| The land-atmosphere hydrologic cycles in them closely related the atmospheric water, surface water and ecological water, and the changes in them profoundly influenced on the water resources and the ecological evolution all over the world. It has becoming the current developing trend to carry out the study on the land-atmosphere hydrologic cycles in watersheds under rapidly changing environment. The natural severe scarcity of the water resources was the remarkable characteristics of the arid and semi-arid regions and became the double dependence of the sustainable development for its economy and ecological environment in them. Heihe River Basin had the unique characteristics with the different hydrological functions in each region and typical hydrologic cycle processes, and the conflict between ecological water demand and economic water utilization had becoming serious due to the intensive human activities for a long time. To realize the reasonably utilization and the rational disposition of regional water resources and the sustainable development for their hydrology-ecology-economy, the spatial-temporal distributions of the water vapor content, water vapor flux, water vapor budget and the precipitation should be comprehensively recognized, and the processes of the hydrologic cycles in inland watershed should be deeply understood.Using the data from the high resolution regional climate model, which contains atmospheric temperature, specific humidity, meridional and zonal wind at 11 standard isobaric in Heihe River Basin during 1980-2010, as the main data, the distributed water vapor content and the water vapor flux were analyzed, and the physical-based distributed precipitation in the region were estimated based on the theory of the circulation background field and the topographical uplifting theory. The atmospheric hydrology process in the land-atmosphere hydrologic cycle including the water vapor content, the water vapor budget from the water vapor flux over the Heihe River Basin, and the hydrologic cycle characteristics of land-atmosphere in upstream, middle-stream, down-stream and the whole basin were studied, combining with the detailed-distributed precipitation, the actual evapotranspiration and runoff in each region. The results showed as followed.(1) The low values of the whole water vapor content over the Heihe River Basin located in upstream and the high values of it located in down-stream. Although the seasonal difference between the water vapour contents was remarkable, the distribution pattern of it in Heihe River Basin remained unchanged. Annual average water vapor content was in the range of 31.73～125.62mm, and those in the up-stream, middle-stream, down-stream and the whole basin was 59.24mm,107.05mm,112mm and 101.08mm, respectively. The average water vapor content in January was in the range of 0.88～4.00mm to a minimum, and those in the up-stream, middle-stream, down-stream and the whole basin was 1.62mm,3.34mm, 3.67mm and 3.21mm, respectively. And the average water vapor content in July was in the range of 6.26～23.00mm to the maximum, and those in the up-stream, middle-stream, down-stream and the whole basin was 11.37mm,19.50mm,112mm,20.74mm and 18.70mm, respectively. The average water vapor contents in each region in October were more than those in April.(2) The west wind in zonal direction and the north wind in meridional direction were the major driver of the water transportation over the Heihe River Basin. Among the representative months of each season, the water vapor budget of the up-stream, dowm-stream in July were positive, but negative in the other months. The water vapor budgets of the middle-stream in all months were positive, and the water vapor had a lot of surplus.The annual average water vapor flux over the basin was about 3039.97～7392.36 g/(cm·s). The average water vapor flux in January was about 420.95～133.08 g/(cm·s) to the minimum, and the one in July was about 928.44～395.92 g/(cm·s) to the maximum. The average water vapor flux in October was more than that in April.The water vapor outputs in each region were more than the inputs in zonal direction and the water vapor budget is negative in January, July and October, the water vapor transportation not only crossed over the regions as "transit water", but also took away a large amount of regional water vapor, resulting in water vapor losses. Only in July, because the water vapor transportation brought a lot of water vapor into them, the middle-stream and down-stream had a positive net water vapor budget. The water vapor inputs and the outputs in meridional direction of each region were a minority, but became the main source of the water surplus in them. Only in July, there were the water vapor transportations by south wind and it appeared in the middle and east part of up-stream and the eastern edge of the basin. The annual average net water vapor budget over the whole basin was about 255.32×108 m3, and it was 125.14×108 m3 in July, only a month with surplus water budget among the representative months of the seasons in a year. The monthly average net water vapor budget over the up-stream and down-stream were positive in July, but negative in other representative months of seasons. The annual net water vapor budget over the up-stream was 23.73×108m3, among which the ones in July was about21.58×108m3; The annual net water vapor budget over the down-stream was 11.54×108m3, among which the ones in July was about43.32×108m3; The annual net water vapor budget was 225.73 × 108m3, and the monthly net water vapor budgets over the middle-stream in all representative months of the seasons were positive, among which the ones in July was 61.94×108m3 to the maximum.