Strong increase in convective precipitation in response to higher temperatures

Precipitation changes can affect society more directly than variations in most other meteorological observables1–3, but precipitation is difficult to characterize because of fluctuations on nearly all temporal and spatial scales. In addition, the intensity of extreme precipitation rises markedly at higher temperature4–9, faster than the rate of increase in the atmosphere’s water-holding capacity1,4, termed the Clausius– Clapeyron rate. Invigoration of convective precipitation (such as thunderstorms) has been favoured over a rise in stratiform precipitation (such as large-scale frontal precipitation) as a cause for this increase4,10, but the relative contributions of these two types of precipitation have been difficult to disentangle. Here we combine large data sets from radar measurements and rain gauges over Germany with corresponding synoptic observations and temperature records, and separate convective and stratiform precipitation events by cloud observations. We find that for stratiform precipitation, extremes increase with temperature at approximately the Clausius–Clapeyron rate, without characteristic scales. In contrast, convective precipitation exhibits characteristic spatial and temporal scales, and its intensity in response to warming exceeds the Clausius– Clapeyron rate. We conclude that convective precipitation responds much more sensitively to temperature increases than stratiform precipitation, and increasingly dominates events of extreme precipitation. The Clausius–Clapeyron relation describes the rate of change of saturation vapour pressure of approximately 7% ◦C−1 at typical surface temperatures, and thereby sets a scale for increases in precipitation extremes1. Recent studies on extreme precipitation have indeed found that high precipitation percentiles on short observational timescales generally increase with temperature4–9,11. For the Netherlands, increases of extreme precipitation intensity roughly commensurate with the Clausius–Clapeyron rate at low temperatures but beyond this rate at temperatures above 12 Cwere first reported in 2008 (ref. 4). Remarkably, similar observations were subsequently made for other mid-latitude7,9 and tropical regions8,9 for short timescales. However, the difficulty of identifying precipitation types12,13—namely stratiform and convective rain— and relatively limited data11 have made unequivocal attribution of the high rate above 12 C to either of the types unfeasible. Even statistical effects have been suggested to explain the superClausius–Clapeyron rate11,14. The basic hypothesis is that precipitation intensity changes may be tied to the change in saturation vapour pressure. It hinges on the assumption that precipitation intensity should be proportional