east can support denser vegetation and more seasonal streams. This is why irrigation, pasture and drought policy follow the climate map. These controls also explain why climate maps of Rajasthan should be read with physiography maps: dunes, rocky uplands, saline flats and river basins each respond differently to the same monsoon spell.