(3) The spatial distribution of the precipitation resulted from topographical uplifting effect showed that the high values located in up-stream and and low values located in down-stream, opposite to the spatial patterns of the water vapor content and the water vapor flux over the basin. In January the contributions of the total water vapor input abroad to the precipitations in up-stream, middle-stream, down-stream and all the basin in January was 97%,99%,99% and 98%, respectively, and in July, the rate of the precipitations from the evapotranspiration was 3%,1%,1% and 2%; while the rate of the precipitations from the evapotranspiration of the up-stream, middle-stream, down-stream and all the basin reached 14%,11%,9% and 15%,respectively.The theoretical precipitation under the circulation background field was in the range of 0.07384-98.79mm, and the high precipitation values located around Zhangye, Linze and Jinta in middle-stream, while the low values distributed in up-stream and down-stream, became continuous distribution in down-stream. The effect of the orographic uplift mainly happened in the mountains of up-stream and the spatial distribution of it was different from each other because of different influence in unique atmospheric circulation from each season. The effect of the orographic uplift was to the minimum in January and to the maximum in July. In January the high values and the low values from the effect of orographic uplift in the mountainous up-stream, and April and October appeared in pairs showing the condition of being indented, while disappeared in July, instead of continuous region of high precipitation in July, with the range of -19.41～20.92mm in whole basin.The annual average precipitation of the whole basin was about 139mm,90% of which from water vapor input abroad and 10% from the local evapotranspiration. The annual average precipitation of the up-stream was about 425mm,90% of which from water vapor input abroad and 10% from the local evapotranspiration. The annual average precipitation of the middle-stream was about 147mm,93% of which from water vapor input abroad and 7% from the local evapotranspiration. The annual average precipitation of the down-stream was about 46mm,95% of which from water vapor input abroad and 5% from the local evapotranspiration.The contribution of water vapor input abroad and local evapotranspiration to precipitation differed from each season. The contribution of water vapor input abroad was the most in January and the least in July, and the ones in October were more than those in April. Of all the basin,98% of precipitation was from water vapor input abroad in January while 85% in July. In the up-stream,97% of precipitation was from water vapor input abroad in January while 86% in July. In the middle-stream,99% of precipitation was from water vapor input abroad in January while 89% in July. In the down-stream,99% of precipitation was from water vapor input abroad in January while 91% in July. Correspondingly, the contribution of local evapotranspiration to precipitation was to the minimum in January and to the maximum in July.2% of precipitation was from local evapotranspiration in January while 15% in July in the whole basin, while 3% and 14% in the up-stream,1% and 11% in the middle-stream, and 1% and 9% in the down-stream.(4) In the up-stream, the external cycle and the hydrologic cycle were weaker, but the internal cycle was stronger. The water exchange in it was active and the water vapor retention in it was shortest in up-stream, showing the highest precipitation efficiency. The result was consistent with the fact that the up-stream had the most precipitation in the whole basin. In the middle-stream, the external cycle in was the strongest, but the hydrologic cycle was lower, the water vapor retention in it was longer, and the precipitation efficiency was lower. In the down-stream, the hydrologic cycle was the strongest, but the internal cycle was lower, the water vapor was not active, thus the water vapor in it was difficult to form the precipitation, and the precipitation efficiency was lowest, consistent with the phenomenon of little precipitation in it. All kinds of the hydrologic cycles performed most actively in July with high air temperature and high humidity, while weakest in cold and dry climate of January.The external cycle coefficient measured the degree of involving the precipitation of the water vapor abroad using the times converted from the net water vapor budget. The external cycle coefficient in the whole basin was 1.52, and those in the up-stream, middle-stream and the down-stream were 0.24,6.27 and 0.34, respectively. The internal cycle coefficient showed the contribution of the local evapotranspiration to the precipitation, reflecting the activity of the local water vapor. The internal cycle coefficient in the whole basin was 10%, and those in the up-stream, middle-stream and the down-stream were 18%,5% and 3%, respectively. The hydrologic cycle coefficient reflected the contribution of the water vapor abroad to the precipitation and those were 90%,93%,99% and 90% in the up-stream, middle-stream, down-stream and the whole basin, respectively. The water vapor retention coefficient indicated the days needed converting the water content over the region to the precipitation completely. The shorter the water vapor retention, the higher the precipitation efficiency. The water vapor retention coefficients in the up-stream, middle-stream, down-stream and the whole basin were 4.24,22.15,74.20 and 22.12 days, respectively.The coefficients of hydrologic cycle and the internal cycle in each region reached the maximum in July. The hydrologic cycle coefficients in the up-stream, middle-stream, down-stream and the whole basin were 1.14,7.9,4.39 and 3.41, and the internal coefficients in those were 25%,10%,9% and 18%, respectively. Except for the hydrologic cycle coefficient in middle-stream increased to 9.37, the coefficients of hydrologic cycle and the internal cycle in each region reached the minimum in January. The hydrologic cycle coefficients in the up-stream, down-stream and the whole basin were near to zero, and the internal coefficients in those were 2%,2%,1% and 2%, respectively. Among the water vapor retention in each region, only those of the up-stream in April, July, and October and that in a year were shorter than 10 days. They were 6.85,4.23,6.81 and 4.24 days, respectively, and that in July was shortest, representing the highest precipitation efficiency. The water vapor retentions coefficents of the middle-stream in each presenting months of the seasons were shorter than those in down-stream. |
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