<p>Evaporation is neither a sufficient nor necessary conditions for rainfall to occur over a certain region.</p>
<p>First of all, due to moisture being &quot;moved around&quot; by atmospheric motions, even when rainfall does occur, nothing guarantees you that the droplets falling in that area are made by moisture that was evaporated from the same area. There are many old studies (Budyko) quantifying the ratio of &quot;moisture recycling&quot; and, in general, one can see that the majority of moisture causing rainfall is advected from other areas which could be hundreds (if not thousands) of kilometers away.</p>
<p>Second, and most importantly, as someone already said in the comments, evaporation contributes locally to increase the concentration of water vapour in the atmosphere. However, for rainfall to occur you need many different conditions to be satisfied. There are many dynamical or thermodynamical processes that lead to condensation of water vapour into suspended droplets (clouds) which can then grow and form rainfall. Adding water vapour to the atmosphere locally has a negligible effect in most cases, as it can only change the atmospheric profile close to the surface.</p>
<p>The question still touches an interesting subject, because there are many studies looking at soil moisture-precipitation interaction which suggest that, in some limited cases, more evaporation could lead, in cases where rainfall is triggered by some external factors, to higher rainfall totals. In other words, a wetter soil could lead to more rainfall than a dry soil. However, this only happens in small to nonexistent synoptic forcing, so it is something that you almost never observe in reality. In fact, as soon as you have some wetter/drier patch, mesoscale circulations similar to land-sea breezes form and advect the moist air somewhere else.</p>

CC BY-SA 4.0
2024-02-01T10:42:58.303Z
2024-02-01T10:42:58.303Z
Droid
<p>I've learnt that water evaporates from the Earth's surface into the atmosphere. However, during hot/dry seasons, evaporation and transpiration occurs continuously without any sign of rainfall. What causes the absence of rainfall during dry seasons?</p>

CC BY-SA 4.0
2023-12-14T06:14:00.940Z
Rainfall is not caused by evaporation. Evaporation causes an increase in water vapor in the atmosphere.  Rainfall is caused by cloud formation followed by cooling temperatures, pressure changes, and/or elevated terrain.  I've edited your question a little to address the inaccuracy.
f.thorpe
<atmosphere><precipitation>
What causes the absence of rainfall during dry seasons?
Appiah Biney Kelvin
# What causes the absence of rainfall during dry seasons?

(Asked by: username_0 on 2023-12-13)

I've learnt that water evaporates from the Earth's surface into the atmosphere. However, during hot/dry seasons, evaporation and transpiration occurs continuously without any sign of rainfall. What causes the absence of rainfall during dry seasons?

**Tags:** atmosphere, precipitation

> **Comments:**
> **username_1**: Rainfall is not caused by evaporation. Evaporation causes an increase in water vapor in the atmosphere.  Rainfall is caused by cloud formation followed by cooling temperatures, pressure changes, and/or elevated terrain.  I've edited your question a little to address the inaccuracy.  

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## 1 answers

### Answer by username_2 on 2024-02-01. Score: 1

Evaporation is neither a sufficient nor necessary conditions for rainfall to occur over a certain region.

First of all, due to moisture being "moved around" by atmospheric motions, even when rainfall does occur, nothing guarantees you that the droplets falling in that area are made by moisture that was evaporated from the same area. There are many old studies (Budyko) quantifying the ratio of "moisture recycling" and, in general, one can see that the majority of moisture causing rainfall is advected from other areas which could be hundreds (if not thousands) of kilometers away.

Second, and most importantly, as someone already said in the comments, evaporation contributes locally to increase the concentration of water vapour in the atmosphere. However, for rainfall to occur you need many different conditions to be satisfied. There are many dynamical or thermodynamical processes that lead to condensation of water vapour into suspended droplets (clouds) which can then grow and form rainfall. Adding water vapour to the atmosphere locally has a negligible effect in most cases, as it can only change the atmospheric profile close to the surface.

The question still touches an interesting subject, because there are many studies looking at soil moisture-precipitation interaction which suggest that, in some limited cases, more evaporation could lead, in cases where rainfall is triggered by some external factors, to higher rainfall totals. In other words, a wetter soil could lead to more rainfall than a dry soil. However, this only happens in small to nonexistent synoptic forcing, so it is something that you almost never observe in reality. In fact, as soon as you have some wetter/drier patch, mesoscale circulations similar to land-sea breezes form and advect the moist air somewhere else.


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