Journal of the Meteorological Society of Japan, Vol. 84, No. 3, pp. 543--551, 2006

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NOTES AND CORRESPONDENCE
Climatology and Trends in Summer Precipitation Characteristics
in Mongolia for the Period 1960–98

Nobuhiko ENDO
Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan

Tsutomu KADOTA
Institute of Observational Research for Global Change, JAMSTEC, Yokohama, Japan

Jun MATSUMOTO
Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan

Borjiginte AILIKUN
Institute of Atmospheric Physics, Chinese Academy of Science, Beijing, P.R. China

andTetsuzo YASUNARI
Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan
Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya, Japan(Manuscript received 1 November 2004, in final form 9 February 2006)

Abstract
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 andthe former USSR. Climatologically, mean summer (June to August) total precipitation was greater innorthern 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

Corresponding author: Nobuhiko Endo, Frontier
Research Center for Global Change, JAMSTEC,
3173-25, Syowa-machi, Kanazawa-ku, Yokohama
City, Kanagawa 236-0001, Japan.
E-mail: nobu@jamstec.go.jp( 2006, Meteorological Society of Japan

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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 andsouthern areas, whereas during the same period weaker rainfall events became dominant in the northern part of central Mongolia.

1.

Introduction

Long-term trend in seasonal and/or annual
precipitation is studied on global and local
scales (e.g., IPCC 2001). The trend was positiveon the global scale, while the negative trend observed over large areas. Yatagai and Yasunari(1994; hereafter YY94) examined the summer
total precipitation (hearafter PRJJA) trends
for China and Mongolia during the period from1951 to 1990. They found that a decreasing
trend distributed over the arid and semi-arid
region in Mongolia and northern China.
Temporal changes of precipitation totals arecaused by both changes in precipitation frequency, and precipitation intensity during each
event. Endo et al. (2005) found that summer total precipitation has an increasing trend, withincrease in the precipitation frequency overnorthwest China during summer. On the contrary, summer total precipitation decreased,with a decrease in the precipitation frequency
over north China. However, the precipitation
intensity became more intense over both northwestern and north China. Further heavy precipitation events increased in northwestern
China. Similar results were also found by Zhai
et al. (2005). Sun and Groisman (2000) foundthat the precipitation frequency decreased,with an increase in frequency of heavy precipitation (greater than 20 mm in one day) in thesouthern part of Siberia during summer. However, changes in the precipitation frequency,
the precipitation intensity and precipitation
amounts of heavy precipitation events in Mongolia during summer have not been examined.
Recently, Mongolian daily precipitation dataset was provided by the National Agency
for Meteorology, Hydrology and Environment
Monitoring, of the Ministry of Nature and theEnvironment of Mongolia (hereafter NAMHEM). The newly available dataset gives an opportunity to examine changes in precipitation
characteristics over Mongolia.
In this paper, we first describe climatology ofsummer precipitation characteristics in Mongolia and its adjacent regions. We examine
long-term trends in PRJJA, the precipitation
frequency, the precipitation intensity, and precipitation amount of heavy precipitation eventin Mongolia, and its adjacent regions for summer during the period 1960–1998.
2.

Data and method

2.1 Data
Monthly and daily precipitation data provided by the NAMHEM were used for description of climatology of summer precipitation
characteristics, and examination of long-term
trends in summer precipitation characteristics.
We also utilized the daily precipitation data at
57 stations in China, as compiled by the China
Meteorological Administration (CMA). Daily
precipitation data at four stations in the former
Union of Soviet Socialist Republics (USSR),
from the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME) Siberia baseline dataset (Ohataet al. 2003) and Global Daily Climatology Network Version 1, compiled by the National Climatic Data Center, National Oceanic & Atmospheric Administration, were also employed.
Tretiyakov-type gauges were used in Mongolia (Zhang Yinsheng 2004; Personal communication), and former USSR (Groisman et al.
1991). In China, the Chinese standard precipitation gauge was used for measuring precipitation (CMA 2003). Daily precipitation accumulation in Mongolia is from 00 UTC until 00 UTC
in the next day (Zhang Yinsheng 2004; Personal communication). In China, the same accumulation time period was used for daily
precipitation (CMA 2003). At former USSR stations, precipitation measurements were twice
per day before 1966, and were then increased
to four times per day (Groisman et al. 1991). In
1986, twice daily precipitation measurements
were introduced again. These changes of observation practices in the former USSR, may in-June 2006

