Lecture4 1 interception and ET dung

VFU -2016 Lecture #4.1 Interception Principles of Watershed management Dr Bui Xuan Dung- Department of Environment Management Rainfall Interception Vegetation often modifies the intensity and distribution of precipitation falling on and through its leaves and woody structures Interception is the water retained on plant surfaces during and after precipitation Importance of interception Canopy Interception (Ic) Total Precipitation (Pg) Throughfall (Th) Stem flow (Sf) Interception: Ic = Pg – Th – Sf Throughfall Point measurement Spatially averaged measurement Interception, throughfall and stem flow Rainfall Interception • • • • • • • Coniferous forests: 15-25% (max ~50%); Deciduous forests: 10-20%; Shrublands: 5-15%; Tall grasses: 10-15%; Short grasses or herbs: 5%; Litter: 1-5%; Four studies in forested areas in Thailand yielded values of 4-30%! Canopy Interception in Japan Type of Forest Annual Canopy Rain (mm) Interception (mm) % of interception Reference Red Pine 1024.4 198.5 19.4 Murai (1970) Japanese Cypress 1793.0 457.8 25.5 Iwastubo (1976) Japanese Cypress 1542.5 328.9 21.3 Hattori (1982) Japanese Cedar 1621.6 378.3 23.3 Tange (1982) Japanese Cedar 1702.7 245.3 14.4 Tange (1982) Deciduous forest 1793.3 360.4 20.1 Iwatsubo (1967) Why so much variation??? Controls on interception losses and throughfall •Broadleaf VS Conifer •Growing VS Dormant Season •Snow VS Rain •Stand Density •Energy Availability (Solar Radiation) •Position of under tree canopy ... Red Pine 10 24.4 19 8.5 19 .4 Murai (19 70) Japanese Cypress 17 93.0 457.8 25.5 Iwastubo (19 76) Japanese Cypress 15 42.5 328.9 21. 3 Hattori (19 82) Japanese Cedar 16 21. 6 378.3 23.3 Tange (19 82) Japanese... measurement Interception, throughfall and stem flow Rainfall Interception • • • • • • • Coniferous forests: 15 -25% (max ~50%); Deciduous forests: 10 -20%; Shrublands: 5 -15 %; Tall grasses: 10 -15 %; Short... Tange (19 82) Japanese Cedar 17 02.7 245.3 14 .4 Tange (19 82) Deciduous forest 17 93.3 360.4 20 .1 Iwatsubo (19 67) Why so much variation??? Controls on interception losses and throughfall •Broadleaf