Kang Ersi

Impact of climate change and variability on water resources in heihe River Basin

Studies indicate that the climate has experienced a dramatic change in the Heihe River Basin with scope of temperature rise reaching 0.5–l.l°C in the 1990s compared to the mean value of the period 1960–1990, precipitation increased 18.5 mm in the 1990s compared to the 1950s, and 6.5 mm in the 1990s compared to the mean value of the period 1960–1990, water resources decreased 2.6 × 108 m3 in the 1990s compared to the 1950s, and 0.4 × 108 m3 in the 1990s compared to the mean value of the period 1960–1990. These changes have exerted a greater effect on the local environment and socio-economy, and also made the condition worsening in water resources utilizations in the Heihe Rver Basin.

A distributed runoff model for inland mountainous river basin of Northwest China

In order to predict the futuristic runoff under global warming, and to approach to the effects of vegetation on the ecological environment of the inland river mountainous watershed of Northwest China, the authors use the routine hydrometric data to create a distributed monthly model with some conceptual parameters, coupled with GIS and RS tools and data. The model takes sub-basin as the minimal confluent unit, divides the main soils of the basin into 3 layers, and identifies the vegetation types as forest and pasture. The data used in the model are precipitation, air temperature, runoff, soil weight water content, soil depth, soil bulk density, soil porosity, land cover, etc. The model holds that if the water amount is greater than the water content capacity, there will be surface runoff. The actual evaporation is proportional to the product of the potential evaporation and soil volume water content. The studied basin is Heihe mainstream mountainous basin, with a drainage area of 10,009 km2. The data used in this simulation are from Jan. 1980 to Dec. 1995, and the first 10 years’ data are used to simulate, while the last 5 years’ data are used to calibrate. For the simulation process, the Nash-Sutcliffe Equation, Balance Error and Explained Variance is 0.8681, 5.4008 and 0.8718 respectively, while for the calibration process, 0.8799, -0.5974 and 0.8800 respectively. The model results show that the futuristic runoff of Heihe river basin will increase a little. The snowmelt, glacier meltwater and the evaportranspiration will increase. The air temperature increment will make the permanent snow and glacier area diminish, and the snowline will rise. The vegetation, especially the forest in Heihe mountainous watershed, could lead to the evapotranspiration decrease of the watershed, adjust the runoff process, and increase the soil water content.

The relationship between ENSO cycle and high and low-flow in the upper Yellow River

Firstly, the hydrological and meteorological features of the upper reaches of the Yellow River above Tangnag are analyzed based on observation data, and effects of EI Nino and La Nina events on the high and low flow in the upper Yellow River are discussed. The results show El Nino and La Nina events possess consanguineous relationship with runoff in the upper Yellow River. As a whole, the probability of low flow occurrence in the upper Yellow River is relatively great along with the occurrence of El Nino event. Moreover, the flood in the upper Yellow River occurs frequently with the occurrence of La Nina event. Besides, the results also show dissimilarity of El Nino event occurring time exerts greater impact on high flow and low flow in the upper Yellow River, that is, the probability of drought will be greater in the same year if El Nino event occurs in spring, the high-flow may happen in this year if El Nino occurs in summer or autumn; the longer the continuous period of El Nino is, the lower the runoff in the upper Yellow River is.Firstly, the hydrological and meteorological features of the upper reaches of the Yellow River above Tangnag are analyzed based on observation data, and effects of EI Nino and La Nina events on the high and low flow in the upper Yellow River are discussed. The results show El Nino and La Nina events possess consanguineous relationship with runoff in the upper Yellow River. As a whole, the probability of low flow occurrence in the upper Yellow River is relatively great along with the occurrence of El Nino event. Moreover, the flood in the upper Yellow River occurs frequently with the occurrence of La Nina event. Besides, the results also show dissimilarity of El Nino event occurring time exerts greater impact on high flow and low flow in the upper Yellow River, that is, the probability of drought will be greater in the same year if El Nino event occurs in spring, the high-flow may happen in this year if El Nino occurs in summer or autumn; the longer the continuous period of El Nino is, the lower the runoff in the upper Yellow River is.

Runoff of the upper Yellow River above Tangnag: characteristics, evolution and changing trends

Runoff and its evolution, based on hydrometeorological data from surface measurement stations, are analyzed for the upper reaches of the Yellow River above Tangnag. Some mathematical statistical models, for example, Period Extrapolation-Gradual Regression Model, Grey Topology Forecast Model and Box-Jinkins Model, are applied in predicting changing trends on the runoff. The analysis indicates that the runoff volume in the upper Yellow River above Tangnag is ending a period of extended minimum flows. Increasing runoff is expected in the coming years.

Evaluation of the sap flow using heat pulse method to determine transpiration of the Populus euphratica canopy

The sap flow of the sampled Populus euphratica stems at different radial depths and directions had been studied in Ejina Oasis, in the lower reaches of the Heihe River. Based on sap flow measurements, the transpiration of the entire canopy was calculated. Results showed a linear correlation between the sap flow and the sapwood area of the P. euphratica. Through the analysis of the diameter at breast height in the sample plot, it was found that the distribution of the diameters and the corresponding sapwood area was exponentially correlated, with the coefficient of correlation being 0.976,7. The calculated transpiration of the Populus euphratica canopy was 214.9 mm based on the specific conductivity method.

The relationship between ENSO cycle and temperature, precipitation and runoff in the Qilian mountain area

El Nino and La Nina are the events concerned internationally. The corresponding relationship between El Nino events, temperature, precipitation and runoff in the Qilian mountain area are analyzed according to the date from the weather and the hydrometric stations in the area, the results show that effects of El Nino events to temperature, precipitation and runoff are different in the different time and zones. When El Nino occurs, temperature rises, but precipitation and runoff decrease in the whole Qilian mountain area, especially in the east and middle parts of the area. Temperature rises, precipitation and runoff still decrease in the eastern Qilian mountain area in the next year El Nino occurring, but decrease extent is fewer. There are not obvious relationship between temperature, precipitation and runoff with El Nino events in the western Qilian mountain area.