Long-term (1961-2010) observations of dew data collected at 597 stations over China show that dew frequency decreased by 5.2 days per decade due primarily to near-surface warming and associated decreases in relative humidity (RH). Moreover, the percentage decreasing rate of dew frequency in arid regions (precipitation PR <400 mm yr(-1)) are larger than that in humid regions (PR >= 800 mm yr(-1)). Compared with the 1960s, the mean dew frequency in the 2000s decreased by 28%, 40%, 50% in humid, semihumid (400 <= PR < 800 mm yr(-1)), and arid regions, respectively. Surface warming is larger in arid regions in northwestern China than its humid and semihumid regions during recent global warming, which leads to larger decreases in surface RH and makes dew events less likely. Since dew contributes significantly to surface water balance in arid regions, the large decreases in dew frequency may contribute to "the drier getting drier" response to global warming over arid regions. Plain Language Summary Here we show, by analyzing 50 years (1961-2010) of data collected at 597 stations in China, that dew occurrence in China exhibits a clear decreasing trend, and the decreasing rate of dew frequency in arid regions is higher than that in semihumid and humid regions. Compared with the 1960s, the mean dew frequency in the 2000s decreased by 28%, 40%, 50% in the humid, semihumid, and arid regions of China, respectively. Further analysis reveals that the decreased dew frequency is caused primarily by near- surface warming and drying. Large decreases in surface relative humidity in arid regions associated with large warming makes dew events less likely. This could make the region drier as dew is a significant water source in arid regions.
