Changes in rainfall characteristics over Mongolia and adjacent regions during summer were examined for the period 1960 to 1998, using daily and monthly precipitation data for Mongolia, China and the former USSR. Climatologically, mean summer (June to August) total precipitation was greater in northern Mongolia, and tended to decrease toward the south and southwest. Summer total precipitation contributed more than 60% of annual precipitation in Mongolia. ‘Wet days’ is defined as a day exceeding precipitation more than 0.1 mm. The number of wet days was approximately 40 days in northern Mongolia, while the number of wet days was less than 20 days in the south.
Between 1960 and 1998, trends in summer total precipitation, the number of wet days in summer, and summer mean precipitation intensity were examined. The daily precipitation data were sorted into ascending order, and grouped into 10 classes which have an interval width equal to 10% of total number of wet days. Summer total precipitation increased in eastern and western Mongolia. Trends in heaviest precipitation class were also evaluated. The amounts of precipitation in the heaviest rainfall class, also increased in eastern and southern Mongolia and the Altai Mountains. The number of wet days increased over almost all of Mongolia. The frequency of relatively heavy rainfall events increased in eastern and southern areas, whereas during the same period weaker rainfall events became dominant in the northern part of central Mongolia.