N. ENDO et al.

troduce biases in the daily precipitation records. Although biases of gauge measurements,
such as wind-induced gauge undercatch, wetting and evaporation losses, and underestimation of trace precipitation amounts (Goodison
et al. 1998) may exist in the daily precipitation
data, a bias-correction of the daily precipitation
data was not applied here, because we do nothave daily mean wind speed, daily mean temperature and trace record for Mongolia. In thisstudy, ‘wet day’ is defined as a day exceeding
precipitation more than 0.1 mm, since the daily
precipitation data have a resolution of 0.1 mm.
Although precipitation data before 1960 are
available for some stations in Mongolia, thedata used in this study covered the period from1960 to 1998, since the number of stations withthe daily precipitation records increased in thelate 1950’s. For the Chinese and former USSR
stations, the dataset covered the period from1961 to 2000.
The monthly precipitation data for Mongolia,archived at the National Center for Atmospheric Research (DS579.0), the monthly precipitation data of the Global Historical Climatology Network, version 2 (hereinafter GHCN),and ‘‘The Monthly Climatic Data for the World’’,
prepared by the National Climatic Data Center, NOAA (hereinafter MCDW) were also used
as reference time series for quality control ofthe precipitation data.
The Extended Edited Cloud Report Archive,
compiled by Hahn and Warren (1999), which
covers the period from 1971 to 1996, was also
used for preparing present weather code statistics, which are informative to describe the regional characteristics of dominant precipitation
types.
2.2 Quality check procedure
Daily and monthly precipitation data were
subjected to simple quality checks. The Mongolian monthly precipitation data (hereinafter
DATA_M), were first compared with DSS579.0
for the period from 1960–1982 for each station.
After 1983, DATA_M were compared with the
GHCN. MCDW were used as reference data ifmonthly precipitation data in DSS579.0/GHCN
were missed. Questionable DATA_M were thenflagged.
Next, monthly data from the daily precipitation data for the Mongolian stations were545

compiled (hereinafter DATA_D). DATA_D and
DATA_M were then compared, and any questionable values were flagged. The daily precipitation data were compared between the stations. Correlation on interannual timescales,
between time series of DATA_D for each station, and other stations were calculated. The
station with the highest correlation coefficient
was chosen as the reference station for thestations considered. The correlation coefficients
between the daily precipitation records for eachsummer at the two stations were calculated,
and time series of the correlation coefficient
was checked visually. Questionable daily precipitation data, were examined if the correlation coefficient of one summer differed markedly from that of other summers, and werediscarded if the data obviously differed fromthe precipitation data at surrounding stations.
For example, although the daily precipitation
exceeded 50 mm at a station, the case where
there is no rain is observed at surrounding
stations. In the course of the quality check, 37
summer months in DATA_D were discarded.
As one of the objectives of this study, was toevaluate long-term trends in precipitation
characteristics, not to discuss interannual /interdecadal variations, we allowed up to three
discarded summers for each station in DATA_D.
The quality check procedure described above
can easily pick up questionable very heavy precipitation. On the other hand, distinguish between ‘0 mm’ precipitation amount, and ‘lackof observation’ is scarcely detected. However,questionable high precipitation amounts, andquestionable very long dry spells, with themonthly precipitation data having a certain
value were typical problems, in the daily precipitation data. Therefore, it seems that the
problem of quality check procedure have limited effect on the present study. Although Karland Knight (1998) used proxy data, produced
by a gamma distribution, with a random number generator to fill missing daily precipitation
data, for voided stations, in this study discarded data were not replaced.
Daily precipitation data at 20 stations in
Mongolia, and 4 stations in the former USSR
were kept. Frequency of discarded data was
typically less than 5% at most of 20 Mongolian
stations, and maximum discarded data frequency, was about 10% at one of the 20 sta-

