[1] Changes in indices of climate extremes are studied on the basis of daily series of temperature and precipitation observations from 116 meteorological stations in central and south Asia. Averaged over all stations, the indices of temperature extremes indicate warming of both the cold tail and the warm tail of the distributions of daily minimum and maximum temperature between 1961 and 2000. For precipitation, most regional indices of wet extremes show little change in this period as a result of low spatial trend coherence with mixed positive and negative station trends. Relative to the changes in the total amounts, there is a slight indication of disproportionate changes in the precipitation extremes. Stations with near-complete data for the longer period of 1901-2000 suggest that the recent trends in extremes of minimum temperature are consistent with long-term trends, whereas the recent trends in extremes of maximum temperature are part of multidecadal climate variability.

ABSTRACT:In this study, spatial and temporal patterns of changes in extreme events of temperature and precipitation at 143 weather stations in ten Asia-Pacific Network (APN) countries and their associations with changes in climate means are examined for the 1955-2007 period. Averaged over the APN region, annual frequency of cool nights (days) has decreased by 6.4 days/decade (3.3 days/decade), whereas the frequency of warm nights (days) has increased by 5.4 days/decade (3.9 days/decade). The change rates in the annual frequency of warm nights (days) over the last 20 years (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) have exceeded those over the full 1955-2007 period by a factor of 1.8 (3.4). Seasonally, the frequencies of summer warm nights and days are changing more rapidly per unit change in mean temperatures than the corresponding frequencies for cool nights and days. However, normalization of the extreme and mean series shows that the rate of changes in extreme temperature events are generally less than that of mean temperatures, except for winter cold nights which are changing as rapidly as the winter mean minimum temperature. These results indicate that there have been seasonally and diurnally asymmetric changes in extreme temperature events relative to recent increases in temperature means in the APN region.There are no systematic, regional trends over the study period in total precipitation, or in the frequency and duration of extreme precipitation events. Statistically significant trends in extreme precipitation events are observed at fewer than 30% of all weather stations, with no spatially coherent pattern of change, whereas statistically significant changes in extreme temperature events have occurred at more than 70% of all weather stations, forming strongly coherent spatial patterns.

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A World Meteorological Organization (WMO) committee evaluated the record sea-level pressure (SLP) measurement of 1089.4 hPa on 30 December 2004 in Tosontsengel, Mongolia (1724.6 m). Although instrumentation and data collection procedures were properly followed according to the assessment of the committee, concern was raised regarding the reliability of SLP adjustment from such a high-elevation station. This paper addresses this concern with a number of analyses that look at relationships between SLP extremes and corresponding station elevation and temperature. First, we selected data from stations extracted from the Integrated Surface Database (ISD-Lite) of NOAA's National Climate Data Center. A spatial analysis indicates that elevation shows little to no association (R 2 values essentially zero) to extreme SLP. However, a second analysis between extreme SLP and air temperature indicates that high regionalism exists in spatial correlations (local R 2 ) between those two variables. This relationship to temperature is likely the result of differences in SLP adjustment formulae used around the world. Based on this analysis, on the need to differentiate the SLP values adjusted using extremely cold temperatures (and generally high elevation), and following past WMO SLP guidelines, the WMO Rapporteurs for Climate and Weather Extremes therefore have created two distinct SLP records: (a) highest adjusted SLP (below 750 m), currently 1083.3 hPa recorded on 31 December 1968 at Agata, Evenhiyskiy, Russia; and (b) highest adjusted SLP (above 750 m), currently 1089.4 hPa (by Russian method; 1089.1 hPa by WMO formula) on 30 December 2004 in Tosontsengel, Mongolia. Future WMO guidance regarding SLP adjustment may lead to re-evaluation of this and other SLP records.

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Eurasian snow cover in spring has followed a decreasing trend since the mid-1960s, but winter conditions remain unknown because of a lack of data. To address this issue with a regional focus on the eastern part of Eurasia, we conducted an observational study of winter temperature, precipitation, and snow depth in Mongolia and the associated atmospheric circulation. We used the meteorological data at 21 representative Mongolian weather stations for four winter months (November to February) from 1960 through 2007. Time series analysis was applied to three indices: standardized deviations from the mean for this 4-month period averaged over the 21 stations in Mongolia for snow depth, precipitation, and temperature. This analysis revealed a significant multi-decadal trend in temperature, but not in snow depth.During the 1960s and 1970s deep-snow winters coincided with extreme cold. However, beginning in the winter of 1992-1993, a new type of deep-snow winter with warmer conditions has occurred in some years. Moreover, a synoptic analysis demonstrated that a trough at the 500-hPa level that is usually climatologically located east of Mongolia extended westward to Mongolia during the cold-deep-snow winters. This indicates that enhanced cold surges from the north to Mongolia led to the historically typical deep snow conditions. On the other hand, the warm-deep-snow winters were characterized by a weakened trough, weakened cold surges, and concurrently intensified moisture transport from the west into Mongolia. The new circulation pattern observed here shows that warm winters, which may become more frequent in the future, still have the potential to cause deep snow in Mongolia.

The ongoing desertification and aeolian erosion processes in the southern Gobi Desert are ranked as one of the most significant global environmental disasters. In this study, we analyzed the decadal progress of eolian erosion in the southern Gobi Desert and traced key factors controlling intensified land degradation (LD) and sand and dust (SD) generation employing satellite data and climatic variables. Columnar dust mass density from climatic data re‐analyses as a major SD tracer was combined with the Mann–Kendall (MK) method and the empirical orthogonal function processor. Validation was performed by using ground data sets and field evidence from reference locations. The results revealed that (1) LD/SD patterns and hotspots in the Gobi Desert are significantly controlled by the distribution and trend of precipitation; (2) climatic conditions in the Mongolian Gobi Desert have shifted towards an unfavourable direction with respect to the LD/SD occurrence; (3) surface conditions in southeastern Mongolia have somehow decoupled from the weather factors and the transition zone between the desert and the vegetated terrain has gradually expanded probably due to anthropogenic activities. The correlation analyses between all candidate driving factors of LD/SD indicated that a major control mechanism of spatiotemporal migration of LD/SD in the southern Gobi Desert is the change in precipitation, whereas anthropogenic activity holds a secondary control. The results obtained can be used to prioritize intervention zones in the frame of land use planning processes aimed at adapting to climate change and mitigating LD and SD generation in source areas.