Effects of large daily variation of vapor pressure deficit on evapotranspiration and energy budget of wetland in a subalpine mountain valley
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Energy budget
Variation (astronomy)
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Dew
Bowen ratio
Deposition
Water balance
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The Upper Zambezi River Basin (UZRB) delineates a complex region of topographic, soil and rainfall gradients between the Congo rainforest and the Kalahari Desert. Satellite imagery shows permanent wetlands in low-lying convergence zones where surface–groundwater interactions are vigorous. A dynamic wetland classification based on MODIS Nadir BRDF-Adjusted Reflectance is developed to capture the inter-annual and seasonal changes in areal extent due to groundwater redistribution and rainfall variability. Simulations of the coupled water–carbon cycles of seasonal wetlands show nearly double rates of carbon uptake as compared to dry areas, at increasingly lower water-use efficiencies as the dry season progresses. Thus, wetland extent and persistence into the dry season is key to the UZRB’s carbon sink and water budget. Whereas groundwater recharge governs the expansion of wetlands in the rainy season under large-scale forcing, wetland persistence in April–June (wet–dry transition months) is tied to daily morning fog and clouds, and by afternoon land–atmosphere interactions (isolated convection). Rainfall suppression in July–September results from colder temperatures, weaker regional circulations, and reduced instability in the lower troposphere, shutting off moisture recycling in the dry season despite high evapotranspiration rates. The co-organization of precipitation and wetlands reflects land–atmosphere interactions that determine wetland seasonal persistence, and the coupled water and carbon cycles.
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Based on SEBS(Surface Energy Balance System),an inversion of evapotranspiration of dry season and rainy season in 2012in Hailiutu river basin was carried out.The authors analyzed the spatial distribution of evapotranspiration,and discussed the effects caused by depth of groundwater level.The results show that,in dry season,the major factor of influence is the extent of moisture content of surface soil.In rainy season,the major factor of influence is the covered condition of vegetation and the extent of moisture content of surface soil.According to the result,the total evapotranspiration in Hailiutu river basin in 2012is about 8.76bou8 m3.
Wet season
Dry season
Water balance
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Water vapour from regional evapotranspiration that falls again as rain within the same region is referred to as recycled rainfall. This study estimated the summer rainfall recycling ratios (i.e., the relative contribution of recycled rain to total rain) for an agricultural region of the Canadian Prairies by examining the soil water balance component of the land surface branch of the water cycle along with the atmospheric branch of the cycle for June-July-August of 1997, 1998 and 1999. Recycled rain accounted for 24 to 35% of the total rainfall. For these three summers, this study also estimated the horizontal water vapour flux divergence for the region, and compared the areal average summer evapotranspiration totals determined from land-use weighted soil water balance modelling and as residuals in the atmospheric water balance equation. The horizontal water vapour flux divergence per unit area averaged 36 mm. The mean difference between the evapotranspiration estimates was about 15%. It can be concluded, for the summers of 1997, 1998 and 1999, that: (1) regional evapotranspiration was secondary to advection, yet significant, as a source of water vapour for rainfall on the Canadian Prairies, (2) the agricultural area of the Canadian Prairies was a source region of water vapour – consistent with the arid character of the climate, and (3) the land-use weighted soil water balance estimates of areal average evapotranspiration were reasonably accurate. Key words: Water cycle, horizontal water vapour flux, evapotranspiration, atmospheric water balance, soil water balance
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Water cycle
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Nine years of groundwater monitoring data has documented the important influence that topographic relief and location in the groundwater flow system have on the hydrologic function of interdunal valleys. The western wet valley at the Gudmundsen Sandhills Laboratory in central Nebraska, which is a net discharge area, is more strongly buffered from the effects of annual-scale climatic variability than the eastern dry valley. The east valley is generally an area of net recharge and as such is more responsive to climatic variability. This study employed a simple water balance approach to estimate evapotranspiration (ET) from water level measurements in the west valley for four specific time intervals in 1998-99 that included growing and senescence periods. The estimates of ET ranged between 5-6 mm/day in the mid-growing season and 2-3 mm/day during the period of senescence.
Water balance
Dry season
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[1] High altitude basins in the Sierra Nevada, California, have negligible summer precipitation and very little groundwater storage, making them ideal laboratories for indirectly monitoring changes in evaporative losses between wet and dry years. Dry years typically have greater potential evapotranspiration (ET) due to warmer June and July air temperatures, warmer summer water/soil temperatures, greater solar radiation exposure due to less frequent cloud cover, greater vapor pressure deficit, and longer growing seasons. However, dry years also have limited moisture availability compared to wetter years, and thus actual evapotranspiration is much less than the potential in dry years. The balance of these factors varies with elevation. Here, we use gridded temperature, precipitation, and snow data, along with historic streamflow records in two nested basins of the Merced River, California, and a simple model to determine the following: Annual ET increases in wetter years at midelevations (2100–2600 m), but this pattern can only be represented in model simulations that include some representation of water transfer between higher and lower elevation soil reservoirs. At higher elevations (>2600 m), greater water availability in wet years is offset by shorter growing seasons due to longer snow cover duration. These results suggest that models seeking to represent changes in ET in mountainous terrain must, at a minimum, include both hillslope processes (water transfer down steep slopes) and snow processes (timing of water and energy supply).
Water balance
Elevation (ballistics)
Potential evaporation
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Bowen ratio
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