As an important component of the earth surface system and the core of hydrological cycle, soil water controls the most basic terrestrial ecosystem patterns and processes, which is key for the healthy operation of the terrestrial ecosystem. Soil moisture dynamics is an indispensable part of the research on the interactions and feedbacks between hydrological processes and terrestrial ecosystem processes, which is the result of non-linear interactions among a series of hydrological, climatic, and ecological processes. Consequently, soil moisture dynamics needs to be studied by stochastic methods, which can reasonably describe the characteristics of soil moisture dynamics including the pulse, erratic, and random processes. In this article, we systematically review the development of stochastic modeling of soil water content based on the principle of soil water balance, and focus on the classification and application of these models. This review could supply some useful reference for quantitative studies of stochastic soil moisture dynamic processes and be beneficial to the research on ecohydrology in China. This review also could promote a better understanding of interactions between hydrological cycle and the terrestrial ecosystem, and ultimately contribute to the knowledge base on the sustainable management of water resources and ecosystems.
Human activities, such as water storage in reservoirs and pumping for irrigation, reduce stream flows and deplete unconfined aquifer in the plain area of the Baiyangdian Lake Basin. Without recharges from rivers and groundwater, the Baiyangdian Lake faces the risk of drying up. Considering the impacts of the Baiyangdian Lake on the local environment, biodiversity, and climate, many projects of water transfer for the sustainability of the lake were implemented. However, the result are unsatisfactory due to considerable leakages in the lake. In order to preserve the lake, sustainable groundwater use should be achieved and therefore, it is necessary to study the renewal rate of unconfined groundwater. In this study groundwater was surveyed on the plain area of the Baiyangdian Lake Basin in 2009. thirty six samples from groundwater and surface water were collected for measuring the content of tritium. Tritium content in precipitation since the mid-1950s was rebuilt by comparing the results from linear interpolation, Wu's method and Lian's method. Renewal rate of groundwater in the plain area was estimated based on the tritium data and the well-mixed model. Results show that leakage of the lake slightly increased tritium content in the ambient groundwater. Generally, the renewal rate of unconfined groundwater decreased from 15.0 %/a to 4.0 %/a between the mountain area and the lake. Alluvial fans are the main recharge area with an average renewal rate of 9.8 %/a. The renewal rate dropped to 4.4 %/a in the alluvial plain. We recommend that groundwater development should be restricted in the alluvial plain to recover the renewal rate of unconfined groundwater. Although such recovery may take a long time to occur, it is believed that recharging the lake by shallow groundwater is the only way to maintain a sustainable lake.
In this study the entropy method was adopted to calculate the indicator weights of the water security indicator system and the water security status of the 47 countries in the Asia-Pacific region were then assessed. National water security consists of 5 dimensions—household water security, economic water security, urban water security, environmental water security, and resilience to water-related disasters. The regional disparity of household water security is most significant, while the minimum value of regional disparity is found in resilience to water-related disasters. Regional economic water security is relatively satisfactory in Asia-Pacific; however, compared to other dimensions, resilience to water-related disasters is less satisfactory. The assessment reveals the actual water security status of countries and the result indicates that Australia, New-Zealand, and Malaysia are the most favorable countries in terms of national water security, but Kiribati is the worst country; countries in East Asia and the Pacific are in a much better condition than those in South Asia, Southeast Asia, and Central-West Asia. The overall water security situation in Asia and the Pacific region urgently needs improvement.
