Diminuire vs. calare
The Italian words 'diminuire' and 'calare' both mean 'to decrease' or 'to become smaller', but they have subtle differences in usage and connotation.
Diminuire
'Diminuire' is a more general term for decrease and is often used in formal or technical contexts. It implies a gradual reduction in size, quantity, or intensity.
I prezzi del petrolio stanno diminuendo.
(Oil prices are decreasing.)
La popolazione di api sta diminuendo a causa dei pesticidi.
(The bee population is decreasing due to pesticides.)
Il rumore del traffico diminuisce durante la notte.
(Traffic noise diminishes during the night.)
Calare
'Calare' often implies a more noticeable or rapid decrease. It can also suggest a downward movement or lowering, and is sometimes used in more colloquial contexts.
La temperatura calerà bruscamente questa sera.
(The temperature will drop sharply this evening.)
Il sole cala all'orizzonte.
(The sun is setting on the horizon.)
Le vendite sono calate del 20% questo mese.
(Sales have dropped by 20% this month.)
Summary
While both 'diminuire' and 'calare' mean 'to decrease', 'diminuire' is more general and often used in formal contexts for gradual reductions, whereas 'calare' implies a more noticeable decrease or downward movement and can be more colloquial. Choose 'diminuire' for general decreases and 'calare' for more dramatic or visible reductions.