Impacts of warming and water vapor content on the decrease in light rain days during the warm season over eastern China
2015
Wu, Jian | Zhang, Liya | Zhao, Deming | Tang, Jianping
Based on daily rainfall data collected at 395 gauge stations over eastern China during 1979–2009, the variation in light rain days with intensities of 0.1–10 mm day⁻¹ in the summer half of the year was analyzed. Results indicate that both the light rain amount and the number of light rain days decline distinctly, with trends of −4.89 mm (10 year)⁻¹ and −2.48 days (10 year)⁻¹, respectively. The first two principal components of EOF analysis on light rain days not only show a long-term decrease, but also depict regional differences; specifically, light rain days decline more distinctly in northeastern and southern regions of eastern China. Spatial and temporal features, as well as the periods derived from the EOF analysis of temperature, precipitable water content, and relative humidity in the lower troposphere, coincide with those of light rain days. Composite analysis also suggests that there are fewer light rain days in years with lower relative humidity and precipitable water content in the lower troposphere, while there are fewer light rain days in years with higher tropospheric temperatures. According to the Clausius–Clapeyron equation and the relative humidity equations, relative humidity over eastern China during the period studied decreases by 5.5 % due to lower-tropospheric warming, and decreases by 0.16 % because of the decrease in specific humidity in the same period. Both warming and water vapor content are the reasons for light rain reduction, and warming is deemed the primary cause.
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