Interesting concept Feldeinsamkeit. Thirst does somewhat coincide to a certain extent with the quality/quantity of birds in a country.
"I'd like to suggest a metric on a scale of 1-10 (with 1 being thirstiest, 10 the least)" - I do understand that but I think it's more straight-forward, intuitive and simple for the the more thirsty = higher score, and the less thirsty = lower score. Everyone recognises thirst as a negative aspect, so if a place is more thirsty than it should have a higher score on the thirstometer.
"I'd like to suggest a metric on a scale of 1-10 (with 1 being thirstiest, 10 the least)" - I do understand that but I think it's more straight-forward, intuitive and simple for the the more thirsty = higher score, and the less thirsty = lower score. Everyone recognises thirst as a negative aspect, so if a place is more thirsty than it should have a higher score on the thirstometer.