Amu Darya is the largest river in Central Asia that provides water resources to downstream water users and flows into the Aral Sea. Runoff of the Amu Darya River is dominated by snowmelt and glacier melt originating from the alpines. Quantification of snowmelt and glacier melt contribution to the runoff is important for understanding the dynamic characteristics of the streamflow. This study investigates the glacier and snow melt processes in the headwaters of Amu Darya by using a glacier-enhanced SWAT model. The simulations were run through 1951 to 2005. The results indicate that the SWAT-RSG model could well estimate the monthly streamflow process of the Amu Darya River Basin, and the efficiency coefficient and absolute value of PBIAS in the calibration period (1961-1975) and validation period (1976-1985) could be higher than 0.6 and lower than 25%, respectively. Snowmelt and glacier melt contributed 67% and 15% of the annual runoff. The Amu Darya River is mainly supplied by melting high-mountain snow and glaciers, which was concentrated in March to July and June to September, respectively. Owning to the combined effect of rainfall, snowmelt, and glacier melt, the runoff is concentrated in April to September, accounting for 83% to the total runoff, and the peak occurred in July. The results of Mann-Kendall trend analysis indicate that precipitation showed a significant decreasing trend and temperature showed a significant increasing trend from 1951 to 2005, and experienced a sudden jump in 1995. Due to the change of temperature and precipitation, snowmelt showed a decreasing trend and the value during 1996 to 2005 (Period Ⅱ) was 20% lower compared to that in 1951 to 1995 (Period Ⅰ). Due to the shrink of glacier area and reduction of precipitation, glacier melt showed a non-significant decreasing trend between 1951 and 2005 and the annual glacier melt in Period Ⅱ was 4% less than that in Period Ⅰ. Despite that the rainfall had slightly increased, the rain runoff was reduced by 35% as a result of the increased evapotranspiration. Consequently, the streamflow was reduced by about 260 million m3 each year from 1951 to 2005. The runoff showed a 21% reduction from Period Ⅰ to Period Ⅱ. The study of runoff generation characteristics in the headwaters of the Amu Darya River can provide references for the water resource management in the Amu Darya River Basin and Central Asia.
Based on the monthly precipitation of a 0.5°×0.5° grid dataset and the daily precipitation observations of 135 meteorological stations released by the National Meteorological Information Center of China, this study analyzed the spatiotemporal variation of extreme precipitation in north and south of the Qinling-Huaihe region during 1960-2013, using the methods of trend analysis, Sen+Mann-Kendall model, and correlation analysis. More specifically, we analyzed the relationship between ENSO and the observed extreme precipitation. The results are as follows: (1) the precipitation showed an increasing trend in the lower reach of the Yangtze River and a decreasing tendency in the other regions; (2) extreme precipitation analysis indicates a declining trend in rainy days and an increasing trend in precipitation intensity. The number of continuous drought events increased. Spatially, the regions with increasing intensity of extreme precipitation were mainly distributed in the Qinling-Bashan Mountains and the lower reaches of the Yangtze River and Yellow River, whereas there were more drought events in the Guanzhong Plain, Wushan Mountains, and Sichuan Basin; (3) Extreme precipitation had a close relationship with ENSO in the study region. In El Niño years, more precipitation was found in the spring but there was less precipitation in the summer and the whole year. In La Niña years, there was less precipitation in the spring and more precipitation in the autumn and the whole year. The responses of extreme precipitation events to El Niño exhibited spatial differences. Most of the regions with decreasing extreme precipitation in El Niño years were distributed in the lower reach of the Yellow River, the Guanzhong Plain and Qinling-Bashan Mountains, as well as the Sichuan Basin, while the region with increasing extreme precipitation was the Huaihe Plain. The lower reach of the Yangtze River and the Wushan Mountains showed no clear response to ENSO.
Stable isotopes of atmospheric water vapor have been used as informational tracer in understanding global earth surface processes and hydrological cycle. Based on the physical process of water transportation, this article introduces the theoretical basis of water vapor isotopic fractionation, including equilibrant and non-equilibrant fractionation such as evaporation process, transportation, and considerations, and reviews traditional measurement methods and new techniques such as laser spectrometer and satellite remote sensing infrared spectrometer. It shows that real-time and remote sensing observations have become useful methods for water vapor isotope research. The paper also summarizes the main progresses on water vapor isotopic theory and the general/regional climate models enabled with isotopic module. Iso-GCM/RCM has advantages in global and regional climate process research and environmental information reconstruction, and will be widely used in future research. Emerging focuses of atmospheric isotope research are high spatiotemporal resolution measurement and application of new indices such as 17O-excess and Iso-GCM/RCM.