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Fig. 1. Weather station distribution in
Mongolia. Solid circles and open
squares are the stations with daily precipitation data and monthly precipitation data, respectively. M, D and B are
Moron (44231), Dalanzadgad (44373)
and Baruun-urt (44305), respectively.

tions. The quality of the Chinese precipitation
data had already been checked by Endo et al.
(2005). DATA_M for 28 stations in Mongolia
passed the quality check. The station distribution is shown in Fig. 1.
2.3 Classification and trend evaluation
Changes in PRJJA can be caused by a change
in the frequency of precipitation events, achange in the precipitation intensity per event,or by a combination of both. All daily precipitation data were sorted into ascending order, andgrouped into 10 classes for each station. Each of
the 10 classes had an interval width equal to
10% of the total number of wet days in theanalysis period. In this study, the lightest precipitation class was PR_C1, followed by PR_C2,
PR_C3, and so on up to PR_C10, the heaviest
precipitation class. This classification can describe relative contributions of the changes ineach class to the changes in the seasonal total
precipitation.
Figure 2 shows a histogram of daily precipitation at two Mongolian stations for the period
1960–1998. Most of the daily precipitation
amounts, are less than 5 mm per day in thesestations. On the other hand, precipitation
larger than 20 mm per day, is infrequent
during the study period. Since the lighter precipitation classes were consisted of many tiedvalues, we will show only the results for
PR_C10 in this study.
The nonparametric Mann-Kendall test (Kendall 1938), was applied to detect the precipita-

Fig. 2. Histogram of daily precipitation
for the period of 1960–1998 at a) Moron(44231) and b) Baruun-urt (44305). Alpha and beta are the shape parameterand the scale parameter of the Gamma
distribution (e.g., Wilks 1990).

tion trend at each station. Magnitude of trend
was obtained, by applying the linear regression. A significance level of 0.05 was usedthroughout this analysis.
3.

Results

Climatologically PRJJA was more than
200 mm in northern Mongolia, and decreased
southward and southwestward (Fig. 3a).
PRJJA was less than 100 mm in southern andsouthwestern areas, and constituted more than
70% of the annual precipitation, in central andeastern Mongolia (Fig. 3b). These findings are
similar to the results of Tuvendendorzh andMyagmarzhav (1985) and YY94, even though
their study periods, were different from thepresent study. The number of wet days during

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547

Fig. 3. Climatological distribution of a) summer total rainfall (Unit: mm), b) summer rainfall ratio toannual rainfall (Unit: %), c) number of wet days (Unit: days) and d) seasonal mean rainfall intensity (mm day1 ).

summer, is used as a proxy of the precipitation
frequency. There were approximately 40 wetdays in the Selenga River basin, and the Hentiyn Mountains (Fig. 3c), whereas there wereless than 20 wet days in southernmost Mongolia and Gansu Province, China. We definedsummer mean precipitation intensity as PRJJA
divided by the number of wet days during summer. Summer mean precipitation intensity wasapproximately 5–6 mm day1 in northeastern
Mongolia, decreasing toward the south andwest (Fig. 3d).
Figure 4a shows the climatological frequency
of non-showery precipitation events (drizzle,
rain, and snow). The frequency of non-showery
precipitation observed was 6% in northern
Mongolia, while non-showery precipitation wasless frequent in southern Mongolia. The spatial
distribution of showery precipitation frequency(thunder storms), is shown in Fig 4b. Showers
were more frequent around Lake Baikal, andin Inner Mongolia, and were infrequent overthe southern part of Mongolia.
The trend in PRJJA during the whole investigated period was generally upward in westernand eastern Mongolia (Fig. 5a). However, only
two stations had statistically significant trends.
A downward trend was observed in central
Mongolia, but it was not statistically significant.
The frequency of heaviest precipitation class(PR_C10), increased in eastern and western
Mongolia (Fig. 5b). Statistically significant upward trends were observed at three stations ineastern Mongolia. The upward trends in theeastern and western regions correspond wellwith the trends in adjacent regions of China,
whereas there are downward trends in theeastern part of the Hangay Mountains in central Mongolia.
The number of wet days increased in most ofMongolia (Fig. 5c). Statistically significant up-

