Abstract:A long-term set of daily maximum and minimum temperature and precipitation data are analyzed for the Hövsgöl Basin area, Mongolia. Six indices of extreme temperature and eight indices of extreme precipitation are examined. Results suggest that climate conditions over northern Mongolia are changing as indicated by a warming trend identified during the study period. Significant increases are detected in the annual number of hot days and warm nights in this region. Associated with these changes are concomitant decreases in the annual number of cold days and cold nights. The number of days with precipitation has increased slightly while the annual total precipitation has not significantly increased in northern Mongolia. On an average, there was no significant decrease in the maximum number of consecutive dry days or increase in the wet days. The 5-day precipitation total showed a small increase.
Extreme precipitation often persists for multiple days with variable duration but has usually been examined at fixed duration. Here we show that considering extreme persistent precipitation by complete event with variable duration, rather than a fixed temporal period, is a necessary metric to account for the complexity of changing precipitation. Observed global mean annual‐maximum precipitation is significantly stronger (49.5%) for persistent extremes than daily extremes. However, both globally observed and modeled rates of relative increases are lower for persistent extremes compared to daily extremes, especially for Southern Hemisphere and large regions in the 0‐45°N latitude band. Climate models also show significant differences in the magnitude and partly even the sign of local mean changes between daily and persistent extremes in global warming projections. Changes in extreme precipitation therefore are more complex than previously reported, and extreme precipitation events with varying duration should be taken into account for future climate change assessments.
Mongolia has an arid and cold climate due to its geographical settings of inland and mid-latitude highlands. The soil moisture varies seasonally, depending mainly on the balance of precipitation and evapotranspiration as well as on winter soil-freezing and spring snowmelt. Soil moisture climatology (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) for Mongolia is presented with a focus on three vegetation zones: the forest steppe, steppe, and Gobi Desert. For this purpose, we used soil moisture observations based on the gravimetric method for the top 50-cm soil layer from 26 grass-covered field sites during April-October of the 20-year period. In general, there was a latitudinal gradient in soil moisture content, with the southwestern soils being drier than northeastern soils. The seasonal change in soil moisture was small and the seasonal pattern was similar throughout Mongolia. The seasonality was characterised by three major phases of the warm season: the spring drying, summer recharge, and autumn drying phases, although each phase differed somewhat in timing and length between zones. In the northernmost forest steppe zone, the recharge phase was longer than that in the southern steppe and Gobi Desert zones, while the two drying phases were shorter in the forest steppe zone. This difference had a significant effect on the plant phenological timings of Stipa spp.; these were earlier in the forest steppe zone and later in the Gobi Desert zone. A simple water balance model was developed to examine the observed soil moisture dynamics, which implicitly simulated snow accumulation and soil freezing. The model simulated the observed seasonal and inter-annual soil moisture variations reasonably well (r = 0.75, p < 0.05). The results demonstrated that the three phases of seasonal change were produced by a subtle balance between precipitation and evapotranspiration. This model will provide a useful tool for a reliable and timely monitoring of agricultural drought for decision-makers and herders in Mongolia.
Aeolian processes in temperate grasslands are unique in that the plant growth-decay cycle, soil moisture/snowpack dynamics, and induced grazing interactively affect seasonal and interannual variations of dust emission. This study uses process-based ecosystem model DAYCENT and unique saltation flux measurements to (1) identify primary land surface factors that control dust emission with soil moisture and vegetation components (live grasses, standing dead grasses, and litter) in a Mongolian grassland and (2) test the dead-leaf hypothesis proposed by previous observational studies that correlates plant biomass in summer and dust events the following spring. In general, the DAYCENT model realistically simulates seasonal and interannual variations of the vegetation components and soil moisture that were captured by field observations during 2003-2010. Then, the land surface components are correlated with measured daily saltation flux in the springs of 2008-2009 and the frequency of monthly dusty days during March-June 2002. Results show that dust emission had a similar amplitude of significant correlation with wind speed and a combination of all land surface components, which demonstrates a memory of the preceding year. The memory analysis reveals that vegetation and soil moisture anomalies during spring dust emission are significantly autocorrelated with the preceding year's (autumn) corresponding anomalies, which were controlled by rainfall during a given summer. Most importantly, of the vegetation components, the standing dead grasses had the strongest memory and simultaneous correlation with spring dust emission, suggesting the validity of the dead-leaf hypothesis.
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