UPSC Prelims 2024 Q89: Red Sea Rainfall and River Inflow — Explained
Consider the following statements:
1. The Red Sea receives very little precipitation in any form.
2. No water enters the Red Sea from rivers.
Which of the statements given above is/are correct?
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Answer: (c) Both 1 and 2
Statement-wise explanation
- 1: correct — The Red Sea lies in the desert belt between north-east Africa and the Arabian Peninsula. Average rainfall over the sea and its coasts is only a few centimetres a year, commonly given as about 6 cm, and it falls in short showers. Evaporation is far higher, more than 200 cm (about 80 inches) a year, so the sea loses much more water to the air than it gets from the sky.
- 2: correct — No perennial river drains into the Red Sea. Britannica says plainly that no water enters the Red Sea from rivers. The coasts on both sides have only dry wadis, which flow briefly after rare storms. The water lost to evaporation is replaced by surface inflow from the Gulf of Aden through the Bab-el-Mandeb strait, not by rivers.
How to eliminate
This question can't really be solved by elimination. Neither statement uses a trap word like 'only' or 'always'. Both statements are absolute ('very little', 'no water'), and an aspirant who distrusts absolutes may wrongly drop statement 2. Basic map knowledge helps. The Red Sea is enclosed by the Sahara–Nubian and Arabian deserts, so very low rainfall is a safe call. Then ask which big river could reach it. The Nile flows north into the Mediterranean, not east into the Red Sea, and the Arabian side has no permanent rivers. The fact to remember: the Red Sea has no river inflow, gets scant rain and loses over 200 cm a year to evaporation. That is why it is one of the saltiest seas.
Know more
Why the Red Sea is so salty
The salinity of a sea depends on its water balance. Evaporation adds salt (it removes fresh water). Rainfall, river inflow and melting ice dilute it. Mixing with the open ocean evens it out.
The Red Sea is at the extreme end on every factor:
- Rainfall: only a few cm a year, because it lies in the subtropical desert belt.
- Rivers: none. Only ephemeral wadis.
- Evaporation: more than 200 cm a year, driven by heat and dry winds.
- Ocean link: narrow. It meets the Gulf of Aden only through the Bab-el-Mandeb strait (about 30 km wide). In the north, the Suez Canal adds little exchange.
The result is a salinity of about 36‰ in the south, near the Gulf of Aden, rising to about 41‰ in the north. The average open ocean is about 35‰. Exchange at Bab-el-Mandeb works in two layers. Less salty surface water flows in from the Gulf of Aden, and dense, salty water sinks and flows out at depth.
| Sea | Salinity vs ocean (~35‰) | Main reason |
|---|---|---|
| Red Sea | Much higher (36–41‰) | No rivers, scant rain, high evaporation, narrow outlet |
| Mediterranean Sea | Higher | Evaporation exceeds inflow; narrow Strait of Gibraltar |
| Arabian Sea | Higher than Bay of Bengal | High evaporation, little river input |
| Bay of Bengal | Lower | Large inflow from the Ganga–Brahmaputra and monsoon rain |
| Baltic Sea | Much lower | Many rivers, low evaporation, nearly enclosed |
Pattern for similar questions: enclosed seas in hot, dry belts are saltier than the ocean. Enclosed seas in cool, wet regions with many rivers are fresher.
In the news
The question itself is static. The Red Sea was in the news through late 2023 and early 2024, when Houthi attacks on merchant shipping near Bab-el-Mandeb disrupted a key India–Europe trade route. That probably made the sea's physical geography a timely topic.
NCERT Concepts to Revise
- Red Sea: Both statements are about this sea's climate setting and what feeds it water.
- Red Sea salinity: Rainfall and river inflow are two of the main controls on this sea's well-known salinity.
- Bab-el-Mandeb: This strait is the Red Sea's only natural link to the open ocean, which matters for where its water comes from.
- Gulf of Aden: The Red Sea exchanges water with the Gulf of Aden, so it matters when asking where the sea's water comes from.
- Salinity: Salinity is set by the balance of evaporation, precipitation and river inflow, the factors these statements test.
- Mediterranean Sea salinity: Another enclosed sea in a dry belt, useful for comparing how rainfall, rivers and evaporation shape seawater.