Changes in event number and duration of rain types over Mongolia from 1981 to 2014

In addition to the total amount of precipitation, the number, type and duration of rain events play a critical role in hydrological cycle, land surface processes, vegetation and land cover dynamics in such semi-arid regions as Mongolia where water availability is the main determinant of ecosystem functioning and services. However, only a limited number of studies have so far focused on certain aspects of changes in rain types and durations for Mongolia as a whole, while a relatively large number of studies have examined trends observed in total annual precipitation for the country. In the present study, we evaluated changes in not only the amount, but also in the number and total duration of rain types using the data on start-to-end times of all rain events from 55 meteorological stations scattered throughout Mongolia between 1981 and 2014, a period for which this type of analysis was made possible for the first time. Our study confirms that there has been no significant change in the amount of mean summer precipitation for almost all parts of the country for the last 34 years, with only a few stations showing a significant decreasing trend. In terms of rain types, the number and duration of convective rains have increased, while those of stratiform rain events have decreased over Mongolia, a trend that is more pronounced around Khangai mountain area in central Mongolia and south-eastern desert steppe and eastern steppe, suggesting a possible transition from stratiform rains to convective rains. The findings of this research imply that increasing temperature and altered rain type ratios may affect each other as the decreasing number and duration of stratiform rain events allow for progressively longer sunshine period, possibly feeding back to the increased temperature. The release of this latent heat fuelling the upward movement of moisture and producing the convective rains could be one of the reasons of the significant rise in convective rain frequency for the study period. The observed changes in rain patterns have significant implications in ecosystem functioning and resource management.