Browsing by Subject "water balance"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Yan, Dongjun (Helsingfors universitet, 2009)
    Industrial plantations of eucalyptus are sharply increasing in Asia. Although supplying raw material for the pulp and paper industry, easing deforestation on native forests and increasing carbon sequestration to help counter global warming, there are several concerns about the environmental effects of industrial eucalyptus plantations. These concerns include invasiveness of eucalyptus and loss of biodiversity, loss of land for food production, loss of soil fertility due to short rotation times and biomass removal, and excessive water-use and reduced catchment water yields. With protagonists on both sides, there is a need to research and examine the environmental effects of industrial eucalyptus plantations in southern China. We modelled and mapped the spatial distribution of water balance components across a small (752 ha) catchment in Guangxi province in relation to land-use, including industrial and local community plantations of eucalyptus and agriculture. Studies about the spatial distribution of water-use by eucalyptus across the landscape are few. WATBAL, a water balance model with a monthly time step, was parameterized and used to derive water balance components for 180 selected locations in the catchment. From the model output, continuous (predictive) surfaces for monthly (long-term average) potential (PET) and actual evapotranspiration (AET), evapotranspiration deficit (PET- AET), surface runoff and drainage below rooting zone were generated using GIS (ArcGIS 9.2). Averaged across the catchment, annual (October- September) actual evapotranspiration accounted for 77 %, surface runoff for 15 % and drainage below rooting zone for 8 % of rainfall. Differences between land-use types were relatively small, but areas of highest actual evapotranspiration and lowest surface runoff were associated with the oldest (6-7 years old) forested areas, including pure and mixed eucalyptus industrial plantations and local community, coppiced plantations on the slopes. The areas with the lowest actual evapotranspiration were associated with agricultural crops in the bottom of the catchment. The clear dominance of actual evapotranspiration in the water balance of all land-use types reflects the dominating role of the evaporative potential of the climate, with land-use cover, soil and topography factors playing secondary roles. While water-use was the highest for the forested areas, eucalyptus per se did not use more water than mixed plantations or those of the local community. Tree cover in general reduced surface runoff and therefore would reduce the risk of erosion. Using our modelling and mapping approach, we were able to assess the water-use and other components of the water balance of eucalyptus plantations and other land use types for this catchment. The study showed the importance of having suitable and adequate ground truth data in order to derive reliable and useful interpolation surfaces using ArcGIS.
  • Jaeschke, Eric (Helsingfors universitet, 2014)
    The pocosins of the North Carolina Atlantic Coastal Plain (ACP) region play a vital role in controlling hydrologic patterns and determine wetland development and ecosystem structure and function. However, these low-lying, shallow water table forested watersheds have received little research attention due to the relative scarcity of long-term monitoring data, watershed delineation challenges and scarcity of unmanaged sites. Without holding anthropogenic activities constant, specific hydrological processes such as runoff generation, are difficult to describe because of drainage network influence on soil water storage. The principal goal of this study was to develop and test a water balance framework for investigating runoff characteristics and the active watershed area contributing to runoff of a managed pocosin watershed in the ACP. Using a water balance approach, the first objective was to calculate monthly and annual water balances with particular emphasis on deriving, mathematically, the area contributing to runoff. The second objective was to explore the concept of variable contributing area by converting discharge measured at the outlet to runoff using a watershed area. The watershed area needed to produce runoff values that result in closure of the water balance equation represents the variable runoff contributing area. The calculation was done for different temporal periods: monthly, seasonal, and annual and runoff contributing area values compared to the topographically defined watershed area. The results of the study indicated that water balance components were generally in good agreement and closure tended to occur at longer time scales, decreasing for shorter periods. Lack of system closure at shorter temporal scales suggested that the contributing area to runoff varied and differed from the topographically defined watershed area. Active contributing area clearly varies temporally but on average is estimated to be approximately 600 hectares. Regression predicted watershed size was smaller than expected which could have been due to the difference between measured and predicted streamflow. The extent at which the active contributing area fluctuates depends on the compounding uncertainty of water balance components.