dry rainy season; unusually dry tsuyu
Refers to the rainy season (tsuyu) when there is very little rain, often causing water shortages. A seasonal weather term.
This year the rainy season is dry, and the dam's water level is low.
空梅雨の年は、夏の水不足が心配だ。
In a year with a dry rainy season, we worry about summer water shortages.
Compound of 空 (kara, 'empty') and 梅雨 (tsuyu, 'rainy season'), literally 'empty rainy season'.