Rainfall Interception Loss Research Articles

Rainfall interception and boundary layer conductance in relation to tree spacing

The effect of tree spacing on rainfall interception loss has been investigated in stands of Sitka spruce ( Picea sitchensis (Bong.) Carr) spaced at intervals of 2, 4, 6 and 8 m. The traditional volume balance method was used to measure throughfall, stemflow and interception loss. The variation of throughfall, stemflow and interception loss between the four spacing treatments is analysed. The results obtained showed that, on average, annual intercepton loss as a percentage of gross rainfall was 33, 24, 15 and 9% in the 2, 4, 6 and 8 m spacing treatments, respectively. An estimate of average boundary layer conductance was made by equating interception loss with evaporation rate and inverting a truncated form of the Penman equation. The boundary layer conductance per tree increased with spacing from 0.58 m 3 s −1 in the 2 m spacing treatment to 4.24 m 3 s −1 in the 8 m spacing treatment, whereas boundary layer conductance per unit area declined from 0.17 to 0.07 m s −1 as the density of trees decreased. The difference in interception loss between the spacing treatments was attributed to the difference in the boundary layer conductance.

The temporal distribution of amazonian rainfall and its implications for forest interception

AbstractA model for the temporal distribution of rainfall is derived from measurements made in central Amazonian rainforest. A contrast is made with a rainfall distribution model which has been used in a stand‐alone comparison of land‐surface sub‐models of two General Circulation Models (GCMs). In terms of the rainfall interception loss, it is shown that the central Amazonian model produces an overestimate of 35%, but is within the error bars of the measured interception loss, whereas the latter model overestimates the interception loss by more than 100%. Two other time distributions of rainfall from contrasting regions of the Amazon are derived from published data in order to investigate the possible interception variation due to rainfall pattern variability. the results illustrate the need for GCM modellers to monitor their synthesized rainfall regime against real data and to be aware of the sensitivity of the forest interception loss to rainfall distribution.

The temporal distribution of Amazonian rainfall and its implications for forest interception

A model for the temporal distribution of rainfall is derived from measurements made in central Amazonian rainforest. A contrast is made with a rainfall distribution model which has been used in a stand-alone comparison of land-surface sub-models of two General Circulation Models (GCMs). In terms of the rainfall interception loss, it is shown that the central Amazonian model produces an overestimate of 35%, but is within the error bars of the measured interception loss, whereas the latter model overestimates the interception loss by more than 100%. Two other time distributions of rainfall from contrasting regions of the Amazon are derived from published data in order to investigate the possible interception variation due to rainfall pattern variability. the results illustrate the need for GCM modellers to monitor their synthesized rainfall regime against real data and to be aware of the sensitivity of the forest interception loss to rainfall distribution.

Implications of tropical deforestation for climate: a comparison of model and observational descriptions of surface energy and hydrological balance

Quantitative estimates of the impacts of tropical deforestation on climate can only be considered through use of models of climate that contain adequate treatments of both the land and atmospheric components. Recent global climate model (GCM) calculations by Dickinson & Henderson-Sellers of the effect of removing the Amazon forest attempted to include a detailed canopy model of the forest and the assumed grass replacement. An important role for the structure of the forest canopy was suggested by this study. However, data of Shuttleworth on the seasonal variation of Amazon evapotranspiration show much lower values during the wet season than were obtained in the GCM study and, consequently, much less seasonal variation. The reason for this discrepancy is examined by using results both from the GCM used in the deforestation study and a three-year simulation with a more recent version. The major source of the discrepancy is found to be a large excess of net surface radiation in the GCM simulations, and an excess rainfall interception loss, which is a consequence of this excess radiation. The modelled transpiration appears to agree with the observations.

Evaporation from Amazonian rainforest

The results of a two-year Anglo-Brazilian study of the micrometeorology and process hydrology of undisturbed tropical rainforest at a site in central Amazonia are described. Sample measurements of dry-canopy evaporation from three intensive field campaigns and continuous measurements of rainfall interception loss are used to calibrate a micrometeorological model of evaporation from the forest canopy. Evaporation at this site is calculated by the model from September 1983 to September 1985 by using hourly-average meteorological measurements routinely taken above the canopy, and regular measurements of soil water tension averaged to a depth of one metre. The monthly evaporation derived in this way is compared with the measured precipitation and radiant energy input to the forest, and with calculated potential evaporation rates. Over the whole study period, approximately 10% of rainfall was intercepted by the forest canopy, and this accounted for 20-25 % of the evaporation. The remainder occurred as transpiration from the trees. Over this same period, about one half of the incoming precipitation is returned to the atmosphere as evaporation, a process which requires 90% of the radiant energy input. These proportions exhibit some seasonal behaviour in response to the large seasonal variation in rainfall. The average evaporation over two years was within 5% of potential evaporation. Monthly-average evaporation exceeds potential estimates by about 10% during wet months, and falls below such estimates by at least this proportion in dry months. These data provide the hitherto missing numerical basis for assessing the likely consequences of Amazonian deforestation on surface water and energy balances.

Interception losses of rainfall from Cashew trees

The rainfall interception losses from Cashew trees were quantified, based on the records of 105 selected storms within the range ⩽ 25.0 mm, occurring in a humid tropical region at Kottamparamba, India. The storage capacity of the Cashew trees was worked out as 0.8 mm and the throughfall coefficient as 0.391. The trees under observation were 15–20 years of age with a leaf area index of 1.0–1.25. About 31% of the storm rainfall for storms ⩽ 25.0 mm was intercepted by the Cashew trees and lost to the atmosphere. The measured interception losses from the trees were compared with the estimated interception losses using the analytical model of Gash (1979). The predicted interception losses from the Cashew trees were within ± 10% for storms with total rainfall ⩽ 10.0 mm and within ± 22% for storms with a rainfall of 10.1–25.0 mm.

PREDICTING ABOVE-GROUND NET PRIMARY PRODUCTIVITY OF TROPICAL RAINFORESTS FROM EVAPOTRANSPIRATION DATA

The relationship between above-ground net primary productivity (ANPP) and actual evapotranspiration (AE) has been previously shown by Rosenzweig (1968) to be significant for a variety of mainly temperate terrestrial ecosystems. Our study of ANPP and AE data from the humid tropics showed that AE remains a useful predictor of ANPP in tropical rainforest environments. However, we also noted that 80% of the tropical rainforest data points were depressed below Rosenzweig's original regression line. We attribute these lower-than-predicted ANPP values to transpiration losses and rainfall interception losses that do not result in a corresponding production of biomass.