Interviews of Mongolian herders and high resolution precipitation data reveal an increase in short heavy rains and thunderstorm activity in semi-arid Mongolia

Increases in extreme record-breaking daily precipitation events have accompanied warming temperatures causing increased flooding in many areas of the World, but are not well documented for arid and semi-arid regions. In semi-arid Mongolia where warming has been over 2(o) C from 1940 to 2008, nomadic herders described their concerns over an increase in the number of hot days and a shift from multi-day gentle rains to heavy rains lasting less than one hour that damage their pastures, animals, gers and people, suggesting a transition from stratiform rains to convective storms. The brief intense rains are not seen in daily precipitation data typically reported by meteorological stations, and here the correlation between fine-scale rainfall readings and thunderstorm activity were used to hind cast brief heavy rains. From 2008 to 2012, an automated weather station in Dalbay Valley at Lake Hovsgol, Mongolia, recording at 5-min intervals, detected at least 40 heavy sub-daily summer rains each lasting less than 40 min. Heavy rains in Dalbay were correlated with thunderstorm activity and were 2.5 times more likely to occur when thunderstorms were reported within the previous 24 h at the Hatgal meteorological station (80 km to the southwest of Dalbay) than when no thunderstorms were reported. Daily thunderstorm frequency, recorded at nearby meteorological stations from 1960 to 2012, has increased and thus supports herders' perceptions that the frequency of the short heavy rains have increased. Without high temporal resolution data for precipitation, such as those we report in this study, it is impossible detect shifts in summer rain types, which have many implications in theory and practice.