Landuse Change Summary

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What are the effects of landuse changes on water balances?

        The guiding issue for the landuse change component of PCGAP is, How do changes in landuse affect the movement of water across the landscape?

   Under the tab on Landuse Scenarios, a set of 6 landuse scenarios was created, with the objective of using them as the base for model analysis. The results of applying the calibrated and validated DHSVM model to these scenarios are summarized under the tab Scenario Outcomes. The results of this work are now applied to the landuse isses. Results, as noted elsewhere, this should be regarded as an initial, Phase 1 analysis. Results, particularly of magnitudes, should not be interpreted too literally. Many of the key parameters were taken from the general literature or “guesstimated,” with no local specific knowledge. This is an issue for the rooting depth of the different landuses, especially eucalyptus, soil properties, specific crop mixes, etc. That said, these results are robust enough to be able to begin to address the landuse questions posed to PCGAP.

     * What are the impacts of changes in the practices of agricultural activities on local and regional water balances in the short, medium, and long terms? -- Agricultural activities have a significant impact on regional water balances, where conversion of forest to different crops increases runoff. Effects are likely greater that represented in the model, because irrigation, soil tillage, compaction aren’t included. Consequences for soil erosion are considered elsewhere.

     * What is the effect of the increase in forest cover on the discharge (flow) of streams and rivers? --  An increase in forest cover clearly leads to a reduction in flow, with an increase in ET.

     * Could cultivation of eucalyptus and other monocultures on high land plantations impact the hydrologic flows and water quality in the coastal zone? In what form?  -- The type of monoculture impacts delivery to the coastal zone, depending on the type of landcover replaced. If eucalyptus were to replace primary forest, differences would likely be small. If it replaced low-lying vegetation, discharge would be reduced and ET increased. If the monocultures was a crop, discharge would increase.

     * How would the augmentation of forest cover impact indices of biodiversity in the basins? What are the priority areas for upgrading to increase biodiversity? --  Biodiversity per se has been considered by the overall FpV project as essentially synonymous   with primary forest. This study has not explicitly considered more specific definitions of biodiversity (number of species/ha, more involved indices, etc). The default assumption for increasing biodiversity is the increase in primary forest; ie. afforestation.

     On what spatial and temporal scales is it possible to produce: scenarios of planning, maps of adaptability, and zoning for agricultural activities? What are the benefits? --  The discussion above focused on the discharge results at specific points, where river gauges exist. But the models themselves are geospatially-explicit; i.e. they compute the water balance (P, ET, R, changes in soil moisture) on a grid basis, every 150m. This doesn’t mean that there are measurements of all parameters for each cell, but it does provide the basis for making detailed maps for planning purposes. For example, the spatial map of ET computed for the SMV for different scenarios shows the value for each cell across the landscape. Each cell of this map could be queried to get that value, and evaluate the consequence of the decision/scenario taken, relative to a baseline.

    Spatial map of (preliminary modeling of) ET across the SMV, for a set of scenarios, relative to the base map of IEMA2007


     These capabilities establish the base for maps of planning adaptability, zoning, and consequences. As most such planning activities occur over longer time periods, results could be aggregated (as was done above), to say seasonal (3-month) or annual averages. The critical point here is that such mapping is entirely feasible. It depends on refining the models to the confidence required, and then developing the scenarios required.