Irrigation Systems in India Decrease Monsoon Rainfall

india monsoon begins photo

Image credit: Shamih ( iZZo )/Flickr
Monsoon rainfall, researchers have found, is decreasing in parts of rural India where irrigation systems have been used to support agricultural production. At the same time, rainfall is increasing in heavily-developed urban areas.

Based on more than 50 years of rainfall data, a new study conducted at Purdue University has uncovered one possible reason for this shift that has serious implications for India, and the world.Dr. Dev Niyogi, associate professor of agronomy and earth and atmospheric sciences, explained:

In the rural areas, we're seeing premonsoon greening occurring two weeks earlier than what it did 20 years back as the demand for agricultural intensification to feed India's people increases...The landscape has also moved in some places from what was once a traditionally rural setting to large urban sprawls. Both of these phenomena have affected monsoon rains.

Initial investigations of the data indicated that monsoon rainfall had remained stable during the period of measurement. Closer inspection, however, revealed some regions, like the north western part of the country, experienced decreases in rainfall by as much as 40 percent of the historical mean. Analysis of the region's soil moisture showed that the ground became as much as 300% wetter immediately before the monsoon season, a result of more intensive agriculture.

This wetter soil cools the air in the region and dissolves the monsoon rain clouds. Dr. Niyogi explained that:

Unless this is checked and controlled, the problem is going to become more and more severe...with more irrigation, we will have less monsoon rain. With less monsoon rain, you will need more irrigation, and the cycle will continue.

At the same time, rainfall in urban areas, especially those experiencing rapid growth, has increased dramatically. Two theories are typically used to explain this phenomenon. One is that growing cities generate intense heat that fuels the convective forces of storms. The other theory is that pollution particles in cloud masses cause water vapor to condense at a faster rate, a process that releases heat and further fuels a storm.

Either way, the trend has implications that extend far beyond the cities of India. Dr. Niyogi explained that, "if urbanization is affecting the Indian monsoon season, it has the ability to affect patterns here in the United States...this likely isn't localized in India."

The study did not look at historical data from other countries and, Dr. Niyogi admits that it is likely India's hotter climate that is fueling this process. As global temperatures rise, however, he believes this trend could appear in even more temperate climates, like that of the United States, if it hasn't already.

Read more about climate change:
Floods, Monsoons, Heat Waves, Drought: Climate Change In Asia Now
Abrupt Climate Change Could Drag Monsoon Over the Ocean, Decreasing Vegetation Growth
20 Million People in Bangladesh Displaced by Rising Seas - But Less Land Than Previously Thought Lost

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