Precipitation interception in Australian tropical rainforests by wA7VNT61


									 Precipitation interception in
Australian tropical rainforests
 Measurement of stemflow, throughfall and cloud

         D. McJannet, J. Wallace, and P. Reddell
          Hydrologic Processes 21: 1692-1702
 Measurements
  – Rainfall
  – Throughfall
  – Stemflow
 Cloud Interception
  – Gauge
  – Canopy water
 Results
 Environmental
   Average daily rain – 12.1 mm
   Tipping bucket gauges
   2 m height
   Wind loss correction
   Horizontal precipitation inputs
 Throughfall - Precipitation
  that is intercepted by
  canopy that falls to the
 2 throughfall
  measurements systems
  per site
 6 m by 100 mm troughs
 Collection area of 2.4-3.6
 Leads to a tipping bucket
 Stemflow - Vegetation-
  intercepted precipitation that
  reaches the ground by flowing
  down the stems or trunks of
 Large number of different
 Spiral collar of clear vinyl
 All trees linked together with a
  tipping bucket
 12 trees, basal area 1.19 m2
 13 trees, basal area 1.73 m2.
      Cloud interception gauge
 Cloud Interception -
  Interception of cloud
  droplets by the canopy
 Collection surface of
  aluminum screen
 Placed under
  0.8x0.8 m plywood
 Measured through
  tipping bucket
           Canopy water balance
 Developed equation from
  one of the rainforest sites
 P = 1.14(Sf+Tf)+3.58
 Large storm Ci =
  {1.14(Sf+Tf)+3.58} – P
 Small storm Ci =
  {(1/Cg)*(Sf+Tf)} – P
 P = Precipitation,
  Sf = Stemflow,
  Tf = Throughfall,
  Ci = Cloud interception,
  Cg = Canopy gap
 Closed circles – Ci,           If precipitation falls below
  Open circles – No Ci            the line, Ci occurred
           Results – Throughfall
 Replicated throughfall troughs received similar amounts of
  water at each site
 Throughfall troughs worked well under high precipitation
 Throughfall decreased as precipitation event time
            Results – Stemflow
 Stemflow was
  measured 93% of
  precipitation days
 Stemflow was not
  changed by DBH and
  species composition
 Percentage of rough
  and smooth bark trees
  did not alter the results
          Cloud interception
 Gauge interception
  was increased with
  wind speed
 Gauge interception =
  0.41*Estimated Ci
 Canopy water balance
  was a better measure
  of cloud interception
  than the interception
Rainfall vs Cloud Interception by Month
 I = P + Ci – Tf – Sf
 Interception rates are
  high for these lower
  montane forest sites
 ~1000 mm of
  evaporation annually
    Environmental Importance
 Throughfall and stemflow sampling worked
  well in the remote sites tested
  – Even under intense periods of rain
  – Monthly servicing
  – Under more variable canopies, more
    throughfall gauges may be necessary
  – Can give a good idea about the canopy water
    balance of a site
    Environmental Importance
 Water balance vs cloud interception gauge
  – Canopy water balance determined Ci better
    than a Ci gauge
  – Gauge does a good job of assessing presence
    of cloud interception
  – Small storms can show no Ci through canopy
    water balance
     All Ci held in the canopy
    Environmental Importance
 Cloud interception can be a large
  contribution to the water budget of a
  tropical rainforest
  – Up to 70% of total throughfall and stemflow
  – Important source of water during the dry

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