RAIN SHADOW EFFECT

1. Context

After the deficient monsoon last year, the Maharashtra government declared many parts of the State to be drought-hit. The impact of the deficiency manifested across the region this summer as wells ran dry and officials brought tankers to provide drinking water and water for irrigation. This situation is in sharp contrast with the State’s coastal areas, where rainfall has often been in excess, leading to severe flooding. Marathwada’s predicament is shaped by its location, topography, soil type, agricultural practices, and crop choices.

2. What is a Rain Shadow Effect?

A rain shadow region is an area that receives significantly less rainfall than the surrounding areas due to the presence of a mountain range that blocks prevailing winds. Here's how it works:

Moist Air Ascends: Moist air carried by winds approaches a mountain range.
Orographic Lift: As the air rises over the mountains, it cools and condenses, leading to precipitation on the windward side of the range.
Dry Air Descends: After releasing most of its moisture on the windward side, the now-dry air descends on the leeward side of the mountains.
Warming and Drying: As the air descends, it warms and its relative humidity decreases, resulting in much drier conditions.

Marathwada is situated in the rain shadow area of the Western Ghats. When moist winds from the Arabian Sea meet the mountains, they ascend and cool, leading to substantial rainfall (2,000-4,000 mm) on the western side. However, by the time these winds pass over the Ghats and descend into Western Maharashtra and Marathwada, they have lost most of their moisture, resulting in significantly drier conditions in Marathwada (600-800 mm)

Examples

This phenomenon creates a dry area known as a rain shadow on the leeward side of the mountain range. Examples of rain shadow regions include:

The eastern side of the Sierra Nevada range in California, which contributes to the arid conditions of the Great Basin.
The Atacama Desert in Chile, which lies in the rain shadow of the Andes mountains.
The eastern side of the Cascades in Washington state, which results in the dry conditions of the Columbia Plateau

3. How does the Rain Shadow effect affect Agricultural Crops?

The rain shadow effect can have a significant impact on agricultural crops due to its influence on local climate and precipitation patterns.

Here are several ways the rain shadow effect affects agriculture:

Areas in the rain shadow receive much less rainfall than the windward side of the mountain range. This limited water supply can make it challenging to grow crops that require consistent and substantial moisture
Farmers in rain shadow regions often rely more heavily on irrigation to provide water for their crops. This can increase production costs and place pressure on local water resources, especially in arid regions
The type of crops that can be grown in rain shadow regions is often restricted to those that are drought-resistant or require less water. Crops such as millet, sorghum, and certain legumes might be favoured over water-intensive crops like rice or sugarcane
The dry conditions in rain shadow regions can lead to poorer soil quality. Without adequate rainfall, soils may become dry and less fertile, requiring more soil management practices such as the use of fertilizers and organic matter to maintain productivity
The variability and often limited rainfall in rain shadow areas increase the risk of crop failure due to drought. This unpredictability can make farming more challenging and risky
The need for additional resources to manage water scarcity, such as irrigation infrastructure and soil amendments, can increase the cost of farming. This can impact the economic viability of agriculture in rain shadow regions, potentially leading to lower agricultural incomes and economic hardship for farmers

Marathwada Region

Marathwada's agricultural practices are ill-suited to its low rainfall levels. The region's water crisis is significantly exacerbated by the cultivation of sugarcane, a crop that requires 1,500-2,500 mm of water during its growing season.
While pulses and millets need irrigation only four or five times throughout their growth, sugarcane requires near-daily irrigation.
The area devoted to sugarcane steadily increased from the 1950s to the 2000s, leveling off in the past decade. Currently, sugarcane covers 4% of the region's cropped area but uses 61% of its irrigation water.
Consequently, the average river outflow in the upper Bhima basin has nearly halved. Government policies supporting sugarcane pricing and sales have promoted its irrigation, limiting the water available for more nutritious crops.
Since December 2023, the government has encouraged the production of ethanol from sugarcane juice, a potentially unwise decision for this water-scarce region, given that 82% of Maharashtra's sugarcane is grown in low-rainfall areas.
Despite the 1999 recommendation from the Maharashtra Water and Irrigation Commission to ban sugarcane cultivation in areas receiving less than 1,000 mm of rainfall annually, production has continued to rise

4. What Causes Rain Shadow Effect?

The rain shadow effect is caused by the following process:

When moist air masses, typically coming from large bodies of water like oceans or seas, move inland and encounter a mountain range, they are forced to rise due to the topography
As the air ascends the windward side of the mountains, it cools and expands due to the lower atmospheric pressure at higher altitudes. This cooling causes the moisture in the air to condense and form clouds, leading to precipitation on the windward side of the mountain range
The condensation and precipitation (rain or snow) occur primarily on the windward side, resulting in a wetter climate with substantial rainfall
After the air mass has lost much of its moisture on the windward side, it crosses over the mountain peak and begins to descend on the leeward side. As it descends, the air warms and its relative humidity decreases
The descending, warmer air on the leeward side creates much drier conditions because it no longer contains much moisture. This dry area is known as a rain shadow

5. Way Forward

In a low-rainfall region, managing water demand includes practising water-efficient irrigation, cultivating drought-resistant crops, and diversifying livelihoods. Marathwada must also shift to other high-value, low-water-using crops, while sugarcane production must move to Uttar Pradesh, Bihar, and West Bengal

For Prelims: Southwest Monsoons, El Nino, La Nina

For Mains: GSI, GS III-Rain Shadow effects on Agriculture and Crop Pattern

Previous Year Questions

1. Rain shadow effect is associated with (UPSC NDA 2015)

A.Cyclonic rainfall

B.Orographic rainfall

C.Convectional rainfall

D.Frontal rainfall

Answer (B)

The rain shadow effect is directly associated with orographic rainfall, which occurs when moist air is lifted over a mountain range, causing the air to cool and condense, leading to precipitation on the windward side and dry conditions on the leeward side

Source: The Hindu

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RAIN SHADOW EFFECT

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