Seasonal change of soil moisture in Mongolia: its climatology and modelling

Abstract

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.

Temporal variations in phenological events of forests, grasslands and desert steppe ecosystems in Mongolia: a remote sensing approach

“…After mid-October, soil moisture was assumed to be constant when the daily air temperature was <0°C. This pattern of the soil moisture model generally corresponds with the pattern of precipitation in Mongolia (Xue 1996, Nandintsetseg & Shinoda 2011. So, the seasonal variation of the precipitation cycle suggested that the plant emergency may occur around the transition period from Phase I to Phase II, which was identified as late May to early June, if precipitation recharging lately or anomalously.…”

“…Peaks of NDVI and EVI values, indicative of high photosynthetic and biomass accumulation, were found in late July to late August, which can be explained by being the period with the highest precipitation in Mongolia. Moreover, the occurrence of peak values was consistent with the peak of soil moisture during phase-2 (Nandintsetseg & Shinoda 2011). Around 85 percent of the precipitation falls in the warm period of the year between April and September, of which 50-60 percent is received in July-August (Natsagdorj et al 2005).…”

“…Based on this advantage of EVI over NDVI it would be expected that EVI should be more appropriate for vegetation phenology extraction. However, with regard to the responses of different vegetation types to the specific pattern of climatic factors and the consistency of NDVI derived timing of phenological events of each vegetation type with the results of previous studies (Yu et al 2003(Yu et al , 2004Jigmed 2006, Shinoda et al 2007, Nandintsetseg et al 2011, the performance of NDVI and EVI in the determination of the phenological activity should be studied continuously in particular with the aid of monthly and daily-based climate data.…”

Habitat Fragmentation by Railways as a Barrier to Great Migrations of Ungulates in Mongolia

“…Annual average precipitation in this area is less than about 350 mm, but its interannual variation is large (Vandandorj et al 2015;Yu et al 2004), which is typical for drylands. Because precipitation and snowfall increase and temperature decreases from south to north (Morinaga et al 2003;Nandintsetseg and Shinoda 2011), vegetation correspondingly changes from desert to drylands and forest steppe ecosystems. Droughts and severe winters are a cause of high mortality among livestock (Fernandez-Gimenez et al 2012Tachiiri and Shinoda 2012) and wild animals (Kaczensky et al 2011a).…”

The effects of ocean SST dipole on Mongolian summer rainfall

“…The northernmost zone consists of taiga forest and forest steppe, while the southern region contains steppe, desert steppe, and desert. The northern part of Mongolia is covered by forested mountain ranges with a dry sub-humid climate, whereas the southern part encompasses the Gobi Desert at lower elevations with a drier climate (Nandintsetseg and Shinoda, 2011). In this study, we used monthly precipitation data collected from twelve stations well distributed across Mongolia during the period 1979-2013.…”