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Fig. 4. Climatological distribution of a)frequency of non-showery precipitation
and b) frequency of showery precipitation. Both frequencies were estimatedfrom present weather codes from 1971
to 1996. Unit is %.

ward trends were observed in eastern Mongolia, and in the Altai Mountains. Although thenumber of wet days increased, both in the Altai
Mountains and northwestern China, even if
those regions have faced across the border, thetrends in the number of wet days in Inner
Mongolia are opposite to the trends in eastern
Mongolia, which faced across the border. Precipitation measurement when weak precipitation occurs, is generally sensitive to the different observational practices, and the different
gauges. Therefore the opposite trends would be
partly caused by the different observational
practices, and the use of different gauges. Impacts of different threshold value for defining
wet days on the trends in the number of wetdays were examined. The threshold value of
0.5 mm, and that of 1 mm were used. The examination showed that the opposite trends, inVol. 84, No. 3

the number of wet days in eastern Mongolia
and Inner Mongolia were also observed when
the different threshold values were used. Thus
the opposite trends in the number of wet days,
were not caused by the different observational
practices and the different gauges. Mechanism
which produces the different trends in the number of wet days between eastern Mongolia andInner Mongolia, is an issue we will examine in
future research.
Changes in seasonal average precipitation intensity, were unevenly distributed (Fig. 5d).
Two stations in central Mongolia had statistically significant downward trends, while seasonal average precipitation intensity tends toincrease significantly at two stations in southern Mongolia.
The regional characteristics of trends showednotable differences between eastern Mongolia
and the northern part of central Mongolia. Detailed descriptions of the trends in the two regions are warranted. At the weather station inMoron, located in the northern part of central
Mongolia (marked as M in Fig. 1a), PRJJA decreased at a rate of about 15 mm per decade(Fig. 6a). PRJJA in the 1960s was about
200 mm, whereas in the 1990s it was about
150 mm. Conversely, the number of wet days
increased from about 37 days in the 1960s toabout 53 days in the 1990s. The median andthird quartile of daily precipitation values foreach summer tended to decrease; the averagevalue for the third quartile of the 1960s wasapproximately 7.4 mm, dropping by approximately half by the 1990s (3.8 mm). Thus, more
frequent, but weaker precipitation events became dominant at Moron.
At Baruun-urt in eastern Mongolia (marked
as B in Fig. 1a), PRJJA increased significantly
at the rate of 20 mm per decade, and the number of wet days increased slightly (Fig. 6b).
Concurrently, larger third quartiles of daily
precipitation for each summer were observed
four times after 1989. The largest third quartile
appeared in 1994, and higher third quartiles
were observed in 1989, 1990, and 1998. The increase in the frequency of heavy precipitation
events was the cause of the upward trend in
PRJJA at Baruun-urt. Changes in the number
of wet days were similar at both the Moronand Baruun-urt stations. However, the trends
in heavy precipitation events at the two sta-June 2006

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Fig. 5. Spatial distribution of trends in a) summer total precipitation, b) heaviest precipitation class,c) number of wet days and d) mean precipitation intensity. Trend is expressed as a ratio to its climatological value. Triangles and inverted triangles indicate increasing and decreasing trends
larger than 10%, respectively. Small square is trend less than 10%. Solid marks indicate statistically significant trend tested by the Mann-Kendall test.

