"Scarce" means in short supply, making it the opposite of "abundant."
"Imminent" means something that is about to happen, so "approaching" is the synonym.
"Candid" means being open, honest, and straightforward in speech or expression.
"Deteriorate" means to worsen or decay over time, especially due to neglect or damage.
"Monotonous" means dull, repetitive, and lacking in variety, making it the best fit for this context.