Abstract:Soil moisture and its isotopic composition were observed at Spasskaya Pad experimental forest near Yakutsk, Russia, during summer in 1998Russia, during summer in , 1999Russia, during summer in , and 2000. The amount of soil water (plus ice) was estimated from volumetric soil water content obtained with time domain reflectometry. Soil moisture and its υ 18 O showed large interannual variation depending on the amount of summer rainfall. The soil water υ 18 O decreased with soil moisture during a dry summer (1998), indicating that ice meltwater from a deeper soil layer was transported upward. On the other hand, during a wet summer (1999), the υ 18 O of soil water increased due to percolation of summer rain with high υ 18 O values. Infiltration after spring snowmelt can be traced down to 15 cm by the increase in the amount of soil water and decrease in the υ 18 O because of the low υ 18 O of deposited snow. About half of the snow water equivalent (about 50 mm) recharged the surface soil. The pulse of the snow meltwater was, however, less important than the amount of summer rainfall for intra-annual variation of soil moisture.Excess water at the time just before soil freezing, which is controlled by the amount of summer rainfall, was stored as ice during winter. This water storage stabilizes the rate of evapotranspiration. Soil water stored in the upper part of the active layer (surface to about 120 cm) can be a water source for transpiration in the following summer. On the other hand, once water was stored in the lower part of the active layer (deeper than about 120 cm), it would not be used by plants in the following summer, because the lower part of the active layer thaws in late summer after the plant growing season is over.

No abstract

No abstract

No abstract

Abstract:The effects of land-use changes on the runoff process in the midstream plain of this arid inland river basin are a key factor in the rational allocation of water resources to the middle and lower reaches. The question is whether and by how much increasingly heavy land use impacts the hydrological processes in such an arid inland river basin. The catchment of the Heihe River, one of the largest inland rivers in the arid region of northwest China, was chosen to investigate the hydrological responses to land-use change. Flow duration curves were used to detect trends and variations in runoff between the upper and lower reaches. Relationships among precipitation, upstream runoff, and hydrological variables were identified to distinguish the effects of climatic changes and upstream runoff changes on middle and downstream runoff processes. The quantitative relation between midstream cultivated land use and various parameters of downstream runoff processes were analysed using the four periods of land-use data since 1956. The Volterra numerical function relation of the hydrological non-linear system response was utilized to develop a multifactor hydrological response simulation model based on the three factors of precipitation, upstream runoff, and cultivated land area. The results showed that, since 1967, the medium-and high-coverage natural grassland area in the midstream region has decreased by 80Ð1%, and the downstream runoff has declined by 27Ð32% due to the continuous expansion of the cultivated land area. The contribution of cultivated land expansion to the impact on the annual total runoff is 14-31%, on the annual, spring and winter base flow it is 44-75%, and on spring and winter discharge it is 23-64%. Once the water conservation plan dominated by land-use structural adjustments is implemented over the next 5 years, the mean annual discharge in the lower reach could increase by 8Ð98% and the spring discharge by 26Ð28%. This will significantly alleviate the imbalance between water supply and demand in both its quantity and temporal distribution in the middle and lower reaches.

No abstract

Abstract:We attempted to clarify the runoff characteristics of a permafrost watershed in the southern mountainous region of eastern Siberia using hydrological and meteorological data obtained by the State Hydrological Institute in Russia from 1976 to 1985. We analysed seasonal changes in the direct runoff ratio and recession gradient during the permafrost thawing period. Thawing depth began to increase from the beginning of May and continued to increase until the end of September, exceeding 150 cm. Annual precipitation and discharge were in the range 525-649 mm and 205-391 mm respectively. The sum of the annual evapotranspiration and changes in water storage ranged from 235 to 365 mm. The mean daily evapotranspiration in June, July, August and September was 1Ð5 mm day 1 , 1Ð7 mm day 1 , 1Ð5 mm day 1 , and 0Ð5 mm day 1 respectively. The direct runoff ratio was highest in June, decreasing from 0Ð8 in June to 0Ð2 in September. The recession gradient also decreased from June to September. Since the frozen soil functioned as an impermeable layer, the soil water storage capacity in the thawing part of the soil, the depth of which changed over time, controlled the runoff characteristics.

Abstract. We conducted 2 yr (2005)(2006)(2007) of in situ meteorological and glaciological observations on the Gregoriev Glacier, a flat-top glacier within the Inner Tien Shan, Kyrgyzstan. Relative carrier-phase GPS surveys reveal a vertical lowering at the summit of the glacier. Based on snow density data and an energy-mass balance model, we estimate that the annual precipitation and summer mean temperature required to maintain the glacier in the current state are 289 mm and −3.8 • C at the glacier summit (4600 m a.s.l.), respectively. The good agreement between dynamically derived precipitation and the long-term observed precipitation at a nearby station in the Tien Shan (296 mm at 3614 m a.s.l. for the period suggests that the glacier has been in a near steady-state in terms of mass supply. The glacier massbalance, reconstructed based on meteorological data from the Tien Shan station for the past 80 yr, explains the observed fluctuations in glacier extent, particularly the negative mass balance in the 1990s.