7. Discuss how rainwater harvesting in semi-arid regions of Rajasthan is carried out.

Rainwater harvesting in semi-arid regions of Rajasthan is a crucial practice due to the region's scanty rainfall and high dependency on groundwater. Here's how it is typically carried out:

1. Rooftop Rainwater Harvesting: One of the most common methods is to capture rainwater from rooftops. Rainwater from rooftops is collected through gutters and directed towards storage tanks or underground reservoirs. This method is relatively simple and cost-effective.

2. Check Dams: Check dams are built across small streams or seasonal rivers to slow down the flow of water during the rainy season. This helps in recharging the groundwater aquifers and preventing soil erosion. These dams also create small reservoirs of water which can be used for irrigation and other purposes.

3. Percolation Ponds: Percolation ponds are constructed to allow rainwater to seep into the ground, replenishing groundwater levels. These ponds are designed with permeable bottoms and sides to facilitate the infiltration of water into the soil.

4. Subsurface Dykes: Subsurface dykes are barriers constructed underground to slow down the flow of water and allow it to percolate into the soil. These dykes help in recharging groundwater aquifers and reducing surface runoff.

5. Traditional Water Harvesting Structures: Rajasthan has a rich tradition of water harvesting structures such as 'talabs' (small ponds), 'beris' (step wells), and 'johads' (earthen dams). These structures are designed to capture rainwater and store it for future use. They also help in recharging groundwater and sustaining local ecosystems.

6. Percolation Tanks: Percolation tanks are constructed in natural depressions or low-lying areas to capture rainwater and allow it to percolate into the ground. These tanks help in recharging groundwater aquifers and improving soil moisture levels.

7. Artificial Recharge Wells: Artificial recharge wells are drilled into the ground to inject rainwater directly into aquifers. This method helps in replenishing groundwater levels and preventing the depletion of underground water resources.

8. Community-based Water Harvesting: In many semi-arid regions of Rajasthan, communities come together to implement water harvesting projects. This may involve the construction of check dams, percolation ponds, and other structures to capture rainwater and recharge groundwater.

Overall, rainwater harvesting plays a vital role in mitigating water scarcity in semi-arid regions of Rajasthan, providing a sustainable solution to meet the water needs of local communities and agriculture.