Fig. 6. Time series of summer total precipitation, numbers of wet days, seasonal mean precipitation
intensity, and median (square) and third quartile (triangle) of daily precipitation data for eachsummer, respectively. Long-dashed line indicates linear trend. a) Moron (44231, Lat. ¼ 49 38 0 N,
Lon. ¼ 100 10 0 E, Height ¼ 1283 m), b) Baruun-urt (44305, Lat. ¼ 46 41 0 N, Lon. ¼ 113 17 0 E,
Height ¼ 981 m), and c) Dalanzadgad (44373, Lat. ¼ 43 35 0 N, Lon. ¼ 104 25 0 E, Height ¼ 1465 m).

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tions were opposite, and these changes regulated the changes in PRJJA.
Figure 6c indicates no trend in PRJJA at Dalanzadgad in southern Mongolia (marked as D
in Fig. 1a). PRJJA were higher in the period
from the mid 1970s to the early 1980s, and in
the 1990s. However, PRJJA in the period fromthe mid 1980s, to the early 1990s were relatively small. Daily precipitation characteristics
changed significantly with a downward trend
in the number of wet days. The third quartileof daily precipitation each summer, became significantly larger after the late 1990s, up from avalue of 7.9 mm in the 1990s, indicating thatthe frequency of heavy precipitation events has
increased in recent decades.

number of heavy precipitation events in eastern and western Mongolia, corresponded wellwith the increase in the number of the heaviest
precipitation events in Inner Mongolia andnorthwest China. The trends in the number ofwet days are opposite, between eastern Mongolia and Inner Mongolia.
This study has described the regionality ofchanges in precipitation characteristics. The
regional characteristics of precipitation systems and mechanisms, contributed to changes
in heavy precipitation events should be further
explored, with the aid of satellite image analysis and regional model development.

4.

Precipitation data for Mongolia were provided by the National Agency for Meteorology,
Hydrology and Environment Monitoring, of the
Ministry of Nature and the Environment ofMongolia. This work was jointly supported by
the China National Key Planning Developmentfor Basic Research (Grant No. G1999043405).
We also wish to thank the National Climatic
Data Center, NOAA and the National Center
for Atmospheric Research for providing data.
The Extended Edited Cloud Report Archive
was obtained from the Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Department of Energy, USA. The
author is thankful to the reviewers of thismanuscript as their comments improved themanuscript content.

Summary

Changes in precipitation characteristics over
Mongolia and adjacent regions during summer
were examined using daily and monthly precipitation data for Mongolia, China and the former
USSR. Summer total precipitation values werehigher in northern Mongolia, and tended to decrease toward the south and southwest. The
contribution of summer total precipitation, toannual precipitation was more than 60%. ‘Wet
days’ is defined as a day exceeding rainfall
more than 0.1 mm. The number of wet days
was approximately 40 days in northern Mongolia, while the number of wet days, was lessthan 20 days in the south.
Between 1960 and 1998, trends in summer
total precipitation, the number of wet days insummer, and summer mean precipitation intensity were examined. The daily precipitation
data were sorted into ascending order, andgrouped into 10 classes which have an interval
width equal to 10% of total number of wet days.
Trends in heaviest precipitation class werealso evaluated. Summer total precipitation increased in eastern and western Mongolia. The
precipitation amounts in the heaviest rainfall
class (PR_C10) also increased in eastern andsouthern Mongolia, and the Altai Mountains.
In the same period, the number of wet days increased over almost all of Mongolia. In summary, the frequency of relatively heavy precipitation events increased in eastern and southern
Mongolia, whereas relatively weak precipitation events became dominant in the northernpart of central Mongolia. The increase in the

Acknowledgments

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