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If evapo-transpiration is high then more water vapor is taken up to the atmosphere and more condensation takes place resulting in more rainfall. But in the book The Environment of Pakistan by Huma Naz Sethi, she writes that high rate of evapo-transpiration is a consequence of ineffectiveness of rainfall.

I do not understand this. How does high evapo-transpiration contribute to less rainfall?

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    $\begingroup$ I don't understand what `ineffectiveness' is, when describing rainfall. Maybe that rainfall is scant, and never penetrates far into warm soil, so ET is high? I am guessing at the use of terminology. $\endgroup$ – cphlewis Apr 19 '15 at 4:53
  • $\begingroup$ I have the same question regarding 'ineffectiveness'; perhaps there is a translation problem. It sounds like she is saying the high evapotranspiration results from 'ineffective' rainfall, rather than causing 'ineffective' rainfall. Perhaps the issue is that evapotranspiration:rainfall ratio is high. $\endgroup$ – haresfur Apr 19 '15 at 23:09
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    $\begingroup$ Perhaps it is related to the concept of “effective precipitation” (or eff. rainfall), i.e. the amount of rainfall that is not “lost” to ET or runoff. In this case, high ET → low effective rainfall, which could be described as “ineffective rainfall”. $\endgroup$ – Florian Jenn Apr 20 '15 at 14:04
  • $\begingroup$ It's possible to look up parts of her book on line. It might help with a chapter and page so we could read what she's saying in context. Based on what you wrote, I'd agree with you. That makes no sense. $\endgroup$ – userLTK Apr 20 '15 at 16:35
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I just read the paragraph about the Effectiveness of Rainfall in UNIT.2 Climate of Pakistan, p. 30.

The author bring the topic of the rain being ineffective in a context where the rain is expected for crops and farming, or in other words, on the potential usefulness of the said rain for crops, which is quite low considering the climatic context in this area. I do not think the author is trying to explain the actual process of evapotranspiration for the area.

This is a summary of the factors bring by the author on why the current pluvial regime on Pakistan is not 'effective':

  1. Rainfall is mainly from monsoon. Monsoon rain is not regular (and therefore unreliable for planning long term with rain as an only source of water). For instance ,distribution, amount and timing varies.
  2. High temperatures during the monsoon season imply high potential evapotranspiration so a greater proportion of the rainfall is evaporated rather than infiltrated to be available for crop growth
  3. Rain when it occurs is quite intense, with often a low infiltration rate and flow away instead of recharging ground moisture
  4. Insufficient rain during winter to compensate

Therefore, irrigation and other means to store and distribute water should be used in the long term to efficiently use the water input, in regard with the potential use for water.

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  • $\begingroup$ Would `effective for agriculture' be a reasonable gloss? $\endgroup$ – cphlewis Apr 23 '15 at 23:41
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    $\begingroup$ To answer the original question directly, perhaps expand on 2. to say, "High temperatures during the monsoon season imply high potential evapotranspiration so a greater proportion of the rainfall is evaporated rather than infiltrated to be available for crop growth." Note although this is characterised by ET, the transpiration would be part of crop (or weed) growth but evaporation is 'lost'. $\endgroup$ – haresfur Apr 24 '15 at 1:52
  • $\begingroup$ @haresfur to the point, I added your input in the answer $\endgroup$ – Etienne Godin Apr 24 '15 at 13:17
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    $\begingroup$ @cphlewis yes I agree - because there is plenty of water from the monsoon - just that too much erode the soil and flow away for instance. 'Ineffective rainfall ' is a strange way to say it alone without context or in a purely physical sense, but taken in an agricultural context it makes much more sense IMO $\endgroup$ – Etienne Godin Apr 24 '15 at 13:23

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