Karnataka monsoon rainfall is not simply increasing or decreasing; it is being redistributed across the state. A study by agrometeorologists from Bengaluru says coastal Karnataka and the western slopes of the Western Ghats have recorded a 10–15% decline in rainfall, while northern and southern interior districts have gained an additional 100–200 mm during the monsoon. The finding points to a changing relationship between climate, geography, agriculture and water management across Karnataka.
The study, led by Prof MB Rajegowda, former professor of agrometeorology at the University of Agricultural Sciences’ Gandhi Krishi Vigyan Kendra in Bengaluru, analysed rainfall data from 1901 to 2020 and projected rainfall patterns up to 2035. Its central conclusion is that warmer conditions are altering how moisture-laden monsoon clouds move across the Western Ghats. The result is a geographical shift in where rainfall is released, rather than a uniform change affecting every part of the state in the same way.
That distinction matters because Karnataka’s water and agricultural systems are organised around sharply different climatic zones. The coastal belt and the western slopes receive heavy rainfall as monsoon clouds arrive from the Arabian Sea, while the interior lies beyond the Ghats and traditionally receives less precipitation. If more rain crosses the mountain range and reaches the hinterland, the physical geography that has shaped cropping, irrigation and settlement patterns begins to operate under different conditions.
## Karnataka monsoon rainfall is becoming more uneven
The study reported that Karnataka’s average annual rainfall rose from 1,140 mm during 1900–1950 to 1,218 mm during 1980–2000, alongside an average temperature increase of 1.5 degrees Celsius. The increase in the state-wide average, however, masks a sharp regional divergence. According to the report, coastal and Western Ghats areas have lost rainfall while interior districts have gained substantially during the monsoon.
Prof Rajegowda attributed the change to uneven warming over land and in the atmosphere. The study says nearly 75% of clouds originating over the Indian Ocean and entering the western coast through the Arabian Sea release their moisture over the coastal belt and the western slopes of the Ghats. The remaining 25% cross the mountain range and travel towards the plains.
As temperatures rise, clouds blocked along the western slopes are reported to expand, lose density and rise higher. Subsequent cloud formations are then pushed towards the eastern side of the Ghats, allowing more rain-bearing clouds to reach interior Karnataka. The study also identifies cyclones and other climatic events as contributors to the increase and redistribution of rainfall.
This explanation places the Western Ghats at the centre of Karnataka’s changing rainfall geography. The range is not only a biodiversity landscape or a barrier between the coast and the interior; it also acts as a climatic trigger that determines where moisture is released. A change in atmospheric conditions around that barrier can therefore produce different outcomes for districts separated by relatively short distances.
The projected trend is not a return to a uniformly wetter Karnataka. The study’s models indicate that rainfall along the coast and western slopes will continue to decline in the coming decades, while interior Karnataka could receive more monsoon showers. The state’s average annual rainfall is projected to reach 1,235 mm between 2020 and 2035, compared with 1,218 mm during 1980–2020, according to the report.
The reported numbers suggest that the more important issue is distribution. A higher state average cannot by itself show whether farms, reservoirs, towns or ecosystems are receiving water when it is needed. Nor does an increase in monsoon rainfall automatically mean greater water security. The location, timing and intensity of rainfall determine whether water is stored, absorbed, used by crops or lost as runoff.
## The agricultural system is already changing
The rainfall shift is occurring alongside a major expansion of Karnataka’s agricultural and horticultural footprint. The study says the area under agriculture nearly doubled from 50–60 lakh hectares in the 1950s to 100–105 lakh hectares in 2020. Agricultural production rose from 40–50 million tonnes to 130–135 million tonnes over the same period.
Horticulture expanded as well. By 2020, the area under horticultural cultivation had reached 22–24 lakh hectares, while production touched 180–185 million tonnes, according to the study. These figures show that the state’s land-use and production systems have grown considerably during the period in which rainfall and temperature patterns were changing.
The evidence supplied does not establish a direct causal link between the rainfall redistribution and the entire expansion in agricultural or horticultural production. It does, however, place both trends next to each other. More cultivation and changing rainfall create a planning problem: districts may need to manage a different mix of water availability, crop demand and climatic exposure than the one for which existing systems were designed.
Interior districts receiving additional monsoon rainfall could benefit from improved water availability in some years, particularly for rain-fed agriculture. But the study does not say that the rainfall will be evenly spread across the season or that all crops and locations will benefit equally. A change in the seasonal pattern can create new risks even when the total rainfall increases.
The coastal and Western Ghats districts face a different challenge. A reported 10–15% decline in annual rainfall could affect areas that have historically depended on high precipitation, even though the study does not quantify the consequences for rivers, reservoirs, groundwater, forests or settlements. The same geography that once concentrated rainfall along the western slopes may no longer deliver water at the earlier level.
## The policy question is larger than the forecast
The findings also enter an existing policy debate over the Western Ghats. Prof Rajegowda said there was no need to implement the recommendations of the Gadgil and Kasturirangan committees exactly as proposed or make them binding, particularly when the regions examined by those committees were experiencing a gradual decline in rainfall. That is a position attributed to the study’s lead researcher, not an established policy decision.
The rainfall analysis does not, on its own, settle the questions raised by the two committees. Those debates involve ecological protection, land use, development controls and the institutional management of a sensitive mountain system. The study does show why rainfall cannot be treated as a fixed background condition in that debate. Climate patterns are changing across the same landscape where development and conservation decisions are being contested.
For Karnataka’s administration, the institutional challenge is to connect climate evidence with decisions that are usually handled separately. Agriculture departments monitor crops, water agencies manage storage and supply, disaster authorities respond to extreme events, and local governments deal with drainage, roads and settlement-level impacts. The supplied study does not assess the performance of these institutions, but its findings indicate that a state-wide rainfall average is insufficient for district-level planning.
The urban implications are indirect but important. Interior towns and cities depend on surrounding catchments, reservoirs, groundwater and agricultural regions for water and livelihoods. Coastal settlements face the opposite possibility of declining rainfall in a landscape historically associated with abundant precipitation. The report does not provide city-level projections or establish specific consequences for Bengaluru or other urban centres. It does, however, underline the need to understand urban water systems as part of a wider regional climate geography.
That regional perspective is especially relevant because Karnataka’s agricultural area and production have expanded while the distribution of rainfall has shifted. More cultivation can increase demand for storage, irrigation and transport infrastructure. At the same time, changing rainfall across the Ghats can alter the assumptions behind reservoir operations, watershed management and local water planning. The study’s evidence supports the need for closer examination of those links, without establishing how individual projects or districts will be affected.
The strongest conclusion from the report is therefore not that one part of Karnataka will simply gain while another loses. It is that a warmer climate is changing the state’s internal rainfall map. The projected rise in average annual rainfall to 1,235 mm between 2020 and 2035 may appear reassuring when viewed as a single number, but the reported decline in the west and increase in the interior reveal a more complex picture.
What remains uncertain from the supplied material is how rainfall will be distributed within seasons, how intense individual events will become, and how the changes will affect groundwater, reservoirs, forests, crops and urban water supplies. Those questions will determine whether additional rainfall becomes a resource or a source of new exposure. For policymakers, the next task is not merely to track how much rain Karnataka receives, but where it falls, when it arrives and which institutions are prepared to manage the change.
